Oxidation kinetics of fayalite (Fe2SiO4) |
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| Authors: | Stephen J Mackwell |
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| Institution: | 1. Department of Geosciences, The Pennsylvania State University, 16802, University Park, PA, USA
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| Abstract: | Single crystals of fayalite (Fe2SiO4) have been oxidized either in the hematite or the magnetite stability field to investigate the kinetics and mechanisms of oxidation. For samples heated in air at 770° C, a two-phase region composed of fine-grained iron oxide and silica phases formed as the reaction front moved into the sample, and an iron oxide layer formed external to this two-phase region. The presence of the single-phase oxide layer coating the specimens indicates that oxidation occurs by the migration of iron from the fayalite to the gas-solid interface rather than by the movement of oxygen in the opposite direction. For oxidation in air, the kinetics followed a parabolic growth law, with the rate of oxidation limited by the diffusion of iron from the internal reaction front to the gas-solid interface through the iron oxide. When fayalite was oxidized in the magnetite stability field, using a CO/CO2 gas mixture at 1030° C, oxidation was controlled by the reaction at the gas-solid interface, yielding an oxidation rate considerably slower than that predicted for diffusion-controlled growth of the oxide layer. |
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