Physical chemistry of binary organic eutectic and monotectic alloys; 1,2,4,5-tetrachlorobenzene−β-naphthol and 1,2,4,5-tetramethylbenzene-succinonitrile systems

Phase diagrams of 1,2,4,5-tetrachlorobenzene–β-naphthol and 1,2,4,5-tetramethylbenzene–succinonitrile systems which are organic analogues of a nonmetal–nonmetal and a nonmetal–metal system, respectively, show the formation of a simple eutectic (melting point 103.7°C) with 0.71 mole fraction of β-naphthol in the former case and a monotectic (melting point 76.0°C) with 0.07 mole fraction of succinonitrile and a eutectic (melting point 52.5°C) with 0.97 mole fraction of succinonitrile in the latter case. 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, suggests that the data obey the Hillig–Turnbull equation, v=u(ΔT)ⁿ, where v is the growth velocity, ΔT is the undercooling and u and n are constants depending on the nature of the materials involved. From the values of enthalpy of fusion determined by the DSC method using Mettler DSC-4000 system, entropy of fusion, interfacial energy, enthalpy of mixing and excess thermodynamic functions were calculated. The optical microphotographs of pure components and polyphase materials show their characteristic features.