Boron and boron carbide coatings by vapor deposition

The Bureau of Mines investigated the formation of boron and boron-carbide coatings by vaporphase reactions. Optimum parameters were determined for hydrogen reduction of boron trichloride and for the formation of boron-carbide coatings on graphite by reaction with the deposited boron. At 1300°C, about 85 pct of the boron was deposited. Tungsten substrates did not react with the boron deposit; other substrates reacted to various extents. The hydrogen reduction of boron tribromide was briefly investigated. Boron carbide was deposited at 1300°C by adding methane to the boron trichloride-hydrogen feed gas. The chemical composition of the vapor-deposited boron carbide approximated B₄C. A method of etching B₄C was developed to study its microstructure. When boron was deposited on graphite at 1500°C, very hard, uniform, strongly adherent coatings of B₄C were formed that might be useful in applications such as rocket nozzles and chemical reaction and processing vessels.