Diamonds produced by the high-pressure high-temperature (HPHT) method and those produced by the chemical vapor deposition (CVD) method have the following differences:

• 1. Preparation principle

HPHT diamond：

Under high-temperature （generally above1000℃）and high-pressure（above5GPa）conditions, the carbon source(such as graphite) undergoes a phase transition under the action of a metal catalyst. The arrangement structure of carbon atoms changes from the layered structure of graphite to the cubic lattice structure of diamond.

It needs to be grown in a closed environment of equipment such as a six-anvil press, under high-temperature and high-pressure conditions, mimicking the formation conditions of natural diamonds inside the Earth.

CVD diamond:

Under the low-pressure conditions, a mixture of carbon-containing gas (such as methane) and hydrogen is excited and decomposed at high temperature and a pressure lower than standard atmospheric pressure. Carbon atoms in a plasma state are formed and deposited on the substrate to interactively grow into polycrystalline diamond.

Or, by controlling the deposition and growth conditions, single- crystal diamond or quasi-single- crystal diamond can be deposited and grown. The growth temperature is generally between 900-1200℃, and the pressure is in a low-pressure environment below standard atmospheric pressure. Inside equipment such as vacuum plasma reactor, carbon-containing gases are decomposed by means of microwaves, etc., and then deposited and grow on the substrate.

• 2. Growth rate

HPHT diamond:

The growth rate is relatively fast. Diamonds of a certain size can be obtained in a short period, making it suitable for large-scale industrial production of small-sized diamonds.

CVD diamond:

The growth rate is slow. It takes several days or even weeks to grow a diamond with a certain thickness. However, it can produce diamonds of relatively large sizes.

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