• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.6
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• pp.290-297
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• 2004

The color enhancement of natural ruby produced from Mong Hsu were carried out by the heat treatment using gas diffusion. The natural ruby in this paper has a colored patch of which the color ranges from blue to a color close to black. The most favorable heat treatment conditions were as follows; range of temperature $1400~1600^{\circ}C$, duration 12 hrs, $O_2$ atmosphere. The color tone of ruby obtained under the optimum conditions was overall clear red by partial removal of colored patch. From EPMA results, part of blue or black colored patch within ruby were found to occur by charge transfer between $Fe^{2+}{\;}and{\;}Ti^{4+}$ . These results are consistent with the XRF that contents of $Fe(Fe^{2+}{\;}or{\;}Fe^{3+}$) and $Ti^{4+}$ ion to cause a blue or black colored patch after heat treatment became slightly less than with non-treated ruby. The silk formed on the surface of ruby heat treated for 12 hrs at $1700^{\circ}C$ were found to be generated by re-crystallization of rutile $TiO_2$ by XPS analysis.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.2
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• pp.90-94
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• 2009

Mong Hsu rubies from Myanmar were heat treated in oxidizing(oxygen) atmosphere at $1650^{\circ}C$ for 1 hour. The investigations of the micro-structural defects in the samples before and after heat treatment have been carried out by the variety of analysis techniques of FTIR, UV-VIS-NIR and SEM-EDS. It was found that after heat treatment the dark blue cores region were disappeared and turned to orange red color with the presence of the dense cloudy brownish colored tiny particles in and near former blue zoning. As-received ruby samples only revealed the presence of FTIR absorption peaks of diaspore, boehmite and O-H stretching, at 1986, 2115 and $3078/3319\;cm^{-1}$ respectively. The UV-VIS-NIR absorption of as-received and heat treated ruby samples similarly showed peaks at 405, 554 and 693 nm associated with $Cr^{3+}$, but for the same samples, the absorption peak of heat-treated ruby samples at 693 nm was somewhat stronger than that of the untreated ruby samples. Especially the presence of $Cr^{3+}$ peaks at 659 and 675 nm was found obviously in as-received ruby samples only. The SEM-EDS investigation disclosed the micro-porous defect structures commonly related to the core regions of the untreated ruby samples, which after heat treatment in an oxidizing environment those defect features have been dissolved into the host phase resulting in the lightening or disappearance of the dark coloration of ruby core.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.2
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• pp.55-59
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• 2011

Mong Hsu rubies from Myanmar include typically the dark core and blue patch but most of the previous research has merely focused on the dark core. This work is aimed to understanding clearly the characteristic of the dark core and blue patch of Mong Hsu rubies. It was found from the FTIR analysis that the dark core and blue patch region showed the absorption peaks of boehmite ($1986\;cm^{-1}$), diaspore ($2115\;cm^{-1}$) and water ($3400{\sim}3900\;cm^{-1}$) but the absorption peaks of O-H stretching ($3309\;cm^{-1}$ and $3078\;cm^{-1}$) were found only in blue patch region. The UV-VIS-NIR analysis of the dark core region revealed the stronger absorption of $Cr^{3+}$ at 405 and 554 nm compared to the blue patch region. In range of 600~800 nm, the UV absorption characteristic at 659, 675 and 693 nm assigned to $Cr^{3+}$ of core group samples is distinct from that of blue patch. The SEM-EDS examinations disclosed the existence of lots of micro-cracks and pores in the core regions compared to blue patch region.