Measurement and Analysis of the Naphthalene - Octafluoronaphthalene Phase Diagram: Complex Formation in Solid and Liquid

Naphthalene-octafluoronaphthalene room pressure solid-liquid phase diagram has been assessed by means of differential scanning calorimetry and powder X-ray diffraction analyses. Thermodynamic properties are analysed through the associated liquid model. The solid states consists of six crystalline phases with well defined composition: one for naphthalene, two for octafluoronaphthalene and three for an equimolecular intermolecular compound. This complex melts congruently at (406.3 +/- 0.3) K, i.e., about fifty degrees higher than its components and the resulting liquid is moderately associated. The solid-solid phase transitions of this complex are strongly energetic. The corresponding overall change of entropy stands for two third times the entropy of fusion. The consecutive increasing of crystalline symmetry and positional disorder is clearly visible on diffraction patterns.