The co-development of the two technical routes pushes up the production of cultured diamonds. After years of research and development, there have been a variety of methods to prepare and cultivate diamonds. At present, there are only two technical routes of commercial high temperature and high-pressure method (HPHT) and chemical vapor deposition (CVD). HPHT method and CVD method use completely different synthesis principles and technology and produce different product types and product characteristics. In 2020, among the 7 million carats of global cultivated diamond rough production, the HPHT method and CVD method are 3.2 million carats and 3.8 million carats respectively.
Domestic HPHT synthesis technology is the world’s leading, its synthesis principle is graphite powder under ultra-high temperature, high pressure, and catalytic action of gold catalyst powder transformation growth of the diamond crystal, synthesis speed, high single yield. HPHT synthetic diamond is mainly tower-shaped, with a fast growth rate, low cost, and slightly poor purity. However, it has advantages in comprehensive benefits, especially in 1-5CT diamond synthesis. In 2020, the domestic production of the diamond blank is about 3 million carats, accounting for 43% of the global output, of which the output of the HPHT method is about 2.8 million carats, almost monopolizing the global production of the HPHT method.
CVD cultivation technology has been used in foreign countries for many years. Its synthesis principle is that carbon gas (CH4) and hydrogen mixture are excited to decompose activated carbon atoms under ultra-high temperature and low-pressure conditions. By controlling the deposition and growth conditions, activated carbon atoms are promoted to deposit and intergrow into diamond crystals on the matrix. The diamond synthesized by CVD is tabular, the color is not easy to control, the cultivation cycle is long, the cost is high, but the purity is high, and it is more suitable for the diamond synthesized by cultivation above 5CT.
Different technical routes complement each other, diamond rough convergence. At present, the HPHT method and CVD method each account for about half of the supply of cultivated diamond rough, while the HPHT method is the main method in China. Due to the capacity limitation of upstream equipment, neither the HPHT method nor the CVD method can rapidly expand production. Core manufacturers pay attention to patent protection to limit technology spillover, so the supply pattern is difficult to change in a short time. For a long time, it is generally believed in the industry that 1) the HPHT method has more obvious color advantages, without the need for later color modification, but the synthesis process needs to add a metal catalyst, so the clarity is slightly inferior; 2) The purity of the blank under CVD method is higher, and most products are above VS, but the color is slightly inferior, mostly brown.
We believe that HPHT and CVD products are gradually homogenized after technological improvement. Domestic HPHT process line mature, occupy the main market share, equipment supply is mainly in China. CVD technology is applied in many countries, and overseas equipment suppliers are more dispersed.
1) Under the HPHT method, major manufacturers can mass-produce white diamond (DF color), and the clarity can reach more than VS; 2) Under THE CVD method, most of the purity of the blank is above VS, and some manufacturers can directly grow white without changing the color in a later stage.
Can produce large carat products: consumer cultivation diamond 1-2 carats best, corresponding to the need for 3-6 carat rough. 1) Under THE HPHT method, domestic head manufacturers have broken through the 3-6 carat blank technology, and the large-carat technology is mature; 2) Under the CVD method, the blank is relatively larger and has certain advantages.
The economic effects are similar: the payback period of equipment investment is within 2 years. 1) Under the HPHT method, the unit price of 850 press is about 2 million yuan, the annual output value is about 1.5 million yuan, and the payback period is 1.33 years. 2) Under the CVD method, the unit price of high-end equipment is about 3 million yuan, the annual output value is about 2.1 million yuan, and the payback period of investment is 1.43 years.