Studies of Solidification Behavior and Molecular Interaction in Benzoic Acid–o-Chloro Benzoic Acid Eutectic System

Abstract

Phase diagram of benzoic acid (BA)–o-chloro benzoic acid (o-CBA) system has been studied by thaw melt method and the results show the formation of a simple eutectic mixture. Heats of fusion values of the components and eutectic mixture were determined with the help of differential scanning calorimeter. Excess Gibb's free energy (GE), excess enthalpy (HE), and excess entropy (SE) of mixing of pre-, post-, and the eutectic mixture were calculated. FT-IR spectroscopic studies and ab initio calculations were done to have an idea about the nature of interaction between the molecules in the eutectic mixture. Linear velocities of crystallization of the two components and the eutectic mixture were determined at different undercoolings. Microstructural studies of BA and o-CBA showed the formation of broken lamellar and lamellar type microstructure, whereas for the eutectic mixture growth of flat crystals in different directions from a particular point was obtained. The isotropic as well as the anisotropic solidification behavior was studied. Jackson's roughness parameter was calculated. Modulus of ruptures of pure components and the eutectic mixture were determined. Results show that eutectics are nonideal mixtures, and some weak interactions are involved between the two components.