Process for producing an improved boron nitride crucible

A process for producing a boron nitride crucible having a multi-walled structure comprising an outer wall, an inner wall, and at least one intermediate wall, said process comprising:

• (1) reacting ammonia and a boron halide in vapor phase at a temperature of from about 1850.degree. C. to about 2100.degree. C. under a pressure no greater than about 1 mm. of mercury absolute to produce boron nitride, and depositing a first layer of said boron nitride upon a mandrel having the shape of the desired crucible;
• (2) interrupting the reaction between the ammonia and boron halide and the further deposition of boron nitride upon the mandrel;
• (3) lowering the temperature of the boron nitride layer to below 1750.degree. C.;
• (4) reacting additional ammonia and boron halide in vapor phase at a temperature of from about 1850.degree. C. to about 2100.degree. C. under a pressure no greater than about 1 mm. of mercury absolute to produce additional boron nitride and depositing a second layer of said boron nitride upon the first boron nitride layer;
• and (5) repeating steps 2, 3 and 4 at least one additional time so as to deposit at least one additional layer of boron nitride upon the second boron nitride layer, all of said boron nitride layers being weakly bonded to each other, the outer layer being of greater thickness than the other layers, and the intermediate layers being of no greater thickness than the inner layer.