Der Einfluß der Temperatursymmetrie des Verneuilofens auf die Qualität der Korundeinkristalle

Corundum boules were grown in Verneuil furnaces with eliptical cross sections of the isotherms perpendicular to the growth axis. The as grown single crystals were heated with a rate of 250° C/h to a temperature of 1850°C. The number of single crystals wich split during heating was evaluated with regard to the angle ϱ of the c-axis with the growth axis as well as with regard to the angle α. The angle α is enclosed by two planes. The first plane ist established by the growth axis and by the longer axis of the eliptical cross section of the isothermes. The second plane ist established by the crystallographic c-axis and by the growth axis. The greatest stability is always observed with single crystals with the angle α 45°, the lowest with those having α 90° or α 0°.