SYNTHETIC DIAMONDS - CVD

SYNTHETIC DIAMONDS CVD - WHAT IS A CHEMICAL VAPOR DEPOSITION (CVD) DIAMOND?

CVD stands for chemical vapor deposition and is another method used for making diamonds in a lab. Diamonds grow from a hydrocarbon gas mixture subjected to moderate pressures and temperatures in a vacuum chamber.

THE CVD DIAMOND GROWTH PROCESS

Diamond seed crystals are placed in a diamond growth chamber.

The chamber is filled with carbon-containing gas.

The chamber is heated to about 900-1200°C.

A microwave beam causes carbon to precipitate out of a plasma cloud and deposit onto a seed crystal.

Diamonds are removed every few days to have the top surface polished to remove any non-diamond carbon before being put back in to grow. Each batch of diamonds may require several stop/start cycles, and the entire growth process can take three or four weeks.

After the synthetic diamond crystals are removed, they are ready to be cut and polished into the final product.

In greater detail, CVD diamond growth takes place inside a vacuum chamber filled with a hydrogen and carbon-containing gas, such as methane. A source of energy — such as a microwave beam — breaks down the gas molecules, and the carbon atoms diffuse towards the colder, flat diamond seed plates. Crystallization occurs over a period of weeks, and several crystals grow at the same time. The exact number depends on the size of the chamber and the number of seed plates. The tabular crystals often develop a rough edge of black graphite that needs to be cut away. They also display a brown color that can be removed by heat treatment prior to faceting. Most CVD-grown colorless material on the market were probably once brown crystals that have been decolorized by HPHT annealing.