Direct observation of crystallization of amorphous Mg-bearing silicate grains into Mg (forsterite)

Free access article

Issue		A&A Volume 436, Number 1, June II 2005


Page(s)		165 - 169
Section		Interstellar and circumstellar matter
DOI		http://dx.doi.org/10.1051/0004-6361:20042374

A&A 436, 165-169 (2005)
DOI: 10.1051/0004-6361:20042374

Direct observation of crystallization of amorphous Mg-bearing silicate grains into Mg $\mathsf{_{2}SiO_{4}}$ (forsterite)

K. Kamitsuji, T. Sato, H. Suzuki and C. Kaito

Department of Nanophysics in Frontier Projects, Ritsumeikan University, Kusatsu-shi, Shiga 525-8577, Japan
e-mail: rp007988@se.ritsumei.ac.jp

(Received 17 November 2004 / Accepted 20 January 2005 )

Abstract
The crystallization of amorphous Mg-bearing silicate grains into Mg₂SiO₄ and its temperature dependence were clarified by observing the grains in situ while heating in a transmission electron microscope. The crystallization started from the grain surface at 800 $^{\circ}$ C. Before the crystallization at the grain surface, the formation of a rim-like layer due to prenucleation was observed. The characteristic structure change of the grains was recorded and indicated that prenucleation occurred before crystallization. This phenomenon probably corresponds to the "stall" idea suggested by Hallenbeck & Nuth (1998, Ap&SS, 255, 427) in the crystallization of silicate.

Key words: astrochemistry -- method: laboratory -- stars: AGB and post-AGB -- stars: circumstellar matter -- ISM: dust, extinction

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