Denki Kagaku Kogyo Kabushiki Kaisha

Hiroaki Tanji

Masaharu Suzuki

Takashi Kawasaki

Kenji Nomura

Shojiro Watanabe

Masaji Ishii

Mitsuaki Saito

A pyrolytic boron nitride crucible is provided. The crucible contains at least five wall layers consisting of first and second wall layers. The thickness of each of the first wall layers is 5 to 100 microns and the thickness of each of the second wall layers is 1/50 to 1/1 of that of the first wall layer. The total thickness of the entire wall layers is 0.5 to 3 mm. The first wall layer is bonded to and laminated alternately with the second wall layer.

Pyrolytic boron nitride crucible and method for producing the same

A pyrolytic boron nitride article of the invention has uniform structure and has 0.5 or less nodules/cm.sup.2 in average all through the overall surface of the article and 2 or less nodules in any portion of the unit square centimeter on the surface of the article. The pyrolytic boron nitride article is produced by depositing boron nitride through a vapor phase, using a boron halide gas and an ammonia gas as the starting materials. Upon production, the ammonia gas or a gas mixture containing the ammonia gas is not contacted directly with graphite at 300.degree. to 1850.degree. C.

Method for producing pyrolytic boron nitride article

A pyrolytic boron nitride article has a uniform structure 0.5 or less nodules/cm.sup.2 in average all through the overall surface of the article and 2 or less nodules in any portion of a unit square centimeter on the surface of the article. The pyrolytic boron nitride article is produced by depositing boron nitride through a vapor phase, using a boron halide gas and an ammonia gas as the starting materials. In production, the ammonia gas or a gas mixture containing the ammonia gas is not contacted directly with graphite at 300.degree. to 1850.degree. C.

Pyrolytic boron nitride article

A thermionic cathode includes an electron emitting tip, lanthanum hexaboride tip supporting heaters in close contact with both sides of the tip and supporting the tip, and elastic electroconductive members in pressure contact with outer surfaces of the tip supporting heaters for supplying electric current. The tip supporting heaters are obtained by cutting lanthanum hexaboride having high anisotropy due to its layered structure so as to form a pair of parallel planes perpendicular to a pressing direction when hot-pressed, and abrade-polishing the parallel planes. The tip supporting heaters are brought into close contact with the tip and the elastic electroconductive members at the resulting smooth surfaces thereof. The apparatus of the invention has a prolonged lifetime and high efficiency.

Growing community of inventors

Tokyo, Japan

Hiroaki Tanji