In 1970s GE pioneered the gem diamond growth by using belt apparatuses that were capable to sustain a pressure of 5.5 GPa (55,000 time of atmospheric pressure) and a temperature of 1300°C. The diamond was formed by feeding micron diamond fines to a molten catalyst of iron nickel alloy (Invar). The diamond fines were dissolved in the liquid and precipitated onto a diamond seed (Fig. 11.5).
GE diamonds were 1-2 carats after polishing. They could be colored or colorless depending on the dopant used in the catalyst. For example, the dopant free catalyst proceeded yellow diamond due to the incorporation of nitrogen from air. By adding a few PPM (part per million) of a nitrogen getter (e.g. titanium or zirconium), the diamond turned colorless (Fig. 11.6).
GE's gem diamond growth was costly and the process very slow. In 1980s, Sumitomo Electric used the similar technique to
Diamond Nanotechnology: Synthesis and Applications by James C Sung & Jianping Lin
Copyright © 2009 by Pan Stanford Publishing Pte Ltd
grow larger crystals. In 1990, De Beers grew gem diamond larger to more than 10 carats per crystal (Figs. 11.7 and 11.8).
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