Submicron titanium boride powder and method for preparing same

Abstract

Submicron titanium diboride powder and other hard, refractory metal boride powders, such as zirconium diboride and hafnium diboride powders, are prepared by vapor phase reaction of the corresponding metal halide, e.g., titanium halide, and boron source reactants in the presence of hydrogen in a reaction zone and in the substantial absence of oxygen, either combined or elemental. In a preferred embodiment, the metal halide, e.g., titanium tetrachloride, and boron source, e.g., boron trichloride, reactants are mixed with a hot stream of hydrogen produced by heating hydrogen in a plasma heater. The reaction zone is maintained at metal boride forming temperatures and submicron solid metal boride powder is removed promptly from the reactor and permitted to cool. The preponderant number of metal boride particles comprising the powder product have a particle size in the range of between 0.05 and 0.7 microns. The aforesaid titanium diboride powder can be hot pressed or cold pressed and sintered to articles having densities of at least 90, e.g., 95 percent of theoretical. A metal boride powder product containing a minor concentration of carbon, e.g., from above 0.1 to about 5 percent by weight total carbon can be prepared by adding a source of carbon in the reaction zone. Alternatively, submicron metal carbide powders, e.g., titanium, zirconium, hafnium or boron carbide powders, or finely-divided carbon can be blended physically with the submicron metal boride powder to provide metal borides containing a minor concentration of carbon in the amounts previously indicated. The above described carbon-containing titanium diboride powder compositions can be hot pressed, or cold pressed and sintered to articles having densities of at least 95 percent of theoretical. Such articles can be used as current conducting elements, e.g., cathodes, in electrolytic cells for production of aluminum.