Method of producing monotungsten carbide powder

Claim 1

A process for producing a non-pyrophorric fine tungsten carbide powder having low free carbon comprising (a) mixing tungsten oxide or ammonium paratungstate with powder carbon to form a resulting mixture, (b) substantially reducing the resulting mixture in a non-reducing atmosphere for a sufficient period of time and at a temperature greater than 878 degrees Centigrade to reduce oxides of tungsten present in said resulting mixture and produce at least a partially carburized mixture consisting essentially of tungsten, ditungsten carbide, monotungsten carbide and free carbon, said reducing being carried out in a boat having a bed depth of said resulting mixture whereby the surface of said bed after reducing is depleted in carbon and comprises tungsten and the center core of said bed comprises a higher percentage of monotungsten carbide and ditungsten carbide than said surface, said reducing being carried out in the presence of sufficient carbon to at least partially carburize said mixture and produce a total carbon content including chemically combined carbon and free carbon of less than the stoichiometric amount needed to produce monotungsten carbide, (c) removing said partially carburized mixture from said boat and mixing to form a homogenous mixture, (d) sampling said homogeneous mixture to determine the deficiency of carbon below the stoichiometric amount needed to make monotungsten carbide, (e) adding sufficient carbon powder to said homogeneous mixture to form an adjusted mixture having a total carbon content at the stoichiometric amount needed to make monotungsten carbide, (f) blending the adjusted mixture to form a homogeneous mixture, and (g) carburizing said adjusted mixture in a hydrogen atmosphere at a suitable temperature to form a nonpyrophorric monotungsten carbide having low free carbon.