CVD-Grown Synthetic Diamonds, Part 2: Properties
June 19, 2013
The physical properties of CVD synthetic diamond fall well within the range for natural diamonds in terms of hardness, thermal conductivity, strength and so forth. Therefore, CVD synthetics are as hard and durable as natural diamond and display the same brilliance and fire when cut as a gemstone. The optical properties can be varied over a wide range through the controlled introduction of impurities. For example, crystals can be made colourless to near-colourless by controlling the residual nitrogen level of the gas in the growth chamber. Blue diamonds can be created by adding boron to the gas, while pink, yellow or other variations can be achieved using mixtures of gases, including high nitrogen concentrations. One particular advantage of CVD diamond production is that all crystals in a growth batch have the same colour and clarity, making them easier to grade and match. And the colour can be accurately repeated over an endless number of growth runs, ensuring reproducible colour, clarity and size, and an ongoing supply of high-quality synthetic diamonds for the gem industry. In addition, the ability to control size and purity will expand the uses of synthetic diamond beyond what is possible with natural diamonds, into new areas in optics, medical devices, electronics and applications yet to be identified.
Colourless and near-colourless CVD synthetic diamonds are usually type IIa, while only 2% of natural gem diamonds are type IIa. Type IIa diamonds are characterised by high purity (low nitrogen) and transparency in specific parts of the ultraviolet and infrared optical spectrum. Numerous UV detection instruments on the market can provide the first indication of a possible CVD synthetic. Obviously, additional tests would then be required to confirm whether the sample is CVD-grown or natural. If the gem is not IIa, it is most certainly natural. There will be additional discussion about non-IIa synthetic diamonds and the properties of blue, pink, yellow and other colours in a future article.
A common question in the diamond trade and among consumers is whether CVD synthetics will eventually be manufactured so inexpensively that the value of natural diamonds is endangered. The answer to that question is no. While CVD growth will become more efficient due to scale and manufacturing experience, several factors will only become more expensive with time and inflation. First, the cost of cutting and polishing CVD products is essentially the same as for natural diamond, and highly skilled artisans will still be needed to create beautiful goods. A second factor is that the electricity required to produce one carat of diamond does not scale significantly with the number of seeds or chamber size. Electricity is a major cost, one that is expected to continue to rise in the future, and there is little room for cost reduction here. A third cost is that of producing seeds. This is a significant overhead, and it is unlikely that an inexpensive alternative for a diamond seed will ever be found.
A more persistent threat to integrity and pricing in the diamond industry will be the misrepresentation of cubic zirconia and other imitation materials as “synthetic diamond”. While there are adequate tests for these imitations, they are not readily available for purchases made on the web.
CVD synthetics can be grown in a range of colours and sizes, with high clarity. The gemstones produced are as beautiful and durable as natural diamond, and they are expected to fill an important market niche in the near future. It is important to note that GIA has the ability to detect and grade CVD synthetics, which will continue to protect buyers and the integrity of the diamond industry.
In the next instalment of this series, we will discuss detection of CVD synthetic diamonds.
Dr Robert Linares is owner of the consulting firm Integrated Diamond Technologies, LLC. An expert in crystal growth technologies, he was co-founder of Apollo Diamond Inc., which produced some of the first gem-quality CVD synthetic diamonds. Dr Linares received the US Department of the Navy’s 2002 Berman Award for breakthroughs in diamond-based quantum computing research and applications.