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Boron and Boron Carbide by Vapor Deposition.

Donaldson-JG; Stephenson-JB; Cochran-AA
Electro-deposition and Surface Treatment Elsevier Sequoia S a Switzerland 2:149-163
Boron trichloride can be reduced by hydrogen at 1,300 deg. C with a recovery of approximately 85 pct as elemental boron. The optimum h2 to bcl3 molar ratio was 30 under the test conditions used. No reaction between tungsten substrates and the boron deposits could be detected. Other substrate materials tested, in order of increasing reactivity with the depositing boron, were fused silica, mullite, graphite, titanium, and nickel. Alumina reacted extensively with the chloride gases to form aluminum chloride. Bbr3 can be reduced by hydrogen at slightly lower temperatures than can bcl3, but this advantage is probably outweighed by the lower boron content, lower volatility, and higher cost of bbr2. When stoichiometric amounts of bcl3 and ch4 were reacted with an excess of h2 at 1300 deg. C deposits were obtained. An excess of ch4 in the reaction mixture resulted in the codeposition of b4c and free carbon. B4c deposits contained 74.7 to 76.0 pct boron, compared with 78.3 pct for pure b4c. The specific gravity of the b4c was 2.32, Which is 90 pct or more of the theoretical value. The knoop microhardness of one b4c deposit on a mullite substrate was 3,472. A method of etching b4c was developed and used. Etching revealed that the b4c deposits had a columnar microstructure with the columns perpendicular to the substrate. When bcl3 was reduced with h2 at 1,500 deg. C with a graphite substrate, the depositing boron reacted with the graphite to produce uniform, strongly adherent coatings of b4c on graphite. The knoop microhardness of two of these b4c coatings was 3,065 and
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OP 59-74
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Electro-deposition and Surface Treatment, Elsevier Sequoia S.a. (Switzerland), V. 2, Pp 149-163