DIRECT PROCESS MAKES DIAMONDS FROM GRAPHITE Now GE does it without catalysts, uses heat and static pressure
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GRAPHITE END DISK
PYROPHYLLITE. MOO, TH02, OR AL,O1
GRAPHITE CYLINDER
I
$1 shows design of belt vice which i s placed in hydraulic press.
Conical pistons (ten and
right) push intochamber(center). Graphite, from which diamond
forms, i s ploced in aperture ot center of chamber.
A typical
cylindrical sample for use in the belt anmaratus i s shown in
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INDUSTRIAL AND ENGINEERING CHEMISTRY
eneral Electric Research Laboratory is converting carbon from its ordinary graphite form directly into industrial diamonds in a nonexplosive technique which uses no catalyst. Pressures and temperatures are about three times greater than those required for the original diamond-making process, where a metal catalyst helped achieve the transition of carbon atoms from graphite to diamond crystal structure. The process has important implications for diamond-making technology, but perhaps most significant is the achievement of rearranging carbon crystal structure by pressure and temperature alone, a feat many scientists doubted would ever be accomplished. This success is a big step forward in understanding the atomic forces at work in crystalline materials.
G
Diamond-Making Process
General Electric tint announced its synthetic diamonds in 1955, made and sold them commerciallyin 1957, and revealed some process details in 1959 when a Government secrecy order was lifted. That process used a metal catalyst, pressures from 800,000 to 1,800,000 p.s.i., and temperatures from 2200’ to 4400’ F. The combination of catalyst, pressure, and temperature has since provided a substantial and growing share of the nation’s industrial diamond supply. Now, as a result of new techniques developed by Dr. Francis P. Bundy, it is possible to attain pressures and temperatures so high that the metal catalyst is no longer needed. The new process uses an improved ultrahigh pressure apparatus in a large hydraulic press. The apparatus is a modification of the GE “belt” design developed by H. T. Hall, arranged for greater flank support of its piston elements and higher compression of the sample. This apparatus can achieve simultaneously temperatures above 5000’ K. (9000O F.) and pressures up to 200 kiloban (2.9 million p.s.i.)equivalent to pressures believed to exist 350 miles beneath the earth’s surface. Although refractory materials are used to surround the graphite specimens, temperatures reached are so high that transient heating is used to minimize melting or chemical reactions of the wall materials. Graphite specimens are heated by discharging a large electrolytic capacitor through the sample. Electrical connections are made through the pistons. In carrying out the process, the sample is inserted in the pressure apparatus, pressure in the chamber is raised to the desired value by forcing the pistons together with the hydraulic press, and the sample is flash-heated by the capacitor discharge. Afterward, the pressure is lowered, and the sample can be removed for examination.
New Carbon Knowladoe
The diamond process apparatus is also the key to new understanding of carbon crystal structure, as well as the structure of many other materials. In the course of his studies, Dr. Bundy located the triple point for equilibrium between diamond, graphite, and liquid carbon, and determined the melting point of graphite all the way from the graphite-liquidvapor triple point to the diamond-graphite-liquid triple point (I&EC, November 1962, p. 5). Many other important observations regarding the crystalline behavior of carbon will be published in the Journal of Chcmical Physics. Dr. Bundy admits that discovery of the direct transition from graphite to diamond came as something of a surprise, because there had been so many previous unsuccessful attempts. At least one theory had been put forward saying that this direct transition might never occur. Now there is no doubt that it can, and many substances other than carbon are being put into the new pressure chamber. -J.
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H. OLIN, ASSISTANT EDITOR
DIAMOND
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Presswe-lmpmatwc phase diagram p e w i t s best concept of carbon cpuilibrio, bared on Dr. Bundy’s work and on preuiotrr c x p w i n a t r by o r b s . Solid 111 at upper left of diagrnm isproposed by Dr. Bundy as a metallic stdc, 75 to 20% more dmsc than diamond VOL 55
NO. 1
JANUARY 1963
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