Structural and energetic behavior of mixed samples in the hexacosane (n-C26H54)/octacosane (n-C28H58) system; Solid-solid and solid-liquid equilibria

The combination of the experimental (microcalorimetric and X-ray diffractio n) methods and thermodynamic analyses enabled us to determine the phase dia gram of the system hexacosane (n-C26H54)/octacosane (n-C28H58). Isothermal X-ray measurements performed on mixed samples at 'low temperature' ( T 308 It) revealed three crystalline forms: two monoclinic (M-011 and M-dci) and one orthorhombic (O-p). Four of the Eve rotator phases were observed at 'hi gh temperature': R-I, R-11, R-IV, and R-V. Fourteen solid-solid and two sol id-liquid two-phase regions were observed, as well as one peritectic, one e utectoid, one metatectoid, and five peritectoid three-phase equilibria. The thermodynamic calculations of the phase-equilibrium relations, carried out with the polynomial functions described in a previous paper and new ones g iven here. showed full consistency with the experimental data, evidencing t he reliability of these polynomial Functions.