Trittschack, Roy Grobéty, Bernard Brodard, Pierre 2014-03-01 The dehydroxylation reactions of chrysotile Mg₃Si₂O₅(OH)₄ and brucite Mg(OH)₂ were studied under inert nitrogen atmosphere using isothermal and non-isothermal approaches. The brucite decomposition was additionally studied under CO₂ in order to check the influence of a competing dehydroxylation/carbonation/decarbonisation reaction on the reaction kinetics. Isothermal experiments were conducted using in situ high-temperature X-ray powder diffraction, whereas non-isothermal experiments were performed by thermogravimetric analyses. All data were treated by model-free, isoconversional approaches (‘time to a given fraction’ and Friedman method) to avoid the influence of kinetic misinterpretation caused by model-fitting techniques. All examined reactions are characterised by a dynamic, non-constant reaction-progress- resolved (‘<em>α</em>’-resolved) course of the apparent activation energy <em>E</em> _a and indicate, therefore, multi-step reaction scenarios in case of the three studied reactions. The dehydroxylation kinetics of chrysotile can be subdivided into three different stages characterised by a steadily increasing <em>E</em> _a (<em>α</em> ≤ 15 %, 240–300 kJ/mol), before coming down and forming a plateau (15 % ≤ <em>α</em> ≤ 60 %, 300–260 kJ/mol). The reaction ends with an increasing <em>E</em> _a (<em>α</em> ≥ 60 %, 260–290 kJ/mol). The dehydroxylation of brucite under nitrogen shows a less dynamic, but generally decreasing trend in <em>E</em> _a versus <em>α</em> (160–110 kJ/mol). In contrast to that, the decomposition of brucite under CO₂ delivers a dynamic course with a much higher apparent <em>E</em> _a characterised by an initial stage of around 290 kJ/mol. Afterwards, the apparent <em>E</em> _a comes down to around 250 kJ/mol at <em>α</em> ~ 65 % before rising up to around 400 kJ/mol. The delivered kinetic data have been investigated by the <em>z</em>(<em>α</em>) master plot and generalised time master plot methods in order to discriminate the reaction mechanism. Resulting data verify the multi-step reaction scenarios (reactions governed by more than one rate-determining step) already visible in <em>E</em> _a versus <em>α</em> plots application/pdf https://folia.unifr.ch/global/documents/303472 https://folia.unifr.ch/documents/303472/files/Phys_Chem_Minerals_2014_.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1007/s00269-013-0638-9 info:eu-repo/semantics/openAccess License undefined Physics and Chemistry of Minerals. - 2014, vol. 41, no. 3, p. 197–214 Serpentine dehydroxylation Generalised master plot Chrysotile Brucite Thermogravimetry In situ high temperature X ray powder diffraction info:eu-repo/classification/udc/549 Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non-isothermal/isothermal thermogravimetric analysis and high-temperature X-ray powder diffraction study http://purl.org/coar/resource_type/c_6501