Highly pure monocrystalline sapphire prodn. - by the Czochralski process using a molybdenum crucible in reducing atmos.

摘要

Monocrystalline oxide substances of the highest purity, and with a high m.pt., are made by the Czochralski process, using molybdenum crucibles and drawing the crystal in a reducing atmos. The atmos. is pref. at 0.1-1 torr and contains carbon; the Mo crucible is pref. heated indirectly via an induction-heated graphite susceptor and the process is pref. used for the prodn. of sapphire monocrystals. Method avoids use of iridium crucibles which are extremely expensive and can form an oxide which contaminates the sapphire.