U.S. Pat. No. 5,529,804, the disclosure of which is hereby incorporated by reference, discloses a method of coating hard constituent powders with Co and/or Ni with the polyol process disclosed in U.S. Pat. No. 4,539,041 and used today for the manufacture of cobalt and nickel metal powders with a small particle size. According to U.S. Pat. No. 5,529,804, hard constituent powder in suspension in a polyol solution containing an oxide, hydroxide or salt of Co and/or Ni during reduction of cobalt and nickel by the polyol obtains a cobalt and/or nickel metal precipitation on the surface. The metals are precipitated with a quite even distribution over the surface of the carbides without forming separate islands. However, the requirement of a large excess of ethylene glycol and the technical difficulties in separating and removing the ethylene glycol oxidation by-products interfere with the economy of the process. Further, a mixture of by-products are formed during the reduction which complicates separation of un-reacted ethylene glycol. A suitable strategy to improve the process economy is to recycle or decrease an excess amount of ethylene glycol needed for the cobalt or nickel reduction.
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