• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.614-619
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• 2012

We investigated color and graphite layer formation on the surface of Type I tinted brown diamonds exposed for 5 minutes under a high-pressure high-temperature (HPHT) condition in a stable graphite regime. We executed the HPHT processes of Process I, varying the temperature from $1600^{\circ}C$ to $2300^{\circ}C$ under 5.2 GPa pressure for 5 minutes, and Process II, varying the pressure from 4.2 to 5.7 GPa at $2150^{\circ}C$ for 5 minutes. Optical microscopy and micro-Raman spectroscopy were used to check the microstructure and surface layer phase evolution. For Process I, we observed a color change to vivid yellow and greenish yellow and the growth of a graphite layer as the temperature increased. For Process II, the graphite layer thickness increased as the pressure decreased. We also confirmed by 531 nm micro-Raman spectroscopy that all diamonds showed a $1440cm^{-1}$ characteristic peak, which remained even after HPHT annealing. The results implied that HPHT-treated colored diamonds can be distinguished from natural stones by checking for the existence of the $1440cm^{-1}$ peak with 531 nm micro-Raman spectroscopy.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.221-225
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• 2012

It is possible to enhance the color of the natural diamond with a high pressure high temperature(HPHT) process. We employed a pyrophyllite tube cell and cubic press apparatus for HPHT treatment on the brown colored Type II (5.6 GPa/ $1700^{\circ}C$/ 52 min), and Type I aB(5.6 GPa/ $1650^{\circ}C$/ 30 min) diamond samples. We investigated the microstructure, Types, fluorescence, properties of the diamonds with an optical microscopy, FT-IR, photoluminescence(PL) spectroscopy, Diamond-View, and micro-Raman spectroscopy. Two tinted brown diamonds changed into colorless just after the HPHT process. Optical microscopy showed that no crack and significant inclusion evolution occurred during the HPHT process except the small graphite spot appeared in Type I aB sample. FTIR spectrum confirmed that no Type, amber center, and platelet defect change with the HPHT treatment. Diamond-View could not distinguish the HPHT treated diamonds from the naturals. PL spectroscopy showed that N3 and H3 color centers remained even after HPHT process. Consequently, we successfully changed the color of diamonds into colorless by 5.6 GPa HPHT process.