Phase diagram ofn-hexacosane andn-octacosane: experimental determination and calculation

Abstract : The phase diagram of (n-octacosane + n-hexacosane) has been determined experimentally, using a crystallographic and a calorimetric method, in the n-octacosane mole fraction range x = (0.2 to 0.7). In this composition range, the mixtures show an intermediate solid solution at room temperature, denoted beta ", with an orthorhombic structure, identical to the one found in other binary, or ternary systems, and in crude oil. With increasing temperature, this solid solution undergoes two solid-solid transitions, leading to another orthorhombic phase, denoted beta(Fmmm), then to a rhombohedral "Rotator" phase, denoted alpha-RII, before melting. The phase diagram has been calculated by using the following assumptions: ideality of the liquid phase mixture, ideality of the alpha-RII rotator phase mixture, and non-ideality of the mixture in the beta, and beta " phases whose excess Gibbs energies are represented by Margules equations (one- and two-parameter, respectively). The enthalpies of transformation, the temperatures of transformation, and the heat capacities of the pure compounds have been either measured, or extrapolated from the mixtures values. This allows a good representation of the phase diagram through the use of simple expressions.
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Submitted on : Thursday, August 20, 2015 - 4:33:21 PM
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Élise Provost, Daniel Balesdent, Mohammed Bouroukba, Dominique Petitjean, Michel Dirand, et al.. Phase diagram ofn-hexacosane andn-octacosane: experimental determination and calculation. Journal of Chemical Thermodynamics, Elsevier, 1999, 31 (9), pp.1135. ⟨10.1006/jcht.1999.0526⟩. ⟨hal-01185588⟩

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