Critical cooling rates for glass formation in levitated Mg2SiO4-MgSiO3 chondrule melts
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- NAGASHIMA Ken
- Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University Present address: Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University
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- MORIUCHI Yoshinobu
- Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University
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- TSUKAMOTO Katsuo
- Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University Center for Interdisciplinary Research, Tohoku University
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- TANAKA Kyoko K.
- Institute of Low Temperature Science, Hokkaido University
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- KOBATAKE Hidekazu
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
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説明
Using a gas-jet levitator, Mg-silicate glasses containing forsterite (Mg2SiO4) or enstatite (MgSiO3) are obtained, with a particle diameter of 2 mm. The levitator aids in floating the melt droplets using a gas-jet. It can transform the levitated droplets into crystals or glass during cooling. The critical cooling rate for glass formation (Rc) for levitated Mg-silicate melts («10-1-102 K/s) is considerably lower than that for non-levitated melts (>103 K/s) because of the inhibition of crystallization by the sample holder in the former. Furthermore, the crystallization temperature of the levitated Mg-silicate melts is very low (∼ 900 °C). Chondrules in chondrites are assumed to have been formed from the melt droplets in such a levitation environment. Several researchers have concluded that Rc for a chondrule melt held by a platinum wire is equal to the upper limit of the cooling rate for the chondrule melt, estimated to be ∼ 1000 K/h. However, in a levitation environment, SiO2-rich melts do not crystallize at this cooling rate. We conclude that the previously proposed maximum cooling rate for chondrule melts has been greatly overestimated. We infer that spontaneous crystallization of a completely melted chondrule precursor is extremely difficult, and almost all chondrules turn into glass, despite a low cooling rate. For crystallization of chondrule melts, it is necessary that the precursor of the chondrules should be partially melted or the completely melted precursor should be in contact with nebular dust.
収録刊行物
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- Journal of Mineralogical and Petrological Sciences
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Journal of Mineralogical and Petrological Sciences 103 (3), 204-208, 2008
一般社団法人 日本鉱物科学会
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詳細情報 詳細情報について
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- CRID
- 1390001206545698304
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- NII論文ID
- 10020985464
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- NII書誌ID
- AA11460926
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- ISSN
- 13493825
- 13456296
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- 本文言語コード
- en
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- データソース種別
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- JaLC
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