Synthetic diamond prodn - from carbon cpds. free from carbon-hydrogen covalent bonds esp. hexahalobenzenes, hexahaloethanes and tetrahaloquinones

Hard materials, partic. synthetic diamonds, are produced by subjecting a C-contg. compsn. free from convalent C-H bonds to temps. and pressure such as to cause decompsn. with release of C atoms or C atom gps. and convert them to diamonds; maintaining conditions to complete conversion; then releasing press. and reducing temp. to ambient temp. and recovering diamonds from reaction zone contents. Pref. raw materials are hexahalobenzenes, esp. C6C6; hexahaloethanes, esp. C2Cl6 and tetrahaloquinones, esp. chloranil. Explosions, caused by generated halogen gas, are prevented by providing a halogen gas aceeptor, e.g. an alkali or alkaline earth metal, partic. Li. Pref. conditions are 2000 degrees C and 100 kilobar. Above Berman-Simon line, press. is raised quickly and temp. at 20-30 degrees C/min. A gradual temp. and press. rise is preferred for condition below Berman-Simon line.