Potential Applications of Concentrated Solar Energy : Proceedings of a Workshop [1 ed.] 9780309583572, 9780309045773

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PROCEEDINGS OF A WORKSHOP

POTENTIAL APPLICATIONS OF CONCENTRATED SOLAR ENERGY held at the Solar Energy Research Institute 1617 Cole Boulevard Golden, Colorado November 7 and 8, 1990

Committee on Potential Applications of Concentrated Solar Photons Energy Engineering Board Commission on Engineering and Technical Systems National Research Council

NATIONAL ACADEMY PRESS Washington, D.C. 1991

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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Frank Press is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an advisor to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Samuel O. Thier is the president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Frank Press and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council. This is a report of work supported by Subcontract No. XX-9-19012-1 from the Solar Energy Research Institute Division of the Midwest Research Institute through the U.S. Department of Energy to the National Academy of Sciences/National Research Council. Library of Congress Catalog Card No. 91-62494 International Standard Book Number 0-309-04577-0 NAP S-416 Copies available from: National Academy Press 2101 Constitution Avenue, N.W. Washington, D.C. 20418 Printed in the United States of America

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COMMITTEE ON POTENTIAL APPLICATIONS OF CONCENTRATED SOLAR PHOTONS ALLEN J. BARD, (Chairman), Department of Chemistry, University of Texas-Austin, Austin, Texas ADAM HELLER, (Vice Chairman), Department of Chemical Engineering, University of Texas-Austin, Austin, Texas J. LAMBERT BATES, Pacific Northwest Laboratories, Battelle Memorial Institute, Richland, Washington ELSA M. GARMIRE, Center for Laser Studies, University of Southern California, Los Angeles, California ARTHUR GOLDSTEIN, Ionic, Incorporated, Watertown, Massachusetts JACK ST. CLAIR KILBY, Consultant, Dallas, Texas DAVID F. OLLIS, Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina ADEL F. SAROFIM, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts NICK SERPONE, Department of Chemistry, Concordia University, Montreal, Quebec, Canada MICHAEL A. TENHOVER, B. P. Research, Warrensville Research Center, Cleveland, Ohio VERONICA VAIDA, Department of Chemistry, University of Colorado, Boulder, Colorado National Research Council Staff KAMAL J. ARAJ, Study Director, Energy Engineering Board JAN C. KRONENBURG, Study Assistant (to February, 1991)

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ENERGY ENGINEERING BOARD JOHN A. TILLINGHAST (Chairman), Tiltec, Portsmouth, New Hampshire DONALD B. ANTHONY, Bechtel Corporation, Houston, Texas RICHARD E. BALZHISER, Electric Power Research Institute, Palo Alto California BARBARA R. BARKOVICH, Barkovich and Yap, Consultants, San Rafael California JOHN A. CASAZZA, CSA Energy Consultants, Arlington, Virginia RALPH C. CAVANAGH, Natural Resources Defense Council, San Francisco CA DAVID E. COLE, University of Michigan, Ann Arbor, Michigan H. M. (HUB) HUBBARD, Midwest Research Institute, Golden, Colorado ARTHUR E. HUMPHREY, Lehigh University, Bethlehem, Pennsylvania (to February, 1991) CHARLES IMBRECHT, California Energy Commission, Sacramento, California CHARLES D. KOLSTAD, University of Illinois, Urbana, Illinois HENRY R. LINDEN, Gas Research Institute, Chicago, Illinois JAMES J. MARKOWSKY, American Electric Power Service Corporation, Columbus OH (to February, 1991) SEYMOUR L. MEISEL, Mobile R&D Corporation (retired), Princeton, New Jersey DAVID L. MORRISON, The MITRE Corporation, McLean, Virginia MARC H. ROSS, University of Michigan, Ann Arbor, Michigan MAXINE L. SAVITZ, Garrett Ceramic Component Division, Torrance, California HAROLD H. SCHOBERT, The Pennsylvania State University, University Park PA GLEN A. SCHURMAN, Chevron Corporation (retired), San Francisco, California JON M. VEIGEL, Oak Ridge Associated Universities, Oak Ridge, Tennessee BERTRAM WOLFE, GE Nuclear Energy, San Jose, California Staff ARCHIE L. WOOD, Executive Director, Commission on Engineering and Technical Systems and Director, Energy Engineering Board (to January, 1991) MAHADEVAN (DEV) MANI, Director, Energy Engineering Board KAMAL J. ARAJ, Senior Program Officer ROBERT COHEN, Senior Program Officer (retired) GEORGE LALOS, Senior Program Officer JAMES J. ZUCCHETTO, Senior Program Officer JUDITH A. AMRI, Administrative Coordinator THERESA M. FISHER, Administrative Secretary JAN C. KRONENBURG, Administrative Secretary (until February, 1991) PHILOMINA MAMMEN, Administrative Secretary NANCY WHITNEY, Administrative Secretary

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PREFACE

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Preface

The Committee on Potential Applications of Concentrated Solar Photons was formed on May 7, 1990 by the Energy Engineering Board of the National Research Council. Its task was to assess potential applications of concentrated solar energy in nonelectric areas and recommend research needed for further development. To carry out its task, the Committee convened a workshop to assess the current state of the field in a number of potential applications and to discuss technologies for which concentrated solar energy might be utilized. The workshop was held at the facilities of the Solar Energy Institute (SERI) in Golden, Colorado, on November 7–8, 1990. This proceeding is the record of that workshop containing all the summary papers submitted by the speakers as well as the rapporteur reports summarizing the presentations and the discussion. The committee's final report, which will be published separately, draws on these proceedings for background material. The committee trusts that papers included in these proceedings will stimulate further interest and study by the technical community. The committee acknowledges the contribution of Kamal J. Araj, the study director, in organizing and coordinating the workshop and editing the papers that form the proceedings. Administrative secretaries Jan Kronenburg and Susan Clarendon carried out the word processing, revising and rerevising many hundreds of pages of highly technical documents with patience and aplomb. The committee would like to extend its gratitude to Meir Carasso, SERI Project Manger, for his assistance in coordinating SERI technical presentations; and to Diane Christodaro and Linda Horrell, for their assistance in logistical support and administrative arrangements during the workshop. Allen J. Bard, Chairman Committee on Potential Applications of Concentrated Solar Photons

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CONTENTS

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Contents

1.

2.

Session 1 - Water Treatment: Advanced Photooxidation Processes Chemical Models of Advanced Oxidation Processes William H. Glaze Mechanistic Studies of the Photocatalytic Behavior of TiO 2 Particles in a Photoelectrochemical Slurry Cell and the Relevance to Photodetoxification Reactions M.W. Peterson, J.A. Turner, and A.J. Nozik Effect of Light Intensity on Photocatalytic Reaction Craig S. Turchi A Comparison of Advanced Oxidation Processes with Semiconductor-Catalyzed PhotoOxidation Gary R. Peyton Ultrox Operating Experiences with UV/Oxidation; Economics Jack D. Zeff Solar Photocatalyzed Process Economics Hal Link Photocatalyzed Removal of Multiple Contaminants from Water Hussain Al-Ekabi Immobilized Catalysts in Solar Concentrators Mark S. Mehos Photocatalysis with Large-Scale Trough Collectors James E. Pacheco Session 2 - Waste Treatment High-Temperature Photochemistry Induced by Concentrated Solar Radiation Barry Dellinger, John Graham, Joel M. Berman, and Don Klosterman Chemical Processes During Incineration and Implications on Detoxification of Hazardous Wastes Using Solar Photons Wing Tsang Solar Technology Applications in Chemical Waste Management Peter S. Daley

1 6 9

16 20

22 25 28 30 32

35 38 48

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CONTENTS

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3.

4.

5.

6.

Session 3 - Materials Processing And Synthesis Applications of Energetic Particles in Improving Coating Adhesion Properties George R. Fenske Pulsed Laser Processing of Solar Cells Rajiv K. Singh and J. Narayan Surface Modification Technologies Using Concentrated Solar Radiation J. R. Pitts, J. T. Stanley, E. Tracy, and C. L. Fields A Comparison of the Economics of Materials Processing with Solar Furnaces and HighIntensity ARC Lamps Gregory J. Kolb

59 63

Session 4 - Solar Pumping of Lasers Solar Pumped Lasers: Work in Progress at The University of Chicago Roland Winston Blackbody Pumped Lasers Walter H. Christiansen Solar Pumped Lasers and Their Applications Ja H. Lee

97 99

69 78 84

103 106

Session 5 - Photochemical Synthesis Photophysics and Photochemistry of Porphyrin Systems John S. Connolly Potential Industrial Applications of Photons James T. Yardley

109 113

Session 6 - Fuel Processing ADN Thermochemical/Photochemical Cycles Gas Research Institute Experience in Solar Fuel Research Kevin Krist Thermal, Thermalchemical, and Hybrid Solar Hydrogen Production E. Bilgen Chemical Reactions Driven by Concentrated Solar Energy Moshe Levy

117 121

116

124 129

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CONTENTS

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Inexpensive Phenol Replacements from Biomass: An Ongoing Technology Transfer Effort Helena L. Chum

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Session 7 - Advanced Research The Biotechnology of Cultivating Dunaliella Rich in Beta Carotene: From Basic Research to Industrial Production Mordhay Avron Production Potential of Biochemicals from Algae and Other Biotechnological Innovations Enabled by Higher Solar Concentration Lewis M. Brown

137 138

Plenary Session Status of European R&D in Solar Chemistry and Industrial Interest in this Technology Paul Kesselring

141 141

Appendix A.

Workshop Agenda

145

Appendix B.

List of Participants

153

7.

8.

140

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WATER TREATMENT: ADVANCED PHOTOOXIDATION PROCESSES

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SESSION 1 WATER TREATMENT: ADVANCED PHOTOOXIDATION PROCESSES Richard G. Zepp U.S. Environmental Protection Agency Athens, Georgia

RAPPORTEUR'S REPORT Absorbed solar radiation provides the primary driving force for the various chemical, physical, and biological processes that oxidize or reduce substances in the environment. Among these processes are photooxidations that play an important role in cleansing the environment of the waste materials derived from human activities. These oxidations involve an array of direct and indirect photoreactions that are induced primarily by the ultraviolet component of solar radiation. Taking a cue from nature, scientists and engineers have made significant progress during the past few years in optimizing the usage of photochemical reactions to remove undesirable impurities in contaminated water. These advances were exemplified by the nine papers that were presented in the water treatment session of the workshop. David Ollis introduced the session by pointing out that oxidation techniques for treatment of contaminated water initially involved the usage of ultraviolet light from artificial lamps or the addition of some oxidant such as ozone. Ozonation is an old technique that is still being widely used in Europe to treat drinking water. These techniques generally result in partial oxidation of organic pollutants. Recent techniques that achieve more complete oxidation have involved (1) combinations of ultraviolet radiation and oxidants (ozone, hydrogen peroxide) in homogeneous systems or (2) heterogeneous photocatalytic systems that combine near ultraviolet radiation (320 to 390 nm range) with light-activated oxidation catalysts such as titanium dioxide. Current results presented at the workshop indicate that additions of ozone and/or hydrogen peroxide to the catalyst systems further enhance oxidation efficiencies. Systems Considered Systems specifically discussed at the workshop included UV/ozone, UV/hydrogen peroxide, UV/ozone plus hydrogen peroxide, and heterogeneous photocatalysis involving semiconductors. The first three techniques all employed far ultraviolet radiation (> 1) indicates that the observed rate constant for unimolecular thermal-photolytic dissociation is given by

At low pressures ([M] → 0) the expression approaches the pressure dependent rate constant, kdiss = (ka/kf)k1 [M]. At high pressures, the rate constant is independent of pressure and is limited by the rate of energy absorption, i.e., kdiss = ka. If kF increases faster with temperature than k1, then kdiss becomes more pressure dependent with increasing temperature. The effects of the key parameters, k ab, kF, and [M], are all subject to experimental determination. Initial results for monochlorobenzene indicate that the dissociation reaction is not thermally equilibrated and is thus pressure-and collision efficiency-limited. This observation suggests that the destruction efficiency of a solar destruction unit can be significantly increased under the proper operating conditions and choice of both gas or operating pressure. Temperature dependent lifetime experiments as well as QRRK and RRKM calculations are being conducted to further elucidate the key aspects of high temperature photochemical processes. Temperature dependent absorption spectra for monochlorobenzene are depicted in Figure 4. These spectra clearly demonstrate a red-shift and increase in oscillator strength with increasing temperature. The red-shift is largely attributable to thermal population of totally symmetric ground state vibrational levels, reducing the energy required for excitation to S1. The increase in total oscillator strength may be attributable to thermal population of non-totally symmetric vibrations that can vibronically couple the ground state to other electronic states lending intensity to particular So → S1 vibronic optical transitions. The observed high temperature redshift is sufficient to make the S1 accessible with solar radiation. This results in more molecules being amenable to solar destruction through direct excitation of S1 than might be expected based on room temperature absorption spectra.

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WASTE TREATMENT

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These ongoing experiments are addressing issues 1–3. We also plan to study issues 4–6 by studying homologous series of polychlorinated benzenes and other halogenated benzenes. The wavelength dependence (issue 7) is directly addressable with the aid of scannable laser systems. Figure 5 presents thermal decomposition data for monochlorobenzene in helium obtained on the Advanced Thermal Photolytic Reactor System (ATPRS) using a Nd:YAG pumped dye laser as the excitation source. Excitation at 280 nm with an average radiation intensity of 3.00 W/cm2 for 10.0 s residence time, resulted in 99% destruction of MCBz prior to any thermal destruction. As in the case of TCB, thermal decomposition byproducts are destroyed at lower temperatures than for purely thermal destruction. Wavelength dependence studies are currently in progress. Issues 8 and 9 are potentially complex to unravel since they include multi-step, non-primary, nonunimolecular reactions. We have begun to address these issues through development of detailed, elementary reaction kinetic models for data obtained on MCBz and dinitrotoluene (DNT). The well-known Chemkin kinetic code and Senkin kinetic sensitivity analysis code are being used in these analyses. The theoretical models being constructed include the full set of thermal initiation and secondary reactions necessary to model the parent decomposition and product formation. The roles of photochemically induced radical molecule and radical chain reactions are being addressed using this detailed modeling approach. The impact of secondary radical molecules and chain reactions may be particularly evident in complex mixtures. This is particularly important from a practical viewpoint where molecules that do not directly absorb solar radiation may be efficiently destroyed by secondary radical molecule reactions. Thus, it may only be necessary to have one photoactive compound in a waste mixture which may act as a radical photoinitiator for the destruction of other nonabsorbing compounds in the waste. An example of one such mixture that we have investigated is shown in Figure 6. The principal absorbing species in this mixture is nitrobenzene; however, effective total destruction of all components of the mixture as well as products is observed. Applied Research Aspects Available results for the destruction of hazardous wastes using concentrated solar radiation clearly suggest that many compounds are amenable to destruction through direct absorption and unimolecular decomposition, while other weak or nonabsorbing species may also be amenable to destruction through secondary photoinduced, radical molecule reaction pathways. However, for a technology to compete successfully in the waste disposal market, it must demonstrate a technological, cost, or possible social advantage over the available techniques. The principal competition at this point is controlled thermal incineration. There appear to be several advantages of solar destruction over thermal destruction which include 1. 2. 3. 4. 5.

increased destruction efficiency of the parent and by-products; control of vaporization of toxic metals through lower operating temperatures; control of Nox formation through lower operation temperatures; availability of excess thermal energy that can be used for thermal desorption of solids and sludges; control of CO2, CO, and toxic organic emissions through substitution of solar energy for conventional fuels; 6. cost savings due to lower fuel costs, increased materials lifetime, and reduced size and complexity of air pollution control devices; and 7. increased public acceptance through use of a renewable, nonpolluting energy source for a nonincineration waste disposal technology.

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WASTE TREATMENT

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Apparent major disadvantages include 1. the unreliable availability of solar radiation; 2. cost of collection and concentration of solar radiation; and 3. lack of off-the-shelf technology to construct a working pilot-or full-scale system. Our task is to develop an approach that utilizes the advantages to offset or minimize these disadvantages. One approach is to develop a hybrid two-stage system targeted for detoxification of contaminated soil and other solids. With this concept, a hybrid primary unit (possible an indirectly fired rotary drum design) may be used to thermally desorb toxic organics from solids, while a secondary solar reactor would be used to thermalphotolytically destroy the desorbed organics. The excess thermal energy generated in the photoreactor would be used to heat the solid waste in the primary unit. This solar generated thermal energy can be supplemented with auxiliary indirect heating from a gas-fired burner. The auxiliary heat source is necessary to operate the process continuously during intermittent cloud cover and maintain nighttime operation. The desorbed organic matter during dark operation may be stored by cryogenic trapping or sorption on carbon for destruction during light periods. Since the total volume of material desorbed is small, the photolytic reactor should readily handle the stored off-gases during light operation. This approach maintains the previously listed advantages for solar-based waste destruction while minimizing two of the three disadvantages. The hybrid primary unit allows continuous operation, thus eliminating the concern over the unreliability of sunlight. It also uses available technology for construction of the hybrid rotary drum, as the indirect fired kiln and off-gas storage approach has already been developed by Chemical Waste Management, Inc. Further research on development of applied system is, of course, necessary. Specifically, experiments combined with prudent calculations should be performed to prove the listed advantages for a solar-based technology. It is felt that a bench scale, rotary drum-photoreactor system should be constructed and tested using a small solar concentrator to further research the practical aspects of hazardous waste treatment using concentrated solar radiation.

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WASTE TREATMENT

Figure 1 Thermal versus photolytic destruction of 3,3,4,4'-tetrachlorobiphenyl. Data were obtained on the Thermal Photolytic Reactor System (see text) in an atmosphere of flowing air at a gas phase residence time of 10.0 s and simulated solar flux of 95 suns(~9.5W/cm2). Also shown is the photochemically enhanced destruction of the toxic reaction by-product, tetrachlorodibenzofurzan. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute

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WASTE TREATMENT

Figure 2 Energy-reaction coordinate diagram for the thermal and thermal-photolytic destruction of an organic compound. The ground electronic state (purely thermal) reaction rate constant is given by kr(So ) with an activation energy Ea(So ). The excited state (thermal photolytic) reaction rate is related to the rate constant of energy absorption, kab; the rates of reaction from excited singlet and triplet states, e.g. kr(Sl) and kr(T1); the rates of competing deactivation process, e.g. kF; and the rate of achieving excited state thermal equilibrium, e.g., kexc and kvr. Some processes are omitted for clarity. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute

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WASTE TREATMENT

Figure 3 Three state model for thermal-photolytic dissociation in which kab is the rate of absorption; kF is the rate of excited state deactivation; and kl[M] and k-1[M] are the pressure dependent rates of thermal activation and deactivation, respectively. State 1 is the reactive state corresponding to the top of the energy barrier depicted in Figure 2, with the rate of passage over the barrier of kp. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute

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WASTE TREATMENT

Figure 4 Temperature dependent absorption spectra for monochlorobenzene. Clearly shown are the red-shift and increase in spectral intensity with increasing temperature. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute

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WASTE TREATMENT

Figure 5 Thermal versus thermal photolytic destruction of monochlorobenzene. Data were obtained on the Advanced Photolytic Reactor System in an atmosphere of flowing helium, gas phase residence time of 10.0 s, and laser flux of 3.00 W/cm2 at 280 nm. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute

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WASTE TREATMENT

Figure 6 Thermal photolytic destruction of an eight component mixture. The plots are for the total of all undestroyed parent and all observed products. Data were obtained on the TPRS at a gas phase residence time of 10.0 s in air and a simulated solar flux of ~19.0 W/CM2. The mixture contains methylene chloride, trichloroethylene, pyridine, aniline, and nitrobenzene at individual, nominal, gas phase concentrations of 300 ppm and naphthalene, nitronaphthalene, and xanthane at 30 ppm. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute

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WASTE TREATMENT

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CHEMICAL PROCESSES DURING INCINERATION AND IMPLICATIONS OF DETOXIFICATION OF HAZARDOUS WASTES USING SOLAR PROTONS Wing Tsang Chemical Kinetics Division National Institute of Standards and Technology Gaithersburg, Maryland

The use of incineration for hazardous waste destruction has been hindered by environmental concerns regarding the effluents from such systems[1]. Important issues are the capability of incinerators to effect the high levels of destruction that are desired and the possibility that other hazardous chemicals may be formed during the process itself. This discussion is a review of the chemistry of incineration. The aim of the work is to demonstrate that it is possible to explain in semiquantitative terms the nature of failure mechanisms. Comparison with the situation when solar photons are used can lead to conclusions regarding the extra dimensions that such an approach offers. There are no thermodynamic barriers to the transformation of any organic molecules during incineration to their thermodynamic end states[2]. In other words, if one can confine an organic molecule in a hypothetical incineration environment for sufficient time the destruction is total. Failure must, therefore, be due to kinetic effects. These can be divided into physical or chemical. We will be interested in the latter. A consequence of this is the need to examine the reaction pathways. The detailed chemistry of the breakdown of organic chemicals during incineration is complex[3]. Nevertheless, by building upon what is known about hydrocarbon combustion processes and concentrating on the principal issues defined above, the problem can be rendered more tractable[4]. Incineration is essentially combustion with nonconventional fuels. In many, if not most, cases, destruction is carried out in the presence of standard fuels. It is not surprising that the concepts from the combustion kinetics of standard fuels should be a good starting point[5]. Hazardous waste compounds have different reactivity and reaction intermediates. When this is superimposed onto the basic fuel chemistry, one can derive information on mechanisms for hazardous waste destruction. This discussion will be confined to chlorinated organics. They are important components in hazardous waste mixtures. The general procedure is, however, applicable to all organics. In a system containing carbon, hydrogen, and oxygen there are three principal pathways that affect the destruction of organics during combustion[6]. These involve radical attack by OH and H and unimolecular decomposition. There are many other radicals present. Many of the larger organics are not particularly reactive, while other radicals decompose. Small radicals such as O, methyl, and HO2 radicals can make contributions under specialized conditions. The OH radicals are particularly important in fuel-lean situations. They are less important as the fuel content becomes richer. The H atoms are important in fuel-lean and fuel-rich mixtures[7]. The importance of unimolecular mechanisms is solely dependent on the reaction temperature. When chlorinated compounds are added into the fuel mixture at sufficiently low concentrations, the concentration of radicals will not be affected[8]. Destruction mechanisms will only be affected by the reactivities of the chlorinated compounds. The existing data show that chlorine substitution at combustion conditions does not have drastic effects on reactivity, except that thermochemistry prevents OH from abstracting Cl[9]. As the waste concentrations are increased, larger amounts of Cl will be formed. A new channel is now opened for waste destruction. Chlorine atoms

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can arise directly from the decomposition of the waste. Another and more important source is the reaction of OH and H radicals with hydrogen chloride. This has the additional consequence of removing these radicals from the reacting system. Chlorine atoms are quite reactive as long as there are no thermodynamic constraints. This is particularly serious for chlorine attack on chlorinated compounds, since direct abstraction of chlorine is highly endothermic. Since H and OH radical concentrations are reduced, an extra degree of stability is offered to highly chlorinated compounds. The decrease in H atoms means that the chain branching reaction H + O2 → O + OH will be retarded. This is the basis for flame inhibition. However, if one tries to remedy the situation through addition of more oxygen, increasing amounts of chlorine will be released into the system. If organic destruction is total, this will have no consequences. However, in the presence of any organics, chlorination[10], being a very facile process, can occur at temperatures far below that in the combustor. The residence times and temperatures quoted for hazardous waste incinerators are average values. Instead, one has a broad distribution of numbers. The physical picture is that of packets of gas of varying stoichiometries being heated and quenched. For packets with stoichiometric amounts of oxygen or above, the chain nature of the decomposition process means that reaction is either complete or does not proceed. Kinetic effects will therefore not be apparent. However, with insufficient oxygen, product distributions of effluents will be a reflection of the relative rates of reactions under pyrolytic situations. This means H-atoms and unimolecular decomposition are important. In the presence of large quantities of chlorine, the reactivity of Cl atoms must also be factored in. The sharp differences in reactivity may not be reflected in the effluents since some substances may not have reacted at all. The use of solar photons can lead to direct photodecomposition or thermal decomposition through heating. For the former, photons are simply another reactant. The most important requirement is for the system to be optically thin. This may be an important constraint in large-scale systems. An important parameter is the quantum yield for photodissociation. For many of the possible hazardous wastes such data do not exist. Particularly interesting will be those at higher temperatures where one expects that the photo processes may be more efficient. Thermal decomposition with solar energy is equivalent to pyrolysis with photons as the extra reactant. As noted earlier, pyrolysis is not a truly efficient destruction mechanism. In any large concentrations of hazardous wastes, the formation of solids will increase the optical density of the media. However, the presence of the particulates may provide a more efficient means of heating the reaction mixture or providing reactive sites for destruction. Solar-assisted combustion will probably not offer unique advantages since, as noted above, the oxidation mechanism is already highly efficient and the true need is to obtain mixtures with the desired stoichiometry. Proper assessment of the potentialities of solar powered destruction of hazardous waste is hindered by the lack of fundamental information. It probably cannot be as versatile a tool as incineration. However, there are many specific applications where it can play a major role. These will involve very dilute mixtures of photodecomposable materials in a variety of matrices. The fact that solar power can heat as well as photolyze represents an extra dimension that should be exploited. Particularly interesting candidates are nitro compounds (military wastes) or other compounds with chromophores. It may also be useful in hybrid systems where it can be used for pre-or posttreatment. In all cases, however, there is the need for additional photochemical data, particularly at the higher temperatures.

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References 1. Oppelt, E.T. 1986. Hazardous Waste Destruction. Environmental Science and Technology 20:312–318. 2. Tsang, W., and W. Shaub. 1982. Chemical Processes in the Incineration of Hazardous Materials. in Detoxification of Hazardous Wastes, J. Exner ed. Ann Arbor Press, Ann Arbor, Michigan, p. 41. 3. Hucknall, D.J. 1985. Chemistry of Hydrocarbon Combustion. Chapman and Hall, London. 4. Tsang, W., and R.F. Hampson. 1986. Chemical Kinetics Data Base for Combustion Modeling: I: Methane and Related Compounds. J. Phys Chem. and Chem. Ref. Data 1087: 15. 5. Tsang, W. 1986. Fundamental Aspects of Key Issues in Hazardous Waste Incineration. ASME Publication 86-WA/HT-27. 6. Tsang, W. 1990. Mechanisms for the Formation and Destruction of Chlorinated Organic Products of Incomplete Combustion. Combustion Science and Technology (in press). 7. Cui, J.P., Y.Z. He, and W. Tsang. 1989. Rate Constants for Hydrogen Atom Attack on Some Chlorinated Benzenes at High Temperatures. J. Phys. Chem. 93:724. 8. Tsang, W., and D. Burgess. The Incinerability of Perchloroethylene and Chlorobenzene. Combustion Science and Technology (submitted). 9. Atkinson, R.A. 1990. Kinetics and Mechanisms of the Gas Phase Reactions of the Hydroxyl Radical with Organic Compounds. J. Phys. Chem. Ref. Data Monograph No. 1. 10. Poutsma, M. 1969. Free Radical Chlorination of organic Molecules. In Methods in Free Radical Chemistry, Vol. 1, E.S. Huyser, ed. Marcel Dekker, New York, p. 79.

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SOLAR TECHNOLOGY APPLICATIONS IN CHEMICAL WASTE MANAGEMENT Peter S. Daley Chemical Waste Management, Inc. Geneva, Illinois

Introduction Using solar energy to destroy waste chemicals and toxic materials has great appeal to environmentalists, industrialists and the public. Using free sunlight to resolve one of the industrial age's most troublesome problems is almost magically attractive. For the magic to become reality, solar destruction must demonstrate that it competes favorably with current approaches in many ways: Economic

Environmental

Capital cost

Residuals' production

Operating cost

Air emissions

Labor

Public acceptance

Chemicals

Permitting difficulty

Energy Versatility Reliability

Among economic factors, versatility and reliability are truly components of both capital and operating Costs; they are separated here because of their great importance in chemical waste management applications. Regarding versatility, it is essential that waste management technologies tolerate extremely wide changes in waste-feed composition. Small changes in industrial processes may easily result in enormous (orders of magnitude) changes in the quantity and quality of waste produced. It is not unusual for operating changes to cause whole new classes of waste to be generated. Demand for versatility in waste treatment is the key reason for success of rotary kiln incinerators for chemical waste destruction; they can accept virtually any solid, liquid, or gaseous feed and can destroy an extremely broad range of chemicals. The versatility need is dramatized by the fact that our company alone manages over 100,000 substantially different waste streams from over 10,000 different customers. It is economically impossible to sort these streams into more than a few categories. Reliability is crucial to waste technology success for reasons beyond simple economics. From an operating standpoint, waste generators demand reliability because they may be shut down if they can't dispose of their wastes. Because one disposal facility may service several plants, the impact of a shut-down can be especially serious. Perhaps more important, performance standards demanded of waste treatment systems by the public are uncompromising. The products produced by chemical waste treatment systems (clean air, water, and solids) must generally achieve zero defects' over long operating periods. Failure to do so will, at best, give the operator a public black eye and, at worst, may yield serious health or environmental risks or loss of operating permits. Table I lists several technologies that have failed to live up to expectations and offers some reasons why. Factors related to both versatility and reliability are frequent.

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The Vanishing-Niche Problem Figure 1 shows that there is strong and expected correlation between the price of a specific wastewater disposal service and the volume of wastewater treated by a specific technology. Similar figures can be constructed for other waste disposal markets. Technologies with costs below the line should be commercial successes, but they will not achieve volumes greater than those garnered by existing technologies unless they represent major technical breakthroughs. The most important conclusion from the graph is that market size for high-cost technologies is small, on the order of 100 million gallons per year, and highly fragmented. The current price in this market is about $1.00 per gallon. Recalling that our company alone manages over 100,000 different waste streams, one can see that this market includes widely varying materials and each stream or group of streams only comprises a relatively small volume. If one were to develop a technology that could address 10% of the market, several thousand streams, the market size would be $10 million. In our company it requires about $1.25 in capital to generate $1.00 in sales; therefore, one can afford to spend only about $12.5 million to develop and commercialize a technology to serve a 10 million gallon, many-thousand-waste-stream niche. For technologies capable of addressing fewer waste streams, the limit on development and commercialization cost is proportionally more restrictive, if one hopes to achieve a reasonable return on investment. These observations hold true for all waste market segments. This generalization is born out by John Skinner's (U.S. EPA Deputy Assistant Administrator for Remedial Technology Development) observation that one of the biggest problems in the hazardous waste site clean up program is that the Agency cannot identify test sites compatible with the specific attributes of many innovative technologies; i.e., the size of the niche has diminished to zero, even when the entire inventory of waste sites is examined. This problem is compounded by the high cost of waste technology development. Development-related permitting and regulatory compliance can easily cost hundreds of thousands of dollars, and these costs for the commercialization phase are likely to reach millions. In addition, regulatory issues should be expected to double or triple development time, adding more costs as people and equipment go underutilized and interest accumulates. High Associated Costs: Chemical waste treatment operations are laden with high Costs not directly related to the treatment technology used. Failure to recognize this can lead to many misdirected development efforts. The simple conclusion from the ''vanishing niche'' discussion above is that even if the niche is only $10 million, a dollar a gallon is a lot; a small business should be able to do well. Unfortunately the $1.00 is price not cost. The price must obviously cover the basic treatment cost, regulatory compliance, feed and product analysis, feed preparation, residuals' disposal, profit, and a host of other factors. In our experience, the central disposal unit process in a chemical waste disposal facility accounts for only about 15% of capital and a third of operating costs (Figure 2 shows some generalized cost distributions as well as actual cost distributions for X*TRAX, a CWM thermal separation technology to clean soils). Thus, the amount one may spend to develop a new technology is substantially less than the $12.5 million discussed earlier; a few million is a much more realistic estimate. Application to Solar Treatment Technologies Solar technologies necessarily target markets that are energy intensive and compatible with the intermittent nature of sunlight. The chemical waste

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market, with very few exceptions, is adequately served by the wide range of technologies now available. Prices, exclusive of taxes, are generally stable or slowly dropping as engineers adjust to the rapidly changing treatment rules. Each new regulation tends to engender near-term price increases, but prices drift downward as waste reduction efforts and evolutionary process improvements take hold. Certain versatile and low-cost technologies are now underutilized because of social and regulatory barriers. The two most important are chemical incineration in cement and aggegate kilns, and use of wastes in building materials. Cement and aggregate kiln destruction and/or stabilization of organic and inorganic wastes is growing rapidly with dozens of kilns now permitted versus only a few five years ago. For solar applications to be commercially successful, they must offer waste generators and treaters sufficient incentive to switch disposal technologies. As Figure 2 shows, energy is not a large part of the typical cost of chemical waste disposal. Since 'typical' encompasses a wide range of actual technologies, there are some niches in which energy is critical. For example, the treatment of groundwater at remote sites generally involves high pumping costs. Also, the destruction of dilute contaminants in high-volume exhaust air systems is energy intensive, especially if afterburners are used. The intermittent nature of sunlight presents a major problem for solar applications given the importance of reliability in chemical waste treatment. To be compatible with this importance, solar-based systems must shut down during low-sun periods or be equipped with alternative energy sources. Since most chemical waste treatment technologies are capital intensive, additional cost for solar equipment is not attractive. The present incineration business structure is instructive in gauging the importance of energy in solar-based chemical waste treatment. Few U.S. chemical incinerators operate with energy recovery in spite of the fact that they may release a large amount of energy. The reasons are several. First, to get a significant value for recovered energy, the supply must be reliable. This is inconsistent with chemical waste incinerators which typically operate about 85% of the time. Incinerators are very complex and are typically subject to about 50 automatic shutdown conditions, and high performance standards demand frequent maintenance. Complexity is the second reason operators reject energy recovery; adding more complex systems threatens to reduce operating rates and adversely affect profitability. Given the current situation as described above, it will be difficult to find the right combination of energy needs, reliability requirements, and versatility to justify investment in solar-based technologies for the chemical waste business. The best opportunity may well be the groundwater treatment market cited earlier. This market is energy intensive and compatible with intermittent energy supply. In fact, there is some move toward intermittent pumping of aquifers for cleanup as the optimum approach. Conclusion Solar-based technologies offer limited opportunities for chemical waste applications because they add additional capital costs and system complexity without providing proportional energy savings. This is largely because energy is not a major factor in most chemical waste disposal activity. Overhead associated with regulatory compliance, chemical analysis, feed preparation, residuals' disposal, environmental permit, etc., typically dominates the cost equation. In addition, the great importance given to treatment reliability in the eyes of operators, regulators, and the public means that solar energy sources would require conventional energy backup in most applications. This would add significant costs to an already capital-intensive business and may compromise reliability by adding more complexity to the system. Further reducing the likelihood of success for solar-based applications is that the niches open to the approach are likely to be small and not big enough to justify the development costs.

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One niche that is promising is solar systems for treatment of groundwater at remote sites. In this case, intermittent operation is acceptable, even desirable, and energy costs are high.

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Table 1 Lagging Chemical Waste Treatment Technologies Technology

Prime Reason Not Implemented

Plasma destruction

High fundamental cost and complexity

In situ vitrification

Cost, by-products, uncertain destruction performance

Electric furnaces

Energy cost, capital cost

Moving hearth furnaces

Narrow applicability.

Supercritical separators

Narrow applicability, cost

Freeze purification

Narrow applicability

In situ soil cleaning

Narrow applicability, uncertain performance

Alkali-metal polyethylene glycol dechlorination

Narrow, cost, residuals management

Sodium metal dechlorination

Safety and cost

White-rat fungus for halocarbon destruction

Narrow applicability

Biotreatment, general

Narrow, failure to achieve low residual standards

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Figure 1 Wastewater treatment market. Reprinted with Permission from: Chemical Waste Management, Inc.

56

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WASTE TREATMENT

Figure 2A Typical Hazardous Waste Treatment costs. Reprinted with Permission from: Chemical Waste Management, Inc.

Figure 2B Projected Model 200 X*TRAX treatment costs. Reprinted with Permission from: Chemical Waste Management, Inc.

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MATERIALS PROCESSING AND SYNTHESIS

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SESSION 3 MATERIALS PROCESSING AND SYNTHESIS

Bruce M. Clemens Stanford University Stanford, California

RAPPORTEUR'S REPORT INTRODUCTION This workshop was organized to assist the Committee on Potential Applications of Concentrated Solar Photons in achieving the goals of its study. These goals, as listed in the Committee's statement of work, are • assess the knowledge base for photon/matter interaction phenomena underlying the use of concentrated solar flux for prospective new non-electric applications; • critically evaluate the merits of potential new applications for both near-and long-term use of concentrated solar energy, particularly those applications that address national needs and have the potential for being cost-effective through research and development; and • recommend research paths and priorities to enhance the scientific basis of, and increase the potential for, the development of successful applications. Due to strong absorption, solar radiation will interact with the surface region of most materials. Thus, in Session 3, Materials Processing and Synthesis, the technology area judged to be most amenable to application of concentrated solar photons was surface treatment and modification. The first two speakers in Session 3 addressed this area, with descriptions of current surface modification and thin film growth technologies. A summary of the various current techniques was made, and the features which make each viable were accentuated. The third speaker discussed current research at the Solar Energy Research Institute aimed at exploring the application of concentrated solar photons to surface treatment. Proof of concept experiments have been performed in several application areas. The fourth speaker discussed the economic analysis of solar furnaces versus conventional intense light sources. Points raised during the discussion included the unique aspects of solar light which might make applications feasible and recommendations for future work. This report is organized in a manner analogous to the presentations. The first section concerns current surface modification and thin film growth technologies. The second section is a discussion of the possible applications of concentrated solar photons. The third section summarizes the results of an economic analysis, and the fourth has suggestions for future research and organizational needs. PRESENT SURFACE TREATMENT TECHNIQUES Surface treatment is used to impart desirable properties to the surface of a sample or part without the added expense in materials and energy required

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to alter the bulk. This gives the ability to independently optimize the bulk and surface properties; for instance, a surface region may need to be hard or corrosion resistant, while mechanical toughness is required of the bulk. In the first talk of Session 3, William D. Sproul of Northwestern University, discussed several current surface modification technologies. Surface Heating with Light Since visible light is absorbed in about the first 30 nm in most metals and opaque materials, intense light fluxes can be used to selectively heat the surface region. Techniques which use light to heat surfaces can be classified according to the interaction time and energy density. In general, the processes which have a short interaction time (10-4-10-10 sec.) have a high energy density (104 -1010 W/m2). Short interaction time processes can achieve extremely high heating and cooling rates (1012 K/sec.), and thus can be used to produce nonequilibrium phases such as metallic glasses. Laser glazing of a previously applied thin film can heal pinholes and defects as well as promote adhesion and densification. Slower interaction time processes can be used to anneal or harden the surface region or melt a previously applied powder or film. Powder melting can produce a dense well-adhered film. These films can be several mils to over a hundred mils thick. One of the primary disadvantages is that the surface tends to be quite rough and requires a postmachining process. Lasers can be used to ablate material to pattern the surface on a very fine scale. Printing roles are patterned in this manner to achieve optimum inking characteristics. Thermal Spray/Plasma Arc In the techniques of thermal spray or plasma arc, powder is fed into a heat source (either a flame or electric arc) where it is melted and then accelerated as molten droplets into the surface where it condenses into a film. This is a relatively inexpensive and rapid process for forming a surface film, but the films which result have a high density of several types of defects, including unmelted particles, voids, and oxidized particles. The process is extremely complex, with many parameters that affect the final film properties in a complicated manner. Nonetheless, this is a widely used process, particularly in the aerospace industry where a typical gas turbine engine has 15 pounds of thermal spray coatings. Chemical Vapor Deposition Chemical vapor deposition (CVD) uses thermal energy to decompose precursor molecules which results in deposition of a film. This technique is widely used in the semiconductor and metallurgical coatings industries to produce Si, SiO2, TiN, and Al2O3, among others. of particular interest is photo-assisted CVD where light is used to not only heat the surface region, but to photolytically assist in breaking the precursor molecule bonds. Principal disadvantages are the high temperatures required and the toxicity of the precursor materials. Advantages are nondirectionality of deposition, which results in uniform coatings on complex shaped parts, and low cost. Physical Vapor Deposition In physical vapor deposition, films are produced by physical transport of atoms from source to substrate. Evaporation techniques use resistance or electron beam heated hearths to evaporate the source atoms, while sputter deposition forms films from atoms ejected from the source by bombardment by energetic particles, usually inert gas ions. Both techniques need a vacuum environment, and the film properties are strongly affected by the energy and surface mobility of the arriving species.

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Ion Beam Techniques George Fenske, of Argonne National Laboratory, discussed several techniques that utilize bombardment with energetic ions to alter the surface properties. These techniques can be classified as ion mixing, ion implantation, or ion-assisted deposition. In ion mixing, an ion beam is used to posttreat a film to achieve mixing at the interface resulting in improved adhesion. Ion implantation uses ion beams to directly enrich the surface region in the ion species. Both these techniques require expensive ion sources and are inherently slow. Ionassisted deposition uses ion bombardment during vapor deposition to enhance mixing with the substrate and arriving species mobility, resulting in improved film qualities. In addition, ion bombardment can be used prior to film deposition to clean and roughen substrates and thus improve film adhesion. These later two uses of ion beams can utilize less expensive lower energy ion sources than ion beam mixing or implantation. MATERIAL USES OF CONCENTRATED SOLAR PHOTONS In order to assess the application of concentrated solar photons for materials, it is instructive to examine the properties obtainable in concentrated solar beams. J. Roland Pitts of the Solar Energy Research Institute discussed solar radiation, its concentration, and several possible applications. The solar spectra is (not coincidentally) mainly in the visible spectral range and has a penetration depth of about 20–50 nm in many metals and opaque materials. Thus highly concentrated solar beams are ideally suited for surface heating. Solar furnaces can obtain concentration factors of up to 10,000 resulting in fluxes of 1000 W/cm2. Solar light can be delivered at a fraction of the energy cost of conventional sources such as lasers or arc furnaces. During discussion, the relevant characteristics of solar light were proposed to be • its radiative nature, allowing its use for surface heating; • the ability to concentrate solar light to produce high flux-high area light sources; and • the spectral characteristics of solar light. The possible applications which utilize these characteristics can be classified into thermal and photolytic. Thermal Applications This class of applications utilizes concentrated solar flux to heat sample surfaces. There are many technologies that can utilize this ability, and Pitts discussed many proof of concept experiments which have been performed at SERI. Included in these was powder melting or cladding, surface film glazing, including the initiating of self-propagating reactions of multilayer Ni/Al films, and hardening of steel surfaces. Concentrated solar photons were used to form the desired high-Tc, phase during rapid thermal annealing of a thin film in an oxygen atmosphere, as well as for thin film deposition by CVD. Films formed in this manner included diamondlike carbon and TiN, and SiC. In addition the high flux capability of a solar furnace could be used for rapid thermal chemical vapor deposition. Other applications suggested during the workshop included using solar energy as a heating source for evaporation. This could be used in environments where electron beams cannot be used, such as in evaporation in a partial vacuum to produce nanophase powders. Also suggested was the use of concentrated solar photons to heat a substrate either prior to or during deposition. This application is

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attractive in cases where extremely high temperatures (~2000 K) are needed, as these are difficult or impossible to obtain in other manners. Photolytic Applications Photolytic applications would utilize solar light to directly break chemical bonds. Due to the broadband characteristics of the solar spectra, there is relatively little power at any given wavelength. Thus a photolytic application should take advantage of as much of the solar spectrum as possible. Furthermore, most absorption processes need shorter wavelength photons than are available in the solar spectrum, so some control of absorption processes is needed for these applications. This may be possible with absorption of molecules on surfaces. One area where these types of processes may be useful is in polymers, where bonds can be readily broken by solar radiation. No applications were suggested in the workshop, and a need for concepts in this area was expressed. ECONOMIC ANALYSIS Greg Kolb, of Sandia National Laboratories, presented the results of his study comparing the relative economic advantages of solar furnaces and high intensity arc lamps. Arc lamps are cheaper initially and are unaffected by weather. They perform better for assembly line continuous processes since they can be operated continuously. However, the energy costs of arc lamps are much higher, and as the cost of energy rises, the solar furnace will become more practical. In addition, for applications involving batch processing of parts which utilize 5000 suns or more, a solar furnace is more economical to run even with current energy prices. The solar furnace can also have a long distance between workpiece and optical elements, allowing for greater flexibility of process design, particularly in cases where the process generates dirt which can damage optical elements. The outline of a second study by Walter Short comparing solar furnaces with CO2 lasers was also circulated. CO2 lasers, which are widely used for surface annealing, have several advantages over solar furnaces. These include high intensity, availability, and control, as well as independence from the weather and the ability to use an existing building. However, CO2 lasers are even more energy inefficient than arc lamps, and thus solar furnaces have an even greater advantage. They can also deliver high power over larger areas and have better absorption characteristics than CO2 laser light. SUGGESTIONS FOR FUTURE RESEARCH AND DEVELOPMENT Future research should concentrate on areas that take advantage of the unique characteristics of concentrated solar photons. The ability to deliver high flux over a large area suggests that a solar furnace could be used for rapid heating and cooling of large areas. The limits on cooling and heating rates for solar furnaces should be explored. The surface absorption of solar light also implies that high gradients can be produced. In other words, the surface can be heated to high temperatures without affecting the bulk. Of course this also leads to high cooling rates, and applications exploring the formation of metastable phases should be explored. In addition solar furnaces can possibly be used to obtain extremely high temperatures (~2000 K). The limits on this ability should be explored and applications which need high temperatures should be sought. Applications in the areas of polymers should be researched. In general, it is felt that there needs to be a mechanism established to find applications. The researchers involved in solar methods need to connect with researchers and technologists working in the application areas. It was suggested that perhaps the solar furnaces could be made available to outside researchers to foster this interaction.

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Also needed is more detailed economic analysis on specific applications to assess the practicality of the substantial investment required to fabricate a solar furnace.

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APPLICATIONS OF ENERGETIC PARTICLES IN IMPROVING COATING ADHESION PROPERTIES* George R. Fenske Argonne National Laboratory Argonne, Illinois

Introduction In many engineering situations, material selection is often based on a compromise of bulk-mechanical properties and near-surface properties, with neither set of properties at its optimum value. Often the material of choice (e.g., high-Cr steel in corrosion applications, or TiN or WC in wear applications) cannot be fabricated into bulk components due to limitations based on cost, fabrication, and mechanical properties. In such cases, various processes are available to deposit coatings of the desired material on components fabricated from materials with desirable bulk properties. A key property of any coating process is adhesion of the coating to the substrate. Without adequate adhesion, the coating will be lost and thus can no longer protect the substrate. Numerous surface-modification processes can be used to modify the surface properties of a wide range of materials. These processes range from surface heat treatments (e.g., thermal hardening, carburizing, nitriding, carbonitriding, boriding, and metalliding) that rely on thermal processes (primarily diffusion) to produce the desired property in near-surface regions, to surface coating processes (e.g., electro-and electroless chemical deposition, chemical vapor deposition [CVD], physical vapor deposition [PVD], spraying processes, and welding processes) in which material is formed or deposited on the surface. Adhesion is usually not a major concern with surface heat treatments because thermal diffusion produces a gradual change in composition. In surface coating treatments, however, the transition from the bulk material to the coating material is much more abrupt and thus adhesion is a very important factor that must be addressed in selecting the deposition process. This paper addresses one approach (ion-beam-assisted deposition, or IBAD) that utilizes energetic ion beams to enhance the adhesion of metallic films to metallic and ceramic substrates. In one application, IBAD is used to improve the adhesion of silver films to ceramic substrates that are subjected to sliding wear conditions at elevated temperatures(1). In another application, the IBAD process is used to improve the adhesion and modify the microstructure of chromium films deposited on low-Cr steel[2]. Both applications suggest that adhesion can be increased by a number of mechanisms including (a) physical and chemical sputtering of surface contaminants (e.g., hydrocarbons and adsorbed water molecules); (b) preferential sputtering of a particular element of a compound, thus producing a surface enriched in a species that is chemically active with the depositing species; (c) activating chemical states; (d) mechanically toughening the surface, producing more surface area for bonding and sites to arrest surface cracks; and (e) recoil mixing during the initial stage of film deposition.

* Work supported by the U.S. DOE Office of Transportation Materials Tribology Project under Contract W-31-109ENG-38.

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Ion-Beam-Assisted Deposition A description of IBAD processes can be found elsewhere [3–5]. The main feature that separates IBAD from other PVD processes is that the film being deposited is also bombarded by energetic ions/atoms during deposition. This bombardment affects a number of phenomena (film nucleation and growth, film density, film crystallinity, and film orientation) that determine the adhesive strength of the film to the substrate. Figures 1A and 1B show the effect of sputter-cleaning on the adhesive strength of Ag films deposited on alumina and zirconia substrates, respectively[1,6]. The size of the error bars corresponds to one standard deviation in the measured values. In tests using an Ar beam only, the adhesion of Ag to Al2O3 increases with ion dose, rapidly at first and then reaching a steady-state value of approximately 55 MPa after presputtering for approximately 300 s, which corresponds to an ion dose of 5.6 × 1016/cm2. When an Ar + O beam was used, the adhesive strength increased at a faster rate as a function of time (compared to Ar ions only). Presputtering for 3 s was sufficient to raise adhesive strength to approximately 35 MPa. After 30 s of cleaning with Ar + O, the adhesive strength of the Ag to the Al2O3 exceeded the tensile strength of the epoxy bonding agent (approx. 60– 70 MPa). In tests that used an Ar + O beam to sputter-clean and bombard the film during deposition[7], adhesion was higher than that for sputter-cleaning only with Ar and O. For Ar sputter-cleaning of ZrO2 (Figure 1B), adhesive strength increased with ion dose (time), rapidly at first and then peaking at approximately 50 MPa after presputtering for 300 s to an ion dose of 7.5 × 1016/cm 2. Beyond 300 s, adhesive strength decreased to 34 MPa after 2000 s (5 × 1017/cm2) and then increased above 65– 70 MPa (failure in the epoxy rather than at the Ag/ZrO 2 interface) for cleaning times of 3000 s (7.5 × 1017/cm2). When Ar + O was used to sputter-clean the zirconia, adhesion increased very rapidly to values in excess of 65– 70 MPa. As seen in Figure 1B, only 30 s (7.5 × 1015/cm2) of cleaning with Ar + O was required to exceed the tensile strength of the epoxy. A number of mechanisms have been proposed to account for the increased adhesion observed in Figures 1A and 1B[8]. These include (a) physical and chemical sputtering of surface contaminants (e.g., hydrocarbons and adsorbed water molecules); (b) preferential sputtering of Al, Zr, or O that produces a surface enriched in a species that is chemically active with the depositing species; (c) activating chemical states; (d) mechanically roughening the surface, which produces more surface area for bonding and sites to arrest surface cracks; and (e) recoil mixing during the initial stage of film deposition. Sputter-cleaning, either by Ar alone or with Ar + O ions, is effective in removing surface contaminants, particularly adsorbed water and hydrocarbons[9]. The substrates used in these tests were cleaned with a series of three organic solvents before insertion into the IBAD system[10]. Thus, part of the improved adhesion observed in Figures 1A and 1B can be associated with the removal of organic residues on the substrate surfaces. The higher rates of increases in adhesive strength with sputter time (or dose) seen with the Ar + O beams relative to those for Ar alone can be attributed to a chemical (or reactive) sputtering process in which volatile compounds (such as CO) may have been formed by the reaction of O ions with organic contaminants. Preferential sputtering of one of the substrate species (such as O), leaving a surface layer enriched (and perhaps chemically active) with Al or Zr, is feasible. Monte Carlo TRIM calculations[11] of physical sputtering of Al2O3 by Ar + O indicate that O is preferentially sputtered. However, impingement of the sputtered surface by residual 02 in the vacuum chamber, particularly during the Ar + O sputter-cleaning (approximately 10-2 Pa of O2) probably negated the preferential sputtering effect, leaving a near-stoichiometric Al2O3 or ZrO2 surface.

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Once a clean surface is established, continued bombardment of the surface could produce chemically active O atoms that react with depositing Ag atoms to form a stable compound. Silver is known to form stable oxides (such as Ag2O) at room temperature[12]; thus, it is feasible that the first monolayer of Ag reacts with O atoms to form a ternary Al-OAg compound across the interface similar to that found for Cu deposited on Al2O3[13]. Mechanical roughening due to sputtering is a viable process; however, the amount of material removed by sputtering is only about 40 nm, and measurements[14] of the center-line-average surface roughness before and after sputter-cleaning (from 17 nm before sputtering to 20 nm after sputtering) reveal that this is not a significant factor. Cross-sectional transmission electron microscopy (TEM) of IBAD silver-coated Al2O3 substrates[15], which shows a sharp interface between the deposited Ag and Al2O3 substrate, also indicates that dynamic mixing is not responsible for the improved adhesion of the Ag films tested. For Cr films deposited on metallic substrates[2] the situation is different. Here, the deposited Cr atoms can be mixed into the substrate through a combination of dynamic mixing and radiation-enhanced mixing processes. The radiation-enhanced processes are dominant in this case because one is dealing with diffusion of Cr in a metallic substrate that already contains Cr, rather than with diffusion of Ag in ceramic substrates. Chromium films deposited by pure PVD or IBAD with 100 eV Ar ions exhibited a gap between the film and the substrate (indicative of degraded adhesion), as observed in cross-sectional TEM micrographs. In contrast, Cr films deposited by IBAD with 300 or 1000 eV Ar ions exhibited no gap between the film and the substrate. The 300 and 1000 eV IBAD films also had an intermixed Cr-enriched layer (approximately 30 to 50 nm deep) in the substrate material; this layer can act as a 'glue' to enhance adhesion of the film to the substrate. Another difference between Ag and Cr deposition is the role of internal stresses on film adhesion. Cr films are known to delaminate from the substrate if large internal stresses exist. This situation is not as critical for Ag films because they are pliable and will easily undergo creep to alleviate high stress levels. Differences in the microstructures[2] and porosity of the IBAD films deposited with 100 to 1000 eV Ar ions suggest that internal stresses of the films can be controlled by proper selection of the Cr atom deposition rate, ion flux at the surface, and energy of the incident ions. Discussion The above examples illustrate the effects that energetic ions/atoms can have on the adhesion of coatings to substrates. The major effects observed were the (a) preparation or cleaning of the surface of the substrate prior to deposition, (b) promotion of strong chemical bonding at the interface, and (c) inducing mixing of deposited material into the substrate. Concentrated solar beams provide an alternative approach for obtaining comparable effects via pyro-and photolytic reactions. With pyrolytic approaches, intense solar beams could be used to heat substrates and vapor sources to elevated temperatures. Solar heating of the substrates to elevated temperatures before deposition could be used to desorb common surface contaminants (adsorbed water and organic cleaning compounds), thereby providing a clean or chemically active surface for improved chemical bonding to films deposited in subsequent steps. In conventional PVD processes, where substrate heating is commonly used to improve adhesion and nucleation and growth characteristics[16], this step is typically performed in a vacuum because of the requirements of the vapor sources. With solar heating, however, this step could be performed in an inert atmosphere or, alternatively, in a reactive environment (e.g., halide gases) to chemically assist the formation of volatile compounds from the surface contaminants. Concentrated solar beams could also be used to deposit films. In one approach, solar energy could directly heat and evaporate elements from a crucible. The power densities envisioned for intense solar beam systems (in

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excess of several kW/cm2) exceed those typically found in electron beam evaporation sources that operate at power levels of 1 to 20 kW with a 5 cm diameter source (0. 05 to 1 kW/cm2) to evaporate pure elements. Alternatively, solar beam heating of the substrates could be used in CVD thin films in a manner similar to conventional CVD of coatings for electrical, decorative, and tribological applications. Such applications of solar beams the beam energy to produce pyrolytic phenomena—processes that require elevated temperatures. In many instances, elevated processing temperatures are undesirable. For example, steel components are often heat treated to achieve a certain hardness and toughness. Exposing these components to temperatures above their annealing point degrades these properties. It is therefore difficult to coat many steel components at elevated temperatures without some type of postdeposition heat treatment (which often distorts the component) to return the component to its original specifications. Consequently, processes that can deposit coatings at low substrate temperatures (such as ion-beam techniques) are often desirable. The energy associated with the incident ions can impart sufficient energy to local regions of the coating and near-surface regions of the substrate to produce effects typically achieved at elevated temperatures. Another example of a low-temperature process—and more germane to this workshop—is the use of energetic photons to photolytically activate processes for both cleaning surfaces and depositing coatings. A process known as photo-enhanced chemical vapor deposition (PHCVD) is receiving considerable attention in semiconductor applications as a low-temperature process for deposition of Si, SiO2, and GaAs[16]. The process is based on photodissociation of gas-phase molecules and typically uses UV light and/or excimer lasers to break the chemical bonds. PHCVD processes are strongly dependent on the absorption of photons with the appropriate wavelength to break the chemical bonds between atoms in the gaseous compound. A majority of the compounds used in PHCVD require UV light to dissociate the molecules, and thus a major obstacle to be overcome in implementing intense solar beams for PHCVD will be to identify compounds that photodissociate (either directly or through a catalytic reaction) at wavelengths that are more abundant in the solar spectrum. Summary Coatings are used in a wide number of applications where the properties of the underlying substrate will not suffice. Concentrated solar beams show potential as a viable energy source for a number of coating processes based on pyrolytic and photolytic reactions. References 1. Fenske, G.R., R.A. Erck, A. Erdemir, V.R. Mori, and F.A. Nichols. 1990. Ion-Beam-Assisted Deposition of Adherent, Lubricious Coatings on Ceramics. Paper presented at 17th Leeds-Lyon Symposium on Tribology (Vehicle Tribology), Leeds, England, Sept. 4–7, 1990. 2. Cheng, C.C., R.A. Erck, and G.R. Fenske. 1989. Microstructural Studies of IAD and PVD Cr Coatings by Cross Section Transmission Electron Microscopy. Mat. Res. Soc. Proc., 140:177. 3. Smidt, F.A. 1990. Use of Ion Beam Assisted Deposition to Modify Microstructure and Properties of Thin Films. Int. Mat Rv. 35 (2):61. 4. Handbook of Ion Beam Processing Technology. Cuomo, J.J., S.M. Rossnagel, and H.R. Kaufman, eds. 1989. Noyes Publication, Park Ridge, N.J.

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5. Fenske, G.R., A. Erdemir, R.A. Erck, C.C. Cheng, D.E. Busch, R.H. Lee, and F.A. Nichols. 1989. Ion-Assisted Deposition of HighTemperature Lubricious Surfaces. Presented at 35th STLE/ASME Tribology Conference, Ft. Lauderdale, Fla., Oct. 16–19, 1989, STLE preprint 89-TC-2E-2. 6. Erck, R.A., and G.R. Fenske. 1990. Adhesion of Silver Films to Ion-Bombarded Alumina. Mat. Res. Soc. Symp. Proc. 157:85. 7. Erck, R.A., A. Erdemir, and G.R. Fenske. 1990. Effect of Film Adhesion on Tribological Properties of Silver-Coated Alumina. Proceedings of 17th International Conference on Metallurgical Coatings. April 2–6, 1990, San Diego, Calif. 8. Baglin, J. 1989. Interface Structure and Thin Film Adhesion. In Handbook of Ion Beam Processing Technology. Cuomo, J.J., S.M. Rossnagel, and H.R. Kaufman, eds. Noyes Publication, Park Ridge, N.J., p. 279. 9. Beglin, J.E.E. 1985. Adhesion at Metal-Ceramic Interfaces: Ion Beam Enhancement and the Role of Contaminants. Mat. Res. Soc. Symp. Proc. 47:3. 10. Erdemir, A., G.R. Fenske, F.A. F.A. Nichols, and R.A. Erck. 1989. Solid Lubrication of Ceramic Surfaces by IAD-Silver Coatings for Heat Engine Applications. Presented at 35th STLE/ASME Tribology Conference, Ft. Lauderdale, Fla., Oct. 16–19, 1989, STLE preprint 89-TC-2E-1. 11. TRIM-89. The TRansport of Ions in Matter. Computer program provided courtesy of J.F. Ziegler, IBM Research, Yorktown, N.Y. 12. CRC Handbook of Chemistry and Physics, 60th ed., CRC Press, Boca Raton, Fla. 13. Schrott, A.G., R.D. Thompson, and K.N. Tu. 1986. Interaction of Copper with Single Crystal Sapphire. Mat. Res. Soc. Symp. Proc. 60:331. 14. Erck, R.A., and G.R. Fenske. 1990. Adhesion of Silver Films to Ion-Bombarded Zirconia, to be presented at STLE/ASME Tribology Conference, Oct. 7–10, 1990, Toronto, Ontario. 15. Erdemir, A., G.R. Fenske, R.A. Erck, and C.C. Cheng. 1990. Ion-Assisted Deposition of Silver Films on Ceramics for Friction and Wear Control. Lubr. Eng. 46:23. 16. Handbook of Thin-Film Deposition Processes and Techniques. 1988. K.K. Schugraf, ed. Noyes Publication, Park Ridge, N.J.

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Figure 1 Adhesive strength of silver films deposited on (A) alumina and (B) zirconia as a function of sputtercleaning time(0.04 mA/cm 2). Reprinted with Permission from: Argonne National Laboratory

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PULSED LASER PROCESSING OF SOLAR CELLS Rajiv K. Singh University of Florida Gainesville, Florida J. Narayan North Carolina State University Raleigh, North Carolina

Abstract Pulsed nanosecond excimer lasers can be effectively used for fabrication of silicon based solar cells having controlled junction depths and sheet resistivities, and high minority carrier lifetimes. By using pulsed beams, the ion implanted layers are melted and the underlying ''defect-free crystal'' provides a seed for subsequent crystal growth, resulting in 100% electrical activation of the dopant atoms. The understanding of the laser-solid interactions throws insight into the thermal effects of solids irradiated with pulsed laser beams. For metallization of the p-n junctions, the excimer laser beams can also be used to deposit stoichiometric good quality TiN thin films by evaporation of bulk TiN targets. Introduction Pulsed excimer laser beams (wavelength λ = 0.193–308 µm, pulse duration τ = 15–45 × 10-9 sec) are ideally suited for fabrication of efficient (shallow junctions) solar cells [1,2]. High quality p-n junctions can be fabricated from polycrystalline silicon by ion implantation followed by laser annealing. By using pulsed nanosecond laser beams, the whole process (melting and resolidification) is completed within 200 × 10-9 sec [3,4]. Since the solidification velocities are typically 4 to 5 m/sec, and the specimens are subjected to very short times at high temperature, impurity segregation at the grain boundaries is completely eliminated. The depth of pn junctions can be controlled by varying the laser and ion-implantation parameters. This process leads to formation of "defect-free" p-n junctions with response in the blue region close to that of p-n junctions fabricated from single crystals. In addition, since the substrate temperature remains close to the ambient value during laser annealing, minority carrier lifetime (MCL) of the substrate is not degraded as often happens during conventional furnace annealing. This factor leads to higher quantum efficiency for longer wavelengths in the red region. Thus, the overall efficiencies of solar cells are considerably improved. The next important step in the formation of solar cells, after the formation of p-n junctions, is the metallization process. This step assumes additional importance, particularly for shallow junctions. Recently, we have identified a pulsed laser evaporation technique [5–9] for TiN film fabrication at very low temperatures (25–400ºC). The TiN films are polycrystalline with grain size of ~100 Å, and electrical properties close to that of bulk TiN. This technique can be successfully used for metallization of shallow junctions without adversely affecting the junction characteristics. Laser-Solid Interactions The understanding of the laser-solid interactions provides information on the effect of laser parameters including pulse energy density, wavelength, pulse duration on the maximum melt depths, melt lifetimes, surface temperatures, and solidification velocities. The photon energy of a

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nanosecond excimer laser beam is absorbed by the semiconductor by electron-hole excitations and other absorption mechanisms resulting in thermal equilibrium of the carriers in less than 10-13 sec. The laser energy is transferred to the lattice by photon emission processes (heat) in times of the order of 10-12 sec, and thus for nanosecond irradiation regimes, the plasma effects of excited carriers are negligible [3]. The laser energy manifests itself in the form of heat, and the thermal effects of nanosecond laser irradiation can be determined by the solution of one-dimensional heat flow equation with appropriate boundary conditions, while taking into account the phase changes occurring in the material. A three-dimensional solution is not required because of the very short processing times (~200 ns) and the large transverse dimensions of the laser beam, which result in thermal gradients many orders of magnitude greater in the perpendicular direction to the surface than compared to the transverse directions [3,4]. The one-dimensional heat-flow equation is given by where, x refers to the direction perpendicular to the plane of the sample and t is the time, and the subscripts i = 1,2 refer to the solid and liquid phase, respectively. The terms ρ, C, K, R, and α correspond to the temperature dependent mass density, specific heat capacity, thermal conductivity, reflectivity and absorption coefficient of the incident laser beam, respectively. Io corresponds to the time dependent laser intensity striking the surface. The boundary conditions at the front and back surface assume that there are no thermal losses which approximately hold for nanosecond processing times. The solid-liquid interface is assumed to be at the melt temperature, and the position of the interface S is determined by the heat balance equation at the interface given by where Ks and K1 are the solid and liquid thermal conductivities at the interface, and L is the latent heat per unit volume of the material. The presence of a moving solid-liquid interface, and the temperature dependent thermophysical and optical properties make the analytical solution of the heat flow equation intractable, and thus approximate numerical techniques have to be applied. To solve Equation (1), we have adopted a higher order implicit finite difference method in which the thermal gradients at the interface are accurately determined for calculating the interfacial velocity[4]. The temperature dependent optical and thermal properties and the time dependent laser intensity have been taken into account in this solution. The laser irradiation of ion-implanted samples leads to the removal of the implantation damage up to the distance of the maximum melt depth. The underlying defect-free substrate acts as a seed for subsequent crystal growths, resulting in removal of ion-implantation damage and electrical activation of the dopant atoms. To verify the working of the heat flow program the simulated values of the maximum melt depths were compared with the experimental values obtained by excimer laser irradiation of ion-implanted samples at various energy densities. Figure 1A shows TEM micrographs of boron-implanted samples which were irradiated with XeCl laser having a trapezoidal pulse shape and full width at half maximum (FWHM) of 25 and 70 × 10-9 sec, and energy density varying from 1.0 to 2.5 J/cm2. A complete removal of the dislocation loops in the annealed region together with a sharp transition between the annealed and unannealed regions is observed. The V-shaped dislocations are created because the melt front intersects the dislocation loops, and the two segments of the dislocation grow back to the surface because the dislocation cannot end inside the perfect lattice.

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The kinetics of the melt front is crucial in understanding the nature of laser-solid interactions. Figure 2A shows the position of the solid-liquid interface of XeCl laser irradiated samples as a function of time for different pulse energy densities and durations. The slope of the curves corresponds to the velocity of the melt front at any instant. The figure shows that above a certain energy density and after a certain time interval, the surface starts to melt, and the melt front penetrates several thousands angstroms before heading back to the surface. The solidification velocity is approximately a few meters per second, which is about five orders of magnitude greater than the normal crystal growth velocity. The maximum solidification velocity dS/dt can be estimated as

where D corresponds to the thermal diffusivity, Tm the melt temperature, and C is constant factor between 1.5 to 2.0, the exact value depending on the shape of the laser pulse. The maximum melt depths for excimer XeCl laser irradiation of silicon at different energy densities and pulse durations is shown in Figure 1B. For both 25 and 50 ns laser pulses, the maximum melt depth is found to be proportional to the energy density. The x intercept corresponds to the minimum energy required for propagation of the melt front into the substrate (Eth). The melting threshold can be estimated from energy balance considerations [4], and is approximately equal to

where R1 is the liquid reflectivity and τ correspond to the pulse duration. If we perform an energy balance, the maximum melt depth ∆xt as a function of energy density is given by

where C1 = (1-R1)/(ρCpTm + L) is constant for a particular material and corresponds to the slope of the graph in Figure 1B. The value of C 1 for silicon is 3800Å J-1 cm2, which is quite close to the value obtained from detailed heat flow calculations (3870Å J-1 cm2). Another important aspect in the understanding of the laser-solid interactions are the temperature profiles generated during intense nanosecond laser irradiation. Figure 2B shows the surface temperature of silicon as a function of time for a 25 ns excimer laser pulse having different energy densities. It is seen from this figure that the surface temperature rises rapidly until it reaches the melting point of the material, where it pauses momentarily until the change in reflectivity upon melting of silicon is compensated, and then rises again until its maximum value. On cooling, the surface temperature quickly drops to the melt temperature and remains there until the interface recedes to the surface. From energy balance considerations, we can estimate the temperature rise as a function of energy density. The temperature rise above the melting temperature ∆T is equal to

This expression shows the parabolic nature of the surface temperature rise above the melt temperature with increasing pulse energy density. For silicon, the value of the constant in Equation (6) is equal to 242 K/(J cm-2)2 for a 25 ns pulse, which corresponds closely to the value of 242 K/(J cm-2)2 obtained from detailed heat flow calculations.

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Electrical Properties of Laser Annealed Samples The melt depth corresponds to the thickness to which the annealing of the implantation damage is observed. Laser annealing of ion-implanted damage yields significant improvement in the electrical properties important for photovoltaic applications. The number of electrically active implanted ions found to be present at the substitutional sites after laser annealing is much higher than conventional thermal annealing. After laser annealing, the ion-implanted specimens are completely free of extended defects, whereas a high density of loops and dislocations is observed in furnace-annealed specimens. Figure 3A shows a plot of the carrier concentration as a function of implanted dose after laser and conventional furnace annealing. A 100% electrical activation is realized after laser annealing compared to a less than 80% electrical activation after furnace annealing. Since pulsed melting involves subsequently non-equilibrium rapid quenching, the dopant concentrations far exceed the equilibrium solubility limits which can be incorporated into substitutional lattice sites via solute trapping phenomena[10]. It has also been observed that the laser annealing does not degrade, in contrast to thermal annealing, the minority carrier lifetime in the substrate or the base region because of the very short thermal diffusion lengths[1]. The laser annealing allows precise control of parameters especially junction depth, sheet resistivity, and MCL, which result in increased yield and improved cell performance. The wavelength of the laser beam was found to strongly affect the solar cell characteristics. Under optimum annealing conditions, all the cells had open circuit voltage ranging from 600–610 mV and fill factors (FF) in the range of 0.77–0.80. However, there was noticeable difference in the short circuit current, Jsc. In general, the excimer laser annealed samples showed better Jsc than the ruby annealed ones; whereas among the excimer laser annealed samples, the BF3 implanted cells had higher Jsc than cells obtained by direct 5 kV implantation of boron. The results can be understood from internal quantum efficiency measurements before the application of antireflection coatings. The results shown in Figure 3B clearly indicate that the BF3-implanted, excimer laser annealed cells have the highest blue response. This can be attributed to the high quality shallow junctions formed from shallow implantation (1 kV) and extremely uniform annealing obtained with excimer laser. The best discharge implanted, excimer laser annealed solar cells obtained so far have the parameters Voc = 610 mV, Jsc = 34.7 mA/cm2, FF = 0.79, which result in an efficiency of 16.7%. This efficiency is comparable to the highest efficiency of Si solar cells made by more sophisticated conventional methods. The excimer laser can be used effectively for the metallization of the solar cell by depositing thin layers of TiN using the pulsed laser evaporation technique (PLE). In this method, a pulsed excimer laser is used to evaporate thin a TiN target material in a high vacuum chamber, and the film is deposited on a substrate which is placed parallel to the target [6–8]. An important advantage of this technique is that under optimized laser conditions, the film retains its stoichiometry over a large area. Because of-the high kinetic energy and the mobility of the species, the TiN films can be fabricated in a temperature range of 25 to 400ºC. Figure 4A shows a typical Auger electron spectroscopy spectrum for a TiN film deposited on silicon at 400ºC and 5 J/cm2. The Auger spectrum of the films shows that the principal peaks corresponding to nitrogen and titanium are overlapped, thus complicating the analysis of the film. However, the Auger peaks are similar to the TiN bulk target, including the oxygen peak at 508 eV (as shown in Figure 4B. From the similarity of the two spectra, it is concluded that the material resistivity behavior with temperature, with a room temperature value of approximately 150 mW cm. These films are characterized by very small grains (~100 Å) which are randomly oriented to each other. In conclusion, we have shown that laser processing of solar cells can be very effectively used to control junction depths, sheet resistivities, and

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result in large minority carrier lifetimes. The excimer laser can be further used to evaporate stoichiometric nitride layers for metallization of the solar cells. References 1. White, C.W., J. Narayan, and R.T. Young. 1979. Science 204:461. 2. Young, R.T., J. Narayan, W.H. Christie, G.A. Van der Leeden, J.I. Levatter, and L.J. Chen. 1983. Solid State Technol. 26:183. 3. Wood, R.F., and G.E. Giles. 1981. Phys. Rev. B23:2923. 4. Singh, R.K. and J. Narayan. 1989. Mat. Sci. and Engr. B3:217. 5. Biunno, N., J. Narayan, S.K. Hofmeister, A.R. Srivatsa. and R.K. Singh. 1990. Appl. Phys. Lett. 54:1519. 6. Narayan, J., N. Biunno, R.K. Singh, O.W. Holland, and O. Auchiello. 1987. Appl. Phys. Lett. 51:1845. 7. Singh, R.K. and J. Narayan. 1990. Phys. Rev. B41:8843. 8. Singh, R.K. and J. Narayan. 1990. J. Appl. Phys. 68:233. 9. Singh, R.K., N. Biunno and J. Narayan. 1988. Appl. Phys. Lett. 53:1013. 10. Narayan, J. R.T. Young and C.W. White. 1987. J. Appl. Phys. 49:3912.

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Figure 1A XTEM micrographs showing depth of melting as a function of energy density for 25 and 70 ns laser pulses: (a) 1.0; (b) 1.5 J/cm2 with pulse duration τ = 70ns; (c) 1.0; and (d) 2.0 J/cm2, with τ = 25ns. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

Figure 1B Calculated depth of melting as a function of energy density and pulse duration for XeCl laser irradiated Si samples. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

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Figure 2A Melt from for 25 and 50 ns laser pulse. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

Figure 2B Surface temperature for 25 ns laser pulse as a function of time for Si samples irradiated with XeCl excimer lasers at different energy densities. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

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Figure 3A Carrier concentration as a function of implanted dose in thermally and laser annealed specimens. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

Figure 3B Comparison of the internal quantum efficiency between cells fabricated using excimer laser annealing after BF3+ (1kV) and 11B+ (5kV) implantations. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

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Figure 4A Auger electron spectrum taken from a TiN film grown at 5 J/cm2 and 400ºC. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

Figure 4B Auger electron spectrum taken from a bulk TiN target irradiated after 4 min Ar sputtering. Reprinted with Permission from: Materials Sciences & Engineering Department, North Carolina State University

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SURFACE MODIFICATION TECHNOLOGIES USING CONCENTRATED SOLAR RADIATION J.R. Pitts, J.T. Stanley, and E. Tracy Solar Energy Research Institute Golden, Colorado C.L. Fields Dept. of Chemistry University of Northern Colorado Greeley, Colorado

Abstract A recent report by the National Research Council, entitled Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Materials, presents "a unified view of recent progress and new directions in materials science and engineering." In particular, it describes important new areas of research and development, the roles of the federal and private sectors as they relate to a balanced national materials effort, and areas of work deemed crucial to the strength of the U.S. economy and defense. Research conducted at the Solar Energy Research Institute (SERI) during the past three years addresses a number of the critical areas described in this report and has explored the possibility of using highly concentrated solar radiation to induce beneficial surface transformation. The principal goal is to develop new coatings and processes that improve the performance and lifetime of materials at reduced processing costs. Highly concentrated radiant energy provides a controllable means of delivering large flux densities to solid surfaces, where the resulting thermal energy can cause phase changes, atomic migrations, and chemical reactions on a surface without greatly perturbing the bulk properties; alternatively, the photons may directly interact with species on the surface. These changes may result in improved properties of the materials by making the surface harder, more resistant to corrosion or wear, thermally resistant, or with lower coefficients of friction. In a solar furnace, this flux can be delivered in large quantities over large areas, or it can be tailored to match the demands of a particular process. Furthermore, this occurs without the environmental liability associated with providing power to more conventional light sources. Recent work at SERI has used fluxes in the range from 100 to 250 W/ cm2 for inducing such beneficial surface transformations. Significant results have been obtained in the area of phase transformation hardening of steels and melting powders and preapplied coatings to form fully dense, wellbonded coatings on the surface. New directions in coating technology using highly concentrated solar beams to induce chemical vapor deposition processes are described here. Application areas that have not been researched in detail but would appear to be good matches to the solar technology are also reviewed. INTRODUCTION Several years ago, when the price of oil dropped below $20 per barrel, interest in generating electricity with alternative sources waned. However, a substantial technology base for concentrating solar energy existed. The natural question to ask was, "Is there anything unique or something that has commercial potential that can use highly concentrated solar radiation?" We embarked upon a study of this question and determined that there is no salient uniqueness to exploit but that there are commercial potentials in areas of technology that require the supply of large amounts of radiant energy[1]. Solar radiation can be directed and concentrated with reflectors that lose

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only 5–10% of the radiation at each reflection. Lasers and arc lamps, on the other hand, operate with total conversion efficiencies in the range of 4–9%. Therefore, for processes that require large amounts of radiant energy and where the solar resource is compatible, substantial cost savings might be obtained by using solar furnace technology[2,3]. We have looked at performing surface modification processes with highly concentrated solar beams in some detail. Most of the work has used solar fluxes in the range from 100 to 250 W/cm2. Recently, however, there has been a push to raise the available flux using secondary concentrators, and fluxes up to 2000 W/cm2 have been produced[4]. The potential to go to even higher fluxes for some applications exists, but we have obtained interesting results at the relatively modest flux levels available for most of our experiments. The topical areas that we have experimented with include phase transformation hardening, cladding, radiant joining, initiating selfpropagating high temperature synthesis (SHS) reactions, and rapid thermal film growth in controlled atmospheres. Other areas of interest that have been identified are rapid thermal annealing, zone melt recrystallization, rapid thermal processing of ceramic materials, metallization of ceramics, and joining ceramics. Progress in the former areas is described, and the potential of applications in the latter areas is outlined. PROGRESS Phase Transformation Hardening Experiments using solar beams to modify the surface properties of metals have been relatively successful. Hardenable steels (A2, 4340, and nitride grade) have been pulsed and scanned to produce hardened zones on the surface[5]. In addition, we have performed some hardening and annealing procedures on some Cu alloys to demonstrate that near surface regions can be modified without affecting the bulk of the material. These experiments were accomplished on substrates varying in thickness from 1 mm to 1 cm and with pulses varying from 1 to 30 s. With fluxes in the range from 100 to 250 W/cm2, surface regions from 1 to 4 mm can be fully hardened. However, the heat affected zones (HAZ) are not sharp and extend to the back side in samples with longer exposures. Processing at 250 W/cm2 is not viable for most surface hardening tasks because of the depth of penetration of the HAZ. It is known that at flux levels 4 times greater, very nice surface hardening processes can be performed, and applications in selectively hardening plow blades are fully developed[6]. Cladding Experiments in cladding corrosion and wear resistant materials onto steel substrates have been quite successful. We have been able to clad a variety of powders to 4340, A2, and 1040 steels, as well as to pure iron and nickel substrates. The powders used to date are commercially available plasma spray powders: NiCr alloy (#761), 316 stainless steel, WC in a Co matrix, nickel aluminides, and chrome oxide. The principal difficulties in performing the cladding operations is not the flux levels available, but the control of the atmosphere during the cladding operation, and the horizontal geometry of the beam line in the available facilities. Powders absorb the radiation very well through multiple reflections and heat rapidly because of relatively poor conduction to the substrate. The geometry of the available furnaces dictated mounting the target surfaces vertically, and this meant that the powders had to be fixed to the surface with a binder. Gravity and the outgassing of the binder caused some difficulties, which had to be overcome by applying the appropriate thermal profile. For some samples, substrate oxidation at elevated temperatures prevented the melt from wetting the surface. In these cases, metallurgical bonding did not occur, and it was necessary to go to controlled atmospheres to prevent oxidation and get a good quality clad. The

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results of these experiments and micrographs of the metallurgical cross-sections are presented elsewhere [7]. Radiative Joining Certain aluminum/bronze alloys are under development for use in forms to lay up carbon fiber composite structures for aerospace vehicles. There are a variety of reasons that this material development is needed for the composite manufacturing. The most important are that the forms are easily designed by CAD/CAM procedures and cast in near net shape, and the materials may be selected such that they precisely match the coefficient of thermal expansion of the cured composite structure. Further, the expected lifetime of the forms is long compared to the monolithic graphite forms now in use, and they can be assembled from subunits so that the casting procedures are simple and inexpensive. The problem that is solved by radiative joining is that of making the seams gas-tight to 100 psig without warping the form. This requirement rules out any conventional means of brazing because the forms have an unusual honeycomb configuration that warps at low temperatures. So a radiative joining technique is the only one that works. Laser welding is effective but expensive compared to the other steps in the process, and it leaves a surface bead that must be postmachined. The material is highly reflective in the infrared, so laser brazing procedures are difficult to carry out. Using absorber coatings for the laser results in so much heat being put into the surface that the near surface melts or evaporates before penetration to braze alloy depth is achieved. A solar beam in the range of 300 W/cm2 provides the right heating rates and depth of penetration for an effective brazing procedure. Experiments were carried out on small coupons at first, until the appropriate combination of flux and braze alloy were found. Successful joints were made with these coupons. Initial experiments with a pilot scale test piece using the full honeycomb structure resulted in severe warping of the plates. This was caused by the size of the beam at the Sandia Solar Furnace and the large total thermal delivery on target. With a water-cooled aluminum mask between the beam, and the target seam positioned such that only a strip 2 mm wide was illuminated, a good metallurgical joint was achieved, thereby demonstrating the viability of the process. Optimization of the process remains. This will require a substantial commitment in terms of R&D effort and equipment. About 2 kW total power is needed in a beam of 4 mm diameter, with a peak flux of about 500 W/ cm2. Two axis flexibility in the light optics is also needed (perhaps a fiber optic delivery system!), as well as a three axis manipulator for the target piece. This would be a very nice engineering project with important implications in the future for applications in space [8]. Self-Propagating High Temperature Synthesis Reactions The SHS reactions are characterized by being so exothermic that the heat released upon initiation of the reaction is sufficient to allow propagation throughout the bulk of the mixed reactants until all of the reactants are consumed. The classic example is the thermite reaction. When powders of starting materials or layers of thin films are used, it is sometimes found that the reactions do not propagate uniformly. Further, for some materials the reactions can only be sustained or the right product can be obtained only if the reaction mixture is maintained above a defined (high) temperature. Both of these situations can be addressed by supplying additional energy to the reaction mixture prior to and during the reaction. For the production of coatings, delivering radiant energy to the surface of the target is the most convenient and conservative method of supplying the extra energy required to produce the desired phase. We have experimented with several SHS reactions designed to deposit high quality ceramic and intermetallic materials on ordinary metal substrates. The research is in a very early stage, but encouraging results can be reported.

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Three types of experiments have been carried out. Mixtures of pure powders have been glued to Fe, Ni, Ti, Mo, and 4340 steel substrates. Exposure to a 1–6 a pulse in a solar furnace is sufficient to initiate the reactions, and coatings of various nickel aluminides, TiB2, and TiC have been formed. Because these exposures were performed in air, some of the film quality is poor. In some cases, parts of the films either lifted off or did not wet the substrate material. In other cases, so much energy was deposited on the surface of the substrate that substantial melting and surface roughening occurred during the reaction. Other experiments involved exposing multiple layers of vacuum-deposited thin films. In this case, the films were too thin to allow propagation over the whole surface and depended upon the radiative input of energy to drive the reaction. High quality nickel aluminide films were formed approximately 1 µm thick. The third type of experiment involves reacting preapplied plasma spray coatings with their substrate material to form a new alloy phase on the surface. The specific sample set used plasma sprayed aluminum on Fe, Ni, and Ti substrates. Exposures were conducted in air. Aluminides with the substrate materials were formed as a result of exposure in the solar beam. Thin Film Growth in Controlled Atmospheres Early experiments pointed out the need for inert atmospheres over most target materials to control oxidation. A high-vacuum-compatible target chamber was constructed to allow this. By modifying the chamber to allow us to control the flow of reactive gases over the target during exposure to the solar beam, we produced the capability of conducting rapid thermal chemical vapor deposition that results in thin film growth directly on the target. This system allows programmable control of gas constituents (up to four gases simultaneously), flow rate, pressure, and target temperature. The near-term objective for this research is to explore the growth of several ultrahard coating materials (hard carbon, TiN, SiC, and TiB2) on substrates of steel, Fe, Ni, and Si. Longer-term objectives include the growth of multilayer electronic materials, especially photovoltaic materials. Thin films of carbon have been grown on Ni and Si substrates using CH4 and H2 as precursors. The carbon growth on Ni results in a graphitic phase. Experiments with Si substrates have produced thin films of SiC and diamond-like carbon films, as well as graphitic carbon, depending upon the growth conditions. The objective of this area of investigation is to define the process parameters required for diamond thin-film growth. Current technology requires using large amounts of energy to grow diamond thin films, and this may be an area where the solar-based technique can have a substantial advantage over the more conventional techniques employing microwave plasmas or hot filaments. FUTURE AREAS OF RESEARCH AND DEVELOPMENT When one considers the nature of the energy resource and the method of delivery, it becomes obvious that the areas of applicability of solar furnace technology are processes that require very high temperatures, or very high heating rates, or where the cost of energy is one of the major factors driving the cost of the process. Further advantage for the solar technology is gained when we can exploit either the large area capability or the ability to operate in remote locations more effectively than conventionally powered resources. These criteria suggest several candidate areas of future research and development: • Rapid thermal processing of ceramic materials — This would include selective structural refinement, metallization, joining, and bonding ceramics to metals. In addition, SHS reactions could be used to deposit ceramic coatings on either ceramic, composite, or metallic materials.

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Zone melt recrystallization — This process remelts and recrystallizes materials that have been previously formed. The objective is to produce larger crystals or crystals with fewer defects. • Metalorganic deposition — In this process, substrate materials are dipped, sprayed, painted, or spincoated with metalorganic materials that are dried and fired in a rapid thermal process to derive special properties in the coatings or at the interface, or to minimize interaction with the substrate. These processes can be used to deposit metal, optical, and electronic coatings. • Rapid thermal processing of electronic materials — This would include initiating and controlling diffusion processes and the rapid thermal chemical vapor deposition of multilayered electronic structures. Wide-area applications would be of primary interest and would include the growth of photovoltaic films and high temperature superconductor coatings. • Materials science and processing and construction in space — A number of extraterrestrial applications exist for providing radiative energy for materials processing, repair, or refurbishing, and construction in space.

•

References 1. Pitts, J.R., J.T. Stanley, and C.L. Fields. 1990. Solar Induced Surface Transformation of Materials (SISTM). Proceedings of the Fourth International Symposium on Solar Thermal Technology, Santa Fe, N.M., June 13–17. B.P. Gupta and W.H. Traugott, eds. Hemisphere Publishing Corp., New York, p. 459. 2. Kolb, G.J. 1990. A Comparison of the Economics of Materials Processing with Solar Furnaces and High-Intensity Arc Lamps. Sandia National Laboratories, Albuquerque, N.M., (in preparation). 3. Short, W. Solar Energy Research Institute, Golden, Colorado. Private communication . 4. Lewandowski, A. Solar Energy Research Institute, Golden, Colorado. Private communication. 5. Stanley, J.T., J.R. Pitts, and C.L. Fields. Solar Induced Surface Transformation of Steel Samples. Proceedings of the Fifth Annual Northeast Regional Meeting (TMS): Protective Coatings: Processing and Characterization, May 3–5, 1989, Stevens Institute of Technology, Hoboken, N.J. R.M. Yazici, ed. TMS, Warrendale, Pa. in press. 6. Tan, R.K., N.L. Arrison, D.A. Parfeniuk, and D.M. Camm. 1988. Surface Treatment Using Powerful White Light Sources. VORTEK Industries LTD, October 7. 7. Pitts, J.R., C.L. Fields, J.T. Stanley, and B.L. Pelton. 1990. Materials Processing Using Highly Concentrated Solar Radiation. Proceedings of the 25th Intersociety Energy Conversion Engineering Conference , Reno, Nev., August 12–17. P.A. Nelson, W.W. Schertz, and R.H. Till, eds. American Institute of Chemical Engineers, New York. 6:262. 8. Pitts, J.R., T. Wendelin, and J.T. Stanley. 1990. Applications of Solar Beams for Materials Science and Processing in Space. Ibid. 1:553.

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A COMPARISON OF THE ECONOMICS OF MATERIALS PROCESSING WITH SOLAR FURNACES AND HIGH-INTENSITY ARC LAMPS* Gregory J. Kolb Sandia National Laboratories Albuquerque, New Mexico

Abstract The cost and performance of treating materials with a solar furnace were compared to similar treatment with high-intensity electric-arc lamps. Qualitative results indicate that because of the long focal length of the solar furnace, it is capable of performing much dirtier materials processing tasks than the arc lamp. Quantitative results indicate that if the furnace is located in a good solar region, the solar furnace can beat the economics of the lamp by as much as a factor of three under certain operating scenarios. In other scenarios, the lamp is more cost-effective. The scenario that appears most promising for the furnace is batch processing that employs flux levels near 500 W/cm2 or greater. At lower flux levels, or in assembly-line-type processing tasks, the arc lamp is preferred. Introduction High-intensity white light is finding increased usage within the materials processing community. White light sources with intensities ranging from 1000 to 22,000 times the terrestrial solar flux have been used by industry to perform transformation hardening of metals, rapid thermal processing of semiconductors, and advanced thermal testing of materials[1]. These applications are currently using an arc lamp developed by Vortek Industries Limited. The arc lamp is being used because it is a cost-effective alternative to processing with lasers. Concurrent with the deployment of these systems, the Solar Energy Research Institute (SERI) is conducting research sponsored by the U.S. Department of Energy to demonstrate materials processing using a high-intensity solar furnace. A furnace is being explored because it is much less dependent on conventional, nonrenewable energy resources and it may possess some unique capabilities. To date SERI's work has demonstrated case hardening of steel, powder coating and brazing of metals, as well as chemical vapor deposition [2]. Since the intensity and spectral content of the light emanating from the arc lamp and solar furnace are similar, it is feasible that these devices could perform similar materials processing tasks. The decision of which one to use would be determined by an economic comparison as well as other factors. If the processing factory is located in a poor solar region a furnace would not be practical and an arc lamp would be chosen. However, if the factory is located in a sunny region, such as the U.S. Southwest, a solar furnace could be the best choice. The purpose of this paper is to compare the economics of energy delivery from an arc lamp with a solar furnace located in the Southwest. Qualitative features of the systems are also discussed.

* This work is supported by the Department of Energy under contract DE-AC04-76DP00789.

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Description of the Arc Lamp System The arc lamp system chosen for study is Model 110-100c built by Vortek. The white light emanates from a single arc tube. Water and gas are injected into the arc tube with high angular momentum and spiral down inside the tube. The water forms a thin layer on the inside surface of the tube and the gas (argon, krypton, or xenon) forms a vortex within the liquid wall. The gas vortex stabilizes the arc along the tube axis and the Water-WallTM restricts the arc diameter. Electrodes are internally water cooled. The Water-WallTM cools the arc tube and reduces the amount of electrode debris that reaches the tube. The spiraling water over the inside surface of the tube improves cooling and permits input powers up to 30 kW/cm of arc length and currents over 1200 amps. The Model 110-100c requires an electrical power input of 105 kWe. Uniform-focus and line-focus reflectors deliver approximately 31 and 20 kW of optical power to the target, respectively. By using the uniform reflector, the flux level at the target is 100 W/cm2, i.e., 1000 times terrestrial insolation or 1000X. This flux is uniformly distributed over a rectangle measuring 20 cm × 12 cm. By using the line reflector, the flux level at the target is 5000X with the peak occurring along a 20 cm line with a 50% reduction in flux 1.5 cm away from the line. The target is placed in the focal point which is a few centimeters away from the reflector/lamp assembly. To protect the assembly during a sputtering materials processing task, an air curtain is often installed between the focal point and the assembly. A typical Vortek arc lamp system is pictured in Figure 1. Description of the Solar Furnace System Many experimental solar furnaces exist throughout the world. These facilities are rated at power levels from a few kilowatts to several megawatts at flux levels ranging from 1000 to 1700X. Each of these systems is unique, and a commercial manufacturer of these systems does not exist. However, it is plausible that given a market need and favorable economics, a solar furnace industry could arise. Based on Sandia's experience with building two solar furnaces[3,4], we were able to make a reasonable projection of a commercial design. One of the Sandia furnaces is pictured in Figure 2. Solar flux is initially reflected by a flat mirror assembly called a heliostat. The reflected beam passes through an attenuator to a secondary parabolic concentrator where it is redirected toward the target located several meters away from the concentrator. Due to the long focal length, the concentrator would be protected from damage that could occur during a sputtering materials processing task. A control system is used for heliostat tracking of the sun and to adjust power level via movement of the attenuator. (The attenuator controls light much like a common window blind.) The secondary concentrator is composed of several individual facets that can be aligned to produce a variety of flux shapes and peak flux values on the target. Optical power delivered to the target has a peak value of 16 kW. The hypothetical commercial furnace chosen for study here consists of components representing newer and more simplified technology than was employed in the 16 kW furnace. For example, rather than using the glass heliostat, glass concentrator, and stand-alone attenuator depicted in Figure 2, a commercial furnace could be composed of a stretched-membrane heliostat[5] and a stretched-membrane concentrator[6], and could employ a simple attenuator that is incorporated into the side of the building. The newer technology is much more lightweight and is estimated to cost significantly less. We performed an annual performance calculation using actual insolation data[7] recorded at 15 minute intervals to determine the optimum optical design of the commercial furnace. This analysis indicated that a circular heliostat with a diameter of 13.8 meters in combination with a 10-meter concentrator, gave the best annual performance. This design produced a peak

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MATERIALS PROCESSING AND SYNTHESIS

86

power of near 50 kW with a steady state power of 38 kW. This steady state power was chosen because it is in the same range as the 31 kW Vortek arc lamp and it was identified as the optimum that can be produced with a single large heliostat. To be comparable to the high quality of the arc lamp beam, we assumed that the flux level and shape of the beam from the furnace must remain relatively constant while in operation.1 This can be accomplished by adjusting the attenuator to maintain a constant power and by keeping the concentrator completely covered with light from the heliostat. If the concentrator is not completely covered, a skewed flux pattern could occur on the target. Because of these restrictions, a fraction of the solar power reflected early and late in the day is not usable because the power is too low or because the angle of the sun relative to the heliostat causes a heliostat image that is too small. Given the constraint of a high quality beam, we calculate that the commercial scale furnace would be able to operate an average of 6 hours per day over the course of a year. Definition of Case Studies We will compare the economics associated with materials processing tasks that require flux levels of either 1000 or 5000X with a total power of between 20 and 40 kW. An example of a task conducted at 1000X is rapid thermal annealing of semiconductors. We will also investigate assembly-line vs. batch processing tasks. In an assembly-line application, the materials processing task performed by the lamp or furnace is only one task of an assembly line that operates continuously. For example, initial tasks in an assembly line could be to manufacture a metal part. This part would travel down the line and subsequently undergo surface treatment by the arc lamp or furnace. The assembly line is assumed to operate 24 hours a day when using a lamp and during the daytime when using the furnace. An operating crew is employed to only perform actions related to the assembly line. The crew size is assumed to vary depending on the complexity of the assembly line process. If the lamp or furnace is unavailable due to equipment failures, or if the furnace is unavailable due to bad weather, the crew does not perform other tasks. When comparing the economics of arc lamps and furnaces within an assembly line, we included costs related to the size of the crew because one technology may have an advantage related to optimum utilization of crew time. For example, in a poor solar region the arc lamp should beat the economics of a furnace because the crew would waste time waiting for sunny conditions.2 In a batch processing application, the lamp or furnace would only be operated a fraction of the work day. In this analysis we investigate situations in which they are operated an average of 2, 4, or 6 hours per day. When comparing the economics of arc lamps and furnaces within a batch process, we did not include costs related to the size of the crew because they can perform other constructive tasks when the lamps and furnaces are unavailable. It should be noted that most of the lamps Vortek has sold are used in a batch mode.

1 This is a conservative assumption since certain materials processing tasks may be able to use variable power levels and flux shapes. 2 In a poor solar region the arc lamp would also beat the furnace because capital equipment located in the assembly line would be underutilized. As a first cut we have not included this effect and have implicitly assumed that the cost associated with the crew is more important than the capital expense.

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MATERIALS PROCESSING AND SYNTHESIS

87

Economic Models We compared the levelized energy cost (LEC) of delivering power to the target. Assuming that inflation and escalation do not occur during the life of the equipment (constant dollar analysis), the LEC can be calculated with the following equation:

The annualized capital cost is the fraction of the installed capital costs that must be paid every year during the life of the equipment (assumed to be 30 years) to repay the principal and interest on the loan and other smaller items. This fraction is reduced to include depreciation allowances. It is calculated by multiplying the installed capital costs by a fixed charge rate. In this analysis we used a typical fixed charge rate of 10.5% [8]. The annual operating and maintenance (O&M) costs include items such as parts replacement, electricity to run the equipment, and general repair and maintenance. The annual energy is the summation of the optical power delivered to the target over the course of a year and is expressed in kilowatt-hours. In Table 1 and 2 we compare estimates for installed capital costs, O&M costs, annual energy, and LEC for the arc lamps and solar furnace for a batch mode operation in which they are operated 6 hours per day. Blank entries in the tables imply that the cost and performance item is identical to that listed in the column to the left. In Table 1 arc lamp costs are given for the 1000X and 5000X systems by assuming two different prices of electric power. Since the arc lamp systems use a significant amount of electric power, this parameter was varied to gauge its effect on LEC. The cheap electric power case assumes $0.05/kWh and the expensive, $0.094. The former case is typical in many parts of the United States, and the latter is what is charged for power in Albuquerque, New Mexico, home of Sandia National Laboratories and an excellent solar region. The anode and cathode within the lamp degrade after a few hundred hours of operation and must be replaced. In addition, we have assumed that the lamp and reflector must be changed once per lamp-year (8760 hours of operation). Since the target is only a few centimeters away from the lamp and reflector, it is plausible that a sputtering materials processing task or some other accident could damage these items. The costs related to the cooling tower and water are needed to cool the lamp, as described previously. The arc lamp system is also expected to have an electric hookup charge, beyond what would be needed by the furnace, because of the current and voltage ratings of the equipment. It can be seen in Table 1 that each arc lamp reflector delivers different amounts of optical power to the target; the 1000X model furnishes nearly 31 kW and is more efficient than the 5000X model which supplies 19.2 kW. This performance penalty associated with increased concentration is not expected with the solar furnace system. In Table 2 costs of solar furnaces are given for two different assumptions regarding the capital costs of the heliostat and concentrator. For the expensive case, the prices were estimated based on Sandia's experience with building our two experimental solar furnaces. These costs are high because they were specially built for us and we could not benefit from cost reductions due to mass production. For the cheap case, the prices were estimated by assuming a mass production scenario of approximately 2500 heliostats and 2500 concentrators per year. Such a scenario is predicted to

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MATERIALS PROCESSING AND SYNTHESIS

88

occur when solar central receive and Stirling dish power plants are built in the Southwest[8].3 Case Study Results Figure 3 displays the results for batch processing of materials. The LEC is reduced as operating hours per day increase because the systems deliver more annual energy to the target, given a fixed capital cost; i.e., the systems are utilized more fully. We have limited the chart to 6 hours per day because we calculate the commercial scale furnace could operate up to 6 hours a day, on the average, over the course of a year in the U.S. Southwest. It can be seen that the economics of the furnace and the 1000X lamp are similar for batch operations less than 4 hours per day. Beyond 4 hours the furnace has the advantage. It is also seen that the furnace beats the economics of the 5000X lamp for every case. Depending on the combination of assumptions depicted in the Figure 3, the LEC from the furnace is from 25 to 75% less than the 5000X arc lamp. The furnace has a greater advantage over the 5000X lamp because, as stated earlier, the 5000X reflector is less efficient than the 1000X reflector. Finally, it should be noted that if Figure 3 is modified by replacing LEC with the present value of the capital and annual O&M costs, given a 30 year life and a 6.5% discount rate, the conclusions do not change. Figure 4 displays the results for continuous processing of materials. These LEC curves are dominated by the wages paid to the crew members (the loaded salary was assumed to be $7000/man-years). The 1000X arc lamp is seen to take a significant advantage as the crew size associated with the process train becomes larger. The primary reason the furnace is not as good as the 1000X lamp is because the crew is not being used optimally. The process train and the crew are idle during cloudy periods, as well as during early morning and late afternoon when the insolation is poor. Operation of the lamp, on the other hand, is not affected by the weather. It can also be seen that the economics of the 5000X lamp is similar to the furnace. The 5000X lamp lost the advantage the 1000X lamp had over the furnace because of the efficiency drop described previously. Summary and Conclusions The arc lamp and solar furnace each have their own set of advantages. The advantages of each are summarized below. Arc Lamp Advantages • Arc lamps are more convenient since they are not dependent on the weather. The materials processing business can precisely schedule their use. • The materials processing industry does not have to be located in a sunny region such as the Southwest. • Because of better utilization of the operating crew, the arc lamp is recommended for materials processing tasks located within a continuous process. • The capital cost of an arc lamp is lower than that of a solar furnace. • The arc lamp is much smaller than a solar furnace and would be easier to implement within an existing building.

3 We have increased the costs of the heliostat and concentrator beyond what is quoted in these studies because solar furnaces are small relative to power plants and do not enjoy the same economies of scale.

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MATERIALS PROCESSING AND SYNTHESIS

89

Solar Furnace Advantages • • • • • •

Since the focal point is much further from the reflector, the furnace will be able to operate in conjunction with dirtier materials processing tasks. The economics of the furnace is not dependent on the price of electricity. For Southwest locations, the furnace is significantly more economical than the lamp for batch processing tasks requiring concentrations near 5000X or greater. Operation of the furnace does not require cooling water. The solar furnace has lower operating and maintenance costs. The solar furnace will have less of an environmental impact than the are lamp because it uses an insignificant amount of electricity.

In closing, it should be noted that for applications requiring significant exposure times at very high concentrations (< 10,000X), the solar furnace should significantly beat the economics of the are lamp. Currently, the lifetimes of arc lamp components are short at such high-intensity levels. Acknowledgements I would like to thank Jim Pacheco of Sandia for developing the heliostat image equations used in the optical calculation for the solar furnace. I also appreciate the efforts of Gary Albach of Vortek Industries Limited. He provided cost and performance information regarding the arc lamp and performed a detailed technical review of the analysis. References 1. Tan, R.K., H.L. Arrison, D.A. Parfeniuk, and D.M. Camm. 1988. Surface Treatment Using Powerful White Light Sources. Vortek Industries, Ltd., Vancouver, B.C. (October). 2. Pitts, J.R., J.T. Stanley, and C.L. Fields. 1990. Solar Induced Surface Transformation of Materials (SISTM). Solar Thermal TechnologyResearch, Development, and Applications. Proceedings of the Fourth International Symposium, B.M. Gupta, ed. Hemisphere Publishing Corporation. 3. Edgar, R.M., and J.T. Holmes. 1982. The Horizontal-Axis Solar Furnace at the Central Receiver Test Facility. High Temperature Technology . (November). 4. Cameron, C.P. 1991. 60 kW Horizontal-Axis Solar Furnace. (to be published). 5. Alpert, D.J., and R.M. Houser. 1989. Evaluation of the Optical Performance of a Prototype Stretched-Membrane Mirror Module for Solar Central Receivers. ASME Journal of Solar Energy Engineering. 111:37-43. (February). 6. Solar Kinetics, Inc. 1978. Development of a Stretched-Membrane Dish. SAND88-7031. (October). 7. Randall, C.M. 1978. Barstow Insolation and Meteorological Data Base. Aerospace Report No. ATR-78 (7695-05)-2. The Aerospace Corporation, El Segundo Calif. (March).

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MATERIALS PROCESSING AND SYNTHESIS 90

8. Pacific Gas and Electric Company. 1988. Solar Central Receiver Technology Advancement for Electric Utility Applications, Phase 1 Topical Report, Report No. 007.2–88.2. San Francisco Calif. (September).

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MATERIALS PROCESSING AND SYNTHESIS

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Table 1 Cost/Performance of Arc Lamps Operated 6 Hours per Day 1000X Reflector Cheap Electricity

5000X Reflector Expensive Electricity

Cheap Electricity

Expensive Electricity

Capital cost ($) Lamp system

136,500

147,000

Cooling tower

6,000

6,000

Electric hookup

5,500

5,500

Building

50,000

50,000

Total capital cost

198,000

208,500

Annual operating cost ($) Electricity

11,700

22,000

Water

140

140

Lamp replacement

70

70

Reflector replacement

6,600

9,200

Argon gas

120

120

Anode replacement

9,500

9,500

Cathode replacement

3,300

3,300

General maintenance

5,000

5,000

Total O&M cost

36,400

46,700

11,700

39,000

22,000

49,300

Annual performance Annual operating hours

2,190

2,190

Power to target (kW)

30.8

19.2

Annual energy to target (kWh)

67,450

42,100

Levelixed Energy Cost ($/kWh)

0.86

1.01

1.47

1.72

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MATERIALS PROCESSING AND SYNTHESIS

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Table 2 Cost/Performance of Solar Furnaces operated 6 Hour per Day Cheap Capital Cost

Expensive Capital Cost

Capital cost ($) Building

130,000

Attenuator

50,000

Heliostat

22,000 ($150/m2)

100,000 ($670/m2 )

Concentrator

16,000 ($230/m2)

50,000 ($1700/m2 )

Test table

25,000

Computer

30,000

Clock

2,000

Installation

28,000

46,000

Total capital cost

303,000

503,000

Annual operating cost ($) Electricity

10 Hz, and similar phenomena are sometimes claimed for lower rates of flashing, although such effects are by no means well accepted. Also, there has been no practical application of these results especially with concentrated solar photon sources. Much of the work has been done outside of the United States, and even the research that has been performed in the United States has been in the basic science (biochemistry) of photoinhibition. Application of concentrated solar photon technology for algal biotechnology is unlikely to take place in the United States as there is no support for such work. Leadership in this area is with Japan with its strong research programs in photobioreactor design, application of concentrated solar photon intensities, and search for high-value bioactive products from algae. Efforts in Israel have been an early demonstration of the potential of this approach.

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PLENARY SESSION STATUS OF EUROPEAN R&D IN SOLAR CHEMISTRY AND INDUSTRIAL INTEREST IN THIS TECHNOLOGY

141

PLENARY SESSION STATUS OF EUROPEAN R&D IN SOLAR CHEMISTRY AND INDUSTRIAL INTEREST IN THIS TECHNOLOGY Paul Kesselring Paul Scherrer Institute Villigen, Switzerland

ABSTRACT A short, noncomprehensive summary of the European situation is given and some technical aspects of the European R&D activities are sketched. In conclusion, the long-term prospects for solar chemistry are considered to be good, which justifies an increased R&D effort. The expectations of short-term, strong impact applications, however, should not be boosted. INTRODUCTION The picture of the status of European R&D in solar chemistry as described in this contribution is mainly based on contacts and knowledge gained by international cooperation, in particular within the International Energy Agency (IEA). Thus, whereas it may not be comprehensive, it will characterize the general situation properly to a good extent. GENERAL In order to understand the European R&D situation, it helps to sketch briefly a point of view with regard to solar chemistry (which is more or less widely accepted in Europe): If solar energy is expected to replace some of the functions which fossil fuels fulfill in today's energy systems, then the production of synthetic secondary energy carriers is indispensable. These functions are mainly seasonal storage and long distance transportation, in conjunction with many applications such as individual traffic or domestic heating. The idea is to import solar energy from the well-insulated, usually less industrialized southern parts of Europe or North Africa to the cold, energy-demanding and, in general, heavily industrialized parts of northern Europe. These are considered to be quite important, however clearly long-term prospects for solar energy. In contrast, solar electricity production is expected to have a moderate mid-term and even a small short-term impact (remote applications and ''solar pioneers''). These considerations, together with the fact that solar chemistry is a "young" technology (which has received much less attention during the last 15 years than solar heating and cooling or electricity generation), have led to the following situation: • Only a few larger scale (kW range) experiments exist. There are no practical engineering applications as yet. • On the university level there are modest to medium, definitely increasing, basic R&D efforts. However, there is a much larger, as yet untapped, potential of expertise at universities. Many scientists are not aware of the fact that their knowledge and know-how could be very valuable for solar chemistry R&D and its application.

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• Industry begins to pay attention to the development but, in general and for the time being, is reluctant to invest as there is no short-term market in sight. • Money mostly comes from government authorities who can afford an interest in long-term energy issues. In general, funds have been increasing during the last five to ten years. As an example, Switzerland spent almost nothing on solar chemistry ten years ago. Today the annual budget is about 2 million dollars, which corresponds to roughly $0.30 per inhabitant. Provided good proposals will be available, this budget could possibly double or triple during the next five years. SOME TECHNICAL ASPECTS R&D Issues The R&D objectives in Europe are similar to those in the United States, although priorities might be different. The main issues are • synthetic secondary energy carrier (e.g., hydrogen or methanol; probably higher priority than in the U.S.). • production of high value chemicals; and • detoxification of hazardous waste (probably lower priority than in the United States). To reach these goals, all different forms of solar chemistry are investigated: 1. 2. 3. 4. 5. 6.

photochemistry (near ambient temperature) thermochemistry (using solar heat) electrochemistry (using solar electricity) and the combinations thereof: photoelectrochemistry photo-assisted thermochemistry high temperature electrochemistry

Topics 1, 2, 4, and 5 are the fields receiving most attention at present. Topics 3 and 6 are not always considered to belong to solar chemistry, which is a mistake (at least in my opinion). The solar-specific boundary conditions may lead to requirements which go beyond those of ordinary electrochemistry, and their consequences should not be underestimated. Photochemistry and Photoelectrochemistry In Europe the splitting of water and the reduction of CO2 seem to be the dominant issues. The "scientific background" is given by 20 years of research in photography, photochemistry with lasers, and investigations of natural photosynthesis. Research is concentrated in universities and scientific research institutes. Basic research problems clearly dominate. They are the same in Europe as in the United States, e.g., charge transfer questions in redox systems or corrosion mechanisms in photoelectrochemistry. Countries involved are Germany, Italy, Switzerland, Sweden, Great Britain, and France. The order given corresponds more or less to the importance of the efforts in the respective countries (according to a necessarily somewhat subjective judgment of a colleague of mine, working personally in the field). International contacts are made and cooperation is stimulated mainly by the biannual International Conference on Photochemical Conversion and Storage of Solar Energy, the proceedings of which usually appear in the Journal of Photochemistry (last conference: Palermo, 1990). High Temperature Thermochemistry and Photo-Assisted Thermochemistry In Europe, topics 5 and 6 are intimately connected to the International Energy Agency's Small Solar Power Systems Project (IEA-SSPS-Project).

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PLENARY SESSION STATUS OF EUROPEAN R&D IN SOLAR CHEMISTRY AND INDUSTRIAL INTEREST IN THIS TECHNOLOGY

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European countries involved are mainly Germany, Spain, Switzerland and, to a small extent, Sweden. The scientific and technical background consists, on the one hand, of experience gained in solar thermal electricity generation (collection and handling of solar high temperature heat) and, on the other hand, of knowledge from nonsolar thermochemistry. A typical example of the latter are the nuclear process heat applications, studied mainly during the 1970s. Examples: Steam-reforming of methane and the sulfuric acid watersplitting cycle ("GAprocess") are being adapted to the special solar conditions (experiments under way and in preparation, respectively). Compared to the conventional processes, they have additional difficulties (e.g., transients) but also definite advantages (e.g., direct absorption of radiation in volumetric receiver-reactors). The main issues here are of a technological, and not of a basic scientific, nature. A completely different situation exists with respect to the combination of thermochemistry and photochemistry at high temperatures or, to a somewhat lesser extent, to light-induced/assisted catalytic reactions at medium temperatures. In this interesting and promising field we have neither good theoretical understanding nor can we draw upon past experimental experience. There is the intention to improve this situation considerably by a double effort within the five-year follow-up program of the IEA-SSPS project, which is currently under discussion. The first part consists of a basic R&D program, centered around gas/gas or solid/gas reactions at high temperatures combined with high solar fluxes and catalyzed reactions under high solar fluxes and medium temperatures (e.g., < 300°C). The second part should bring a larger-scale experiment, demonstrating the potential of this more recent branch of solar technology. The main institutions involved in this program will be (and are already) universities and research institutes. There are indications that some companies will participate also. Remark Concerning Comparison Criteria for Different Solar Technologies In the years to come, we will have the problem of judging and selecting the different evolving chemical processes with respect to their future potential for practical applications. It is my personal opinion that we should do more to develop sound criteria for this selection process. Very generally speaking, the properties inherent to solar radiation lead to the following requirements: • Minimize the use of material in collecting solar energy (low power density of radiation) • Use as much of the solar spectrum as possible • Minimize response times at the "front end" of a process (transients) It would lead us too far into detail to show that including such solar-specific criteria into a ranking procedure might change its outcome considerably. In the past, this has been neglected too often. CONCLUDING REMARKS In Europe, solar chemistry in recent years has been and still is on the upswing. However, it is a young technology still in need of a major effort in basic R&D. Near-term applications will very probably be limited to niches. In this situation it is important not to oversell this technology—in particular to resist the temptation to sell it as a short-term solution to the "greenhouse problem." The real importance of solar chemistry lies in its long-term potential to substitute functions that are fulfilled now by fossil fuels. Thus, in the long run it actually may help to mitigate the CO2 problem. In order to shorten the basic R&D phase and accelerate practical application, an increased R&D effort is justified. However, a crash program based on exaggerated expectations would do more harm than good. What we need are not crash programs but continuity of R&D on a reasonable funding level.

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PLENARY SESSION STATUS OF EUROPEAN R&D IN SOLAR CHEMISTRY AND INDUSTRIAL INTEREST IN THIS TECHNOLOGY 144

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APPENDIX A 145

APPENDIX A

National Academy of Sciences/National, Research Council COMMITTEE ON POTENTIAL APPLICATIONS OF CONCENTRATED SOLAR PHOTONS WORKSHOP AGENDA November 7 and 8, 1990 at the

Solar Energy Research Institute 1617 Cole Boulevard Golden, Colorado

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APPENDIX A

146

WORKSHOP AGENDA QUICK OVERVIEW Wednesday, November 7, 1991 8:30 – 9:00

Plenary Session-Introduction (Araj/Bard/Heller)

9:00 – 9:15

Break

9:15 – 12:15

Parallel Sessions Session 1: Water Treatment (Ollis*) Session 2: Waste Treatment (Sarofim*) Session 3: Materials Processing & Synthesis (Tenhover*/Bates*)

12:15 – 1:30

Lunch

1:30 – 3:00

Parallel Sessions Continued

3:00 – 3:30

Break

3:30 – 5:30

Plenary Session-European Perspective and Rapporteur Reports

Thursday, November 8, 1990 8:30 – 11:30

Parallel Sessions Session 4: Solar Pumping of Lasers (Tenhover*) Session 5: Photochemical Synthesis (Vaida*/Kilby*) Session 6: Fuel Processing & Thermo-/Photo-chemical Cycles (Serpone*)

11:30 – 12:45

Lunch

12:45 – 2:45

Session 7: Advanced Research (Heller*)

2:45 – 3:00

Break

3:00 – 5:00

Plenary Session-Rapporteur Reports and Wrap-up

* Session chair(s)

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APPENDIX A

WORKSHOP AGENDA National Research Council Committee On Potential Applications of Concentrated Solar Photons PROGRAM Wednesday, November 7, 1990 8:30

Plenary Session-Overview

9:00

Break

9:15

PARALLEL SESSIONS Session 1: Water Treatment: Advanced Photo-oxidation Processes (17-4-West) Chair: David Ollis Speakers: William Glaze, University of North Carolina " Advanced Oxidation Technology Fundamentals: UV/ozone and UV/H2O2" Arthur Nozik, Solar Energy Research Institute "Mechanistic Studies of the Photocatalytic. Behavior of TiO2 Particles in a Photoelectrochemical Slurry Cell and the Relevance to Photodetoxification Reactions" Craig Turchi, Solar Energy Research Institute''Effect of Light Intensity on Photocatalytic Reaction" Gary Peyton, University of Illinois "A Comparison of the Advanced Oxidation Processes with Semiconductor-Catalyzed Photooxidation'' Jack Zeff, Ultrox, Inc. "ULTROX Operating Experiences with UV/Oxidation; Economics" Hal Link, Solar Energy Research Institute "Solar Photocatalyzed Process Economics" Hussain Al-Ekabi, NuLite, Canada "Photocatalyzed Removal of Multiple Contaminants from Water" Mark Mehos, Solar Energy Research Institute "Immobilized Catalysts in Solar Concentrators" James Pacheco, Sandia National Laboratories "Immobilized Photocatalysts in Large-Scale Trough Collectors" Rapporteur: Richard G. Zepp, U.S. Environmental Protection Agency Discussion: Session participants Issues: Chemistry, Catalysts and Oxidants, Concentrators, Economics.

147

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APPENDIX A

9:15

Session 2: Waste Treatment Chair: Adel Sarofim Speakers: Barry Delinger, University of Dayton "High Temperature Photochemistry Induced by Concentrated Solar Radiation" Wing Tsang, National Institute of Standards and Technology "Chemical Processes During Incineration and Implications of Detoxification of Hazardous Waste Using Solar Photons" John F. Cooper, Lawrence Livermore National Laboratory ''Hazardous Mixed Wastes'' Peter Daley, Chemical Waste Management "Economics of Waste Destruction" Terry Galloway, Synthetica Technologies, Inc. "Waste Destruction by Very High Temperature Steam Reforming" Rapporteur: Alan Pasternak, Energy Consultant Discussants: Ron Kagel, Dow Chemical Company Tom Milne, Solar Energy Research Institute

9:15

Session 3: Materials Processing and Synthesis Chairs: Michael Tenhover/J. Lambert Bates Speakers: W.D. Sproul, Northwestern University "Surface Engineering" George Fenske, Argonne National Laboratory "Application of Energetic Particles to Coating Adhesion and Properties" Roland Pitts, Solar Energy Research Institute "Surface Modification Technologies Using Concentrated Solar Photons" Greg Kolb, Sandia National Laboratories "Economic Comparisons of Alternative Sources" Rajiv K. Singh, University of Florida J. Narajan, North Carolina State University* "Pulsed Laser Processing of Solar Cells" Rapporteur: Bruce M. Clemens, Stanford University Discussants: Michael Aziz, Harvard University M. Nastasi, Los Alamos National Laboratory Kurt Sickafus, Los Alamos National Laboratory

* Submitted to Workshop but not presented.

148

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APPENDIX A

12:15

Lunch

1:30

Resume PARALLEL SESSIONS

3:00

Break

3:30

Plenary Session Paul Kesslering, Paul Scherrer Institute "Status of European R&D in Solar Chemistry and Industrial Interest in this Technology" Rapporteur Reports of Sessions 1 – 3

5:30

Adjourn

Thursday, November 8, 1990 9:00

PARALLEL SESSIONS Session 4: Solar Pumping of Lasers Chair: Michael Tenhover Speakers: Roland Winston, University of Chicago "Overview of the University of Chicago Work" Walter Christiansen, University of Washington "Blackbody Pumped Lasers" Ja H. Lee, NASA, Langley "Solard-Pumped Lasers and Their Applications" Rapporteur: Lloyd Chase, Lawrence Livermore National Laboratory Discussants: Session participants

149

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APPENDIX A

8:30

Session 5: Photochemical Synthesis Chair: Veronica Vaida Speakers: John Connolly, SERI "Photophysics and Photochemistry of Porphyrin Systems" James Yardley, Allied Signal "Potential Industrial Applications of Photons" Rapporteur: David Eaton, E.I. Du Pont de Nemours & Co., Inc. Discussants: Mostafa A. El-Sayed, UCLA Arthur Nozik, SERI David Whitten, University of Rochester

8:30

Session 6: Fuel Processing and Thermochemical/Photochemical Cycles Chair: Nick Serpone Speakers: Kevin Krist, Gas Research Institute "GRI Experience in Solar Fuel Research" Ertugrul Bilgen, University of Montreal "Thermal, Thermochemical and Hybrid Solar Hydrogen Production" Moshe Levy, Weizmann Institute of Science "Chemical Reactions Driven by Concentrated Solar Energy'' Helena Chum, Solar Energy Research Institute ''Inexpensive Phenol Replacements from Biomass An On-Going Technology Transfer Effort" Rapporteur: Arlon Hunt, Lawrence Berkeley Laboratory Discussant: William A. Summers, Westinghouse Electric Company

12:00

Lunch

1:00

Session 7: Advanced Research Chair: Adam Heller Speakers: Mordhay Avron, Weizmann Institute of Science "The Biotechnology of Cultivating Dunaliella Rich in Beta-Carotene: From Basic Research to Industrial Production" Lewis M. Brown, SERI "Production Potential of Biochemicals from Algae and Other Biotechnological Innovations Enabled by Higher Solar Concentration"

150

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APPENDIX A

5:10

151

Rapporteur: Lewis M. Brown, SERI

Discussants: All Workshop Participants

3:00 Break

3:10 Plenary Session

Rapporteur Reports of Sessions 4 – 6

Wrap-up

Adjourn

Copyright © 1991. National Academies Press. All rights reserved.

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APPENDIX A 152

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APPENDIX B

153

Appendix B National Academy of Sciences/National Research Council COMMITTEE ON POTENTIAL APPLICATIONS OF CONCENTRATED SOLAR PROTONS WORKSHOP PARTICIPANTS AND ATTENDEES Invited Speakers, Rapporteurs and Discussants Hussain Al-Ekabi Research and Development Manager NuLite 317 Consortium Court London,Ontario N6E 2S8 Canada

Helena Chum Chemical Conversion Research Branch Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401

Mordhay Avron Professor of Chemistry Weizmann Institute of Science Rehovolt 76100 Israel

Bruce M.Clemens Department of Materials Sciences and Engineering Stanford University Stanford, California 94305

Michael Aziz Division of Applied Science Harvard University 29 Oxford Street Cambridge,Massachusetts 02139 Ertugrul Bilgen Department of Mechanical Engineering Ecole Polytechnique University of Montreal Post office Box 6079 Station A Montreal,Quebec H3C 3A7 Canada Lewis M.Brown Manager,Algae and Plant Sciences Section Biotechnology Research Branch Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401 Lloyd Chase University of California Lawrence Livermore National Laboratory Post office Box 808 Livermore,California 94550 Walter Christiansen Department of Aeronautics and Astronautics FS-10 University of Washington Seattle,Washington 98195

John Connolly Photo Conversion Research Branch Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401 John F.Cooper University of California Lawrence Livermore National Laboratory Post Office Box 808 Livermore,California 94550 Peter Daley Senior Director,R&D Chemical Waste Management,Inc. 2000 S.Batavia Geneva,Illinois 60134 Barry Dellinger University of Dayton Research Institute Environmental Sciences Group 300 College Park Dayton,Ohio 45469-0132 David Eaton E.I.Du Pont de Nemours and Company, Inc. Central R&D Experimental Station Post office Box 80328 Wilmington,Delaware 19880-0328 Mostafa A.El-Sayed University of California-Los Angeles 405 Hilgard Avenue Los Angeles,California 90024

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APPENDIX B

154

George Fenske Argonne National Laboratory Building 212 Argonne,Illinois 60439

Tom Milne Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401

Terry R.Galloway Synthetica Technologies,Inc. 5327 Jacuzzi Street Building 3-0 Richmond,California 94804

J.Narayan Materials Sciences &Engineering Dept. North Carolina State University Raleigh,North Carolina 27695-7916

William Glaze Environmental Science &Engineering University of North Carolina Chapel Hill,North Carolina 27599

M.Nastasi Los Alamos National Laboratory Mail Stop K765 Los Alamos,New Mexico 87545

Arlon Hunt University of California-Berkeley Lawrence Berkeley Laboratory 1 Cyclotron Road Mail Stop 902024 Berkeley,California 94720

Arthur Nozik Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401

Ron Kagel Dow Chemical Company 2030 Willard H.Dow Center Midland,Michigan 48674

James Pacheco Sandia National Laboratories Solar Thermal Collector Technology Division 6216 Post Office Box 5800 Albuquerque,New Mexico 87185

Paul Kesselring Paul Scherrer Institute CH-5232 Villigen PSI Switzerland

Alan Pasternak Energy Consultant 4 Middle Road Lafayette,California 94549-3353

Greg Kolb Sandia National Laboratories Organization 6217 Albuquerque,New Mexico 87185

Gary Peyton Water Survey Research University of Illinois at Urbana-Champaign Urbana,Illinois 61801

Kevin Krist Gas Research Institute 8600 West Bryn Mawr Avenue Chicago,Illinois 60631 Ja H.Lee Mail Stop 493 NASA Langley Hampton,Virginia 23665-5225 Moshe Levy Center for Energy Research Weizmann Institute of Science Rehovolt 76100 Israel Hal Link Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401 Mark Mehos Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401

Roland Pitts PD Measurements and Performance Branch Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401-3393 Kurt Sickafus Los Alamos National Laboratory Mail Stop K762 Los Alamos New Mexico 87545 W.D.Sproul Basic Industry Research Laboratory Northwestern University 1801 Maple Avenue Evanston,Illinois 60208 William A. Summers Westinghouse Electric Company Advanced Energy Systems Division Post Office Box 10864 Pittsburgh,Pennsylvania 15236

Copyright © 1991. National Academies Press. All rights reserved.

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APPENDIX B

155

Wing Tsang National Institute of standards and Technology Gaithersburg,MD 20899

SERI Attendees

Craig Turchi Thermal Systems Research Branch Solar Energy Research Institute 1617 Cole Boulevard Golden,Colorado 80401

John Anderson Dan Blake Mark Bohn Greg Gl atzmaier Brian Gregg Steve Hauser Gary Jorgensen Dean Levi Kim Magrini Tom Milne L.M.Murphy Mark Nimlos Gerry Nix Mark W.Peterson Michael Seibert Robert Stokes Ed Tracy Kate Zeller

David Whitten University of Rochester Department of Chemistry 404 Hutchison Hall River Campus Rochester,New York 14627 Roland Winston University of Chicago 5720 South Ellis Avenue Chicago,Illinois 60637 James Yardley Allied Corporation Box 1021R Morristown,New Jersey 07960 Jack Zeff Ultrox,Incorporated Senior Vice President of Engineering 2435 South Anne Street Santa Ana,California 92704 Richard G.Zepp U.S.Environmental Protection Agency Environmental Research Laboratory Athens,Georgia 30613 Committee Members Allen Bard,Chairman Adam Heller,Vice Chairman J.Lambert Bates Jack St.Clair Kilby David Ollis Adel Sarofim Nick Serpone Michael Tenhover Veronica Vaida NAS/NRC/EEB Attendees Kamal J.Araj Committee Study Director Archie L.Wood,Executive Director Commission on Energy and Technical Systems H.M.Hubbard,Member Energy Engineering Board

Meir Carasso B.P.Gupta,Operations Manager

SNL Attendees Jeremy Sprung Craig Tyner Other Attendees John Collins,NALCO Chemical Co. John Copeland,TDA Research Stephen Coy,MIT Garth B.Freeman,Georgia Institute of Technology Werner R.Haag,SRI David Huestes,SRI International Don Lorents,SRI International Tom McKinnon,University of Colorado Jeffrey Steinfeld,MIT Rodney Stramel,Kerr-McGee John Wright,TDA Research US DOE Attendees Frank Wilkins U.S.Department of Energy