Resistance-heated pyrolytic boron nitride coated graphite boat for metal vaporization

摘要

Resistance-heated vaporization boats for the vacuum vaporization of metals, such as aluminum, chromium, copper or the like, are made by machining a boat cavity in at least one side of a graphite bar. The bar is totally encapsulated over its entire outer surface, including the boat cavity, with a continuous coating of pyrolytic boron nitride (PBN). The PBN coating is removed from areas at both ends of the bar to provide electrical contact zones for connecting the bar to a power source. The sides and ends of the boat cavity have smooth contours without sharp corners and the ends of the cavity have a hemispherical configuration to resist longitudinal expansion of the PBN coating thereby preventing separation of the PBN coating from the surface of the graphite bar. The PBN coating is deposited from a gas at a temperature of 1750° C. to 2300° C. and has a thickness of at least 0.010 inch.