Abstract: An apparatus for the synthesis of diamond by the vapor-phase process using a combustion flame is provided with a cover set in place in the peripheral region of a combustion burner for enveloping the combustion flame and provided, when necessary, with gas inlets. A method for the synthesis of diamond by the vapor-phase process using the apparatus described above effects the diamond deposition by forming a combustion flame for synthesis of diamond and, at the same time, varying the relative parallel positions of the combustion flame and the substrate.

Abstract: A composite diamond grain which comprises a heat-resistant grain as a nucleus and discrete diamond crystal particles distributed on the surface of the grain or diamond crystal films formed to cover the entire surface of the grain and a method for producing the composite diamond grain by the vapor-phase process are disclosed. For the filament method which is one form of the vapor-phase method, tantalum is useful as the material for the filament. Since tantalum is susceptible of embrittlement by hydrogen, a treatment to be performed on tantalum for the elimination of this drawback is also disclosed.

Abstract: Composite diamond granules using granules of a ceramic substance line SiC as cores and covering the cores with a polycrystalline diamond coating are produced by the vapor phase method. The granules clearly manifest an automorphic diamond face and possess pyramidal projections, square faces, or rectangular faces on their surface. They are highly useful as abrasive granules for grinding. A grindstone obtained by mixing these granules with resin, metal, and vitrified binder and molding the resultant mixture is highly useful.

Abstract: A composite diamond grain which comprises a heat-resistant grain as a nucleus and discrete diamond crystal particles distributed on the surface of the grain or diamond crystal films formed to cover the entire surface of the grain and a method for producing the composite diamond grain by the vapor-phase process are disclosed. For the filament method which is one form of the vapor-phase method, tantalum is useful as the material for the filament. Since tantalum is susceptible of embrittlement by hydrogen, a treatment to be performed on tantalum for the elimination of this drawback is also disclosed.

Abstract: A method for vapor-phase synthesis of diamond comprises burning a raw material compound for synthesis of diamond thereby forming a combustion flame, disposing a substrate for deposition of diamond in said combustion flame, and keeping said substrate at a prescribed temperature, thereby inducing deposition of diamond on said substrate.