| 摘要 |
During the process of pulling sapphire tubes from a melt with the aid of a seed, the longitudinal temperature gradient in the zone between the solidified front and the region of pulling where the temperature is between 1850 and 1900 deg. C. is maintained not in excess of 30 deg. C./cm. The tube so grown is annealed at a temperature between 1950 and 2000 deg. C. by increasing the temperature at a rate of 30 to 40 deg. C./min and keeping the tube at said temperature during a period between 3 and 4 hours. After that the tube is cooled down to room temperature at a rate of 30-40 deg. C./min. Disclosed is also an apparatus which enables said temperature gradient to be maintained while pulling the tube. |
