What about the CVD method: “growing diamonds”?

What about the CVD method: “growing diamonds”?

1.What is chemical vapor deposition (CVD) method?

CVD stands for chemical vapor deposition and is another method of creating diamonds in a laboratory. Specifically, diamonds are grown from a mixture of hydrocarbon gases and subjected to moderate pressures and temperatures in a vacuum chamber.

2.CVD diamond growth process

·The diamond seed crystal is placed in the growth chamber.

·The chamber is filled with carbonaceous gas.

·The chamber is heated to approximately 900-1200°C.

·The microwave beam precipitates carbon from the plasma cloud and deposits it onto the seed crystal.

·The diamonds are removed every few days to polish the top surface 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 growing process may take three to four weeks.

·Once the synthetic diamond crystals are removed, they can be cut and polished into the final product.

In simple terms, the CVD diamond growth process takes place in a vacuum chamber filled with hydrogen and carbon-containing gases such as methane. An energy source—such as a microwave beam—breaks up the gas molecules and the carbon atoms diffuse toward the cooler, flat diamond seed plate. Crystallization occurs over several weeks, and several crystals grow simultaneously. The exact number depends on the size of the chamber and the number of seed plates. Platy crystals often develop rough edges of black graphite that need to be cut away. They also exhibit a brown color that can be removed by heat treatment before faceting.As with the HPHT diamond growth process, CVD methods continue to improve and allow for larger diamond sizes with improved color and clarity.

3.The History of CVD Grown Diamonds

The history of CVD-grown diamonds can be traced back to 1952. William Eversole of Federal Silicon Carbide Company in the United States successfully grew lab-grown diamonds using carbon-containing gas under low-pressure conditions. However, the growth rate of CVD diamond is very slow, and it is not certain whether this growth rate can be used for commercial applications. So for many years, the conventional wisdom was that diamonds could only form under high-pressure, high-temperature (HPHT) conditions.

However, in the early 1980s, CVD cultured diamond technology made a major breakthrough. In 1982, Japan's National Research Institute of Inorganic Materials (NIRIM) announced that the growth rate of cultured diamonds had exceeded 1 micron per hour.

In the late 1980s, De Beers began to engage in research on CVD-grown diamonds, and then quickly achieved a leading position in this field, providing many CVD polycrystalline diamond industrial products.

It was not until the 21st century that the research and development of gem-grade CVD single crystal cultivated diamonds made a breakthrough: the American Apollo Diamond Company successfully cultivated the first batch of colorless gem-grade CVD diamonds in 2007.

4.China’s CVD diamond technology

Compared with foreign countries, China's CVD technology started late. According to relevant reports from CCTV in 2019, the laboratory of the Ningbo Institute of Materials, Chinese Academy of Sciences has been able to "grow" a 1-carat rough cultivated diamond in just one week. This news has attracted widespread public attention.

On March 9, 2020, IGI International Gemological Institute appraised a 7.06-carat CVD-grown diamond. The final result was that the diamond weighed 7.06 carats, was F color, VVS2 clarity, and 3EX cut. It is currently the world’s largest diamond. The world's largest high-quality CVD diamond. The birth of this diamond also marks the increasing maturity of my country’s high-quality, large-carat CVD-grown diamond technology.

Although the scale of my country's CVD-grown diamond companies is not large in the world, many companies already have the ability to produce large-sized, high-quality CVD diamonds. In the future, as the quality of CVD diamonds continues to improve, it will bring more benefits to the entire diamond market. Lots of variations and options.