Investigations on Nucleation and Growth Kinetics of Urea Crystals from Methanol

Abstract

The induction period of urea in methanol has been measured experimentally by the visual observation method. The induction period, which is inversely proportional to the nucleation rate, has been used to estimate the interfacial tension between the urea crystal and the methanol solution and hence the nucleation parameters like critical radius (r*), number of molecules in the radius (i*) and Gibbs' free energy change for the formation of a critical nucleus (ΔG*) have been calculated. The fundamental diffusion equation is solved numerically and the concentration profiles and growth rate of urea for successive intervals of time are determined using computer simulation model. The simulation has been carried out under different experimental conditions. Single crystals of urea were grown from methanol and their second harmonic generation was observed using Nd: YAG laser.