devitrify

Devitrify is a term used to describe the transformation of a glassy, non-crystalline material into a crystalline solid. Devitrification refers to the process by which a glass develops crystalline phases, typically through heat treatment, aging, or geological conditions. The concept applies in both geology, where volcanic glasses may gradually crystallize, and materials science, where controlled devitrification is used to produce glass-ceramics.

The mechanism involves heating a glass above its glass transition temperature and into a temperature range where nucleation and crystal growth become favorable. Crystals form within the amorphous matrix and grow over time. The rate and extent of devitrification depend on the glass composition, cooling history, the presence of impurities or moisture, and the duration of thermal exposure. The resulting microstructure comprises crystalline inclusions or precipitates embedded in a vitreous matrix, which can alter optical, thermal, and mechanical properties.

Compositional control determines which crystalline phases appear. In silica-rich glasses, crystals such as quartz or cristobalite may form, while aluminosilicate systems can yield mullite or other alumina-containing phases. Natural devitrification can occur in volcanic or obsidian glasses over geological timescales. In industrial practice, deliberate devitrification is used to produce glass-ceramics with improved toughness, hardness, or thermal stability; undesired devitrification can cause opacity, brittleness, or stress concentrations in otherwise transparent glasses.

Detection and analysis commonly employ differential scanning calorimetry to observe crystallization exotherms, X-ray diffraction to identify crystalline phases, and microscopy to study the microstructure.