Abstract: A coated particle for synthesizing diamond includes: a single crystal of a fine diamond particle coated with at least one layer which contains at least one kind of solvent metal powder for synthesizing diamond and/or at least one kind of solvent metal powder with organic bonding material. Diamond abrasive particles for sawing are produced by a process which includes the steps of: coating fine diamond particles with at least one layer which contains at least one kind of solvent metal powder for synthesizing diamond and/or at least one kind of solvent metal powder with organic bonding material, filling a molding with the coated fine diamond particles, compacting, arranging a compact in a synthesizing vessel, heating the compact to a temperature above a solvent metal-graphite melting point under a pressure condition in which diamond is thermodynamically stable, and recovering the diamond abrasive particles.

Abstract: Granular diamond suitable for use as an abrasive grain for polishing is synthesized from gaseous phase by a process for the synthesis of granular diamond, comprising subjecting a mixed gas containing an organic compound and hydrogen to a treatment to form plasma and depositing diamond on substrate grains dispersed and fluidized in the resulting plasma space, characterized in that the substrate grains are dispersed and fluidized by the mixed gas fed at a flow rate of at least the terminal velocity of the grains and an AC or DC electric field is applied to a zone whose grain concentration in the space is in the range of 1 to 20% by volume.

Abstract: In a method of manufacturing a cubic boron nitride p-n junction body, cBN seed crystals (1) of a first conductivity type are made coexist with original BN (3) and a solvent (2) containing a doping material of a second conductivity type, to grow cBN of the second conductivity type from the seed crystals (1). The solvent (2) contains 0.1 to 5 percent by weight of the doping material. The seed crystals (1) are disposed one by one in a plurality of blocks of the solvent (2), which blocks are separated from each other, to be in contact with nothing but the solvent (2). Due to such disposal, no spontaneous nucleation is caused in portions other than the seed crystals (1). A large-grained cBN p-n junction body is obtained as the result.

Abstract: Cubic system boron nitride crystals are synthesized by using a synthesizing vessel separated into a plurality of synthesizing chambers by one or more partition layers. After preparing the synthesizing vessel it is heated under extra-high pressure to achieve a required temperature gradient from chamber to chamber. A plurality of solvents having different eutectic temperatures with respect to boron nitride (BN) sources are placed in the chambers according to the temperature gradient. The BN sources are placed in contact with solvent portions heated to relatively high temperatures. At least one seed crystal is placed in each solvent portion heated to relatively low temperatures. At least one cubic system boron nitride crystal is grown in each of the solvents in the chambers by the above heating of the synthesizing vessel under conditions of ultra-high pressure and temperatures assuring the required temperature gradient.