Shamim, Mostofa and Mukhopadhyay, Tapas Kumar and Dana, Kausik (2015) Kinetic pathway for thermal exfoliation of pyrophyllite. Applied Clay Science, 114. pp. 40-47. ISSN 0169-1317

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The thermal exfoliation of pyrophyllite on heating above 600 degrees C was studied to discern its kinetic pathway and correlate it with dehydroxylation. The irreversible thermal expansion data of pyrophyllite was collected from a thermomechanical analyzer at different heating rates (beta). A detailed kinetic analysis was performed on the data using model-free and regression analysis (both linear and non-linear) methods. Multivariate non-isothermal kinetic analysis was used to fit the expansion data at all heating rates simultaneously using eighteen kinetic models. It is found that, the exfoliation of pyrophyllite can be successfully fitted with three kinetic models, viz., n-dimensional Avrami (An), two-dimensional diffusion (D2) and three-dimensional diffusion (D3) model with acceptable kinetic parameters. D2 model (E-a, activation energy = 392 kJ.mol(-1), regression coefficient = 0.998) provides the most realistic mechanistic pathway by considering the planar geometric constraint of nucleation and growth in the layered structure of pyrophyllite. Electron microscopic images of exfoliated pyrophyllite shows distinct exfoliated layers indicating escape route for heated gas and supports the choice of D2 model. Although this exfoliation process is a consequence of dehydroxylation reaction, its complexity due to diffusional and geometric constraints is reflected by the high energy barrier (E-a) reported consistently by every kinetic model compared to that of dehydroxylation. (C) 2015 Elsevier B.V. All rights reserved.

Item Type: Article
Subjects: Structural Clay Products
Divisions: Refractory
Depositing User: Bidhan Chaudhuri
Date Deposited: 08 Jan 2016 06:27
Last Modified: 08 Jan 2016 06:27

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