Devitrification, also known as devitrification, is a natural defect that occurs in quartz glass. From a thermodynamic perspective, quartz glass exists in a metastable state with higher internal energy compared to crystalline cristobalite. When the temperature exceeds 1000°C, this metastable condition becomes unstable, leading to a gradual transformation of the amorphous structure into a crystalline one over time. As the temperature increases, the molecular vibrations of SiO₂ intensify, allowing for the formation of crystals through reorganization and alignment. The rate at which these crystals nucleate determines the overall devitrification process. The crystallization primarily occurs on the surface of the material, followed by internal defects. These areas are more prone to contamination, which leads to the accumulation of impurity ions—especially alkali ions like potassium (K), sodium (Na), lithium (Li), calcium (Ca), and magnesium (Mg). These ions can disrupt the silica network, reducing viscosity and accelerating the devitrification process. This makes the surface and internal imperfections key sites for crystal growth under high-temperature conditions. Quartz glass has a thermal expansion coefficient and specific gravity that closely match those of β-cristobalite, the crystallized form. As a result, even when the crystallization zone expands continuously during prolonged high-temperature use, the volume change remains minimal, allowing the material to maintain its structural integrity. This helps reduce plastic deformation and enhances the refractory properties of the glass. However, when the material cools down to around 800°C, a fine crack network may develop within the crystallized layer. Further cooling to between 200°C and 275°C triggers a structural transformation of cristobalite from the high-temperature β-form to the low-temperature α-form. This phase transition involves a volume change, and if the crystallized layer is deep, it can lead to cracking or even rupture of the quartz glass. Given that impurities often act as nucleation sites for crystallization, the initial surface condition of the quartz glass before high-temperature use, as well as the surrounding refractory materials and atmosphere, play a crucial role in preventing unwanted devitrification. The following sections will discuss important precautions for the proper use of quartz glass. Tungsten End Mills For Sale,Endmills For Steel For Sale,Tungsten Milling Cutter JIANGYIN GOLD STAR INDUSTRY CO.,LTD , https://www.jygoldstarindustry.com