The Glass Transition

Most solid mineral compounds and elements form liquids of low viscosity (several centipoises) when they melt, and when the temperature is reduced, they solidify again to form a crystalline solid. Alternatively, there are materials which become liquids with a very high viscosity (105–107 P) when melted. When they are cooled below their melting point, these liquids do not solidify instantaneously but remain in a supercooled state, the viscosity of the liquid increases significantly when the temperature is reduced, and they then “freeze” in the form of a glass, which is a noncrystalline solid state. We say that the liquid has undergone a glass transition and that a glassy or vitreous state has formed.