Importance

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Abstract

The inventive vessel, e.g. crucible, made of a refractory inorganic material such as boron nitride has a multi-layered wall structure which is an integral alternate lamination of layers of higher density and layers of lower density. Such a multi-layered structure can be formed by the procedure of pyrolytic chemical vapor deposition in the course of which the concentration of the gaseous reactants, e.g. boron trichloride and ammonia, in the atmosphere is changed, i.e. increased or decreased, under control so that the resultant deposited boron nitride layer has different densities in the portions deposited before and after the concentration change. By virtue of the multi-layered wall structure, the vessel has outstandingly improved resistance against thermal shock and can withstand prolonged use or many times of repeated use at high temperatures without breaking or crack formation.

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First Claim