SOME PHYSICOCHEMICAL STUDIES ON BINARY ORGANIC EUTECTICS

Solid-liquid equilibrium data on binary systems of phenanthrene with p-chloronitrobenzene, p-dibromobenzene and diphenyl show the formation of simple eutectics in each case. The linear growth velocity (upsilon) of pure components and eutectics at different undercoolings (DELTA-T) obey the Hillig-Turnbull equation upsilon = u(DELTA-T)n where u and n are constants. The observed solidification behaviour of the eutectics is explained by the mechanism proposed by W.C. Winegard, S. Mojka, B.M. Thall and B. Chalmers, Can. J. Chem., 29 (1951) 320. The experimental values for the heat of fusion of eutectics, compared with the theoretical values calculated from the law of mixtures, suggest a cluster formation in the eutectic melt. Using heats of fusion data, excess thermodynamic function, surface energy and critical radius were calculated in order to throw light on the mechanism of solidification and the nature of the interaction between the components forming the eutectic. The microstructural examinations of pure components and eutectics suggest thinly branched eutectic structures resulting from coupled growth of the component phases.