Other

Mark W Wilkins

Carl F Cline

Alan W Hare

Method and apparatus for compaction of powder of high density boron nitride, having an initial particle diameter of at least two microns, into a high density crystal aggregate of between 1 mm up to about 1 cm in diameter, the resulting crystal aggregate having a zincblende form, the wurtzite form or mixtures of the zincblende and wurtzite forms. High density aggregates of boron nitride, preferably having particle sizes with diameters at least 2 .mu.m, are placed in a hollow, substantially cylindrical first container of metal, and the first container is surrounded by a fluid-like material of metal or metal powder having a shock wave velocity V. The first container and fluid-like material are placed in a substantially cylindrical second container that is purged of substantially all air and sealed. The second container has a rigid side wall and two rigid end walls. A high explosive, having a detonation velocity D of at least 6 km/sec and preferably at least 8 km/sec, is positioned at one end wall and along at least a portion of the side wall of the second container. The high explosive is detonated, and an approximately radially directed pressure wave moves through the fluid-like material and the boron nitride powder toward the center of the second container. A second, approximately radially directed pressure wave, separated in time from the first pressure wave, subsequently moves outward through the fluid-like material and the boron nitride powder. These two pressure waves produce boron nitride aggregates of density at least 95 percent of the theoretical maximum density (3.49 gm/cm.sup.3) and of sizes at least 1 mm in diameter. A solid mandrel can be positioned near a center line of the second container to improve the quality of the resulting product. Grain sizes as small as 0.005-0.05 gm are produced. Boron nitride aggregates with Knoop hardness parameters in the range of 4300-5000 Kgm/mm.sup.2 can be produced in this manner.

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Pleasanton, CA, United States of America

Mark W Wilkins