What conditions can convert graphite into a diamond?
Graphite is at a pressure of 50,000 to 60,000 atmospheres (i.e. (5-6) × 103MPa) and a high temperature of 1,000 to 2,000 degrees Celsius. Then metal iron, cobalt, nickel, etc. are used as catalysts to convert graphite into diamond powder.
With the help of high temperature and pressure and catalyst, graphite can be converted into the diamond. Although both are composed of carbon elements, the structure of carbon atoms has undergone significant changes, so this process is not a physical change, but a chemical change.
There are two main synthetic diamond methods: high temperature and high-pressure method and chemical vapour deposition method. The high temperature and high-pressure method technology has been very mature and has formed an industry. My country's domestic output is extremely high, the highest in the world. The chemical vapour deposition method still mainly exists in the laboratory.
In the presence of static high pressure, high temperature and transition metals, the mechanism of graphite turning into diamond mainly changes with pressure.
Graphite is dissolved by metal and recrystallized into diamond under low-pressure conditions. This is the case for diamond growth by seeding. With the increase of pressure, the direct conversion of graphite into diamond increases, and graphite can be directly converted into full rigid stone without metal until 130,000 atmospheres and 3000°C.