Abstract: An apparatus for operation in the temperature range above 1000 degrees Centigrade and at pressures above 50 kilobars, for making industrial diamonds or the like, includes arrangements for more reliably maintaining uniform temperature while compressing the charge. The high pressure cavity includes the usual insulating cylindrical liner made of a salt, or other insulating material, to facilitate the application of electricity to heat the charge, and the liner stops short of the end of the cylindrical high pressure cavity to avoid deformation as the main piston moves into the end of the high pressure cavity. A ring or rings of zinc and/or lead and/or a zinc-lead alloy, may be located immediately adjacent the end of the insulating liner, and a thin layer of lead may extend across the main piston, to insure confinement within the cavity. Heating arrangements are provided to compensate for the cooling which occurs along and at the ends of the high pressure cavity to thereby achieve more uniform temperature.

Abstract: A piston type system for forming industrial diamonds is provided with a pressure vessel which includes a tungsten carbide member having a central opening which has a tapered mouth at one end, and which is lined with a salt bushing. A charge including invar and graphite to be converted to diamond is inserted within the pressure chamber inside the salt bushing. An end load plate has a central opening of substantially the same diameter as the opening in the salt bushing and has a tapered flange which fits into the tapered mouth in the tungsten carbide pressure vessel. A tungsten carbide piston which has a diameter about 0.003 inch less than the diameter of the opening in the end plate, and which has a lead gasket between its surface and that of the opening in the end plate, is forced through the end plate and applies high pressure at high temperatures to the charge, thereby converting the graphite to diamond after the passage of a suitable period of time.