Materials and Methods
Eighteen samples (Table 1) were received from Mr. Thamrong Charasaiya. All samples were of a bright blue color and weighed between 0.35 to 4.99 carats. Internal features were examined using standard gemological (Gemolite) microscopes and horizontally oriented immersion microscopes and captured at up to 180 x magnifications with a Nikon SMZ 1500 system using darkfield, brightfield, and diffused illumination, together with a fiber-optic light source for oblique illumination when necessary.
Chemistry was determined using a Thermo Scientific ARL QUANT’X EDXRF Spectrometer, using an X-ray tube voltage up to 50kV. In this study, the voltage was set to 20 keV, current of 0.14 mA, no filter and a count time of 100 seconds in vacuum. For a more detailed analysis, LA-ICP-MS technology with a Thermo Fisher scientific iCAP-Q induced coupled plasma - mass spectrometer (ICP-MS) coupled with a Q-switched Nd:YAG Laser Ablation (LA) device operating at a wavelength of 213 nm, was used. Laser conditions were 55 μm diameter laser spots, a fluency of around 8±1 J/cm2, and a 15 Hz repetition rate. Various spots were analyzed on each wafer in different color areas. For the ICP-MS operations, the forward power was set at ~1350 W and the typical nebulizer gas flow was ~0.80 L/min. The carrier gas used in the laser ablation unit was helium, set at ~0.50 L/min. The criteria for the alignment and tuning sequence were to maximize beryllium counts and keep the ThO/Th ratio below 2%. NIST 610 and 612 glasses were used for calibration standards. All elemental concentrations were calculated by applying 24Mg as an internal standard, with Mg concentration calculated from the theoretical value of spinel (17.08 wt%).
Materials and MethodsEighteen samples (Table 1) were received from Mr. Thamrong Charasaiya. All samples were of a bright blue color and weighed between 0.35 to 4.99 carats. Internal features were examined using standard gemological (Gemolite) microscopes and horizontally oriented immersion microscopes and captured at up to 180 x magnifications with a Nikon SMZ 1500 system using darkfield, brightfield, and diffused illumination, together with a fiber-optic light source for oblique illumination when necessary.Chemistry was determined using a Thermo Scientific ARL QUANT’X EDXRF Spectrometer, using an X-ray tube voltage up to 50kV. In this study, the voltage was set to 20 keV, current of 0.14 mA, no filter and a count time of 100 seconds in vacuum. For a more detailed analysis, LA-ICP-MS technology with a Thermo Fisher scientific iCAP-Q induced coupled plasma - mass spectrometer (ICP-MS) coupled with a Q-switched Nd:YAG Laser Ablation (LA) device operating at a wavelength of 213 nm, was used. Laser conditions were 55 μm diameter laser spots, a fluency of around 8±1 J/cm2, and a 15 Hz repetition rate. Various spots were analyzed on each wafer in different color areas. For the ICP-MS operations, the forward power was set at ~1350 W and the typical nebulizer gas flow was ~0.80 L/min. The carrier gas used in the laser ablation unit was helium, set at ~0.50 L/min. The criteria for the alignment and tuning sequence were to maximize beryllium counts and keep the ThO/Th ratio below 2%. NIST 610 and 612 glasses were used for calibration standards. All elemental concentrations were calculated by applying 24Mg as an internal standard, with Mg concentration calculated from the theoretical value of spinel (17.08 wt%).
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