boron carbide (CBN), diamond, or other materials with a hardness greater than that of alumina as the abrasive...http://www.google.es/patents/US6425805?utm_source=gb-gplus-sharePatente US6425805 - Superhard material article of manufacture B???squeda avanzada de patentes N???mero de publicaci???nUS6425805 B1Tipo de publicaci???nConcesi???n N???mero de solicitudUS 09/559,745 Fecha de publicaci???n30