Phase diagram ofn-hexacosane andn-octacosane: experimental determination and calculation
✍ Scribed by Elise Provost; Daniel Balesdent; Mohammed Bouroukba; Dominique Petitjean; Michel Dirand; Véronique Ruffier-Meray
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 212 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0021-9614
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✦ Synopsis
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 β , 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 β(Fmmm), then to a rhombohedral "Rotator" phase, denoted α-RII, before melting. The phase diagram has been calculated by using the following assumptions: ideality of the liquid phase mixture, ideality of the α-RII rotator phase mixture, and non-ideality of the mixture in the β, and β 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.