Glass-ceramic engineering:tailoring the microstructure and properties

Traditionally, glass-ceramics are inorganic non-metallic materials obtained by the controlled crystallization of a glass. A modern definition has widened this class of materials to solid materials containing at least one glassy and one crystalline phase. The glass is usually obtained by quenching a melt. Re-heating it to a temperature slightly above the glass transition temperature allows nucleation while an often applied second annealing step at a higher temperature causes most of the crystal growth. As in most materials, the composition and the microstructure of glass-ceramics widely governs their properties. The morphology, i.e., size, and aspect ratio of the crystal phases is of special significance and depends on the crystal structure and the occurring growth mechanism. The morphology is also affected by the chemical composition and the temperature/time schedule of the crystallization process, here components of minor concentrations can have a great effect. This review addresses the effects of nucleating agents, phase separation, crystal orientation alignment and stress introduction as tools to tailor the properties of glass-ceramic materials. Future developments in the field of glass-ceramics are discussed.