| 摘要 |
PURPOSE:To obtain the title product of high durability without heat distortion and devitrification and with complete prevention of contamination, by growing crystal layers from the nuclei of a dopant on the outer surface of a clear quartz glass tube of Na, K and OH group contents below specific values respectively. CONSTITUTION:Naturally occurring quartz are pulverized, sieved and cleaned by dipping in HF. The purified powder is fused in an electric furnace for about 10-12hr and the melt of less than 10ppm OH content is formed into a clear quartz tube. The tube is placed in a heating furnace and heat-treated for several hours, as Cl2 or HCl gas is allowed to flow to give a tube of 0.1ppm Na and K and 0.3ppm Li. The tube is coated with a solution containing a trivalent cation dopant such as Al on the outer surface and heated over the softening point to effect doping. Further, the doped quartz tube 1 is placed in an electric furnace at a desired stage and heated at about 1,300 deg.C for about 10-15hr to develop the crystalline layer of cristobalite 10-100mu thick. |
