Crystallization experiments on amorphous silicates with chondritic composition: Quantitative formulation of the crystallization

K. Murata, H. Chihara, A. Tsuchiyama, C. Koike, T. Takakura, T. Noguchi, T. Nakamura

研究成果: ジャーナルへの寄稿学術誌査読

26 被引用数 (Scopus)

抄録

In order to make clear crystallization process of silicates in circumstellar environments of oxygen-rich young stars, we have performed laboratory experiments on crystallization of a silicate material by use of a synthetic sample with the chondritic composition for the first time. The aim of this work is to analyze the crystallization process quantitatively using the amorphous material with the chondritic composition. The starting amorphous material was synthesized by the sol-gel method. The sample was heated at 660°-1200°C for 0.5-12 hr to investigate the temperature and time dependence of the crystallization. The run products were analyzed using infrared absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Olivine [(Mg, Fe)2SiO4] was mainly crystallized from the starting amorphous material. We performed infrared spectral fittings of the heated samples using individual spectra of olivine and amorphous silicate, and estimated the degree of crystallization quantitatively. The time-dependent crystallization process could be formulated using the Johnson-Mehl-Avrami equation with the power of about 1.2, which is consistent with theoretical crystallization model of three-dimensional diffusion-controlled growth from a state that a number of nuclei is constant. The constant number of nuclei corresponds to the starting material, which contains crystallites of magnetite (Fe3O4) and ferrihydrite (5Fe2O3 · 9H2O) as nucleation sites of olivine crystals. From the quantitative analyses, we suggest that crystallization processes in circumstellar regions should depend on properties of the interstellar amorphous silicates such as existence of crystallites and/or FeO content.

本文言語英語
ページ(範囲)285-293
ページ数9
ジャーナルAstrophysical Journal
668
1 I
DOI
出版ステータス出版済み - 2007
外部発表はい

!!!All Science Journal Classification (ASJC) codes

  • 天文学と天体物理学
  • 宇宙惑星科学

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