Studies on physicochemical properties of the eutectic and monotectic in the urea p chloronitrobenzene system

The phase diagram of an organic analog of a nonmetal-nonmetal-type system involving urea and p. chloronitrobenzene shows the formation of a eutectic (0.982 mole fraction of p. chloronitrobenzene) and a monotectic (0.020 mole fraction of p. chloronitrobenzene) with a liquid miscibility gap in the system. The linear velocity of crystallization (v) data determined at different undercoolings (Delta T) by measuring the rate of advance of an interface in a capillary obey the Hillig-Turnbull equation, v=u(Delta T)(n), where u and n are constants depending on the solidification behaviour of the materials involved. From the enthalpy of fusion of the pure components, the eutectic and the monotectic, enthalpy of mixing, excess thermodynamic functions, entropy of fusion and interfacial energy were calculated. Optical microphotographs of the eutectic and monotectic give their characteristic features.