Glass is a non-crystalline, often transparent amorphous solid. It was first prepared in Egypt. Although the atomic-scale structure of glass shares characteristics of the structure of a super-cooled liquid, glass exhibits all the mechanical properties of solid. Chemically, it is a homogeneous mixture of silicates of various alkaline metals of non-crystallized and transparent or non-transparent chemicals.
The ordinary glass (soda glass or window glass) has approximately the composition Na2O.CaO.6SiO2. It is prepared by melting sand (silica), sodium carbonate (soda), and calcium carbonate (limestone) in proper proportions and at moderate temperature. Scrap glass (cullet) is also added to the mixture as flux which makes the mixture fusible.
NOTE: Glass that is crushed and ready to be re-melted is called cullet.
Due to its ease of formability into any shape, glass has been traditionally used for vessels: bowls, vases, bottles, jars and drinking glasses. In its most solid forms, it is also used as paperweights and marbles.
The refractive, reflective, and transmission properties of glass makes it suitable for manufacturing optical lenses, prisms, and opto-electronic materials. Glass can be coloured by adding metal salts or painted and printed with vitreous enamels, leading to its use in stained glass windows and other glass art objects. The atomic structure of a glass lacks the long-range periodicity observed in crystalline solids.
ANNEALING OF GLASS
In this process, glass utensils are allowed to cool down slowly, steadily and moderately. If glass is cooled very slowly, it becomes opaque and if, it is cooled very rapidly, it becomes brittle and fragile
TYPES OF GLASSES AND THEIR USES
1- Flint glass- Optical instruments like lens of camera, prisms, microscopes, telescope and in electric bulbs.
2- Crown glass- Optical instruments.
3- Crook’s glass- Eye lenses used in different eye defects.
4- Jena glass- Bottles for keeping acids and alkalies in laboratory.
5- Lead crystal glass- Various ornamental items, costly glass containers.
6- Quartz glass or silica glass- In making bulb of ultraviolet lamps, and laboratory equipments.
7- Pyrex glass (Borosilicate glass)- Laboratory glassware & kitchenware
8- Potash glass or hard glass- Eyeglasses, glassware, televisions and computer monitors.
9- Soda glass or soft glass- Window glass, bottles, dishes, tubelights, domestic utensils, etc
10- Photo chromatic glass- Eye lenses and goggles.
IMPORTANT FACTS
1- Safety glass has a transparent plastic layer of vinyl acetate resin in between two glass layers.
2- Optical fibre is used in telecommunication and endoscopy.
3- Coloured glasses for goggles have lanthanide oxide.
4- Ground glass is produced by grinding ordinary soda glass with emery and turpentine oil.
5- Water glass is basically a compound of sodium silicate(Na2SiO3) and prepared by heating sodium carbonate with silica. it is soluble in water