An experimental study of enstatite formation reaction between forsterite and Si-rich gas

Details An experimental study of enstatite formation reaction between forsterite and Si-rich gas An experimental study of enstatite formation reaction between forsterite and Si-rich gas

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.118...21i&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 118, no. 1-4, p. 21-30.

Physics

8

Chemical Reactions, Cosmic Gases, Enstatite, Nucleation, Reaction Kinetics, Silicon, Condensing, Single Crystals, Solar Corona, X Ray Diffraction

Scientific paper

Experiments on the reaction between forsterite and Si-rich gas were carried out in a vacuum furnace, using a newly designed double-capsule technique. A thin layer of enstatite was formed on the surface of the forsterite by the reaction. The thickness of the enstatite layer changes in proportion to the square root of time (parabolic rate law), indicating that the rate is controlled by diffusion in the enstatite layer. The activation energy and the logarithm of the preexponential term of the parabolic rate constant were obtained at 505 +/- 188 kJ/mol and 3.6 +/- 5.6 sq cm/s, respectively. It is difficult to definitely determine the mechanism of the reaction from these values, but consideration of strain generation due to the volume change during the reaction may suggest that the counterdiffusion of Si and Mg takes place along the grain boundary in the enstatite layer. The degree of the reaction of forsterite with Si-rich residual gas in the primordial solar nebula is discussed based upon the measured reaction rate, and it is suggested that very little enstatite was formed by this reaction in the cooling nebula if the grain size of the forsterite crystals was controlled by homogeneous nucleation theory.

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