Kinetics of thermal dehydroxylation of aluminous goethite |
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Authors: | H D Ruan R J Gilkes |
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Institution: | (1) Soil Science and Plant Nutrition, Faculty of Agriculture, University of Western Australia, 6907 Nedlands, WA, Australia |
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Abstract: | The kinetics of dehydroxylation of synthetic aluminous goethite was studied using isothermal and non-isothermal thermogravimetry. The complete isothermal dehydroxylation can be described by the Johnson-Mehl equation with up to three linear regions in plots of lnln 1/(1–y)]vs. Int Kinetics for the initial stage of dehydroxylation changed from diffusion to first-order through the temperature range 190 to 260°C. The rate of dehydroxylation was reduced by Al-substitution and increased with temperature. Activation energy for dehydroxylation, calculated from the time to achieve a given dehydroxylation extent, varied depending on the extent of dehydroxylation and Al-substitution. Non-stoichiometric OH existed in goethite and some remained in hematite after the complete crystallographic transition. |
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Keywords: | dehydroxylation goethite hematite kinetics |
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