Synthetic diamonds

Synthetics – Is it a threat or the future for the diamond industry?

24.02.2014

If you spend several years being earnestly engaged in research trying to understand the techniques of growing lab-made diamond crystals, you can definitely achieve a breakthrough, and this is what was successfully done by a Russian diamond holding, which includes three companies - Inreal, Nevsky Brilliant and New Diamond Technologies. The holding has developed a unique process for growing colorless, blue (semiconductor) and yellow single-crystal diamonds. This technique permits to grow up to 200 crystals simultaneously in one container. Alexander Kolyadin, Ph.D and CEO of Inreal, told some interesting facts about synthetic diamonds to Rough&Polished to be published for our readers.

Last year, many diamantaires across the world were concerned about synthetic diamonds infiltrating the market of natural diamonds. How much should people be wary of this new industry and is it possible to reassure them in any way?

Today, there is no point in saying that synthetics started to replace natural stones in the jewelry industry, because the number of companies that are engaged in growing colorless single-crystal diamonds can be counted on two hands. Furthermore, the growth rate of single-crystal stones is small enough - for colorless crystals it is 2.1 mg/hr. To grow a crystal of 1 carat (200 mg) you will need more than 5 days. The total number of expensive equipment for growing crystals possessed by these companies does not exceed 1,000 units. There is no threat at the moment, but new techniques are emerging for the simple reason that this material has a bright future due to its unique physical and chemical properties. The synthetic crystal is the most conductive thermally, most durable and able to work in harsh environments, including radiation fields. And everyone is trying to understand what can be done out of this and how it can be used.

The lab-made crystal is a thing of the future and its main destination is to be used for technical purposes in the field of high technologies. Making polished diamonds is just a particular instance of using gem-quality diamonds. We have a slogan saying that if you cannot use a rough diamond to make anything else, make a polished diamond. Naturally, taking into account such a long period in developing diamond cutting techniques, by now people have a rather efficient way to estimate the commercial value of diamonds, depending on their shape, size, color and quality. Therefore, all the companies involved in the diamond cultivation are estimating the value of their production from the jewelry point of view. To estimate the cost of goods for hi-tech is much more difficult because in some areas there are so far no technical requirements for single crystals. For this we need to perform a lot of research and development works to have specific requirements for physical and mechanical properties of crystals. On the other hand, research centers are only now beginning to receive such materials. In the past, there was a general hope that nitrogen-free natural diamond will give a chance to electronics to make a step forward, but later it was found that diamond crystals similar by their defects and impurities are very rare, because their occurrence in nature was less than 2% and each crystal was different. Therefore, nitrogen-free natural diamonds are mainly used in the electronics sector only as individual sensors, such as sensors of ionizing radiation.

What are the main methods used to grow single-crystal diamonds?

There are two main techniques for growing single crystals and these are the CVD method or chemical vapor deposition (making carbon drop out from the gas phase) and the HPHT (high pressure, high temperature) method. These techniques are interrelated and complementary. For growing high-quality CVD single-crystal diamonds you will need a HPHT substrate, i.e. single-crystal plates produced with the help of press equipment. Since the plates made of HPHT crystals are small, from 3 to 10 mm, the resulting CVD-crystals have the same dimensions. Besides, CVD-crystals seldom exceed 1-3 mm in their thickness. If carbon is precipitated on silicon or polycrystalline diamond instead of single-crystal substrate, we shall finally obtain a polycrystalline disc up to 1 mm thick, which does not possess the unique properties of the single crystal and therefore is of limited use in the electronics and optics industries. Currently, such polycrystalline disks may be up to 100 mm in diameter. They can be used for diamond windows, watch glasses, micro equipment, etc. Therefore, only single-crystal diamonds are the new future element base for the electronics, optics, medicine, jewelry and tool industries.

As you know, China is the main producer of synthetic diamonds. Is it possible that a serious threat to natural diamonds will come from there?

Today, China produces more than 10 billion carats of synthetic diamond powder, of which 80% is used within China itself. Ten years ago, Chinese experts purchased a very successful design of cubic press from the Kiev Institute for Superhard Materials, which subsequently allowed them to develop techniques for mass spontaneous synthesis of high-quality diamond powder. Today, every cubic press generates 250-400 carats of diamond powder up to 800 microns in size every thirty minutes or 2-3 polycrystalline diamond disks up to 50 mm in diameter for tool production. Today, there are over 30,000 such presses in China. Diamond powders dropped in price tenfold, from $ 2 to 20 cents. This led to the closure or reorientation of many foreign diamond factories producing powders. The need of the tool industry in single crystals larger than those used in powders made the Chinese research centers to develop techniques for spontaneous synthesis of yellow single crystals from 1 mm to 4 mm in size. However, major manufacturers produce no more than 10,000 carats of such crystals a month, and high clarity crystals among them are scarce. Extensive research is underway to develop techniques for simultaneous cultivation of a large number of crystals using the temperature gradient method on cubic presses, imbedding previously synthesized yellow powders as seeds for crystals. These techniques are not yet very stable and are used on small power presses. The synthesis of colorless single-crystal diamonds is not yet developed.

The technique of growing single crystals by the CVD method is yet another major trend to produce synthetic diamonds booming in China. Flat grown nitrogen-free single crystals have a brown hue. They are cut into cubes of 1-3 mm in size. After that they are being “refined” by way of HPHT treatment (turning colorless), and then they are used to make those infamous small “synthetic” diamonds, which have recently put the entire diamond world into a flutter. The pace of development achieved by the Chinese diamond industry is impressive and I think it will take less than two to three years for the Chinese diamond factories to realign their capacities from producing powders to growing single-crystal diamonds, and if there will be techniques for spontaneous synthesis of colorless crystals ranging in size from 1000-800 microns to  2-3 mm in large quantities – this is the main range of dimensions for diamonds cut in India -  in this case “synthetics” may really  have a heavy bearing on the global industry of natural diamonds.

How difficult is it to distinguish a synthetic stone from a natural one?

It is very simple in case of rough, since synthetic (HPHT) diamonds have a strong cubic- octahedral shape and have a trace from the seed left on their substrate plane. Synthetic (CVD) stones have a shape of plates later turned into cubes or cylinders after preliminary processing. It is harder to deal with finished goods – polished diamonds. For a regular buyer, it is rather difficult to outwardly distinguish a synthetic colorless diamond of high quality (IF-VVS) from a similar natural stone. However, it is possible for an expert equipped with certain devices. In this case diagnostics is based on measuring the absorption spectrum of the diamond. If the expert will find from the absorption spectrum that the stone is nitrogen-free, this is the first indication that it may be synthetic, as there are less than 2% of natural nitrogen-free stones. Further, the diamond is checked for availability and nature of growth sectors in ultraviolet radiation using the Diamond View device. Synthetic polished diamonds have sectoral structure and in colored diamonds this can be viewed through a regular 10x loupe. Unfortunately, there is currently no fairly simple device, which could distinguish a synthetic polished diamond from a natural one just by one touch, but such devices are already being developed. The main problem for industrial application is to create a device that would be able to quickly check a large number of stones. VS- and SI-quality stones have inclusions of graphite and solvent metals, by which one can determine their nature. Moreover, there are other more sophisticated ways to identify synthetic diamonds.

Many buyers are worried that synthetic diamonds may replace natural diamonds in jewelry stores. This problem is also a headache for jewelry companies. How much real is this problem?

Today, production of colorless synthetic diamonds constitutes some hundredths of a percent of the entire natural production. Besides, a number of organizations, including all the gemological centers, are now involved in the work to prevent adulteration of synthetic diamonds under the guise of natural, to identify companies involved in this mixing and to certify synthetic diamonds. In general, today the markets trading in synthetic and natural diamonds have different customers. According to Alexei Zarakhani of D.NEA, one of the leaders in synthetic diamond sales in the U.S., Canadian and European markets, “synthetic diamonds have a strong enough demand among young people, called Hi-Tech generation, who are interested in this kind of goods because of their passion for all modern, ‘man made’ and who are also arguing that in the future there will no significant difference between small synthetic and natural diamonds, because the lion's share in the cost of both natural and synthetic diamonds is taken up by diamond cutters’ wages. Well, let’s wait and see. To date, the value of synthetic diamonds is high enough and it is either equal to half the value of natural diamonds or close to their full value, since the value of synthetic diamonds will go down only when there will be companies growing rough diamonds on an industrial scale.

Veronica Novoselova, Rough&Polished, Saint Petersburg

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