Physical chemistry of binary organic eutectic and monotectic alloys; durene–pyrogallol system

The phase-diagram of durene–pyrogallol system, determined by the thaw-melt method, shows the formation of a eutectic at 79.6°C and a monotectic at 127.7°C containing 0.95 and 0.05 mol fractions of durene, respectively. Growth data for the pure components, the eutectic and the monotectic, determined by measuring the rate of movement of solid–liquid interface in a capillary at different undercoolings (ΔT) suggest the applicability of Hillig–Turnbull equation, v=u(ΔT)n, where u and n are constants depending on the nature of materials involved. The values of enthalpy of fusion of the pure components, the eutectic and the monotectic were determined and from these values, the enthalpy of mixing, size of the critical nucleus, interfacial energy and excess thermodynamic functions were calculated. While optical microphotographs of the pure components showed a faceted microstructure, those of eutectic and monotectic show their characteristic features.