Small particles were produced from trichloroethane and hydrogenated diamond seeds mixture under alkaline hydrothermal conditions. These products were very hard, transparent and unsoluble in the acid mixture used for purification of commercial diamond. Only sp³-bond (1332 cm^-1) was observed in Raman spectrum. It means that the product is a diamond. Despite the XRD pattern also signified pure diamond, it is difficult to divide products from seeds diamond. Therefore, cubic boron nitride was used as seeds. Similar hydrothermal products were observed by SEM photographs, and Raman spectrum of this sample signified that the residue composed of cubic boron nitride and diamond. Thus, it is without controversy proven fact that diamond was synthesized under high pressure alkaline hydrothermal conditions.

Chlorinated organic compound (trichloroethane) is dechlorinated in alkaline hydrothermal solution, and intermediate active carbon species are polymerized on the surface of seeds as diamond. Without diamond/cBN seeds the produced carbon was amorphous. Therefore, the structure of seeds surface supports the formation of diamond phase in area that is far from thermodynamical stability of diamond.

These experimental conditions were considerably lower (pressure up to 1 GPa and temperature 573 K) than the parameters of commercial synthesis of diamond. Commercial diamond is synthesized at over 6 GPa and over 1900 K, therefore, this diamond is very expensive. But, our experimental conditions are relatively inexpensive, and are easy to produce the diamond in large scale as well as large polycrystalline diamond.

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