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

Phase diagrams of 1,2,4,5-tetrachlorobenzene-beta -naphthol and 1,2,4,5-tet ramethylbenzene-succinonitrile systems which are organic analogues of a non metal-nonmetal and a nonmetal-metal system, respectively, show the formatio n of a simple eutectic (melting point 103.7 degreesC) with 0.71 mole fracti on of P-naphthol in the former case and a monotectic (melting paint 76.0 de greesC) with 0.07 mole fraction of succinonitrile and a eutectic (melting p oint 52.5 degreesC) with 0.97 male fraction of succinonitrile in the latter case. The growth behaviour of the pure components, the eutectics and the m onotectic studied by measuring the rate of movement of the solid-liquid int erface in a capillary, suggests that the data obey the Hillig-Turnbull equa tion, v = u(DeltaT)(n) where v is the growth velocity, DeltaT is the underc ooling and u and n are constants depending on the nature of the materials i nvolved. From the values of enthalpy of fusion determined by the DSC method using Mettler DSC-4000 system, entropy of fusion, interfacial energy, enth alpy of mixing and excess thermodynamic functions were calculated. The opti cal microphotographs of pure components and polyphase materials show their characteristic features. (C) 2000 Elsevier Science B.V. All rights reserved .