|
|
Diamond was discovered to be carbon in 1796, and it took more than 150 years from that time until a method of diamond synthesis was invented. The secret was pursued by many scientists but not unlocked until the 1950s, when diamond was synthesized almost simultaneously by Swedish and American researchers. Pressures of over 55,000 atmospheres and 1400C, plus molten iron to facilitate the change from graphite to diamond, were necessary. Now some 80 tons of synthetic diamonds are produced annually by General Electric, De Beers, and many others for industrial firms.
Herbert Strong (right) and J. E. Cheney working on GE's then new 1,000-ton press, capable of achieving experimental pressures of 100,000 atmospheres, in 1955. The GE team used the press to grow diamonds prior to the announcement of diamond synthesis on February 15, 1955. click to zoom in
|
From the time Smithson Tennant showed that diamond was carbon, experimenters tried to synthesize diamond from graphite or lamp black. Attempts over the next 150 years were all fruitless, although the trend toward experiments at high pressure and temperature were in the right direction. The invention of tungsten carbide in the 1930s provided a material that could achieve the pressure containment necessary for growing diamond. Experiments in the 1940s by Harvard professor Percy Bridgman were unsuccessful, but finally in the early 1950s two teams succeeded. The first was led by Baltazar von Platen, at the Allmanna Svenska Elektriska Aktiebolaget (ASEA) Laboratory in Stockholm, Sweden, in 1953, but this initial success was not publicized or published. Thus, on February 15, 1955, the General Electric team of Francis Bundy, Tracy Hall, Herbert Strong, and Robert Wentorf claimed credit for the first reproducible transformation of graphite to diamond. GE went on to become the largest producer of synthetic diamond; De Beers follows, with many other manufacturers also contributing to the annual output of synthesized diamonds.
 The
schematic diagram at left shows the geometry of the growth capsule for growing large diamonds. Small diamonds are placed at the bottom of the active part of the capsule as seeds for the growth of large diamonds. Graphite dissolves into molten metal, usually iron or cobalt, and precipitates as diamond on the seeds at the colder bottom. It takes a few days to grow diamonds a few mm. across. Micro-diamond growth is much faster, taking a few tens of minutes.
Photographs courtesy GE Corporate Research and Development
|
