Method of Preparing Cubic Polycrystals of Boron Nitride

摘要

The following methods are claimed: (1) A method of preparing cubic polycrystals of boron nitride from a boron nitride powder subjected to pressures above 40 kilobars and temperatures above 1200 exp 0 C, characterized by the fact that the treatment is applied to a powder consisting principally of boron nitride of a denser modification, of which at least a part has been previously subjected to a shock wave, as a result of which defects in the crystalline structure are generated that favor the formation of hard polycrystals of cubic boron nitride. (2) A method as in Claim 1, characterized by the fact that the powder of denser modification that is used consists either of powders of cubic boron nitride subjected to the action of a shock wave with an amplitude of at least 40 kilobars, or of a powder of boron nitride of the wurtzite modification obtained by the action of shock waves with an amplitude above 100 kilobars upon graphitic boron nitride. (3) A method as in Claims 1 and 2, characterized by the fact that the powder of denser modification consists of a mixture of 25 to 75% by weight of a powder of the wurtzite modification and 72 to 25% by weight of a powder of cubic boron nitride that has, depending on circumstances, been previously subjected to the action of a shock wave.