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GLASS AND CERAMICS, Syllabus, of, , Concept, , glass, Ceramics, , manufacturing, , idea of, , and their, constituents,, process of glass, Industrial, , Classification, , and, , application, , glass, , of, , uses, , and, , of, , different glass, Eiementary, ceramics., , 13:1. Concept of Glass, Glass is, , very useful substance in, table glass, laboratory, a, , daily life. It has a variety of, applications. It is used as glass, apparatus,, electric, mirrors,, window, bulbs,, for spectacles, glass for cars, buses, trains and, panes, glass doors, glasses, and numerous other items., aeroplanes, Glass is an amorphous, hard, brittle and, transparent or translucent supercooled liquid. Chemically,, glass is & homogeneous mixture of silicates of alkali, and alkaline earth metals. It has no definite, point. Glass may be defined as under:, melting, bottles, plates,, , Glass is an amporphous and transparent or translucent solid which a, homogeneous mixture, ofsilicates of alkali metal and alkaline earth metals with excess of silica., Glass does not have definite, composition. The, Glass is represented by the following formula, , :, , composition of glass changes according to, , its nature., , R0y MO.6Si02 or x M,o.»Mmlo.6sio2, where R, , M, , alkali metal like Na, K and M or M= alkaline earth metal like, Ca, Pb., AlIkali metals are monovalent whereas alkaline earth metals are bivalent metals., or, , =, , Ordinary glass is also called soda glass. Its chemical formula is Nay0.Ca0.6Si02, In some glasses, there may be Al^O3. B,03 or P20s in place of silica, (SiO2)., , General Properties of Glass:, . Glass is, amorphous and transparent, 2. It is rigid and very brittle., , or, , translucent solid., , 3. It has ro definite melting point. It becomes softer and softer on heating and ultimately starts, , flowing., 4. It is a good insulator of heat and electricity., 5. It can take, high polish., 6. It can, , absorb, reflect, , or, , transmit light., , . l t is affected by alkalis and hydrofluoric acid, HF., 8. It is not, , affected by air, water or acids exceptH, 9. It can be formed into articles of different shapes, ,It has no crystal structure and, hence, has high compressive strength.

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266, , Applied Chemistry, , 13-2. Constituents, , or, , Raw materials, , Raw Material of Glass, , required, , for the manufacture of, glass are called its, Following substances are used as raw materials for the manufacture constituenjs., of glass, 1. SandIt is a source of silica, (Si02) which is a major constituent of glass., 2. Alkali metal, (Na,O3) for soda glass and potassium carbonate, , compounds-Soda, , hard glass., (K,CO) for, 3. Alkaline earth, compounds-Calcium oxide as limestone, chalk and lime., 4. Heavy metal oxides-Lead oxide, as, litharge (PbO) or red lead (Pbz04) for flint glass, oxide for heat and, and zine, shock-proof glass., , 5., , Feldspar-it, , temperature., 6., 7., , 8., , is a cheap source of, Its formula is, , AlhO3 which, Naz0. Al,03.6H20., , Borate-As borax and boric acid for heat and, , Cullets-Pieces of broken glass, , Colorants-Some substances, , colorants are as under, , Colorant, Oxides of iron, Cobalt oxide, , or, , are, , cupric, , to impart, , Gold powder, Cuprous oxide, , Colloidal Au, , or cupric oxides, , and Uses of, , it, , a, , desired colour. Some, , Green to yellow, , Yellow, Lemon yellow, , Shades of Ruby, , Cu0, MnO2, SnO2, , Large quantities of ferric, , in, , Blue, , CdS, , Potassium dichromate, Carbon, , change, , Light green, , CoO or CuO, , Cr2O3, K2CrO4, CdSO4, , Stannic oxide, , sudden, , Colour Imparted, , FeO, Fe03, oxide, , to, , shock-proof glass., , increase the fusibility., mixed with fused, glass, , Chromium compounds, Cadmium sulphate, Cadmium sulphide, , Classification, , glass resistant, , Formula, , Manganese dioxide, , 13:3., , to, , makes, , Red, , Violet, Pink, , or, , Milky, , K,Cr207, , Green, , Fe0g or CuO, , Amber colour, Black, , C, , or, , Purple, , greenish yellow, , Different Glasses, , There are several types, of glass. Commerical glasses can be classified, 1. Soft glass or, as follows, soda-lime, 2. Hard glass or, 3. Flint glass or lead, potash lime, glass, 4. Pyrex or, or, 5. Optical or crookes, jena borosilicate, 7. Safety glass, , glass, , 6. Silica, , glass, , 8. Wired glass, , 9. Insulating glass, , or, , vitreosil, , 10. Glass wool, , 1. Soft, , glass-It is a mixture of silicates of, sodium and, chemical composition of, It, glass is Naz0.Ca0.6Si02. It is usedcalcium., soda, to, make, bottles, jars, plates, etc., 2. Hard, , is, , glass-It is a, , K,0.CaO.6SiO2., , glass, , is also called soda, , window, , panes,, , gla., , electric bu|, , mixture of silicates of, potassium and calcium. Its approximate, composition, laboratory apparatus and combustion tubes., , It is used to make

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Glass and Ceramics, , 267, 3. Flint, Its, , glass-lt is also called lead glass, it contains lead oxide is place of, Oxide., approximate composition is K20.PbO.6SiO,.because, calcium, It is used to make, onses, cathode ray tubes, neon sign tubes and, high quality tablewares, optical, artificial jewellery., 4. Pyrex glass-It is also called, borosilicate or jena glass. It contains, mainly silica (80.5%) and, horon (13%) with small amounts of alumina and, oxides, of, and, potassium, sodium. It has high chemical, resist, istance. It is shockproof. It is largely used for, tubes and in industry for pipelines for corrosive superior laboratory apparatus, kitchenwares, television, liquids., , 5. Crookes glass-It is also called, optical glass. It contains phosphorus and lead silicate and a, Iittle cerium oxide which can absorb ultra-violet, light harnmful to eyes. It is used to make lenses., 6. Silica glass-It contains 99.5%, silica. It is also called vitreosil. It is, used in electric heaters,, furnaces, laboratorywares and chemical plants., 7. Safety glasslt is made, by taking two or more flat sheets of, glass with alternate thin layer of, vinyl plastic in between them under slight, It is quite, pressure., and, does not fly into pieces on, tough, breaking. It is commonly used in automobiles and, as wind shields., aeroplanes, 8. Wired glass-It is formed, by embedding a wire mesh at the, casting. On breaking, it does not fall apart into splinters. It is more fire centre of the glass sheet during, resistant than ordinary glass. It is, used for making fire resistant doors, windows and roofs etc., 9. Insulating glass-This, type of glass provides a, insulation against heat. If does not transmit, heat. It is used for separating apartments which remain high, cool during summer and warm during winter., 10. Glass wool-It is wool-like fibrous material, made of fine threads of glass. It is heat, proof and, does not absorb moisture or water. It resists action of, chemicals. It is used for, , (), (ii), ii), (iv), , 13-4., , filtration of corrosive liquids, manufacturing of fibre glass, electrical as well as sound insulation, heat insulation in oven, motors, and vacuum cleaners., , Manufacturing, , Process of Glass, , Following steps are involved in the, manufacture of glass:, , Hot gasesat, 1800°C, , 1. Melting-The raw materials like, , sand, alkali metal compounds (soda ash),, alkaline earth metal compounds (lime stone), and cullets (broken, pieces of glass) are, powdered in grinding mill. These are mixed, , Sand +Soda ash +, lime stonc + cullets, , in proper proportions. The mixed powder is, , TiIimmIiirmmy, , tnen fused in an open or covered furnace at, , Furnace of fire, resistant bricks, , about 1800°C. The charge inelts and fuses at, high temperature. Carbon dioxide formed, , escapes away, in, , the, , manufacture of, , Producer gas, , Air, , Following chemical reactions take place, , Fig. 13-1. Manufacture of glass, , glass, NazCO3+, +SiO2, Soda ash, , Na-SiO +CO2 1, Sod. silicate, , Silica, , CaCO3 + SiO, Lime stone, , Hot bricks, , CaSiO3+CO2 1, , Sand, , Na2COs+ CaCO3 +6SiO2, NazSiO3+CaCO3 +5SiO3, , Cal. silicate, , >, , Na0.CaO.6Si0, +2CO2 1, Na,0.Ca0.6Si02+CO2 1, Ordinary glass, , lHot gases

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268, , Applied, , nistry, , Certain decolorants such as MnO, or nitre are also added and the heating is done till the e, , of CO2 stops., The desired colouring material is added and heating is continued to obtain a homogeneo, When the molten mass is free from bubbles and glass-balls, it is cooled to about 800°C. The glas o, , is called mother glass., 2. Forming and shaping-The molten glass is then worked into articles of desired shas, blowing or moulding or pressed between rollers., , Amed, , sired shapes by, , 3. Annealing-The glass article is cooled slowly to room temperature. This process is, is knau, known as, , annealing., , Glass is a bad conductor of heat. It allowed to cool rapidly, the superficial layer of glasa, leaving inner portion in a state of strain. Due to unequal expansion, the article may crackcools, to, pieces. Hence, the glass article is cooled slowly by passing through different chambers with, descendt, down first, , ding, , temperatures., 4., , Finishing-After annealing, all glass articles are subjected to finishing. This process invalve., cleaning, grinding, polishing, cutting and sand-blasting etc., Tempering of glass, The hot glass article is, dipped in a hot oil-bath. The outer layer of the article shrinks and, hardens, whereas the internal layer is in state of stress. When the, surface of broken, it shatters into, This treatment is called, tempering of glass. The tempered glass is very hard and strong. many pieces, is used for automatic, Tempered glass, doors, big showcases, cars, buses and aeroplanes., 13-5. Industrial, Application of Glass, Glass has many industrial, applications. For, ) Glass is used to make a large number of example, apparatus to be used in laboratories., ii) In medicinal industry, it is used to make bottles, to keep medicines. It is also, used, apparatus like thermometer., , to, , make useful, , (ii) In transport systems, glass is used in cars,, buses, trains and aeroplanes etc., iv) It is used to make mirrors (looking, lenses and goggles etc., glass),, (v) In buildings, it is used to make doors and, windows., (vi) Glass is also used to make kitchen, articles,, decoration pieces, clocks, watches and items, furniture., , of, , 13.6. Ceramics Materials, Ceramics, , is derived from, , items made of clay which, , are, , keramos which, , means, , given desired shapes, , burnt, , stuff Greek, and then heated in fire language. Ceramics include al, to harden them., in, , Ceramics are inorganic non-metallie, materials that are, prepared by high temperature, processes and/or used at high temperatures., Ceramics include silicates, metallic oxides, and their, dinner set, tea set, tiles, sinks, sewer, combination. Ceramics belong to, pipes, refractory bricks and, chinawa, buildings and industrial pots., sanitary fittings for construction, 13-7. Classification of Ceramics, Ceramics are broadly grouped into, elay products and, refractories., Ceramics products are of two types, 1., , Heavy Clay, , Products-They, , include bricks, tiles for, roofs and lanes and, stonewares

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Glass and Ceramics, , 2., , Pottery, , products, , clay, , are, , 269, , Products-They include terracotta,, into, four catecgories, , grouped, , porcelain and different articles made, , of, , clay., , (i) Structural clay products-These are, bricks, tiles, sewer pipes and terracotta items. They contain, iron oxide as one of the mportant constituents., liov cannot be heated at high temperature and Ordinary clay products made from terracota are porous,, they cannot be made lustrous., (i) White pottery-These are prepared from china, clay mixed with some fusible silicates. These, earthe, thenwares are poroiIS and pernmeable. These can be heated, at high, teimperature. These are harder than, terracotta., (i) Stoncware-these are prepared from, refractory clays mixed with crushed stones and pottery., These are generally non-porous and quite, These are used to make wash, strong., basins, sinks, drainage, pipes and bath tubs etc. These articles can be glazed., (iv) Porcelain-These clay products are white and, These are harder than glass., are highly resistant to chemical, reactions. These are the non-porous., These, best, These become transluscent on, claywares., heating at high temperatures., , 13 8. Constituents of Ceramics, The main constituents of ceramics are, clay, china, used as raw materials to make ceramics, , clay, feldspar and sand. Therefore, these substances, products., () ClayThe earth which is highly, plastic when wet but when heated, loses its plasticity and, becomes a hard mass which is unaffected by, water, is called clay. It is composed of, hydrated aluminium, silicates. It is formed by weathering of, igneous and felspathic rocks., are, , 2KAISi3Og +2H,0+CO% KCO +, Potash feldspar, Alh01.2Si0.2H,0+4Si0, ii) China clay-If the clay remains at its, it is primary clay. it is white with low, iron content so that it burns white. It is also calledoriginal location,, china clay or kaolin. When the, clay is transported by, water, wind or glaciers to another location, it is, It contains limestome, secondary, clay., powder, hydrated, oxides, mud and organic impurities., , (i) Feldspar-Following three types of feldspar are used in ceramics, (a) Soda feldspar, , b) Potash feldspar, , NaO.AlL03.6SiO, K0.A1O3.6Si0,, , (c) Lime feldspar, CaO.Al03.6Si02, Feldspar becomes molten quickly at about I150°C. It acts as a flux and binder in ceramics, products., (iv) Sand--Sand is available in nature generally as quartz, flint (chakmak) and, sandstone. It is, non-plastic and non-shrinkable. It melts at about 1700°C., , 13-9., , Industiral Application, , of Ceramies, Ceramics are used in the following industries, )Ceramics are used in the manufacture of bricks and, , tiles. These, , lining of furnaces., , are, , used, , as, , refractory, , 0) They are useful in making statues, jars, drainage pipes and carboys to store acids., They are used to make whitewares, crucibles and spark plugs., They are used to make china clay earthen pots and electric resistant wares., ()Ceramics is used for cutting tools., They, are used to make heat resistant clay and heat resistant bricks., , (Vin) They are used in dental field., , (viil) They are, re used, , in electronic industry as semiconductors., , material in