Chemical vapor deposition of mixed phase α-AlB12-B

A mixed phase of aluminum dodecaboride (α-AlB12) and tetragonal boron was deposited on a Mo or W filament from a gas mixture of AlCl3, BCl3, H2, and Ar in a temperature range of 800-14000C, and was also prepared by aluminizing of elementary boron with a gas mixture of AlCl3, H2, and Ar at 800-13000C. Depostion conditions, and appearance, composition, and microhardness of the deposit were examined. The deposition rate increased with increase of reaction temperature and also of the gas flow ratio (BCl3,AlCl3) in a source gas, and attained a constant value at a temperature above 12000C and a ratio above unity, respectively. The atomic ratio (B/Al) in the deposit was independent of the reation temperature, but dependent on the gas flow ratio (BCl3/AlCl3) in the source gas. Maximum microhardness of about 3900 kg/mm2 was observed in the specimen deposited from an atmosphere of a gas flow ratio (BCl3/AlCl3) of 1-2. (orig.)