Physical chemistry of binary organic eutectic and monotectic alloys; 1,2,4,5-tetrachlorobenzene–α-naphthol and TCB–resorcinol systems

Abstract

Phase diagrams of 1,2,4,5-tetrachlorobenzene (TCB) with each of α-naphthol and resorcinol determined by the thaw–melt method, show the formation a simple eutectic in the former case and a eutectic and a monotectic with large miscibility gap in the latter system. The growth behaviour of the pure components, the eutectics and the monotectic, studied by measuring the rate of movement of the solid–liquid interface in a capillary at different undercoolings (Δ T), suggests that the growth data obey the Hillig–Turnbull equation, v= u, (Δ T) n , where v is the linear velocity of crystallization and u and n are constants depending on the nature of materials involved. Using the values of enthalpy of fusion, determined by the DSC method (Mettler DSC-4000 system), entropy of fusion, heat of mixing, roughness parameter, excess thermodynamic functions and interfacial energies were calculated. The microstructures of the eutectics and the monotectic show their characteristic features.