Geoscience Reference
In-Depth Information
that time, diamond was thought of as a hard glass. When cutting technology was
discovered in the seventeenth century, man began to use diamond as an aristocratic
jewel. Today, an estimated one billion US dollars of diamonds are bought annually
via the Internet.
Industrial application of diamonds started in the beginning of the twentieth
century and the first application of diamond was in a grinding wheel. The wheel
consisted of diamond powder with metal (or polymer) binder, which can be called
a refined material.
In 1955, diamond was produced artificially and the success was closely related
to the discovery of high-pressure technology by General Electric. However, several
thousand crystals were required to produce one carat. Thus, these small crystals
were found to be more practical for grinding purpose than the crushed bort that had
been used for years before. But in 1970, General Electric announced the production
of jewelry grade synthetic diamond in sizes up to slightly over one carat in the
rough. This technology was later applied to the production of sintered diamond,
which can be categorized as a refined artificial material. This technology was also
applied to the production of cubic boron nitride, which is a completely artificial
material. The greatest discovery related to diamond was its synthesis from the gas
phase for the first time by Deriaguin et al. [22] in 1976 and Matsumoto et al. [23]
in 1982. Although many methods have been reported for diamond synthesis from
the gas phase, all methods are basically modified Chemical Vapor Deposition
(CVD) methods. Diamond made by these methods, therefore, is referred to as CVD
diamond. Some three decades ago, no one could have conceived that diamond
would become an electronic material. People considered a diamond mainly as a
jewel, but the discovery of diamond synthesis from the gas phase changed that
image drastically.
The authors believe that the unique properties of diamond contributed to the
enhancement of research on the material, resulting in a wide range of research with
hope for new applications.
There are three major processes of diamond synthesis: (i) high-pressure
high-
temperature (HPHT), (ii) CVD (which are at least 50 and 40 years old, respectively),
and (iii) low-pressure solid-state source (LPSSS). Bundy et al. [24] at General Electric
Co. announced their success in synthesizing diamond under HPHT conditions [25] .
A few tons of industrial diamond abrasive grains are made this way each year in vari-
ous factories around the world. De Vries [26] reviewed CVD diamond synthesis in
detail. Roy and coworkers [27,28] have worked out the growth technology for dia-
mond using LPSSS method in detail. Figure 9.1 shows the schematic diagram compar-
ing three popular methods of diamond synthesis [28] .
It is interesting to note that the nucleation and growth kinetics had won out over
thermodynamics. The CVD process represents the field outside the PT stability
region for diamond. Figure 9.2 shows the phase diagram for carbon crystalline
phases. The equilibrium data for material trapped in inclusions in diamonds indi-
cates final temperatures of 600
31] .
Several researchers have argued a case for the possibility of growing diamonds
under hydrothermal conditions [31,32] . Szymanski et al. [29] have carried out dia-
mond synthesis using relatively low-pressure liquid phase epitaxy on seeds, in an
800 C and pressures up to 10 Mpa [29
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