Method of producing polycrystalline diamonds

A method for producing polycrystalline diamonds which comprises:

• filling a reaction chamber of a device for developing high pressure and high temperatures and having cooled portions with a carbon material;
• subjecting the carbon material in the presence of a metal catalyst to the simultaneous action of high pressures of at least 80 kbar and diamond synthesizing temperatures of at least about 1,200.degree. C. and approaching the minimum temperature of diamond synthesis with the given metal catalyst for a period of time sufficient to obtain diamond crystallization;
• maintaining said reaction chamber in thermal contact with said cooled portions so as to effect removal of heat developed therein in the course of diamond crystallization at a rate of not less than 25 cal/min, said metal catalyst having a cross-sectional area of not more than 0.04 of the area of transverse section of said reaction chamber and being positioned in the carbon material substantially in the center of said reaction chamber, so as to ensure the growth of polycrystalline fine-grain diamond sample containing mutually intergrown crystallites.