Commercial Production Of Diamond Superabrasives

Natural diamond was the only superabrasive capable to machine tungsten carbide tools before 1957. During the World War I, the consumption of natural diamond surged to 0.4 ton a year. When World War II broke out, this demand increased drastically to 4 tons per year. At then only South Africa can export natural diamond, so US has stocked piled strategic supply of natural diamond that was released only after 2000.

In 1941, Percy Bridgman was supported by General Electric, Norton, and Carborandum to explore the possible means of making diamond. This attempted was interrupted by World War II. After the war, Norton continued the trial but without success. In 1951, GE renewed the attempt and it eventually succeeded in making the first diamond in 1954. In 1957, GE introduced the first synthetic diamond superabrasive at its Carboloy department that mass manufactured cemented tungsten carbide. At then only

Figure 4.14. Different precursors of carbon may transform into diamond with various activation energies. The term "flake" refers to the recrystal-ized graphite micro particles that are suspended in a molten metal catalyst. These flakes may be rhombohedral graphite that possesses the layer configuration easily puckerable into diamond structure.

imperfectly grown diamond was used for grinding cemented tungsten carbide. GE soon perfected the diamond growth technology and it continually introduces larger and better grown diamond for making grinding wheels and saw blades.

Because natural diamond was formed billions years ago, its properties are fixed, the only modification can be made is to sort the crystals by size and shape. However, different industrial applications may require diamond to break down in different mode that cannot be satisfied by natural diamond. On the other hand, synthetic diamond can be grown at different rates so their strengths vary. This variation can allow the adjustment of break down mode. Consequently, synthetic diamond became more desirable for most industrial application. Hence, in 1970, the world consumption of synthetic diamond eventually exceeded natural diamond. Today, less than 5% industrial diamond is still served by natural diamond.

In 2002, more than 400 tons of diamond grits (up to 1 mm in size) were made as superabrasives, such as used in circular saws, drill bits, or grinding wheels. Almost all such diamonds are synthesized under high pressure (up to 6 GPa) by converting graphite using a molten metal catalyst (e.g. an iron alloy).

Diamond grits may also be sintered at high pressure to form plates of polycrystalline diamond (PCD). PCD products are widely used as cutting tools, drill bits, and wire dies.

Large single crystals can also be synthesized under high pressure. Such crystals (up to 1/3 of a carat) are commercially available

Figure 4.15. High pressure synthesized sub-carat single crystals manufactured by Element Six (Monocrystals) (left) and Sumitomo Electric (Sum-idia) (right).

as cutting tools (e.g. De Beers' Monocrystals) or heat spreaders (e.g. Sumitomo's Sumidia) (Fig. 4.15).

Some 20 countries are engaged in high pressure syntheses of diamond on commercial scale. They include United States, South Africa, Ireland, Sweden, Germany, France, Greece, United Kingdom, Russia, Ukraine, Romania, Poland, Ctsechslovikia, Alme-nia, Japan, China, North Korea, South Korea, Malaysia, and India.

In the production history of synthetic diamonds, the follow-ings are major milestones. In 1957, GE starts commercial production, before then natural diamond (4 tons) was the only choice of industrial diamond. In 1970, synthetic diamond (20 tons) outweighs natural diamond as the dominant industrial diamond. In

Figure 4.16. Three views of De Beers production plants for diamond synthesis. These pictures disclose the evolutionary trend of press types and plant layouts for the commercial production of industrial diamonds. They were taken at three geographical locations in the last three decades. Top, early small presses used by De Beers in Springs, South Africa; middle, 10000 T presses in Robersfors, Sweden; Bottom, 10000 T presses in Shannon, Ireland (closed in 2001).

Figure 4.16. Three views of De Beers production plants for diamond synthesis. These pictures disclose the evolutionary trend of press types and plant layouts for the commercial production of industrial diamonds. They were taken at three geographical locations in the last three decades. Top, early small presses used by De Beers in Springs, South Africa; middle, 10000 T presses in Robersfors, Sweden; Bottom, 10000 T presses in Shannon, Ireland (closed in 2001).

1993, China became the world leading producer (40 tons) of synthetic diamond in quantity.

China produces the most of synthetic diamond under high pressure (about two/third of the world's total output), but mainly in low-grade materials (about one-tenth of the world's value of superabrasives). Ireland has been the largest exporter of industrial diamonds due to the presence of both General Electric Company of USA, and De Beers Company of South Africa (Fig. 4.16), the two most prominent manufacturers of industrial diamonds.

The major diamond makers are listed in Table 4.5 along with their starting year of research and manufacturing.

Although there are over 400 companies (China has more than 400 of them) that are engaged in commercial production of diamond superabrasives, only General Electric and De Beers were capable of making premium saw diamond that was typically more than twice as valuable as other diamond grits (e.g. for making grinding wheels). However, in 1989 the author designed a manufacturing plant for Iljin Diamond and transferred manufacturing

Table 4.5. History and scale of high pressure diamond synthesis

Country

Research success

Production implementation

2007 Quantity manufactured (tons)

China

1962

1966

800

U.S.A.

1954

1957

60

South Africa

1959

1961

60

Sweden

1953

1962

40

Russia/Ukraine

1960

1962

40

South Korea

1987

1989

40

Japan

1961

1963

20

Germany

1964

1967

20

Ireland

1980

1984

20

Total

1100

Source: Notes: De Beers' manufacturing sites were in South Africa's (Springs), Germany (Winter, discontinued in 2001), Sweden (Scantidiamont), and Ireland (Shannon, discontinued in 2001). General Electric's output included that manufactured in USA (Worthington) and Ireland (Dublin).

Source: Notes: De Beers' manufacturing sites were in South Africa's (Springs), Germany (Winter, discontinued in 2001), Sweden (Scantidiamont), and Ireland (Shannon, discontinued in 2001). General Electric's output included that manufactured in USA (Worthington) and Ireland (Dublin).

technology of making premium saw grit. Iljin Diamond has since become the third largest manufacturer of saw diamond in the world.

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