The cleaning of fused quartz is critical before it is used in any application. The fused quartz should be cleaned by placing it in a 7% maximum solution of Ammonium Bifluoride for no more than ten (10) minutes, or a 10% volume maximum solution of Hydrofluoric Acid for no more than five (5) minutes. After cleaning, using the above method, the fused quartz should be rinsed in deionized or distilled water and then dried.
To further reduce the possibility of contamination, care should be used in handling fused quartz. The use of clean cotton gloves at all times is essential.
Running In Procedure
In order to increase resistance to devitrification and sag of your quartzware, an even layer of cristobalite must be formed on the O.D. of quartz tubes. Expose a new tube to a temperature of up to 1200°C and rotate it 90° every two (2) hours for the first 12 to 24 hours.
Space permitting, fused quartz should be stored in its original shipping container. If that is not practical, at least the wrapping should be retained. In the case of tubing, the end coverings should be kept in place until the product is used. This protects the ends from chipping and keeps out dirt and moisture which could compromise the purity and performance of the tubing.
Because The Products Are Annealed
Both quartz and silica glass are annealed at approximately 1150°C. However, they reach a strain point at about 1120°C. These glass products, if rapidly cooled after use at temperatures above this strain point, will develop strain again. Special care should be taken when using large sized products.
When Joining Fused Quartz And Other Materials
Quartz and silica glass only slightly expand with increases in temperature compared to other materials. Care must be taken when these glass products are connected to other materials and the temperature rises, in order to avoid the development of cracks.
Care Must Be Taken During Furnace Insertion
Quartz and silica glass feature low thermal conductivity. If the glass product comes too close to a heating element, or is put in direct contact with a flame, it may become locally heated and develop cracks. Long glass tubes may also deform at temperatures of 1100°C or higher. Care should be taken to support both glass types, especially large-sized products.
Devitrification of quartz and silica glass means transition from a metastable (vitrified) state to a stable crystallized state of cristobalite. Devitrification occurs when the product is used at high temperatures over a long period of time, or it is heated while impurities adhere to its surface. Even very small impurities on the surface can have a major influence. Under such conditions, devitrification may even occur at temperatures of 1000°C or less. This hardly ever occurs at temperatures of 1150°C or less, if the glass surface is perfectly clean. Devitrification usually starts when the temperature rises to 1200°C or higher, then further develops as the temperature increases.
Special Handling And Precautions
When handling, always wear clean, lint free gloves or powder free latex gloves. Be sure to avoid direct contact of the glass with bare hands. The skin’s natural salts contain alkali metal elements such as sodium and potassium that speed devitrification.