Over 200 years ago, people recognized that diamond is composed of pure carbon. Since then, attempts have been made to synthesize diamond using graphite, which is also composed of carbon. However, due to insufficient knowledge and limited technical capabilities, progress has been extremely slow. Later research revealed that the main reason for the difficulty in synthesizing diamond is that at room temperature and pressure, graphite is a thermodynamically stable allotrope of carbon.
Diamond is a thermodynamically metastable allotrope of carbon, but it is kinetically stable. Therefore, to synthesize diamond, suitable methods and process conditions must be found. General Electric (GE) in the United States was the first to bring synthetic diamond to market. Their method is called High Pressure, High Temperature (HPHT). Diamond synthesized using this method is also called HPHT diamond. This process uses graphite as the raw material, introduces a suitable metal catalyst, and synthesizes diamond at temperatures above 2000K and pressures of tens of thousands of atmospheres.
Synthetic diamond is produced by artificially converting non-diamond carbon into diamond-like carbon at ambient pressure. Larger single crystals and polycrystalline diamonds can also be produced using controlled diamond nucleation and growth techniques, while polycrystalline diamond and diamond composites can be formed using dopant bonding and self-bonding techniques. The research and industrialization of synthetic diamonds are rapidly developing, with numerous methods being employed. These methods can be categorized by the characteristics of the synthesis technology used, including static high-temperature and high-pressure methods (static pressure methods), dynamic high-temperature and high-pressure methods (dynamic pressure methods), and low-pressure or atmospheric high-temperature methods (low-pressure methods).
Based on the characteristics of the growth mechanism, they can be categorized as direct conversion methods (direct methods), solvent-catalyzed or melt-catalyzed methods (melt catalyst methods), and epitaxial growth methods (epitaxial methods). While the high-pressure and high-temperature indirect static pressure method is the most basic and important method for producing this material, another process for synthesizing diamond grains is the direct conversion method.