Estimation of the diffusion coefficient of water evolved during the non-isothermal dehydration of Australian sedimentary opal

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Journal Article
Journal Of Thermal Analysis And Calorimetry, 2007, 88 (1), pp. 231 - 235
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The dehydration of an opal specimen was investigated by thermogravimetric analysis (TG) in powder and bulk forms. The change in geometry resulted in a significant difference in the temperature range in which dehydration occurred with peak temperatures in the differential TG (DTG) curve for the hand ground opal at 203 degrees Cand for the bulk opal at 340 degrees C. This difference waa attributed to time taken for diffusion of feree water in the bulk opal tothe specimen surface prior to evolution as a registered mass loss. A model was proposed to account for the diffusion of water and was used to estimate the diffusion coefficient.
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