One of the methods to distinguish the quality of quartz tubes is annealing. The conventional way of annealing is to put the quartz tube into a thermostatic furnace. The temperature gradually decreased from between 1000 ℃ and 1200 ℃ to 0 ℃.
The reason for the discoloration of quartz tube after annealing is that the metal element content of quartz tubes’ material exceeds the standard. When heated at a certain high temperature, metal elements will rapidly oxidize. So what you seeing of black or white substance on the surface of the tube is the metal oxide.
Can the color-changing quartz tube be used? This depends on the use environment. Under the requirements of high temperature and high transmittance, this must not meet the requirements. However, if only high temperature resistance is required, such color change tubes can also be used. Exceeding the standard of trace elements will not significantly reduce the high-temperature resistance of quartz tubes. In short, if we only have the requirement of high temperature resistance, we can choose quartz tube with excessive metal content. Because its cost is lower.
