Glass

Abstract

AbstractBoth organic and inorganic materials may form glasses if their structure is noncrystalline, ie, if they lack long‐range order. This includes some plastics, metals, and organic liquids. In principle, rapid cooling could prevent crystallization of any substance if the final temperature is sufficiently low to prevent structural rearrangement. Thus glasses are formed primarily for kinetic reasons.Glasses can be prepared by methods other than cooling from a liquid state, including solution evaporation, sintering of gels, reaction sputtering, vapor deposition, neutron bombardment, and shock‐wave vitrification.Conditions favorable for glass formation may be deduced from either geometric or bond strength considerations. Glass formation of individual oxides can be predicted from the melting point, and individual bond energies can be normalized by dividing by the melting point of the oxide. Glass is a good medium for controlled crystallization, and has become the basis for a number of unique crystalline materials known as glass‐ceramics.Most glass articles are manufactured by a process in which raw materials are converted at high temperatures to a homogeneous melt that is then formed into the articles. Molten glass is either molded, drawn, rolled, or quenched, depending on desired shape and use.In a secondary forming, a piece of preformed glass is reheated and reworked into the finished product. Glass manufacture is classified according to the product into flat, container, fiber, or specialty glass.Glasses are used in the electrical and electronic industries as insulators, lamp envelopes, cathode ray tubes, and encapsulators and protectors for microcircuit components. The resistance of glass to chemical corrosion $$$ frequently the reason for its use. However, the durability of a glas varies from highly soluble to highly durable, depending on its composition and the solvent considered. Optical glasses are usually described in terms of their refractive index.