Synthetic diamond market

Frequently, when large, high-quality synthetic diamonds are discussed, the question of their potential use as gemstones is raised. At the time of writing, none of the major manufacturers of synthetic diamonds markets material for gem use. How-... 

Diamond. Diamond [7782 0-3] is the hardest substance known (see Carbon, diamond, natural). It has a Knoop hardness of 78—80 kN/m (8000—8200 kgf/m ). The next hardest substance is cubic boron nitride with a Knoop value of 46 kN/m, and its inventor, Wentorf, beheves that no manufactured material will ever exceed diamond s hardness (17). In 1987 the world production of natural industrial diamonds (4) was about 110 t (1 g = 5 carats). It should be noted that whereas the United States was the leading consumer of industrial diamonds in 1987 (140 t) only 260 kg of natural industrial diamonds were consumed this is the lowest figure in 48 years (4), illustrating the impact that synthetic diamonds have made on the natural diamond abrasive market. 

Many ceramic applications are high value and small volume, so energy expenditure is high. Ferroelectric magnets, electronic substrates, electrooptics, abrasives such as silicon carbide and diamond, are examples. Diamond is found naturally, and made synthetically by the General Electric Company at high pressure and temperature. Synthetic diamonds for abrasives require less energy to make than the value in Table 4 nevertheless, the market is carefully divided between natural and synthetic diamonds. 

In the last 40 yr, the development of synthetic diamond in various forms has fueled a revolution in the use of diamond as an engineering material. The process of HPHT diamond synthesis was responsible for stunning growth in the abrasives market. During that time, the world s consumption of diamond abrasive materials increased from 5 to over lOOtons/yr. 

Carbon in the structural form of diamond is the only element used industrially as a hard material. Each year about ten tons of natural diamond and about twenty tons of synthetic diamond (produced via high temperature high pressure synthesis) are marketed as hard materials. While pure diamond is transparent, a yellow tint results from the replacement of some carbon atoms by nitrogen, and a blue, yellow, or even green tint through substitution of carbon by boron atoms. Polycrystalline diamond with impurities, used as an abrasive, is often black. 

High-pressure synthetic diamond, taking an increasing share of the industrial market, particularly in wear and abrasive applications (reviewed in Ch. 12). 

Until World War II, the diamond business was relatively simple, consisting only of natural diamond. The great majority of the market was gemstones and industrial applic2rtions were limited. The advent of synthetic diamond and the rapid rise of industrial applications have drastically altered the industry, and more changes will undoubtedly take place in the future such as the development of CVD diamond (Ch. 13). The challenge and potential impact of this new technology are well understood by the dieimond producers. 

The growth of high-pressure synthetic diamond is shown in Fig. 12.8.( i The market is now of considereible size with an estimated production of seventy tons in 1992, all for industrial applications. The largest consumer is the U.S., closely followed by Japein and Western Europe. 

High-pressure synthetic diamond, because of its high purity and uniformity, has taken an increasing share of the industrial diamond market and has replaced natural diamond in many areas. 

The applications of natural and high-pressure synthetic diamond were reviewed in Ch. 12. Although these eipplications have a very large market, particularly in gemstones, they are limited because of the small size and... 

Spinel is a colorless magnesium aluminate (MgAl204) of cubic structure. It is hard and durable, but, like white sapphire, it is not a good diamond substitute because it has a low refractive index and lacks brilliance. However, it is readily doped to produce other gems of various colors. Artificial ruby, for example, is often natural red spinel, and most synthetic blue sapphires on the market are actually blue spinel. 

Contrary to the new carbon materials presented so far, diamond films are a product that is already being employed with many variants in large scale applications. Especially the coating of tools and fast turning parts represents a considerable market, but there are also electronic uses and synthetic optical windows on offer. Some of the important fields of appHcation are presented in more detail below. 

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