Physical chemistry of organic eutectics

Abstract

Phase diagrams of urea-α-naphthol and urea-benzoic acid systems, determined by the thaw-melt method, show the formation of simple eutectic in each case. The growth velocity data, determined at different undercooling (ΔT) by observing the rate of movement of interface in a capillary, obey the Hillig-Turnbull equation, v=u(ΔT)n, where u and n are constants depending on the nature of the materials. Using enthalpy of fusion, undercooling (ΔT) and melting point data, entropy of fusion, interfacial energy, enthalpy of mixing, critical radius size and excess thermodynamic functions were calculated. The microstructural investigations give characteristic features of the eutectics.