Currently, the world’s popular high-temperature and high-pressure diamond synthesizing equipment mainly consists of two-sided tops (belt, which is mainly popular in Europe and the United States), six-sided tops (unique to Mainland China), and splitting spheres (barssplitsphere, Russia) or modified splitting spheres (Gemesis Company).
In 1954, before Christmas, the General Electric Company in the United States to High Pressure and High Temperature (HPHT) in 70,000 atmospheric pressure and 1,600 degrees Celsius under the environment of the graphite into diamonds, synthesized the first man-made diamond. But this diamond is very small, only 0.15 mm.
The high-temperature, high-pressure synthesis method is also known as the seed-crystal catalyst method. Graphite is a low-pressure stabilized phase and diamond (the mineralogical name for diamond) is a high-pressure stabilized phase. Direct transformation from graphite to diamond, the required pressure and temperature conditions are very high, generally need 10GPa, 3000 ℃ above the pressure and temperature. If metal catalysts (e.g. Fe, Ni, Mn, Co, etc. and their alloys) are involved, the temperature and pressure conditions required for the transformation of graphite into diamond will be greatly reduced, and this is why high-temperature and high-pressure diamond syntheses are currently carried out with metal catalysts. The metal catalyst, which acts as a solvent, is located between the carbon source (typically graphite) and the diamond seed crystals. The carbon source is at the high-temperature end and the seed crystal is at the low-temperature end. Since the solubility of the carbon source at the high-temperature end is larger than that at the low-temperature end, the difference in solubility generated by the difference in temperature becomes the driving force for the diffusion of the carbon source from the high-temperature end to the low-temperature end, so that the carbon source is precipitated out of the seed crystal gradually, and the diamond crystal grows gradually. Since the driving force for crystal growth is the temperature difference, the method is also called the temperature difference method.
HTHP synthetic diamonds are often cubic, octahedral, or aggregates of the two; the color is often yellow, yellow-brown, and there are often colored bands and metal inclusions inside, and the unfused metal inclusions are needle-like, flaky, small columnar, or irregular in appearance, and they have a metallic luster, which makes synthetic diamonds magnetic.
