Glass-ceramics are polycrystalline materials produced by controlled crystallization of glasses suitable for crystallization. The glass-ceramic comprises one or more crystalline phases formed by controlled crystallization and residual glass which may vary depending on the initial composition and the process temperature. Since the material is converted to the crystalline phase during crystallization, molecular rearrangements occur. Crystallization, which provides the conversion from glass to glass-ceramic material, is achieved by a suitable and careful heat treatment program which enables the nucleation and growth of crystal phases in the glass.
Figure. Phase diagram of SiO2-Al2O3-CaO glass-ceramics.