About crystallization and cleaning method

Devitrification of quartz glass refers to a change from a semi-stable glass to a crystallized stable cristobalite. This phenomenon occurs when quartz glass is used at high temperatures for an extended duration or heated with impurities attached to its surface. In practical applications, the phenomenon almost never occurs at temperatures below 1150  as long as no impurity is attached to the surface. Devitrification normally starts when the temperature rises above 1200 and is accelerated as temperatures become higher. If impurities, even in small amounts, are present on the surface of quartz glass, devitrification can easily occur even at temperatures below 1000 . In particular, alkalis, such as Na, K and Ca, or metal compounds of alkaline earth in the order of less than 0.1 mg per 1 square centimeter can generate devitrification tens or hundreds of times the norm. Also, most metals, such as Al, B, Fe, Ni, Mg, Zn, Cu, Sb, and their compounds, if they are on the quartz glass, can trigger serious damage.
 
Therefore, to prevent these pollution sources attached on the surface of quartz, do not handle quartz glass products with bare hands, do the cleaning work to ensure that the quartz surface cleanliness before used in high temperature . To remove stains from quarts glass products, wash them with 5% to 10% hydrofluoric acid (HF) for about 10 minutes. After washing with hydrofluoric acid, rinse the products well and dry them. Make sure that the products stay wet and do not dry out during washing. After washing, dry them completely. If stains do not wash off, try a stronger hydrofluoric acid solution.