Crucible for single crystal growing - having inner wall with annular space filled with fusible material

摘要

Crucible for holding the melt from which single crystals are drawn has an insert within it. This divides the crucible into two spaces. The first or inner contains the melt. The second is an outer annular space containing a fusible substance whose m.pt. is below that of the melt. Pref. this is a silicate or a mixt. of silicates with m.pts. 1500-1600 degrees C Wollastonite, feldspar or anorthite can all be used. The melt can be partially covered by the insert with openings for charging and removing product crystal. The unit can be formed from concentric tubular sections welded to a base plate. Useful for single crystal growth by the Czochralski process. The main problems with Pt-Ir crucibles for this process are (a) that non-uniform heating causes excessive localised corrosion, (b) that inert gas above the crucible cools the melt surface and means that additional heat must be applied at the base, aggravating the problem (a). The crucible described alleviates these problems.