Papers by Keyword: Topaz

Abstract: In the present work, colorless topaz was designed and developed a dosimeter for routine application. The samples were irradiated with gamma from ⁶⁰Co at dose range 50 - 400 Gy and investigated by thermoluminescence (TL) and electron spin resonance (ESR). The TL grow curve of topaz were revealed two trapping levels at temperature 150 °C and 225 °C. The ESR signals of topaz shown that the g value at 1.966 and 2.012 due to Ti³⁺ and (AlO₄)⁰ center, respectively. The intensities of TL and ESR were increased with increasing dose. The percentage error of dose from TL and ESR signal were 8 and 3, respectively. These experiment indicated that the colorless topaz could be used as a dosimeter.

Abstract: The purpose of this research was to investigate physical properties, configuration and color of topaz. Topazes were irradiated with electron beam linear accelerator at different dose from 40 to 180 MGy. The color of topaz was analyzed by UV-vis and it was shown that the color of topaz was becoming strong color with increased electron beam dose. Crystal structure and function group of topaz were characterized by X- ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the topaz has orthorhombic structure and no other crystalline. After irradiated, topaz released OH indicating higher crystallinity of topaz and this was confirmed with the results of electron spin resonance (ESR). Electron beam dose response of topaz was investigated. ESR results showed that the Al³⁺ ion was substituted in Si⁴⁺ site and Ti³⁺ impurity in Al⁴⁺ site and this result corresponds to the results of FTIR. The experiment result indicated that electron beam could be making defect on crystal structure and color enhancement of topaz.

Abstract: Mullite whiskers were obtained by thermal decomposition of powders of natural topaz, pure and doped with 3 and 5% in weight of La₂O₃ and Y₂O₃, at the temperatures of 1300 and 1400^°C, for 1h, in air. Pure and doped mullite whiskers showed a molar ratio Al₂O₃: SiO₂ close to 2:1, rich in alumina. The aspect ratio (AR) of whiskers varies with dopant concentrations and temperatures. The ARs for pure whiskers were 28 and 31.5, at the temperatures of 1300 and 1400°C, respectively, showing no glassy phase. For the doped whiskers, there were observed a reduction in the ARs, ranging from 14.13 to 16.10 (3 and 5% La₂O₃) and from 6.32 to 7.35 (3 and 5% Y₂O₃), for the temperatures of 1300 and 1400°C, respectively. The Y₂O₃ was not entirely incorporated, and part of it formed Y₂Si₂O₇ and Y₂O_3-δ, with δ = 0.33 according to quantitative X-ray diffraction analysis (XRD analysis) with the presence of small amount of vitreous phase.

Abstract: To find out the characteristics, color’s genesis and identifying features of TCF (Thermal Color Fusion) topaz, and the differences between TCF topaz and the past coating topaz products, this article takes TCF topaz, which appeared recently in the market, and two other common generation of coatings topaz sample as the object of study, and use a variety of gemology testing instruments and wide spectrum and narrow spectrum of X-ray photoelectron spectroscopy to analyze the gemology feature, surface structure and composition of the sample, the results shows that: the difference of the surface layer composition is the basic reason for the color difference of these samples, but the film structure and thickness of the sample do not have a big impact to the color. This article has also carried on the examination to the sample durability, at the same time analyzing and comparing a variety of optimized topaz production process. The TCF topaz technology has the advantages of both two kinds of process of coating and the diffusion, TCF topaz is rich in color compared to diffusion and irradiation product, it is better than irradiation product on high temperature resistance and radioactive residues.