Diamond Growing Process
High Pressure High Temperature (HPHT)
HPHT diamond growth occurs within enormous pressure cookers called cubic presses, which can exert in excess of 70 metric tons. To grow a diamond in a cubic press, small diamond seeds are carefully placed into the bottom of a growth cell. A layer of additional carbon, in form of graphite, is then delicately placed on top of the diamond seeds. The growth cell is then placed into the center of the cubic press and heated to 1,500 degrees C while being subjected to 1 million psi of pressure, which is approximately 70,000 times the pressure at sea level!
At that temperature and pressure, the graphite in the growth cell is melted into a liquid and then very carefully cooled into our favorite form of carbon, a diamond crystal.
Chemical Vapor Deposition (CVD)
CVD diamond production is quite different from HPHT growth in two major ways. First, the diamonds are grown in a vacuum instead of under tremendous pressure. Secondly, CVD growth requires large, flat plates of diamond instead of small seeds.
To grow a CVD diamond, diamond plates are placed into a vacuum chamber, carefully injected a hydrocarbon gas such as methane, and use high power microwave energy to break down the atomic bonds of the hydrocarbon gas. This separates the carbon atoms from the hydrogen atoms, and the resulting free carbon 'rains' down on the diamond plates, vertically growing the diamond atom by atom, similar to the way snow collects on a table.