Ceramics

Glass is a ceramic material consisting of uniformly dispersed mixtures of silica, soda ash, and lime, that is often combined with metallic oxides of calcium, lead, lithium, cerium, etc. Glass is distinguished from solid ceramics by its lack of crystallinity. It is in fact a supercooled liquid. The atoms in glass remain disordered in the solid state, much as they are in the liquid state. Glasses are thus rigid structures whose atomic arrangements and properties depend on both composition and thermal history.

Group 16 elements (oxygen, sulphur, selenium, tellurium) are especially good candidates for glass formation. Oxygen is able to form stable bonds with silicon, boron, phosphorous, and arsenic and thereby form stable structures having oxygen atoms at the corners and one of the other atoms at the center. Pure oxide glasses are very stable because each oxygen atom is linked by electron bonds to two other atoms.

Various two-phase structures may exist as glasses. One such structure is a mixture of glass and crystal. These materials are converted into strong and durable ceramics that are part glass and part crystal by prolonged heat treatment.