Abstract
The oxidation of fayalite to hematite and silica by oxygen and oxygen-nitrogen or oxygen-water vapour mixtures has been studied by TGA, SEM and X-ray diffraction. In the temperature range 690 to 950° C, the isotherms of oxidation are pseudo-parabolic. The Arrhenius plot shows a break near 840° C, related to the quartz-cristobalite transformation, the activation energy being about 230 kJ mol−1. The first stage of oxidation leads to the formation of a covering layer constituted of silica plus iron oxide (mainly hematite). Solid state diffusion of oxygen then takes place through this layer, which progressively evolves with the crystallization of silica and a relaxation of stress due to fracture. After the fracture of the covering layer, whiskers of hematite grow, usually on a silica substrate, and align themselves along linear defects. Under specific conditions, their growth is periodic.
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Gaballah, I., Raghy, S.E. & Gleitzer, C. Oxidation kinetics of fayalite and growth of hematite whiskers. J Mater Sci 13, 1971–1976 (1978). https://doi.org/10.1007/BF00552904
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DOI: https://doi.org/10.1007/BF00552904