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Table of contents :
© Al-Farabi KazNU, 2017
1.1. Definition of the glass. General properties
of the substances in the glassy state
1.2. Classification of inorganic glasses by chemical
2.1. The properties of glass-forming melts
2.2. Mechanical properties of glasses
2.3. Thermal properties of glasses
2.4. Electrical properties of glasses
2.5. Optical properties of glasses
2.6. Chemical stability of glasses
3.1. Main raw materials
3.2. Auxiliary raw materials
BASICS OF GLASS PRODUCTION
4.1. Preparation of the batch
4.2. Glass melting
4.2.1. Stages of glass melting
4.2.2. Defects in the glass melt
4.3. Glass molding
4.3.1. Features of molding
4.3.2. Molding methods
4.4. Annealing and tempering of glass
5.1. Determination of water resistance of glass
at temperature 98 С
5.2. Determination of thermal resistance of glass
5.3. Determination of metal oxides in glass
Printed in the printing office of the «Kazakh university» publishing house.
AL-FARABI KAZAKH NATIONAL UNIVERSITY
G. A. Seilkhanova
CHEMICAL TECHNOLOGY OF GLASS Educational manual
Almaty «Qazaq university» 2017
UDC 666.1/2 (075) LBC 35.41 я 73 S 44 Recommended for publication by the decision of the Academic Council of the Faculty of Chemistry and Chemical Technology, Editorial and Publishing Council of Al-Farabi Kazakh National University (Protocol №2 dated 03.11.2017) Reviewers: Doctor of chemical sciences, professor M.K. Aldabergenov Doctor of technical sciences, professor S.A. Efremov
Seilkhanova G.A. Chemical technology of glass: educational manual / G.A. Seilkhanova. – Almaty: Qazaq university, 2017. – 64 p. ISBN 978-601-04-2997-0 The educational manual presents the theoretical foundations of glass production, its physico-chemical properties, discusses in detail the basic technological stages of obtaining glassware. The textbook contains laboratory works for determining some characteristics of the glass. In order to improve the learning of theoretical material, and also for the control of the students’ knowledge, there are test questions in the textbook. The textbook can be used during the study of the subjects «Chemical technology of silicate materials», «Chemical technology of glass and ceramics». The educational manual is designed for the students enrolled in the chemical- technological specialties, and can also be used by the lecturers and staff working in the field of producing silicate materials. Published in authorial release.
UDC 666.1/2 (075) LBC 35.41 я 73 ISBN 978-601-04-2997-0
© Seilkhanova G.A., 2017 © Al-Farabi KazNU, 2017
1 GLASSY STATE 1.1. Definition of the glass. General properties of the substances in the glassy state There are two types of the solid state – crystalline and amorphous. The glassy state of a substance – is a special case of the solid amorphous state, the characteristics of which are the lack of a strictly ordered structure, isotropy of the properties, and also the absence of a definite melting point temperature. The glassy state is metastable, it does not meet the conditions of thermodynamic equilibrium. The transition from the glassy state to crystalline – is exothermic process which under normal conditions does not occur spontaneously. This is due to the very high viscosity in the solid state and low mobility of the structural elements. In the literature there are several definitions of the glass. The generally accepted one is the following: the glass is all amorphous solids obtained by supercooling the melt irrespective of the chemical composition and the temperature range of freezing point and which have mechanical properties of solids as a result of a gradual increase of the viscosity; the transition process from the liquid state to glassy must be reversible. This definition is based on the single principle of obtaining the glass – from the melt by its supercooling without crystallization. However, there are some ways of producing glassy substances without prior obtaining a melt, for example from aqueous solutions, gels, under vapor condensation or neutron irradiation of the crystalline compounds. In this regard, the presented wording does not fully correspond to the properties of glass, although it still reflects the most typical signs of a glassy state. 3
The glassy state in comparison with crystalline is thermodynamically unstable. Therefore, the increase of the mobility of the particles in the glass when heating causes crystallization. At the same time, the process of the transition from a liquid state to glassy and vice versa is not accompanied by the significant changes in the nature of the spatial arrangement of the particles, and there is no sharp sudden change of the properties. All glassy substances have the following common properties: 1. The excess of internal energy reserve compared to the internal energy reserve of the respective substance in a crystalline state. The glasses are obtained by melt supercooling. They are the systems that are in a metastable nonequilibrium state. Therefore, due to the extremely high viscosity, the glasses can be in a metastable state for a long time without any signs of the transition to steady, crystalline state. However, due to excessive internal energy reserve, crystallization of glassy substance is accompanied with the heat generation and is an exothermic process. 2. The isotropy. All glasses are characterized by isotropy – which is the independence of the properties from the orientations. Isotropy is typical to the amorphous substances with a homogeneous disordered structure. It should be noted that the glasses like any liquids have vectorial anisotropic properties under external and internal tensions. When the mechanical tensions are removed, anisotropy disappears. 3. The ability of a gradual and reversible hardening. In the transition from the molten to the mechanically solid glassy state, a gradual increase in viscosity and changes in the properties of substance does not stop. This is due to the fact that the hardening of the glass is not accompanied by the appearance of a new phase in the system. Hardening is reversible because when heated, an inverse process of continuous viscosity reduction is observed, which means a smooth transition from brittle to highly viscous and then to the liquid, flowable state. Therefore, the glasses have no certain melt temperature, they have temperature range of softening. 4. The presence of the transition temperature range – glass transition interval. It is characterized by a sharp change in the physico-chemical properties of a glassy substance and it is limited by the initial softening temperatures during heating and glass transition. 4
1.2. Classification of inorganic glasses by chemical composition Inorganic glasses by chemical composition can be divided into the following types: elementary, oxide, halide, chalcogenide. Elementary (monoatomic) glasses consist of atoms of one element. Sulfur, selenium, arsenium, phosphorus are obtained in the glassy state. Tellurium and oxygen can be obtained in the glassy state. With the long pyrolysis of organic resins, the glass like carbon can be obtained – glassy carbon, which has great practical significance. However, it always contains oxygen (up to 6%). Oxide glasses are very diverse. They are classified according to the nature of the glass-forming oxide, which is included in the composition of glass as a main component. Typical glass formers, easily passing into the glassy state – oxides В2О3, SiО2, GeО2, Р2О5. With strong cooling in small amounts As2О3, Sb2О3, TeО2, V2O5 transfer in glass. Some oxides in the pure state do not form glasses (А12О3, Ga2О3, Bi2О3, TiО2, МоО3, W03), however in the binary and more complex systems their glass-forming properties are enhanced sharply. There are known classes of silicate, borate, phosphate, aluminate and other oxide glasses. Each of them can be divided into groups. The most common in everyday life and technology are silicate glasses. They are cheap, economically affordable, chemically stable, relatively easy in the industrial production (except quartz glass). Borate glasses can be obtained on the basis of pure В2О3 (but they are very hygroscopic), in binary systems with Ме2О, МеО, Al2O3, SiО2 and in the more complex systems. These glasses effectively absorb slow neutrons, have high X-ray transparency, are resistant to the alkali metal vapor, low-melting, and may be used in an optical technique. Phosphate glasses are usually multicomponent. Their properties are sharply improved by Al2O3. These glasses have a number of disadvantages: a large tendency to crystallize, low chemical resistance, high cost. However, they have also advantages over other glasses: resistance to hydrofluoric acid, the absorption of infrared radiation (heat protective), transparency in the ultraviolet part of the spectrum. Colored phosphate glasses have greater color purity than silicate (light filters). 5
The closest analogues of silicate glasses – are germanate glasses. They have a high glass-forming ability. Melting points are comparatively low. They are easier to melt than silicate glasses, but chemically less stable, have a high resistance to ionizing radiation, absorb X-rays, and they are transparent to infrared rays. The component Ge02 – is insufficient and expensive. Therefore, the practical value of germanate glasses is small. Halide glasses – are glasses based on beryllium fluoride, which are highly resistant to hard radiation (X-ray, gamma-rays), to aggressive environments of hydrogen fluoride and fluorine, have a very low refractive index (may be lower than of water). These unique glasses are with anionic conductivity (transporter of electricity – are fluorine ions). Chalcogenide glasses are the glasses of sulfides, selenides and tellurides. The glass formers in these systems are Se, S, Te or selenides of arsenic, germanium, phosphorus and sulfides of arsenic and germanium. All glasses are nontransparent in the visible spectrum and transparent in the infrared. They are easily and quickly crystallized, low-melting, they have a high linear thermal expansion coefficient, have electronic conductivity, which is intrinsic to semiconductors, and internal photoelectric effect.
2 PHYSICO-CHEMICAL PROPERTIES OF GLASSES 2.1. The properties of glass-forming melts Crystallization ability determines the tendency of the glasses and glass-forming melts towards crystallization. It is necessary to know the temperature ranges, within which the glass can crystallize, and the rate of crystallization in order to set the rational technological regime of glass melting and production. The crystallization process consists of two stages: formation of crystallization centres and crystal growth in these centers. The character of crystallization of glass is determined by the ratio of the rate of formation of crystallization centers and the linear growth rate of crystal growth. Surface tension of glass-forming melts and glasses is determined by the action of intermolecular forces on the particles of the surface layer: а = A/S, J/m2 or N/m, where A – is the work of formation per unit surface area S. Surface tension forces tend to reduce the surface area or the phase separation area. Glass-forming melts have a high surface tension. In industrial glasses, depending on the composition, it ranges from 0,155 to 0,470 N/m. In silicate melts Аl203 and Si02 greatly increase the surface tension, whereas В203, Ti02, Р2О5, F, V2O5 – reduce it. The addition of surface-active substances (surfactants), for example, compounds of chromium, molybdenum, vanadium, arsenic, antimony, wolfram, 7
thorium leads to a sharp decrease in the surface tension. The surface tension of silicate melts is affected by the composition of the gaseous environment. In the reducing environment the surface tension is 15-20% higher than in the oxidative one. Temperature has a slight effect on this property. Viscosity is the property of melts to resist the motion of particles relative to each other. The force required for mutual motion with a certain rate of two parallel layers of the liquid is calculated by the Newton equation F =η SdV/dx, where η is the coefficient of dynamic viscosity; S – is the interface; dV/dx – is the velocity gradient. Viscosity measurement unit is N.s/m2 or Pa.s. The kinetic viscosity of the melt v is equal to the ratio of the coefficient of dynamic viscosity to the melt density. The inverse measure 1/v characterizes fluidity. The viscosity of silicate melts varies from 10 to 1017–1019 N.s/m2 with a change in temperature. The temperature dependence of the viscosity serves as the basis for setting the temperature regimes of glass melting, molding and heat processing. During the glass melting the processes of homogenization and clarification of the glass mass occur. High viscosity prevents homogenization of the melt and its clarification. In the interval of glassware molding from the melt the viscosity determines the working temperature. The viscosity of glasses and glass-forming melts is significantly influenced by the chemical composition. The highest viscosity at the same temperature conditions is inherent to quartz glass. With the introduction of alkaline oxides into such glass, the viscosity drops sharply. Among the alkali-silicate glasses the highest viscosity is possessed by potassium-silicate ones and the least viscosity – by lithium-silicate.
2.2. Mechanical properties of glasses Density of glasses determines the quantitative content of the mass per unit volume, which means d=M/V, kg/m3. The density of indus8
trial glasses varies from 2200 to 7500 kg/m3. The highest density is inherent to the glasses with a significant content of heavy metal oxides – lead, barium, bismuth, wolfram, with increasing temperature the density of glasses decreases. Usually industrial glasses (window, container) have a density of 2500 kg/m3. The lowest density is in quartz glass – 2200 kg/m3. Elasticity characterizes the property of glass to restore the shape and volume after removing the load. The elasticity coefficient E can be determined from the deflection of a glass sample under a certain load. Depending on the chemical composition of glasses, the modulus of elasticity can vary from 44000 to 87000 MPa. For quartz glass it is equal to 73000 MPa. The oxides of calcium and boron increase modulus of elasticity. Alkaline oxides lower it. With increasing temperature the modulus of elasticity of glasses decreases. This is due to the increase in the average distances between the ions and the decrease in the forces of interaction between them. Strength is the ability to resist mechanical destruction under the influence of external loads. There are different types of strength: at fracture, compression, bending, etc. The strength measurement is the ultimate strength, which means the maximum stress not causing the destruction of the material under the influence of a static load. Glass resists stretching much worse than compressing, so the strength in the process of stretching causes the boundaries of applicability of glasses in mechanical and thermal stresses. Hardness is the property of glasses to resist scratching (sclerometric), grinding (abrasive) or indentation (microhardness). In the sclerometric method, the hardness is determined by the width of the scratch applied by a needle under some constant pressure on the glass sample under study. The abrasive hardness, established by the grinding method, is measured by the grinding rate of the surface unit of a glass sample under the appropriate conditions. However, most often the hardness of glasses is characterized by microhardness, measured by a diagonal of the microprint, obtained when the load of diamond pyramid presses the glass. The microhardness of conventional silicate glasses is in the range of 4000-9000 MPa. The highest microhardness is inherent to quartz glass, for which it equals 9500-10 000 MPa. 9
Brittleness is the ability of a material to break down instantly with a slight excess of its ultimate strength. The brittleness is measured by the impact toughness during bending. Specific impact toughness is equal to the work of the impact fracture, referred to the cross section of the sample. 2.3. Thermal properties of glasses Thermal expansion determines the behavior of the glass when heated and the ability to solder it with other glasses and materials. It is characterized by the linear thermal expansion coefficient (LTEC, degree-1), which is found from the relation a=∆l/l∆t, where ∆l – is the change in length when heated by ∆t°, l – is the original length of the sample. LTEC of the glass is determined by its chemical composition and varies within very wide ranges. Minimal LTEC is inherent to pure quartz glass – 5.10-7 degree-1. Alkaline oxides significantly increase LTEC, and the thermal expansion increases with increasing ionic radius of the cation. The thermal expansion of silicate glasses is lowered by В2О3, А12ОЗ, ZrО2. Thermal resistance is the ability of the glass to withstand sudden changes in temperature without destruction. With sudden heating or cooling of the glass, thermal stresses arise in it. If they reach the ultimate strength of the products or exceed it, then destruction occurs. In the process of rapid cooling, the surface layers of the glass are cooled faster than internal ones. Moreover, the surface layers tend to compress, but the inner layers, which are hotter, block this. As a result, tensile forces occur on the surface, which may exceed the actual ultimate strength. With rapid heating, compressive stresses occur on the surface of the glass. Since the glass works better for compression, it has greater thermal resistance during heating than cooling. Thermal resistance of the glass is determined by the maximum temperature difference that it can withstand without destruction during rapid cooling. Among the silicate glasses, quartz glass has the greatest thermal resistance. It can withstand a temperature difference of about 1000 °С. Borosilicate and high-alumina glasses are heat resistant. 10
Heat capacity indicates how much heat should be applied to the object’s mass unit for raising its temperature by one degree. For glasses usually the average heat capacity is measured for a given temperature range at constant pressure Ср. Experimentally determined Ср for quartz glass in the temperature range 0–600 °С is 0,7–1,15 kJ / (kg.K). Depending on the composition, the specific heat capacity of silicate glasses is in the range 0,3–1,05 kJ / (kg.K). Thermal conductivity is characterized by the coefficient of thermal conductivity, which varies from 0,6 to 1,34 W/(m.К) for silicate glasses. The highest thermal conductivity is inherent to quartz glass − 1,34 W/(m.К). Alkaline and alkaline-earth oxides decrease the thermal conductivity.
2.4. Electrical properties of glasses Electrical conductivity (χ – is the specific electrical conductivity) characterizes the ability of the glass to conduct an electric current under the action of an electric field and is the inverse of electrical resistance р. Electrical conductivity and electrical resistance are connected with each other by the relation χ = 1/р. Silicate glasses possess ionic conductivity and belong to the class of dielectrics. The carriers of the current are cations of alkali and alkaline-earth metals. Their specific electrical resistance is 108−1018 Оhm.m. Electrical conductivity of glasses changes sharply with a change in temperature. For solid glasses with ionic conductivity, this dependence is expressed by the equation χ=Аехр(-Е/RT), where A – is a constant; E – is the activation energy of electrical conductivity; R – is the gas constant. Dielectric permittivity is characterized by the polarizability of the constituent parts of the dielectric: electron shells of atoms or ions, dipoles and polar groups. The relative dielectric permittivity (ε) cha11
racterizes the dielectric's ability to reduce the strength of an electric field compared to the vacuum, and it is measured from the change in capacitance of the vacuum capacitor when the studied dielectric is placed between its plates: ε = Сх /C0, where Сх – is the capacitance of a capacitor with a dielectric; С0 – is the capacitance of the vacuum capacitor at the same voltage and sizes. Dielectric losses determine the quality of glass as a dielectric in an alternating field, as well as the energy dissipated by a dielectric in a unit of time, when an alternating electric field is applied to it and which causes heating of the dielectric. There are four types of dielectric losses in glasses: 1) conductivity losses, associated with the through-motion of ions and determined by the electrical conductivity of the glass in a constant field; 2) relaxation losses, caused by hopping of weakly fixed ions over short distances; 3) deformation losses, caused by small deformations in the silicon-oxygen glass framework; 4) resonant (or vibrational) losses arising from the absorption of the the external field’s energy, which frequency is close to the frequency of the natural oscillations of ions. Electrical strength is determined by the electric field strength per unit thickness, at which the loss of the electrical insulating properties of the glass (breakdown) is noted. The highest strength is inherent to borosilicate glasses, the lowest strength – to alkaline glasses.
2.5. Optical properties of glasses The optical characteristics of glass include the refractive index, main and partial dispersions and the dispersion coefficient. In addition, the optical constants include the transmission (or absorption), scattering and reflection of light as a result of the interaction of electromagnetic radiation with the glass. The refractive index determines the ability of the glass to refract the incident light and is measured by the ratio of the sine of the angle of incidence to the sine of the angle of refraction. Dispersion shows 12
the change in the refractive ability of a substance when the wavelength of light changes. The refractive index and dispersion are referred to specific wavelengths, for silicate glasses depending on the composition the refractive index can vary from 1,44 to 2,2, and the dispersion coefficient – from 25 to 100. The refractive index of silicate glasses is sharply increased by PbO, BaO. The transmission and absorption of glass characterize its transparency for visible light rays (400-760 nm). The luminance characteristic for transparent glass can be its transmission coefficient T. The reflection and scattering of light by glass is also significant in establishing the optical properties of glass or a product. The intensity of reflection from the glass surface is determined by the refractive index. The reflection coefficient increases with increasing refractive index and the angle of incidence of light on the surface. High reflectivity of glass surfaces is important for artistic crystal products. In most cases, the surface of the glasses is not perfectly smooth, and some of the reflected light is scattered (diffuse reflection). Sharply increases the scattering of light when matting the surface of the glass. 2.6. Chemical stability of glasses Chemical stability of glass is called its ability to withstand the destructive effect of water, acids, alkalis, salt solutions and other reagents. Most often, chemical stability is determined by the percentage of weight loss of glass, relative to the unit surface at a given temperature and the duration of the reagent’s action, or the amount of soluble components that have passed into the solution. An increase in temperature helps to accelerate the destruction of glass by any reagent. The destruction of glass in aggressive environments is quite difficult. There are two main types of destruction – dissolution and leaching. When dissolved, the glass components pass into the solution in the same proportions as they are in the glass. In leaching, predominantly oxides of alkaline and alkaline-earth elements pass into the solution, as a result a layer with an increased concentration of silicon oxide (a protective silica film) remains on the surface, and the process gradually slows down. In accordance with the nature of the des13
truction of glass, when exposed to reagents, they can be conditionally divided into two groups: 1) reagents with pH = 7 and below (water, acid solutions, acid solutions of salts, etc.), which «leach» the glass; 2) reagents with pH > 7 (solutions of alkalis, carbonates and others, and also hydrofluoric and phosphoric acids), which dissolve the glass. Chemical stability of glasses to reagents, especially of the first group, significantly depends on their composition. Among the silicate glasses, quartz glass is the most stable. High chemical resistance is inherent to aluminum and borosilicate (containing up to 15% of В203) glasses. The introduction of alkali metal oxides into silicate glasses leads to a sharp decrease in chemical stability, and К20 reduces it much more actively than Li20. Silicate glasses with alkaline-earth oxides are characterized by high stability. The silicates of Mg, Ca, Zn are chemically stable, and Ba and Pb are less stable. According to chemical stability to water, the glasses are divided into five hydrolytic classes, determined by the amount of leached sodium oxide: I – not variable by water; II – stable; III – solid hardware; IV – soft hardware; V – are unstable. Most common industrial sodium-calcium-silicate glasses (window, container, etc.) belong to the III and IV classes. The alkali resistance of glasses is less dependent on the composition. Quartz and polyzirconium glasses are more alkali-resistant. The alkali resistance is increased by Sn02, La203. Solutions of hydrofluoric and phosphoric acids actively influence the silicate glass with the formation of fluoride compounds of silicon (volatile substances) and soluble hydrosilicophosphates, which means they destroy the silicon-oxygen mesh of glass, in accordance with the equation: H2SiO3 + 4HF = SiF4 + 3H2O. Depending on the operating conditions, chemical and thermal stability, the chemical-laboratory glass is divided into the following types: CS-I – chemically stable first class; CS-II – chemically stable second class; TS – thermally stable and TS-Q – thermally stable quartz glass.
3 RAW MATERIALS 3.1. Main raw materials All raw materials used for glass production are divided into main and auxiliary materials. The main raw materials form the basis for glass and consist of aluminum oxide, acid, alkali, alkaline-earth and other oxides, which directly determine the properties of the glass. Auxiliary raw materials are various compounds that give the glass melt and glass certain properties or other properties affecting the technological processes of obtaining glass melt. This group includes clarifiers, decolorizers, colorants, opacifiers, oxidizing agents, reducing agents, accelerators. The main glass-forming oxides are acidic – SiО2, В2О3 and Р2О5. Silica (SiО2) is the main component of industrial silicate glasses. The composition of different silicate glasses contains about 55-75 mass fraction (%) of Si02. For including silica in the production of silicate glasses, quartz sands are usually used, the grain composition of which is regulated. Quartz sands should contain not less than 95% of Si02 and a limited amount of coloring impurities. In addition to coloring impurities, quartz sands can contain oxides of А1, Са, Mg, Na, К, which should be taken into account when calculating the composition of the batch. Coloring impurities give the glass an undesirable color. They include oxides of iron, titanium, chromium, vanadium, manganese and others. Certain requirements are also imposed for the consistency of the chemical composition of sand. The grain size in the sands should be in the range 0,1–0,8 mm. The grains larger than 0,8 mm should not be more than 5% and smaller than 0,1 mm – no more than 5%. 15
Sands that do not meet these requirements are enriched. Boric anhydride В2О3 is put into the glass with the help of technical materials – boric acid Н3ВO3, borax Na2В4О7.10Н2О and natural compounds. Boric acid is easily dehydrated when heated, but a significant amount of В2O3 volatilizes. Its losses during heating of the batch can reach 40% (when borosilicate glasses melt – 12-15%). Phosphoric anhydride is added into the composition of glass by orthophosphoric acid Н3РO4 and its salts – phosphates of ammonium and calcium. Apatite concentrate is also used. Amphoteric oxides include А12О3, but in most silicate glasses it plays the role of an acid oxide like silica. А12О3 is put into the glass by technical alumina, feldspars (Na2О-Al2О3-6SiО2 – albite, K2О-Al2О3-6SiО2 – orthoclase), pegmatite (mixture from feldspar-75% and quartz-25%), kaolin (Al2О3-2SiО2-2H2О). Among alkaline oxides, Na2O and К2O are most commonly used. Sodium oxide is added into the glass composition with Na2CO3 soda and sodium sulfate Na2SO4. In glass production, anhydrous, so-called calcined soda is usually used. Sodium sulfate is used as an additive to soda (5-15% of the amount of soda). It contributes to the clarification of the glass mass during melting. The raw materials for adding potassium oxide are potassium carbonate К2СО3 and niter KNО3. Potassium carbonate can be crystalline К2СОз .2Н2О and calcined К2СО3. Anhydrous potassium carbonate is very hygroscopic. Among the oxides of alkaline-earth metals, CaO and MgO are most widely used in glass melting. Calcium oxide CaQ is added by natural calcium carbonate in the form of chalk, marble, limestone (СаСО3) or by dolomite MgСО3.СаСО3. Chalk is a soft sedimentary rock. The content of СаСО3 should be not less than 98%, and the impurities of Fe2O3 impurities should not exceed 0,2%. Marble is a rock, characterized by the highest content of the main substance (99-99,5%). Limestones are sedimentary rocks with a significant variation in composition. For glass melting, limestones containing not less than 95% of the main substance and not more than 0,2% of iron oxide are used. For adding magnesium oxide, dolomite MgCО3. CaCО3 and magnesite MgCО3 are used. 16
The dolomites are characterized by a sharply variable composition. Their suitability for glass production is determined by the content of iron oxide, which should not be more than 0,3%. At the mining and processing plants, the dolomite is crushed and enriched, it is supplied to the glass factories in the form of a powder. Magnesite is a natural raw material, but less common than dolomite.
3.2. Auxiliary raw materials Colorants are used for obtaining colored glasses. Most of colorants provide the glass melt with stable color, which is determined by the colorant concentration and its chemical composition and independent of the secondary thermal processing. They are called molecular or ion-molecular. They include the oxides of heavy metals: cobalt, manganese, nickel, chromium, vanadium, uranium, alkali-earth elements. In addition, the same colorant can give the glass a different color depending on the redox conditions of melting. Some colorants allow coloring, not only regulated by the concentration, but also by secondary thermal processing, which impacts on the formation of colloidally-dispersed colorant particles in the glass, their size and amount. Such colorants are called colloidal, but the mechanism of coloring by them is more complicated than it can be interpreted from the fact of the formation of colloids. These colorants are compounds of gold, silver, antimony, selenium, copper. On the basis of colloidal colorants, glasses colored in red («rubies») are obtained, with the exception of silver coloring them in yellow. The most widespread is selenium ruby. It is obtained by adding a mixture of elemental selenium and cadmium sulphide, sometimes CdCО3, S and Se, into the glass composition. The color of the selenium ruby depends on the ratio of sulphide and cadmium selenide: from yellow at 100% CdS to dark red at high content of CdSe content, under conditions of a weakly reducing medium for melting. Opacifiers are compounds capable of imparting opacity to glass, as well as providing an opalescence effect, or milky-white coloring. As opacifiers, fluorine and phosphoric acid compounds, ZrO2, ZrSiO4 and others are used. To obtain milky-white color, fluorine compounds are added at the rate of 4-6% fluorine (Na2SiF6, 3NaF. AlF3, CaF2, 17
NH4F). Among phosphoric acid compounds, widely used are Са3(РО4)2, apatite concentrate, bone ash, Na2HPО4 . 12Н2O. Very strong opacifiers are zirconium compounds (3-6% ZrO2). Decolorizers are the compounds necessary to eliminate unwanted color of glass or to weaken it. There are physical, chemical and mixed decolorizers. Physical decolorization is coloring the glass melt in a color complementary to green. The overall transparency of the glass is reduced. For physical decolorization, selenium, oxides of cobalt, cerium, nickel are used. In most cases, these oxides are used not in pure form, but in combinations. So, a good decolorizer is selenium together with cobalt oxide. The blue color of cobalt oxide compensates for the slightly yellowish color obtained when selenium is added. Selenium gives the glass more transparency than other colorants. Nickel oxide is used in combination with selenium and cobalt oxide. Chemical decolorization is based on transferring iron oxide II to iron oxide III, which in comparison with it gives 15 times less intense coloring. However, the complete decolorization does not occur. Chemical decolorizers are substances that play the role of oxidizing agents: arsenic oxide, niter, sodium sulfate, fluorides, cerium dioxide. Mixed decolorizers include МnО2, which acts as both chemical and physical decolorizer. During glass melting, МnО2 disengages oxygen, and the resulting oxide Мn2O3 colors the glass in color complementary to yellow. Oxidizing, reducing agents, accelerators and clarifiers are the compounds necessary to create the appropriate melting medium. As oxidizing agents, nitrates of sodium and potassium, arsenic oxide, cerium dioxide are used. As reducing agents – carbon, metallic aluminum, magnesium, tin compounds – are used. Some compounds serve as accelerators for glass melting. They include fluorine compounds, usually their content in the batch is 0,5-1,0% in terms of the fluorine ion. Clarifiers are the materials that are added into the batch to accelerate the processes of clarification of the glass melt – to release it from gas inclusions. They include Na2SO4, NaCl, As2O3, ammonium salts. These compounds release gaseous products, decomposing at high temperatures, which provides clarification of the glass melt. 18
4 BASICS OF GLASS PRODUCTION TECHNOLOGY 4.1. Preparation of the batch Requirements to the batch The batch is a homogeneous mixture of raw materials prepared for glass melting, combined in certain proportions. There are certain requirements to the batch that must be followed to ensure the necessary quality of the glass melt: 1) in order to obtain a homogeneous batch the raw components should be with a certain grain size. Since the rate of melting of the components and their dissolution in the melt varies, there are different requirements to the grain structure. Sand, pegmatite and feldspar are sieved through the mesh 08 and 07 (the size of mesh opening side is 0,8 and 0,7 mm). Quartz sand refers to the components that are the slowest assimilable by the melt. Therefore, the sand grains should not exceed 0,8 mm. Limestone and dolomite are sieved through the mesh 09, chalk, sulphate and sodium carbonate – through the mesh 1,1. In such way the largest grain size of the components is regulated, which allows to obtain a homogeneous batch during the mixing; 2) the batch should have a certain humidity. For the batch with sodium carbonate, the recommended level of humidity is 4-5%, with sodium sulphate – 4-7%. Dry batch easily exfoliates dusts, its reactivity decreases, in contrast to the wet one, which is better mixed and more homogeneous; 3) for a more active flow of glass melting processes, the corresponding requirements are imposed for the content of brighteners in the batch. The optimum content of gaseous substances in the batch should not exceed 15-20%. 19
Preparation of raw materials Most of the raw materials come to the factory in the prepared for the batch form, so they are only sieved. However, a part of the materials requires prior preparation: drying, grinding, removing contaminants. In connection with this, composite plants of glass factories have two branches: the preparatory and the dosing-mixing. The warehouses (compartments) for the storage of raw materials are placed inside the composite plants. The raw materials come to the warehouses though railroad tracks, and they are transmitted for processing by the grab cranes. Outside the main building, the sodium carbonate and toxic materials are stored. Different raw materials during the storage should not be mixed with each other. Each component of the batch is stored and processed in the separate processing line. The quartz sand processing cycle includes its enrichment to remove iron impurities to acceptable limits, drying and sieving. The sands are enriched by flotation-attrition and magnetic separation. Sands, in which iron oxides are included in the clay inclusions, are enriched by washing. The quartz sands, used in the production of ultrapure glass, are subjected to the chemical enrichment with the acid solutions followed by washing and calcination. Carbonate materials (dolomite, limestone and chalk) are supplied to the factory in the form of blocks and pieces. Before drying, they are preliminarily crushed (except chalk) in the jaw crushers to a size of 4-5 cm pieces. Drying is performed the same way as for the sand, in drying drums. The drying temperature is about 400°С, since at higher temperature the thermal dissociation occurs, which is undesirable. Fine milling of the carbonate raw materials is carried out in the hammer crushers or ball mills. Alkali containing raw materials (sodium carbonate and sulfate) come in the bags in the form of powders from chemical plants, which are then sieved. The sieved materials enter the supply bunker, and screenings are milled in the hammer crusher. Since the natural sulfate contains considerable amount of water, it is preliminarily dried in the drying drums at 650-750 ° C. Then it is milled in a hammer crusher and sieved through the mesh 1,1. Pegmatite, feldspar come to the factories in the milled form, they are sieved through the mesh 07 and transported to the supply bunkers. 20
Composing the batch Prepared raw materials come in the supply or intermediate bunkers of the composite plant. Small amounts of them are stored directly in the supply bunkers, over which there are meshes set for control sieving. From the supply bunkers the materials are put to the automatic scales, then to the gathering conveyor belt and fed into the mixing tank. The most common are plate, cone and drum mixing tanks. During the mixing the batch is moistened, the sand is often moistened before entering the mixing tank. After mixing, the batch is fed to the intermediate bunkers or containers, and then to the bunkers of the batch loaders near the furnaces. Dosing-mixing compartments depending on the productivity have at least two automatic processing lines. The productivity of such a line is 500-600 tones of batch per day. Along with the conventional batch composing in some cases the special methods for processing the finished batch are used. They include granulation, preliminary fritting, pulverization. The batch calculation The raw materials, used for composing the batch, along with a basic substance may contain other oxides included in the glass composition. Therefore, the same component, such as SiО2, enters the batch not only through the quartz sand, but also partly through other raw materials (feldspar, limestone, chalk and others). So, the batch calculation should be carried out on the basis of the total amount of components contributed by all raw materials. When calculating the batch, it is needed to consider that most of the raw materials contain volatile substances, which are removed in the glass melting process (water, gaseous components СО2, SO2, etc.). Therefore, these components should enter the batch in excess. When calculating the batch, it is needed to consider also the adjustment for the volatilization of some components. For example, in glass melting volatilized are 5-25% В2О3, up to 3% Na2О, 30-50% F, up to 5% К2О, about 4% ZnO.
4.2. Glass melting 4.2.1. Stages of glass melting In order to obtain the glass, a glass batch is heated in the special glass furnaces to high temperatures – for normal industrial glasses 1450-1550 °C. In this case, in the batch there is a number of complex physico-chemical processes that result in the formed glass melt. The transfer of the batch into a homogeneous glass melt during the thermal heating is called glass melting. Glass melting process is divided into five stages: silicates forming, glass formation, clarification, homogenization and finish cooling. This division is conditional, since in practice the batch is almost always loaded into the high temperature zone, so all of these stages, except for the finish cooling, occur almost simultaneously. Silicates forming – is a phase of chemical reactions. In the batch at 300-400°С the interaction between the carbonates begins, with the formation of double carbonates CaNa2(CО3)2 or MgNa2(CО3)2, and then the dissociation of MgCО3 and СаСО3 occurs. At 400-600 °C, the reactions between the double carbonates and SiО2 with the formation of silicates begin. At 780-880 °C the melt appears in the batch. Vigorous interaction between silicates and their mutual dissolution occurs until the temperature of 1200 °C. Silicates forming is not a limiting stage in glass melting. It should be noted that in the batch of sodium carbonate this stage occurs without big difficulties, whereas in the sulfate batch the reactions proceed more slowly. Glass formation – is the stage of obtaining the melt without residual solid inclusions. Silica is usually injected into the batch in the amount more than it is required for silicates forming reactions. The dissolution of residual quartz sand in the obtained melt is a relatively slow process and its completion takes 60-70% of the time spent on the glass melting. The dissolution rate is dependent on the diffusion rate, melt viscosity, its surface tension and other factors. Clarification – is the stage of liberating the glass melt from the gaseous inclusions. Most of the gases are removed from the glass melt, but some of them rest as gas inclusions. This process is regulated 22
by temperature, glass viscosity, surface tension, pressure of the gas atmosphere over the melt. To speed up the clarification, the additives of the clarifiers are used, which at high temperatures form large bubbles and decrease the surface tension at the «gas-melt». Additives, lowering the viscosity of the glass melt, also contribute to the clarification. Homogenization – is achieving chemical and physical homogeneity by the glass melt. Homogenization takes place simultaneously with the clarification. Heterogeneity of the glass melt is defined as the initial heterogeneity of the grain composition and features of glass formation. The initial heterogeneity of the batch leads to a coarse chemical heterogeneity of the glass melt in the form of layers and stria. Averaging the chemical composition of the melt is also achieved by homogenization. Homogenization occurs due to the reduced viscosity, mechanical mixing, separation of gases from the glass, swirling it with the compressed air. To obtain a homogeneous glass melt, it is needed to have well mixed homogeneous batch. Finish cooling – is the stage of increasing the viscosity of the glass to the extent permitting the formation of the products, such viscosity is called manufacturing. For this, after the previous stages – clarification and homogenization, the glass melt is cooled to 300-400 °C. It should be noted that the basic requirement is a continuous and gradual reduction of temperature while maintaining the constancy of the gaseous environment over the melt. The break of the equilibrium between the liquid and gas phases can cause the appearance of fine gas bubbles (secondary midges) in the glass melt, get rid of which is very difficult. During the finish cooling, thermal homogeneity of the glass melt should be respected carefully. For glass melting, the baths and pot furnaces are used. Most types of industrial glasses are obtained in continuously operating bath furnaces. At one end of the basin of such furnace, the batch and the glass cullet are loaded, and at the other end, the products are manufactured. All stages of glass melting are performed simultaneously in different parts of the furnace, which means they are separated in space. The batch becomes a homogenized glass melt on the surface of the glass melt located in the basin of the furnace, in continuous displacement of the surface layers of the melt from filling up the batch until the generation of finished glass melt. The bath 23
furnaces are heated by the gaseous or liquid fuel. The combustion air is preheated in the regenerators. To heat the glass melt to a high temperature without unnecessary heat loss, the electric furnaces are used, in which the heat is released when a current is passed through the glass melt. In such furnaces there is a production of optical, electric-vacuum, radio-technical glass, crystal and fiberglass. Pot furnaces are used for the production of glass with high light transmission, optical, some technical and colored glass for artistic products. In the pot furnace’s cavity there are from one to 16 pots settled. The pots represent vessels of refractory mass with a capacity of 100-1000 kg. The pots are burned in the special furnaces to temperatures 1000-1200 °C and in a heated state they are moved in the pot furnace, where the final firing is performed to a temperature exceeding the glass melting temperature by 30-50 °C. Then the pot walls are covered with a layer of melted glass obtained from the glass cullet. Glass melting in the pot furnaces consists of a sequence of operations: loading and melting of the batch; clarification and mixing; finish cooling, generation. Thus, the glass manufacturing processes are separated in time. The pot furnaces are heated by gaseous and liquid fuels. The glass melting in periodic bath furnaces is performed similarly to the glass melting in the pot furnaces. Periodic bath furnaces are commonly used for in melting heat-proof, colored and opacified glasses.
4.2.2. Defects in the glass melt Glass defects are various violations of its physical and chemical homogeneity, occurring in the stages of melting and cooling of the glass. Defects can be foreign inclusions: gas bubbles, solid crystalline formations. Almost any glass melt contains inhomogeneities, therefore, for each type of glass there is allowable amount of them. The highest requirements are imposed to the optical glass, followed by technical and float glasses. Less severe restrictions on the content of defects are made for container glass. However, the types, amount and the size of allowable defects are regulated in such way, that their 24
presence do not reduce the mechanical strength and thermal stability of the articles. Defects in the glass melt differ by the origin, appearance, physical properties and chemical composition. There are three groups of defects: gaseous, glassy and crystalline. Gas inclusions – are one of the most common defects of the glass melt. They have various forms and sizes. The gas bubbles of glass contain the following gases СО2, SО2, О2, N2, Н2О and the air. The bubbles smaller than 0,8 mm in the practice are known as "a midge". The bubbles’ form can be spherical, ellipsoid, threadlike. By the origin, there are primary and secondary gas bubbles. Primary bubbles are formed during the process of glass melting and not completely removed during clarification. Secondary bubbles appear during re-heating of the glass melt due to the decomposition of sulfate residues or when violating the technological process at the cooling stage. Glassy inclusions are represented by striae and knots. Striae – are transparent threadlike or fiber-like inclusions of the glass of other composition. Striae adversely affect the optical homogeneity and reduce the mechanical properties of glass. Striae are formed due to inhomogeneity of the batch and glass melt, resulting from the poor mixing of the batch, violation of its chemical composition, involvement of stagnant areas of the glass melt in the output flow, use of cullet of different chemical composition. Coarser glassy inclusions in the form of large droplets, hills and nodes are called knots. They appear due to falling of the drops from the furnace roof into the glass melt, these drops are formed because of the interaction of a refractory with dust and vapors of alkalis. During the dissolving of knots in the glass melt the striae are formed. Crystalline inclusions in the glass melt have different origins. They include batch stones – the result of lack of fusion of the batch, the products of refractories’ destruction, the products of crystallization of the glass melt (crystallization stones), inclusions of the heat-proof foreign impurities (for example, chromium inclusions), falling in the raw materials. The batch stones in most cases are grains of quartz sand, but they may be also particles of chalk, limestone, alumina. The products of crystallization are crystalline formations arising from the crystallization of the glass melt. They appear at the interface 25
of phases: on the surface of the glass melt, on the gas bubbles, on the contacts of the glass melt with a refractory. Formation of crystallization products is due to a violation of technological regime of finish cooling and manufacturing the products.
4.3. Glass molding 4.3.1. Features of molding Molding of various kinds of products from glass is one of the important stages in glass manufacturing. The process of glass molding consists in the transformation of the glass melt from the viscous melt state through an intermediate plastic state into a solid product with a predetermined configuration. There are various methods for glass molding: casting, pressing, rolling, blowing, drawing, bending. Preparing the glass melt for molding is one of the main and complex issues of glass production, and it is necessary to monitor closely the viscosity of the glass melt, its chemical and thermal uniformity (Table 1). Table 1 Values of viscosity (η) of the glass melt during molding Molding method Pressing Blowing Glass ribbon drawing Fiberglass drawing
η, Pa.s 1·103-4·107 5·102-5·106 1·103-1·107
Molding method Rolling Casting Bending
η, Pa.s 1·102-1·107 1·102-1·105 1·105-1·106
During molding of the products, two processes are combined – deformation of the glass melt and its gradual hardening. They occur simultaneously, but they have different duration. The total time required for molding is usually determined by the hardening time of the glass melt, since the deformation time is less than the hardening time. With increasing rate of hardening, its duration decreases, and the 26
time of deformation increases. The most advantageous mode of molding is the one, in which the total time is minimal. The main technological parameters of the molding stage are the working interval of viscosity of the glass melt and the corresponding temperature interval of molding, the time of passing the working interval of viscosity (duration of molding). Molding is carried out in a wide range of viscosity values. Exemplary limits of change in viscosity for different methods of molding are given in Table 1, from which it follows that the practical interval of glass production is 102–108 Pa-s. During glass melting, clarifying and homogenization, the viscosity is 1–10 Pa-s. In the process of molding, surface tension plays an important role, especially during blowing and fiberglass drawing. During free molding, the surface tension forces create an ideally smooth fire-polished surface. The common methods of molding are pressing, blowing, drawing, press-blowing, rolling and float-method.
4.3.2. Molding methods Pressing is a periodic method of forming single-piece products, it is the least laborious and does not require high qualification of workers. Most often, the pressing method is used for making glassware, products for technical purposes, architectural-construction and architectural-artistic details. The key point of the pressing method is as follows. A portion of the glass melt mechanically (by a feeder) or manually is placed in a press-mold, corresponding to the manufactured product. Then, under the action of the lowering ram, the glass melt is uniformly squeezed out, filling the space between the mold and the ram (Figure 1). As seen from the presented figure, a mold ring is pressed against the mold from above, so that the glass melt cannot be above a certain level, and the bottom is not punctured. The ring forms the upper edge of the product. After a short exposure time, which is necessary to achieve viscosity of glass melt, limiting the deformation of products, the ram with the mold ring is 27
raised, and the product is pushed out of the mold. Pressing is carried out in non-detachable or unfolding molds. 5
Figure 1. Scheme of pressing the product in the mold: 1 – a drop of the glass melt; 2 – press-mold; 3 – a limiting ring; 4 – a ram; 5 – a product; 6 – a base
This method has limitations: the products with thin walls (less than 2 mm) cannot be obtained. In addition, the products, obtained by pressing, have low surface quality. Blowing is the molding method, in which the small thickness of the walls of the products is easily achieved, and the high quality of their surface is ensured. Blowing can be done manually – using a glass-blowing tube, or at blowing machines. The method of blowing on a tube is used for molding hollow thin-walled products with a wall thickness of about 2 mm or less. Usually manually complex varieties of thin-walled products are manufactured, as well as thick-walled products are blown out. During blowing on the tube, the upper part of the products remains attached to the tube like a cap or a locking ring and requires additional processing. Blowing the products of a simple form is fully mechanized. Machine blowing is based on the method of double blowing in molds – initially in the blank mold, where the neck is formed, and then in the final mold, where the product is finally formed. Thus, this method is used for producing narrow-necked thick-walled hollow articles with a diameter of a neck up to 30 mm (Figure 2). 28
The blowing method allows molding of hollow products of various shapes and purposes. However, the blowing method on the tube, providing the highest quality of the surface and the smallest wall thickness, is low-productive, and with double blowing in the molds the quality of the products is not high. Press-blowing is a two-stage method, which allows to produce thin-walled packaging with a wide neck of press-blowing. At the first stage, in the blank mold the future product’s neck and a blank part are pressed from a drop of the glass melt by the ram, and then in the final mold the product is blown out of the blank part. In this case, it is possible to obtain the exact dimensions and shape of the neck. The press-blowing method refers to highly effective molding methods.
Figure 2. Scheme of molding wide-necked products by press-blowing: а – feeding the drop into the blank mold; b – pressing the blank part and the product neck; c – transfer of the blank part into the final mold; d – blowing the product in the final mold; 1 – a drop of the glass melt; 2 – a blank mold; 3 – a ram; 4 – a blank part; 5 – a neck form; 6 – a final mold; 7 – a blow head; 8 – a product
Drawing is a method that is used in the production of sheet glass, tubes and fiberglass. The production of sheet glass is based on the principle of continuous drawing of a glass ribbon from the free surface (troughless drawing method) or from a slit embedded in the ceramic body melt (trough method) by the drawing mechanism. Vertical upward drawing is used to produce flat sheet glass with a thickness 29
usually from 2 to 6 mm and a width of the glass ribbon not exceeding 3000 mm.
Figure 3. Scheme of vertical glass drawing 1 – the glass melt; 2 – rollers of the machine; 3 – a glass ribbon; 4 – cooler; 5 – a trough; 6 – a cone
With the trough method, a rectangular chamotte body – a trough with through longitudinal slit, is placed in the submachine chamber of the glass melting furnace. When immersed under the pressure of the trough into a melt under the action of hydrostatic pressure, the glass melt is squeezed out through a slit, forming the so-called cone. This glass melt is drawn upward by asbestos rollers of the machine for vertical drawing (Figure 3). Under the action of water coolers, the glass ribbon quickly hardens, and already solidified glass melt contacts with the rollers. During the drawing process, the glass ribbon undergoes a significant stretching. As the ribbon is raised upward, it tends to narrow under the influence of surface tension forces. This is prevented by rapid cooling of the glass ribbon and the installation of stabilizers. This method has 30
disadvantages – low quality of sheet glass and relatively low productivity. The drawing speed usually does not exceed 100 m / h for a 2 mm thick glass. With the troughless drawing method, the ribbon is formed directly from the free surface of the glass melt. The cone is formed as a result of optimal regulation of the viscosity of the glass melt with the help of coolers and screening of the forming assembly with guarding devices – special edge rollers. Then the ribbon is drawn the same way as in the trough method. The troughless method ensures the production of high-quality sheet glass, and it is more productive than the trough method. The disadvantage of the troughless method is the noticeable variability of the glass thickness and high sensitivity to deviations in the technological regime. The glass tubes of various diameters are obtained by the methods of vertical and horizontal drawing. Thick-walled tubes with a diameter of 50-200 mm are drawn by the troughless method from the free surface of the glass melt. For creating an internal cavity, in the glass melt the chamotte mouthpiece is immersed, through which compressed air is blown. The air forms a tube from the inside and cools it. A cone is formed around the mouthpiece on the surface of the glass melt, from which the tube is drawn. For quick cooling of the glass melt during molding of the tube, ring coolers are installed. Glass tubes with a diameter of 2 to 50 mm and a wall thickness of up to 2 mm are obtained by horizontal drawing. The glass melt in continuous flow runs into a rotating inclined mouthpiece, envelops it and is pulled from the lower end of the pulling machine in the form of a tube (Figure 4). Compressed air is supplied to the inner cavity of the mouthpiece and the tube. Rolling is a method that allows to obtain various types of sheet glass (reinforced, patterned, thickened, large-format, wavy, perforated), carpet-mosaic and facing tiles. Rolling can be performed continuously or periodically. With continuous rolling, a layer of the glass melt, that flows down the drain threshold of the furnace, passes between two horizontal rolling rolls rotating towards each other. These rolls are internally cooled with water. Molded ribbon in plastic state enters the receiving plate and an open roller table. The hardened ribbon on the roller table 31
goes to the annealing furnace. In this way, a ribbon with thickness of 3 to 40 mm and a width of up to 3000 mm is obtained. To obtain reinforced glass, in front of the rolling rolls a metal mesh is placed in the glass met. When rolling a patterned glass, one of the rolling rolls has a corrugated pattern on the surface.
Figure 4. Scheme of horizontal drawing method of tubes: 1 – the glass melt; 2 – a mouthpiece; 3 – a drawn tube; 4 – a channel for air supply
Periodic rolling is carried out by rolling a portion of the glass melt, which is poured out of the glass melting pot on a non-moving metal table. Rolling is performed with one or two rolls. The molded glass is transferred to the annealing furnace. This method is low productive, however it is irreplaceable in the production of thickened and large-format glass sheets, as well as in the molding of specialized products. The float method is a molding method that is used in the production of polished glass by continuous flame polishing of a glass ribbon on a metal melt. The ribbon is formed in a closed bath on the surface of molten tin (float bath) by free expansion of the glass melt, which comes from the glass melting furnace. At a temperature of 1025°C the equilibrium thickness of the glass ribbon is reached. Behind the float bath there is a roller pulling device that continuously pulls the ribbon from the bath and moves it to the annealing furnace. To prevent the narrowing of the ribbon when pulling, it is stretched in width with special rollers that hold the sides. The high quality of the sheet glass surface is ensured by the contact of the lower surface of the ribbon with an ideally smooth 32
surface of the molten metal and the flame polishing of its upper surface. In this way, polished sheet glass with a thickness of 2,5 to 20 mm and ribbon width of 1600-4000 mm is produced. The main disadvantage of the float molding method is the need to use a large amount of tin (the mass of tin in the bath is about 120 tons), as well as the complexity of operating the processing line.
4.4. Annealing and tempering of glass With rapid cooling or heating of the glass due to variation in temperature regime, mechanical stresses arise in the thickness of the product. As a result of the low thermal conductivity of the glass, during the cooling of the glass product molded under the influence of high temperatures, its surface layers cool faster than inner ones. When the outer layers are already hardening, trying to compress, the inner layers remain still liquid and prevent compression of the outer layers. Therefore, the outer layers of the glass product are in a state of tension, while the inner layers are in a state of compression. As the cooling continues, the inner layers start hardening, trying to compress, while already hardened outer layers prevent this. As a result of the final cooling of the glass product, its outer layers are in a state of compression, and the inner ones are under tension. Such stresses are called residual or constant. It should be noted that in addition to the residual stresses, temporary stresses can also appear, which relax, when the temperature levels off, which means they disappear. In order for the product to be strong, it is necessary to remove the stresses by heat treatment or by ensuring the appropriate technological regime of the molded product. Annealing of glass is the process of eliminating or significantly reducing the residual stresses by uniform controlled cooling. For each glass there is a certain temperature interval, in which annealing occurs. The residual stresses are removed faster with low viscosity of the glass and, consequently, high annealing temperature. However, for the molded product the increase in the annealing temperature is limited by the possibility of deformation of the products. Therefore, the annealing stage is characterized by an upper and lower annealing temperature (ТU, ТL). The upper annealing temperature is the 33
temperature at which the stresses disappear quite quickly, without causing deformation (most often it is 20-50°C lower that the softening temperature of glass at a viscosity of 1012 Pa.s.). In this case, up to 95% of the stress is removed within 3 minutes. For industrial glasses, the upper temperature of annealing is 520-530°C. The lower annealing temperature of the glass corresponds to a viscosity of 1013,5 Pa.s, at which about 5% of the residual stresses are removed in 3 minutes. The lower limit of temperature is 50-150°C lower than the upper one. Stresses occurring at the temperature below the lower limit are temporary, which disappear when the temperature levels off. The temperature interval, or annealing zone, is limited by ТU and ТL, in which the annealing of glass products is carried out. It is necessary to cool products to 20-50°C cautiously, since excessive temporary stresses can also cause their destruction. Annealing of glass products is usually carried out in four stages of different duration. At the stage I, the products are heated or cooled to ТU at the rate, at which they do not collapse. At the stage II, the products are kept at ТU until the residual stresses disappear completely. Then, at the stage III, the products are slowly cooled to ТL at the rate, that does not allow the formation of new residual stresses. At the stage IV, the products are cooled quite quickly, but so that dangerous temporary stresses do not arise. The temporary stresses, that appear at this stage, disappear after cooling. The duration of annealing stages depends on the thickness of the product. Annealing of products is carried out in continuously operating conveyor furnaces, in which its individual stages proceed in a sequential order in different zones along the length of the furnace, or in periodic chamber furnaces, in which the annealing stages change each other in time. To all annealing furnaces strict requirements are imposed on the uniformity of temperature distribution and their regulation. Tempering of glass is the process of creating uniformly distributed residual stresses in the glass by special heat treatment, during which the strength of glass products increases. This stage is used to obtain high-strength glass products. During tempering, the increase in the strength of glass products is achieved not only by creating uniformly distributed stresses, but also by forming compressive stresses on the surface of the glass products. Since the destruction of the glass 34
starts from the surface, the compressive stresses will prevent the destruction. Under the influence of the applied bending force, the tempered glass, compared with annealed one, experiences greater compression in the upper layer and lower tension in the lower layer. The mechanical strength and heat resistance of tempered glass depend primarily on the degree of tempering, which is characterized by the magnitude of the stresses in the glass, determined by the temperature change across the thickness of the product during tempering, and the linear thermal expansion coefficient (LTEC). The higher LTEC, the higher are the residual stresses. Quartz glass, which has the lowest LTEC, can hardly be tempered. The maximum degree of tempering for a given glass is determined by the tempering temperature. With increasing temperature, the degree of glass tempering grows to a certain limit, and then remains constant. It should be noted that the higher the cooling intensity of the glass, the greater is the degree of tempering and hardening of the glass. The most common cooling medium is air. As liquid media, mineral oils, organosilicon liquids, melts of salts and metals are used. When the tempered glass is broken, small glass particles with blunt edges appear. Therefore, it is called safe.
5 LABORATORY WORKS 5.1. Determination of water resistance of glass at temperature 98 °С The purpose of the work: to determine the class of water resistance of glass (a type of the glass as assigned by the instructor). Necessary reagents and solutions: − A water bath, providing a water temperature (98 ± 0,5) °С and (20 ± 0,2) °С, − a laboratory thermometer with the scale division of 0,2 °C and the measurement error tolerance of not more than ± 0,2 °C, − a mortar with a pestle made of steel in accordance with GOST 801-78 or GOST 380-71, − an electric hob, a hammer weighing 0,5 kg, − sieve with grids of 315 K; 05 К; 08 K; and 1 K in accordance with GOST 3584-73, − a drying cabinet, providing a temperature of 150 °C, − protective glasses in accordance with GOST 12.4.003-80, − burettes in accordance with GOST 20292-74, with a capacity of 1 cm3, with a scale division of 0,01 cm3 and a capacity of 10 cm3, with a scale division of 0,05 cm3, − pipettes in accordance with GOST 20292-74, with a capacity of 1 and 25 cm3, − volumetric flasks in accordance with GOST 1770-74, with a capacity of 50 cm3 with a ground glass stopper of the first hydrolytic class, − conical flasks in accordance with GOST 10394-72, with a capacity of 100 and 250 cm3, 36
− a beaker for weighing in accordance with GOST 25336-82, − distilled water in accordance with GOST 6709-72. − hydrochloric acid in accordance with GOST 3118-77, 0,01 N solution, − methyl red (indicator) in accordance with GOST 5853-51, − ethyl alcohol rectified technical in accordance with GOST 18300-72 or acetone in accordance with GOST 2603-79. Before the first use, the flasks are boiled twice for 1 hour each time with fresh 0,01 N solution of hydrochloric acid (filled above the mark). After rinsing with distilled water, the flasks are boiled two more times with distilled water for 1 hour. If the glasses of different resistance classes are tested in the flasks one after each other, then after each experiment the internal surface is leached with distilled water. The order of performing the work 1. Preparing the sample A sample of crushed glass is placed in a conical flask with a capacity of 250 cm3, and the adherent dust particles are removed by six-time decantation, using each time 30 cm3 of acetone or ethyl alcohol. To remove residual acetone or alcohol, the flask is placed on the electric hob preheated to a temperature of about 70 °C and then turned off, and after evaporation of all acetone or alcohol, the flask with crushed glass is held for 20 minutes in a drying cabinet at temperature 140 °C. It is necessary to comply with the rules of working with combustible and toxic substances. After removing the flask from the drying cabinet, the crushed glass is poured into a beaker for weighing, then cooled in a desiccator and closed. 2. Conducting the experiment From the prepared sample three shots of 2,000 g each are taken and weighed. Each shot is placed in a volumetric flask with a capacity of 50 cm3, filled up to the mark with distilled water, and the crushed glass is distributed over the surface of the flask’s base. Simultaneously, two control experiments are carried out (without a sample). 37
All flasks without stoppers are immersed above the marks (up to half the neck) into a water bath with a temperature of 98 °C. After 5 minutes the flasks are closed with stoppers. The flasks are heated at a temperature (98 ± 0,5) °С for 60 minutes from the moment of immersion in the bath. Then the flasks are removed, opened, and after cooling in a water bath to a temperature of (20±2) °C, filled to the mark with distilled water. The contents in the flasks are carefully mixed and rest until precipitation of the glass. From each flask 25 cm3 of clear solution is taken by the pipette into conical flasks with a capacity of 100 cm3, then 0,1 cm3 of methyl red solution is added, and the titration by 0,01N solution of hydrochloric acid is performed until the transition of the indicator’s color from yellow to red-orange. The end of the titration is determined by the coincidence of the color shades of 25 cm3 of the buffer solution with 0,1 cm3 of the indicator and the titrated solution. All three solutions and the control experiments’ solutions are titrated in the same way. 3. Processing the results Water resistance of the glass at 98 °С (ХА) in cm3/g is calculated according to the formula
V1 + V2 ) 2 , m
where V – is the volume of 0,01N solution of hydrochloric acid, consumed for titrating 25 cm3 of the analyzed solution, cm3; V1, V2 – are volumes of 0,01N solution of hydrochloric acid, consumed for titrating 25 cm3 of control experiments’ solution, cm3; m – is the mass of the shot of crushed glass, g. The experiment’s final result is taken as the arithmetic mean of the results of three parallel determinations. Water resistance class of the glass at 98 °C is established in accordance with the data specified in the table 38
Consumption of 0,01N solution of hydrochloric acid during titration, cm3/g Up to 0,10 inclusive 0,10 – 0,20 0,20 – 0,85 0,85 – 2,00 2,00 – 3,50
Water resistance class 1/98 2/98 3/98 4/98 5/98
The tolerable discrepancies between the results of each of the three parallel measurements and the mean value should not exceed: ± 15 % – for class 1/98; ± 10 % – for class 2/98; ± 5 % – for class 3/98, 4/98 and 5/98.
5.2. Determination of thermal resistance of glass The purpose of the work: to determine the thermal resistance of glass (a type of the glass as assigned by the instructor). Necessary equipment: A tank with hot water, which should have an inflow and a drainage of water, devices for heating, mixing and ensuring the deviation of the temperature from the set point not more than 10С; direct touch between the baskets with glass products and heating devices is not allowed. The volume of water in the tank must be at least twice more than the total volume of the simultaneously tested samples. The total volume of samples is determined by the sum of the volumes of individual samples, while the volume of the sample is taken as the volume of the space occupied by the sample, and for the hollow article, including its internal cavity. An electric furnace with forced circulation and regulation of air temperature, providing a deviation from the set temperature not more than 5 °C and not more than ±1% during the whole experiment. A tank with cold water with an inflow and a drainage of water. The deviation of the temperature from the set point in the tank should not exceed 1 °C. 39
The volume of water in the tank with cold water must exceed the total volume of simultaneously tested samples by at least 5 times. Instruments for measuring temperature, providing a measurement accuracy of ±1 °C. A basket for samples, with a lid that fixes the stable position of the samples when transferred from a hot water tank or an electric furnace to a cold water tank. Tongs or other means for transferring the samples from a hot water tank or an electric furnace to a cold water tank. The order of performing the work Conducting the experiment (experiments are performed indoors at a temperature not less than18 °С) 1. Method A, with single cooling of heated samples 1.1. The samples are heated in a hot water tank. 1.2. The difference in water temperatures in the tanks with hot and cold water should be not less than the one specified in the regulatory and technical documentation for specific types of glass products. 1.3. When several samples are tested at the same time, they are placed in a basket, open hollow articles with the orifice up, their positions are fixed, and then they are immersed in a tank with hot water. 1.4. Samples should not touch each other, and their upper edge should be at least 5 cm below the water level. 1.5. The duration of holding the samples in a hot water tank is determined from calculating 1,5 min per 1 mm of the sample thickness (the largest), but not less than 10 min. 1.6. After the end of holding, the basket with samples is transferred to a tank with cold water, open hollow items are transferred filled with hot water. Transfer time of the basket with samples from one tank to another is (10±2) s. The holding time of the samples in the tank when cooling is 30-40 s. 1.7. After immersion in a cold water tank, open hollow objects should remain filled with hot water. The water temperature in the cold water tank should be from 5 to 27 °C. 1.8. After the experiment, the samples are taken out of the basket, the hollow samples are poured out of water and examined with the naked eye. 40
Method A, with multiple cooling of heated samples 1.9. The experiments are conducted the same way as in 1.1–1.8. 1.10. Heating and cooling of the samples are repeated many times, and the temperature of hot water in the tank is increased by 5 or 10 °C with each repetition. 1.11. Damaged samples are taken out and not used in further experiments. 1.12. Heating and subsequent cooling are carried out until the specified number of samples are damaged. 2. Method B, with single cooling of heated samples 2.1. The samples are heated in an electric furnace. 2.2. The temperature difference in the electric furnace and water in a tank with cold water should be indicated in the regulatory and technical documentation for specific types of glass products. 2.3. If several samples are tested at the same time, the samples are placed in a basket, and the open hollow samples are placed in such way that when they are immersed in a cold water tank they are filled with water. A basket with samples or individual samples are placed in the electric furnace so that the samples do not touch each other. 2.4. The duration of holding the samples in the furnace is determined from calculating 6 min per 1 mm of the sample thickness (the largest), but not less than 15 min. The counting of the holding time of the samples in the furnace starts from the moment the specified heating temperature is reached. 2.5. At the end of holding, the sample basket or individual samples are taken out of the furnace and transferred to a cold water tank. The transfer time of samples should be (5±1) s, from the moment of taking out the samples from the furnace to the moment they are immersed in a cold water tank to a predetermined depth. 2.6. When taking out individual samples from the furnace, the furnace should not be opened for more than 5 s. Before removing the next sample, it is necessary to wait at least 3 min for the temperature in the furnace to stabilize. 2.7. The method and depth of immersion of the samples in a cold water tank should be indicated in the regulatory and technical documentation for specific types of glass products. 41
2.8. The water temperature in the cold water tank should be from 5 to 27 °C. 2.9. After 30-40 s after immersion in a cold water tank, the samples are taken out and examined with the naked eye. Method B, with multiple cooling of heated samples 2.10. The experiments are conducted the same way as in 2.1-2.9. 2.11. Heating and cooling of the samples are repeated many times, and the temperature of hot water in the tank is increased by 5 or 10 °C with each repetition. 2.12. Damaged samples are taken out and not used in further experiments. 2.13. Heating and subsequent cooling are carried out until the specified number of samples is damaged. 3. Processing the results 3.1. Based on the results of the examination, the number of damaged samples is established. 3.2. The sample is considered damaged, if after removing it from a cold water tank, it has cracks, chips or it is completely collapsed. Damaged samples include samples damaged during immersing in the heating environment, and also during heating. 3.3. The experiment results should contain: − characteristics of the test samples (name, type, size or capacity, etc.); − number of samples tested; − experiment conditions (experiment method, holding time in the furnace or tank); − experiment results; − date of the experiment. 3.4. When testing products by the methods A and B with multiple cooling of heated samples, the number of samples damaged in each experiment is determined, indicating the appropriate temperatures of the heating and cooling environments and the temperature difference between them. The number of damaged samples is also expressed as a percentage of the total number of test samples. 3.5. If the experiments are carried out until all test samples are damaged, it is necessary to indicate the values in accordance with 3.3 42
and calculate the arithmetic mean of the temperature difference, at which the samples are damaged.
5.3. Determination of metal oxides in glass The purpose of the work: to determine the presence of metal oxides in glass Necessary reagents and solutions: Samples of glass products (lime-sodium, potassium-lead), rasp files, 20% solution of hydrofluoric acid, solution of fresh hydrogen sulphide water, solution of potassium iodide, acetic acid, alcohol burners, platinum wire. The order of performing the work Conducting the experiment 1. Determination of the presence of potassium oxide in glass 1.1. Make a cut on the product sample, using the rasp file, and apply a drop of water on it. 1.2. Calcinate the platinum wire in the flame, put its end into a drop of water, and then bring it into the burner’s flame. 1.3. Look at the flame through the filter (cobalt plate) – in the presence of potassium oxide the flame is colored in violet. 2. Determination of the presence of lead in glass 2.1. Determine the presence of lead oxides by the hydrogen sulfide method. Make a cut on the glass product sample, using the rasp file; apply two or three drops of hydrofluoric acid on it, and then two or three drops of hydrogen sulfide water. In the presence of lead oxides a black precipitate appears. Record the course of the chemical reaction. 2.2. Determine the presence of lead oxides by the non hydrogen sulfide method. To do this, make a cut on the glass product sample, using the rasp file, and apply two or three drops of hydrofluoric acid on it. Wash out the concentrated solution of PbF2 with a small amount of water into the test tube. Into the same test tube, add a solution of 43
potassium iodide dropwise until precipitate formation. To the precipitate, add four or five drops of water and four or five drops of acetic acid of 2 N concentration, and then heat. When heated, the precipitate of lead iodide transfers into solution. Cool the solution under a stream of cold water. Investigate the resulting precipitate (the small golden plates). Record the course of the chemical reaction. 3. Processing the results Record the results of the study in the form: №
Sample number containing К2О
Sample number containing PbO
TEST QUESTIONS 1. Silicate materials include: A) metals and alloys B) organophosphorus compounds C) materials, containing silicon compounds D) oxygen-containing polymers E) glass 2. Simple silicate materials are A) SiO2 compounds with potassium or sodium oxides B) SiO2 compounds with potassium or sodium oxides C) Sb2O3 compounds with potassium or sodium oxides D) SnO2 compounds with potassium or sodium oxides E) Sc2O3 compounds with potassium or sodium oxides 3. Complex silicate materials include: A) soluble glass B) metal alloys, complex in structure C) polymeric materials, containing metals D) orthoclase, kaolinite, mullite E) complex oxides 4. Natural silicate materials are A) glass materials characterized by a constant composition and an amorphous structure B) various rocks, consisting of minerals, that are characterized by a constant composition, a pronounced crystalline structure and certain properties, containing SiO2 C) сeramic materials characterized by a constant composition and crystalline structure D) organic materials, containing nitrogen and oxygen in their composition E) high-molecular compounds with increased mechanical and thermal strength 5. Artificial silicate materials are A) various rocks, consisting of minerals, which are characterized by a constant composition, a crystalline structure, containing silica B) organic materials, containing nitrogen and oxygen in their composition C) materials, obtained by appropriate processing natural materials, such as glass and ceramics
D) materials, obtained by processing natural materials, such as wood and metal alloys E) polymeric materials, characterized by increased plasticity and mechanical strength 6. Glasses represent complex systems, consisting of not less than five oxides, the main three of them are: A) CaO, Na2O, K2O B) SiO2, PbO, Na2O C) SiO2, CaO, Na2O D) SnO2, CaO, Na2O E) SiO2, BaO, Na2O 7. What oxide in the glass is more than 70%? A) Na2O B) SiO2 C) BaO D) K2O E) SnO2 8. Crystal glass contains in its composition, in addition to the main components A) SnO2 B) SiO2 C) PbO D) CaO E) B2O3 9. Borosilicate glass contains in its composition, in addition to the main components A) SnO2 B) B2O3 C) PbO D) SiO2 E) CaO 10. Which type of glass has an increased thermal resistance? A) borosilicate B) crystal C) lime-sodium D) calc-potassium E) quartz 11. Characteristics of a number of physical properties of glass can be determined by calculation in accordance with A) the rule of Vant-Hoff
B) Arrhenius equation C) the additivity rule D) the Kohlrausch equation E) the method of least squares 12. The physico-mechanical properties of glass include: A) heat capacity, thermal conductivity, thermal expansion, thermal resistance B) viscosity, surface tension, density, elasticity, tensile and compressive strength, brittleness, hardness C) refraction, reflection, light absorption D) electrical conductivity, electrical permeability and electrical strength E) acid resistance, alkali resistance and water resistance 13. The thermal properties of glass include: A) refraction, reflection, light absorption B) viscosity, surface tension, density, elasticity, tensile and compressive strength, brittleness, hardness C) heat capacity, thermal conductivity, thermal expansion, thermal resistance D) electrical conductivity, electrical permeability and electrical strength E) acid resistance, alkali resistance and water resistance 14. The electrical properties of glass include: A) heat capacity, thermal conductivity, thermal expansion, thermal resistance B) viscosity, surface tension, density, elasticity, tensile and compressive strength, brittleness, hardness C) refraction, reflection, light absorption D) electrical conductivity, electrical permeability and electrical strength E) acid resistance, alkali resistance and water resistance 15. The optical properties of glass include: A) heat capacity, thermal conductivity, thermal expansion, thermal resistance B) viscosity, surface tension, density, elasticity, tensile and compressive strength, brittleness, hardness C) refraction, reflection, light absorption D) electrical conductivity, electrical permeability and electrical strength E) acid resistance, alkali resistance and water resistance 16. Hardness of glass is determined experimentally by A) the mineralogical scale of F. Moos B) Young's modulus of elasticity C) refractive index D) the value of glass density E) the value of glass brittleness
17. What is brittleness of glass? A) the ability of glass to resist the introduction of other materials into it under a certain load B) the ability of glass to break down under the impact of load C) the ability of glass to resist stretching, compression and bending D) the ability of glass to conduct heat E) the ability of glass to withstand sudden temperature fluctuations without breaking down 18. What is thermal resistance of glass? A) the ability of glass to resist the introduction of other materials into it under a certain load B) the ability of glass to break down under the impact of load C) the ability of glass to resist stretching, compression and bending D) the ability of glass to melt at high temperatures E) the ability of glass to withstand sudden temperature fluctuations without breaking down 19. In chemical terms glass is A) stable to short-term exposure of various chemical reagents, except sulfuric acid, at room temperature B) active, at room temperature reacts with dilute solutions of acids and alkalis C) amphoteric compound, which reacts actively with various chemical compounds D) stable to short-term exposure of various chemical reagents, except hydrofluoric acid, at room temperature E) not stable to short-term exposure of various chemical reagents, except hydrofluoric acid, at room temperature 20. High chemical stability of glass is explained by A) hydrolysis of silicates of its surface in interaction with humidity, resulting in the formation of silica gel, which slows down the process of chemical destruction of glass B) the presence of alkali metal oxides in the glass composition C) the presence of alkali-earth elements’ oxides in the glass composition D) the presence of lead oxide in the glass composition E) increased thermal resistance and mechanical strength of glass 21. Red lead is required when receiving A) borosilicate glass B) lime-sodium glass C) crystal glass D) lime-potassium glass E) glass ceramics
22. The following materials are obtained during glass molding by the float method: A) thick-walled tubes B) lighting glass C) electrovacuum glass D) high-capacity containers E) flat glass with polished surface 23. Which method of molding is carried out in a closed bath on the surface of the molten metal? A) float method C) pressing of the glass melt C) blowing of the glass melt D) rolling of the glass melt E) drawing of the glass melt 24. Methods of glass molding are: A) drawing, casting, molding, press-blowing, blowing of the glass melt B) drawing, pressing, blowing, float-method, rolling, press-blowing C) rolling, hot casting, float-method, horizontal drawing, rolling D) float-method, grinding, polishing, vertical drawing E) pressing, press-blowing, casting, plastic molding, drawing 25. What is meant by the mechanical treatment of glass? A) grinding and polishing B) annealing and cooling C) melting and grinding D) pressing and grinding E) heat treatment 26. Indicate the stages of glass melting: A) homogenization, fritting, clarification, spreading and finish cooling C) glass formation, clarification, homogenization and hydration C) silicate formation, melting, clarification, homogenization D) silicate formation, glass formation, clarification, homogenization and finish cooling E) drying, melting, glass formation, clarification and finish cooling 27. What determines the duration of the stages of glass annealing? A) thickness of the product B) annealing temperature C) annealing method D) cooling duration E) composition of the glass
28. What is called sheet pane glass? A) silicate glass, consisting mainly of one silica B) rolled colorless or colored glass, which has relief repeating pattern on the full surface on one or both sides. C) flat glass, the surfaces of which are processed in such a way that they do not allow optical distortion. D) glass products from crystal, colorless and colored glass by the methods of manual and mechanized blowing and pressing. E) glasses, produced in the form of flat sheets, the thickness of which relative to the length and width is comparatively small. 29. What are the colorants in the technology of glass production? A) compounds of various metals, capable of imparting a certain color to the glass B) compounds that facilitate the creation of oxidation and reduction media during melting C) substances, at the introduction of which glass acquires the ability to scatter light D) compounds used to accelerate glass melting E) materials that facilitate the release of glass melt from visible gas inclusions 30. In the technology of glass production, the batch is: A) a liquid mixture of components prepared for glass melting B) a finely ground mixture of raw materials of non-uniform composition for glass melting C) a homogeneous mixture of components prepared for glass melting D) a dry, non-uniform mixture of raw materials E) a plastic homogeneous mixture of components prepared for glass melting 31. What are the opacifiers in the glass production technology? A) substances, at the introduction of which glass acquires the ability to scatter light B) materials that facilitate the release of glass melt from visible gas inclusions C) compounds of various metals, capable of imparting any color to the glass D) compounds that facilitate the creation of oxidation and reduction media during melting E) compounds used for the acceleration of glass melting 32. In the process of glass melting, what does the stage «glass formation» mean? A) obtaining a melt without solid visible inclusions B) glass melting C) obtaining a melt with inclusions D) obtaining solid solutions E) the formation of heterogeneous melt
33. How is the float bath filled during the glass molding by the float method? A) with water B) with lead C) with mercury D) with tin E) with zinc 34. What properties of glass increase during tempering? A) strength and thermal resistance B) the ability to crystallize C) chemical stability and electrical conductivity D) optical properties E) alkali resistance 35. What is the difference between the glass ceramics and glasses? A) molding methods B) amorphous state and chemical composition C) crystal structure D) mode of glass firing E) lower physico-chemical properties 36. What are clarifiers? A) materials that facilitate the release of glass melt from visible gas inclusions B) compounds used for the acceleration of glass melting C) substances, at the introduction of which glass acquires the ability to scatter light D) compounds of various metals, capable of imparting any color to the glass E) compounds that facilitate the creation of oxidation and reduction media during melting 37. Additional heat treatment for release of stresses in the glass products is: A) glass hardening B) glass melting C) homogenization of the batch D) glass opacification E) annealing of the glass 38. Catalysts in the technology of glass ceramics are: A) substances accelerating the homogenization reaction B) substances accelerating the crystallization reaction C) substances initiating the process of nucleation of crystallization centers D) substances initiating the opacification process of glasses E) substances accelerating the process of melting of glass ceramics
39. For what kind of glasses tempering is used? A) safety glasses B) electrotechnical C) chemical-laboratory D) thermomechanical E) optical 40. What are the compounds that give the glass opacity? A) modifiers B) colorants C) inhibitors D) opacifiers E) mineralizers 41. The temperature of sheet glass melting equals, in оС A) 1540 –1580 В) 1400 – 1440 С) 1200 – 1320 D) 1650 – 1730 Е) 1100 – 1200 42. The basis of industrial container glass consists of the compositions of the triple system: A) Na2O-CaO-SiO2 В) MgO-Na2O-K2O С) Al2O3-SiO2-Fe2O3 D) Fe2O3-CaO-SiO2 Е) K2O-CaO-MgO 43. The main characteristics of glass are A) isotropy, ability to gradual and reversible hardening, glass transition interval B) ability to gradual and reversible hardening C) isotropy D) glass transition interval E) ability to gradual and reversible hardening, glass transition interval 44. The process of converting glass to glass ceramics consists of A) 2 stages B) 3 stages C) 4 stages D) 5 stages E) 1 stage 45. The interval of density of industrial glasses is A) 1000-7500 kg/m3 В) 2200-7500 kg/m3
С) 2200-3000 kg/m3 D) 2000-6000 kg/m3 Е) 1000-5000 kg/m3 46. The density of quartz glass is A) 1000 kg/m3 В) 2500 kg/m3 С) 2200 kg/m3 D) 1800 kg/m3 Е) 1200 kg/m3 47. The density of ordinary industrial glass is A) 1200 kg/m3 В) 1000 kg/m3 С) 2200 kg/m3 D) 1800 kg/m3 Е) 2500 kg/m3 48. Auxiliary raw materials in the production of glass are A) clarifiers, decolorizers, colorants, opacifiers, oxidants, reducing agents, accelerators C) clarifiers, decolorizers C) oxidizers, reducing agents, accelerators D) colorants, opacifiers E) decolorizers, colorants 49. Glass melting proceeds in several stages A) silicate formation C) glass formation, clarification C) homogenization, finish cooling D) silicate formation, glass formation, clarification E) silicate formation, glass formation, clarification, homogenization, finish cooling 50. Technological scheme for obtaining glass ceramics A) batch preparation, melting, molding of the products, heat treatment, sitallization B) batch preparation, melting, molding of the products C) heat treatment, or sitallization D) batch preparation, molding of the products, heat treatment, sitallization E) batch preparation, melting, heat treatment, sitallization 51. Technical glass ceramics is obtained on the basis of the system A) К2O-Al2O3-SiO2 В) Na2O-Al2O3-SiO2 С) Al2O3-SiO2
D) Li2O-Al2O3-SiO2 Е) Li2O-SiO2 52. When obtaining spodumene glass ceramics, as catalyst for crystallization 4-6% of the following is introduced A) Al2O3 В) MnO2 С) TiO2 D) Li2O Е) ZrO2 53. When obtaining spodumene glass ceramics, as catalyst for crystallization TiO2 is introduced in an amount of A) 4-6% В) 1-3% С) 7-9% D) 11-13% Е) 8-9% 54. Chemical-laboratory glass is divided into the following types A) CS-I, CS-II, TS B) CS-I, CS-II, TS, TS-Q C) CS-II, TS, TS-Q D) CS-II, TS-Q E) CS-I, CS-II 55. TS-Q is A) thermally stable glass B) chemically stable glass of the first class C) thermally stable quartz glass D) chemically stable glass of the second class E) chemically stable glass of the first and second classes 56. CS-I is A) thermally stable glass B) chemically stable glass of the first class C) thermally stable quartz glass D) chemically stable glass of the second class E) chemically stable glass of the first and second classes 57. CS-II is A) thermally stable glass B) chemically stable glass of the first class C) thermally stable quartz glass D) chemically stable glass of the second class E) chemically stable glass of the first and second classes
58. TS is A) thermally stable glass B) chemically stable glass of the first class C) thermally stable quartz glass D) chemically stable glass of the second class E) chemically stable glass of the first and second classes 59. The specific property, characteristic of glasses, is A) a clear boiling point B) a clear melting point C) absence of boiling point D) a clear subliming temperature E) absence of a clear melting point 60. The specific property, characteristic of glasses, is A) the presence of a temperature interval B) a clear boiling point C) a clear melting point D) absence of boiling point E) all answers are not correct 61. The specific property, characteristic of glasses, is A) lack of properties B) there are no such characteristics C) heterogeneity of properties D) isotropy of optical properties E) anisotropy of properties 62. The raw materials that form the basis of the glass are: A) opacifiers C) decolorizers C) clarifiers D) colorants E) glass formers 63. The raw materials that give the glass the necessary color are A) opacifiers C) decolorizers C) clarifiers D) colorants E) glass formers 64. The raw materials that make glass opaque and milk are A) opacifiers C) decolorizers C) clarifiers
D) colorants E) glass formers 65. The raw materials that eliminate the yellow and greenish color of the glass are A) opacifiers C) decolorizers C) clarifiers D) colorants E) glass formers 66. The raw materials that remove gas inclusions from the glass melt are A) opacifiers C) decolorizers C) clarifiers D) colorants E) glass formers 67. Crystal and colored glass refer to the following type of glass A) artistic В) special C) construction, container D) chemical E) optical 68. Glass consisting of the oxides of silicon, potassium and lead is called A) pyrex В) special C) construction, container D) chemical E) optical, crystal 69. Glass consisting of the oxides of silicon, aluminum, calcium, magnesium and sodium, is called A) pyrex В) special C) construction, container D) chemical E) optical, crystal 70. Materials of completely or partially evenly crystallized glass or slag A) glass ceramics B) cement C) clay D) ceramics F) feldspar
71. For adding potassium oxide in the production of glasses, the following is used A) boric acid, borax B) quartz sand C) potassium carbonate (K2CO3), niter (KNO3) D) ammonium and calcium phosphate E) aluminum hydroxide, feldspars 72. For adding calcium oxide in the production of silicate glasses, the following is used A) boric acid, borax B) quartz sand C) potassium carbonate (K2CO3), niter (KNO3) D) ammonium and calcium phosphate E) chalk, marble, limestone (СаСО3) 73. For adding magnesium oxide in the production of silicate glasses, the following is used A) boric acid, borax B) dolomite (MgCO3⋅CaCO3), magnesite (MgCO3) C) potassium carbonate (K2CO3), niter (KNO3) D) ammonium and calcium phosphate E) chalk, marble, limestone (СаСО3) 74. For adding boric anhydride in the production of glasses, the following is used A) boric acid, borax B) dolomite (MgCO3⋅CaCO3), magnesite (MgCO3) C) potassium carbonate (K2CO3), niter (KNO3) D) ammonium and calcium phosphate E) chalk, marble, limestone (СаСО3) 75. For adding phosphoric anhydride in the production of glasses, the following is used A) boric acid, borax B) dolomite (MgCO3⋅CaCO3), magnesite (MgCO3) C) potassium carbonate (K2CO3), niter (KNO3) D) ammonium and calcium phosphate E) chalk, marble, limestone (СаСО3) 76. For adding aluminum oxide in the production of glasses, the following is used A) boric acid, borax B) soda (Na2CO3) C) potassium carbonate (K2CO3), niter (KNO3)
D) ammonium and calcium phosphate E) alumina, aluminum hydroxide, feldspar 77. For adding sodium oxide in the production of glasses, the following is used A) boric acid, borax B) soda (Na2CO3) C) quartz sands D) ammonium and calcium phosphate E) alumina, aluminum hydroxide, feldspar 78. Colorants in the production of glasses include A) sodium and potassium nitrate, arsenic oxide, cerium dioxide B) carbon, tartaric salt, metallic aluminum and magnesium C) oxides of heavy metals (Co, Mn, Ni, Cr, V, Fe, U, REE) D) ZnO E) fluoride compounds 79. Oxidants in the production of glasses include A) sodium and potassium nitrate, arsenic oxide, cerium dioxide B) carbon, tartaric salt, metallic aluminum and magnesium C) oxides of heavy metals (Co, Mn, Ni, Cr, V, Fe, U, REE) D) ZnO E) fluoride compounds 80. Reducing agents in the production of glasses include A) sodium and potassium nitrate, arsenic oxide, cerium dioxide B) carbon, tartaric salt, metallic aluminum and magnesium C) oxides of heavy metals (Co, Mn, Ni, Cr, V, Fe, U, REE) D) ZnO E) fluoride compounds 81. Accelerators in the production of glasses include A) sodium and potassium nitrate, arsenic oxide, cerium dioxide B) carbon, tartaric salt, metallic aluminum and magnesium C) oxides of heavy metals (Co, Mn, Ni, Cr, V, Fe, U, REE) D) ZnO E) fluoride compounds 82. The drawing method is used for obtaining A) flat polished glass B) sheet glass C) fiberglass D) sheet glass, fiberglass E) sheet glass, pipes and tubes, fiberglass
83. The float-method is used for obtaining A) flat polished glass B) pipes and tubes C) fiberglass D) sheet glass, fiberglass E) sheet glass, pipes and tubes, fiberglass 84. In composition and properties, thermometric glasses are divided into A) high-silica B) high-silica, borosilicate, lead-silicate C) lead-silicate D) borosilicate, lead-silicate E) borosilicate 85. The float-method involves using a melt of A) aluminum B) lead C) zinc D) tin E) copper 86. The Fourcault method is A) float-method B) troughless method of vertical drawing C) float-method and rolling method D) rolling method E) method of vertical drawing of glass 87. The composition of which compounds correspond to the general formula nR2O⋅mRO⋅pR2O3⋅qRO2 A) ceramics B) cement C) silicate glasses D) clay F) feldspar 88. R2O in the general formula of silicate glasses nR2O⋅mRO⋅pR2O3⋅qRO2 means A) silicon oxide B) silicate glass C) acid oxides D) oxides of alkali metals E) oxides of alkaline-earth and other divalent metals 89. RO in the general formula of silicate glasses nR2O⋅mRO⋅pR2O3⋅qRO2 means A) silicon oxide
B) silicate glass C) acid oxides D) oxides of alkali metals E) oxides of alkaline-earth and other divalent metals 90. R2O3 in the general formula of silicate glasses nR2O⋅mRO⋅pR2O3⋅qRO2 means A) silicon oxide B) silicate glass C) acid oxides D) oxides of alkali metals E) oxides of alkaline-earth and other divalent metals 91. RO2 in the general formula of silicate glasses nR2O⋅mRO⋅pR2O3⋅qRO2 means A) silicon oxide B) silicate glass C) acid oxides D) oxides of alkali metals E) oxides of alkaline-earth and other divalent metals 92. Special glass, obtained by heat treatment of ordinary glass in furnaces with subsequent cooling by blowing it with air, is A) tempered (unbreakable) B) foam glass (porous glass) C) there is no such type D) glass fiber E) container glass 93. Special glass, obtained by forcing glass melt through filters or by blowing method, is A) tempered (unbreakable) B) foam glass (porous glass) C) there is no such type D) glass fiber E) container glass 94. In the production of glass, silicate formation is A) obtaining a melt without residual inclusions B) release of the glass melt from gas bubbles C) reaching the chemical and physical homogeneity by the glass melt D) stage of chemical reactions E) increase in the viscosity of the glass melt to the limits that allow molding of the products
95. Glass formation is A) obtaining a melt without residual inclusions B) release of the glass melt from gas bubbles C) reaching the chemical and physical homogeneity by the glass melt D) stage of chemical reactions E) increase in the viscosity of the glass melt to the limits that allow molding of the products 96. Clarification is A) obtaining a melt without residual inclusions B) release of the glass melt from gas bubbles C) reaching the chemical and physical homogeneity by the glass melt D) stage of chemical reactions E) increase in the viscosity of the glass melt to the limits that allow molding of the products 97. Homogenization is A) obtaining a melt without residual inclusions B) release of the glass melt from gas bubbles C) reaching the chemical and physical homogeneity by the glass melt D) stage of chemical reactions E) increase in the viscosity of the glass melt to the limits that allow molding of the products 98. Finish cooling is A) obtaining a melt without residual inclusions B) release of the glass melt from gas bubbles C) reaching the chemical and physical homogeneity by the glass melt D) stage of chemical reactions E) increase in the viscosity of the glass melt to the limits that allow molding of the products 99. The production of sheet glass is carried out by A) vertical drawing B) vertical drawing, rolling, float-methods C) float-method D) vertical drawing, rolling E) rolling 100. The production of sheet glass by the rolling method includes A) production of patterned, reinforced, thickened glass C) production of patterned glass C) production of colored opacified glass D) production of a patterned, reinforced, thickened, colored opacified glass E) production of reinforced, thickened glass
REFERENCES 1. Бобкова И.М., Дятлова П.М., Куницкая Г.С. Общая технология силикатов. – Минск: Высшая школа, 1987. – 288 с. 2. Дудеров И.Г., Матвеев Г.М., Суханова В.Б. Общая технология силикатов. – М.: Стройиздат, 1987. – 560 с. 3. Cулименко Л.М. Общая технология силикатов. – М.: Инфра-М, 2004. – 336 с. 4. Гулоян Ю.А. Технология стекла и стеклоизделий. – Владимир: Транзит-Икс, 2003. – 185 с. 5. Щипалов Ю.К., Комлева Г.П., Овчинников Н.Л. Лабораторный практикум по основам технологии тугоплавких неметаллических и силикатных материалов (раздел «Основы технологии стекла и ситаллов»). – Иваново: ИХТИ, 2005. 6. Химическая технология стекла и ситаллов / под ред. Н.М. Павлушкина. – М.: Стройиздат, 1983. – 214 с.
TABLE OF CONTENTS 1. GLASSY STATE .................................................................................. 3 1.1. Definition of the glass. General properties of the substances in the glassy state ....................................................................................... 3 1.2. Classification of inorganic glasses by chemical composition ............. 5 2. PHYSICO-CHEMICAL PROPERTIES OF GLASSES ........................ 7 2.1. The properties of glass-forming melts ................................................ 7 2.2. Mechanical properties of glasses ........................................................ 8 2.3. Thermal properties of glasses ............................................................. 10 2.4. Electrical properties of glasses ............................................................ 11 2.5. Optical properties of glasses ............................................................... 12 2.6. Chemical stability of glasses ............................................................... 13 3. RAW MATERIALS .............................................................................. 15 3.1. Main raw materials ............................................................................. 15 3.2. Auxiliary raw materials....................................................................... 17 4. BASICS OF GLASS PRODUCTION TECHNOLOGY ....................... 19 4.1. Preparation of the batch ...................................................................... 19 4.2. Glass melting ...................................................................................... 22 4.2.1. Stages of glass melting..................................................................... 22 4.2.2. Defects in the glass melt .................................................................. 24 4.3. Glass molding ..................................................................................... 26 4.3.1. Features of molding ......................................................................... 26 4.3.2. Molding methods ............................................................................. 27 4.4. Annealing and tempering of glass ....................................................... 33 5. LABORATORY WORKS ..................................................................... 36 5.1. Determination of water resistance of glass at temperature 98 °С ........ 36 5.2. Determination of thermal resistance of glass ...................................... 39 5.3. Determination of metal oxides in glass ............................................... 43 TEST QUESTIONS................................................................................... 45 REFERENCES .......................................................................................... 62
Seilkhanova Gulziya Amangeldyevna CHEMICAL TECHNOLOGY OF GLASS Educational manual Typesetting and cover design G. Кaliyeva Cover design used photos from sites www.Blueglass-1.com
Signed for publishing 09.11.2017. Format 60x84 1/16. Offset paper. Digital printing. Volume 4 printer’s sheet. 110 copies. Order №5855. Publishing house «Qazaq university» Al-Farabi Kazakh National University KazNU, 71 Al-Farabi, 050040, Almaty Printed in the printing office of the «Kazakh University» publishing house.