Glass ceramic, heat treated at 750°C for 3 hours

Glass ceramics are materials that are cooled from the melt in the form of a glass, and then heat treated to induce controlled crystallisation of the glass. Heterogeneous nucleation is carried out at a temperature to maximise the nucleation rate (common nucleating agents include TiO2 and ZrO2), and the temperature is then raised sufficiently to cause the nuclei formed to grow rapidly. Glass ceramics are strong, reasonably tough, transparent to IR radiation, have a low coefficient of thermal expansion, a high resistance to thermal shock and a low thermal conductivity, which makes them very useful in domestic applications such as cookware and cooker hobs. The most common glass ceramic system is LAS (Li2O-Al2O3-SiO2), but others include MgO-Al2O3-SiO2, Na2O-BaO-Al2O3-SiO2, and Li2O-MgO-Al2O3-SiO2.