Schmelztiegel

A boron nitride crucible, suitable for the vaporization of aluminum, having a multi-walled structure comprising an outer wall and a thinner inner wall weakly bonded to the thicker outer wall. Because of this structure, the crucible is considerably more flexible than conventional single-walled crucibles and exhibits substantially improved thermal cycling characteristics and longer life. The crucible is produced by depositing pyrolytic boron nitride upon a mandrel having the shape of the desired crucible at a temperature of from about 1850° C. to about 2100° C. until a first layer of boron nitride of suitable thickness has been produced, interrupting the deposition of boron nitride upon the mandrel and lowering the temperature to below 1750° C., and then depositing additional boron nitride upon the mandrel at a temperature of from about 1850° C. to about 2100° C. to produce a second outer layer of boron nitride having a thickness greater than that of the inner layer