Glass is an amorphous, hard, brittle, transparent or translucent, super –cooled liquid of infinity Viscosity, obtained by fusing a mixture of a number of metallic silicates, most commonly of Na, K, Ca and Pb. It possesses no sharp melting point, definite formula or crystalline structure.
Definition amorphous:
Having no determinate form; of irregular; shapelessDefinition transparent: Having the property of transmitting rays of light, so that bodies can be distinctly seen through; pervious to light; diaphanous; pellucid; as, transparent glass .
Definition super-cooled :To cool (a liquid) below a transition temperature without the transition occurring, especially to cool below the freezing point without solidification
a glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising
General properties of glass
· Glass is amorphous, no definite melting point
· Reflect or transmit light, brittle, softens on heating.
· Electrical insulator
Manufacture of glass
Commercially produced glass can be classified as soda-lime, lead, fused silica, borosilicate, or
96 percent silica. Soda-lime glass, since it constitutes 77 percent of total glass production, is discussedhere. Soda-lime glass consists of sand, limestone, soda ash, and cullet (broken glass).
The manufacture of such glass is in four phases: (1) preparation of raw material, (2) melting in a furnace (3) forming and (4) finishing.
1. Melting: CaCO3+ SiO2 → CaSiO3 + CO2 ↑
Na2CO3+ SiO2 →Na2SiO 3 + CO2↑
The basic three raw materials (quartz sand, limestone, soda ash) with the addition of some oxides which act as catalysts to melt the glass, are made into precise batches and are routed to be melted in a glass furnace, i.e. tank furnace, with standing high temperatures of up to 1600 degrees, to produce molten glass. A charger continuously feeds the batch into the furnace.
2. Forming and shaping: Melting glass is then worked into articles of desired shapes by either blowing or moulding or pressing between rollers.
3. Annealing: Glass articles are then allowed to cool gradually to room temperature by passing through different chamber with descending temperatures. It allowed and cools rapidly, glass being bad conductor of heat, the superficial layer cools down first, leaving the interior portion in a sate of strain. Owing To this unequal expansion, the articles are likely to crack to pieces
4. Finishing: Cleaning, grinding, polishing, cutting, sand – blasting, etc.
5. Inspection: The glass containers are channeled individually through inspection stations and are checked for dimensional accuracy, body and neck quality. Inspection can be manual, semi-automatic or automatic to optimize quality.
6-Packing: After the inspection stations, the glass containers are put on pallets and protected with shrink-wrap ensuring safe delivery to its customers
The observation that old windows are often thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a matter of centuries. It is then assumed that the glass was once uniform, but has flowed to its new shape, which is a property of liquid . The pieces were not, however, absolutely flat; the edges of the disk became thicker as the glass spun. When actually installed in a window frame, the glass would be placed thicker side down both for the sake of stability and to prevent water accumulating in the lead came at the bottom of the window. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness. Modern glass intended for windows is produced as float glass and is very uniform in thickness.
References
Doremus, R. H. (1994) Glass Science, 2nd Edition. John Wiley & Sons, New York, 339 pp.
Elliott, S. R. (1994) Amorphous Solids: An Introduction. In: Catlow, C. R. A. (eds.), "Defects and Disorder in Crystalline and Amorphous Solids", NATO Advanced Studies Institutes Series; Series C, Mathematical and Physical Sciences, 418, Kluwer Academic Publishers, Dordrecht: 73-86.
Feltz, A. (1993) Amorphous Inorganic Materials and Glasses. VCH Verlagsgesellschaft mbH, Weinheim/VCH Publishers, New York, 446 pp.
definition of glass from 1945; also Glas – Begriffe für Glasarten und Glasgruppen, September 1986
Zallen, R. (1983). The Physics of Amorphous Solids. New York: John Wiley.
Cusack, N. E. (1987). The physics of structurally disordered matter: an introduction. Adam Hilger in association with the University of Sussex press.
Elliot, S. R. (1984). Physics of Amorphous Materials. Longman group ltd.
