process for the production of sintered or a consolidated melt existing items, in particular from kieselsaeure

摘要

1276855 Fused silica TEXAS INSTRUMENTS Inc 12 June 1969 [10 July 1968] 29851/69 Heading C1M A fused silica crucible, suitable for pulling monocrystalline silicon from a pure silicon melt, is made by supporting on a mandrel a crucible form produced by vapour phase flame hydrolysis of silicon tetrachloride, heating to a presintering temperature in the range 1000‹ to 1300‹ C. in vacuum to substantially free the silica of water and then heating at a sintering temperature in the range 1300‹ to 1500‹ C. and cooled in a helium atmosphere to form a transparent fused silica crucible. Preferably the mandrel is of graphite and has a generally cylindrical portion and a symmetrically curved closed end portion. The crucible form may consist of silicon dioxide particles of diameter in the range 0À01 to 0À1 micron. The presintering may be carried out at a pressure of 0À01 to 10 millimetres of mercury for such a time that the final crucible has an infra-red transmittance of substantially 63% at 2À73 microns.