The Phenanthrene/Anthracene–Picric Acid System

Abstract

Abstract The phase relations in the phenanthrene/anthracene–picric acid system have been determined by calorimetry and X-ray diffraction. Four series of solid solutions occur in this system: the terminal solid solutions P and A, which are based on the parent picrate lattices, and the I and II solutions, which are based on the incongruentlymelting ternary compounds. A eutectic is observed at about 47 mol% anthracene and at 124 °C. Enantiotropic transitions appear at about 76, 103, and 120 °C in the I solid solution and at about 80, 103, and 120 °C in the II solid solution. The Gibbs energy of formation from the solid component compounds has been estimated as −2.04, −1.67, −1.21, and −0.68 kcal/mol for the stable forms at the room temperature of the phenanthrene picrate, the I solid solution (at 34.58 mol% anthracene), the II solid solution (at 58.96 mol%), and the anthracene picrate respectively. The two transitions in the phenanthrene picrate have been shown to be easily detectable by recording the electrical resistivity as a function of the temperature.