Method of coating alumina particles with refractory material, abrasive particles made by the method and abrasive products containing the same

A process for making abrasive particles, each particle of which has an alumina-based core coated with a substantially uniform layer of metal boride, carbide or nitride refractory material, said process comprising

• a) applying sufficient current to a metal cathode to form a plasma of the metal comprising the cathode;
• b) subjecting said plasma to an atmosphere conducive to the formation of the boride, carbide or nitride of the metal of said plasma;
• c) permitting said plasma to be directed in a path through an anode;
• d) maintaining alumina-based particles to be coated within said path;
• e) rotating each alumina-based particle to substantially expose the entire surface of each of said particles to said plasma path;
• f) continuing steps a-e until a substantially uniform coating of refractory material is coated on substantially every alumina-based particle, and
• g) discontinuing steps a-f before the average coating thickness of refractory material on the alumina-based particles exceeds 100 nm.