Experiment (4) FORMATION OF GLASS Submitted By: Submitted To: Dr.M.Ahmed Tindyala 2007-Met-
Formation Of Glass Overview Glass is an inorganic product of fusion which has been cooled to a rigid condition with out crystallization which is hard, brittle, transparent solid. Most glasses contain silica as their main component. Liquid structure of silica is random but when cooled transformed into crystalline form, if cooled very fast transformed into glass(amorphous
solid). Crstalline materials are opaque to light because when light passes through them, there is regular reflection and so cancell out but glass are transparent due to irregular reflection. Types of glas There are many types of glass such as • Soda-lime glasses:It is 90% of the manufacture glass. Soda makes the glass water soluble which is undesireable so we add lime, MgO, CaO for better chemical durability. It contain 70-74% silica • Lead glasses. such as lead crystal, or flint glass is more ''brilliant'' beacause increase refractive index causes more ''sparkle'' while Boron is added to change thermal and electrical property. • Silicate glasses: netformers are based on SiO4, tetrahedral, interconnected through oxygen • acrylic glasses, • sugar glasses • isinglasses Composition of glass: Glass forming oxide = 55-95% Modifiers = 30% Fluxes = 20% Glass Forming Oxides Glass forming oxides are silica, borax, alumina, germinium-oxide, silinium-oxide. When cooled these oxides yield glass. Some Other Ingridiants • Barium: Increase refractive index. • Thorium-Oxide and Lanthium-Oxide: ThO gives high refractive index and low dispersion to produce high quality glass, due to radioactivity replaced by Lanthanum-Oxide in modern glasses. • Iron: Large amount of iron is use to absorb infrared energy such as heat absorbing filters for movie projectors • Cerium-Oxide: to absorb UV wavelength Modifiers
Modifiers are use to modify the properties, some modifiers, their sources, and uses are given below Name sourse uses B2O3 Borax,Barborate, Sodium borate Heat resistance, PbO _ Electrical resistance BaO _ Sulphur removal as SO2 As2O3 _ Remove colour(refining) Sb2O3 _ Remove colour(refining) Al2O3 Nephline,synite,fildspar,calcined Durability alumina Fluxers Fluxers are use to reduce melting point.They decrease the viscosity because their atomec size is large so it give flowable character. Some fluxes are given below and their sourses Name Na2O MgO CaO
sourse Na2CO3 Dolomite,Olivine CaCO3
uses reduce viscosity softening softening
Glass transition temperate: During soldification of crystalline materials, shrinkage is produced so specific volume decreased but in case glass soldification viscosity increased,the temperature where a rubber, plastic type glass suddenly change into solid is called glass transition temperature. Glass Forming Process Materials: Borax, Boric acid Apparatus: Goggles, Pick up, S.S Crucible, Refractory Bricks Furnace,Spatula
The steps for glass forming process are given below 1-Batching 2-Mixing 3-Melting 4-Refining 5-Working Batching: It is process of raw material recovery, the over all recovery is 50%. The mixture of different or single material which is about to be processed according to the requrements is called ''batch'' such as, • Cullet: furnace recycled glass, leads to save raw material and reduce energy consumption, impurities in cullet cause glasss failure. Two major raw materials are 1-Borax 2-Boric acid 3-Both(50%Borax,50%Boric acid)
Mixing: In mixing, we mix network formers with other ingredients including modifiers and fluxers Melting: melting is done for • moisture is to be given out • gases come out by calcination(chemical held water is removed) • element melt by fusion • elements ombine(homogenized)
Refining: It is expensive and time consuming stage. here seet count(bubble formation in specific area) formation is done, when all the bubbles are removed then we take out the material Some fining agents such as sodium sulphate, sodium chloride or antimony oxide are used to reduce bubble content in the glass. Working: It depends on which type of piece we want to make. Procedure: • I tool 50 gm of borax powder. • put the crucible on high flame of burner. • when the crucible is red hot, then step by step dropped the borax powder with help of spatula. Every time allowed the previous powder to be completely melt other wise swelling causes the loss of borax powder. • Dring melting bubbling is produced, allowes the sufficient time to remove the bubbles(seed count). • Put it for some time to solidify it. • After cooling green colour glassy product was obtained. Applications: Optical and phsical properties of glass make it suitable for • flat glass • container glass • optic and electronics material • laboratory equipments • thermal insulators • glass fiber reinforced plastic, or concrete • and art Precautions: • Don't fill the crucible upto neck because borax start fuming and will come out at melting
• when all the seedling bubble come out then take the material out • and pour and weight carefully Observations and Calculations Write yourself Results: actual weight of glass= theoretical weight of glass= Actual wt. of glass < theoretical wt. of glass Comments: Write yourself