Laser Fluorination oxygen extraction system for stable isotope analysis of rock forming minerals
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概要
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High vacuum line made of stainless steel and computer controlled pneumatic valves attached with a 40W C0_2 laser system capable of extracting oxygen from rock forming silicate and oxide minerals in a BrF_5 atmosphere was fabricated. The vacuum line can resist the hazardous BrF_5 reagent used for disintegrating the Si=O bonds in minerals. The oxygen, thus released, is converted to C0_2 in an 0_2→C0_2 converter using graphite heated at 〜 650℃ in a platinum foil holder. We present here the results on vacuum checks, initial setting of laser, reproducibility of the 02→C0_2 converter, background measurements during fluorination and precautions in handling the BrF_5 reagent. The present system can withstand high vacuum conditions without appreciable leaks for intervals required to complete one cycle of measurement. However, due to the toxic nature of BrF_5 reagent, sizeable amount of background 0_2 was released during the pre-fluorination of the system(〜 0.2-0.3 μmoles of 0_2 for 30 minutes of fluorination). Repeated fluorination of the system considerably reduced the background 0_2, however, could not be completely eliminated. Tests were also made for the functional setting of the 0_2→C0_2 converter using ampoules of external 0_2 gas. Optimum conditions for conversion were determined ; temperature of 〜650℃, graphite grain size fraction of 1〜2 mm and reaction time of 15 minutes. NBS-28 quartz standard were pre-fluorinated overnight in the reaction chamber in order to reduce the background effect. δ^<18>0_<SMOW> values of 14 measurements with varying amounts of NBS-28 quartz gave 10.06 ± 1.15‰. The results indicate that a minimum sample size of 250 μg is essential to overcome the background effects. However, this amount is almost four times less than the usual amount of sample used in laser fluorination laboratories elsewhere. Also, it was found that the laser beam should be defocused for precise measurement of small grain size samples. Thus, at present, the presence of background 0_2 released in the reaction chamber is hindering the application of micrometer scale measurement of oxygen isotope measurements in minerals. In order to improve the present system, the background within the reaction chamber should be reduced further.
- 静岡大学の論文
著者
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Satish-Kumar M.
Institute of Geosciences, Shizuoka University
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Wada Hideki
Institute of Geosciences, Shizuoka University
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Matsui Takafumi
Institute Of Geosciences Shizuoka University
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KATO Kazuhiro
Institute of Geosciences, Shizuoka University
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Satish-kumar M.
Institute Of Geosciences Shizuoka University
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Wada Hideki
Institute Of Geosciences Faculty Of Science Shizuoka University
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Satish-kumar M.
Institute Of Geoscience Shizuoka University
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Kato Kazuhiro
Institute Of Geosciences Shizuoka University
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