Crystallization of methylhydrazine monohydrate under adiabatic conditions

Crystallisation kinetics of the methylhydrazine monohydrate is followed under adiabatic conditions. The measurements indicate that two solid phases, a metastable form and a stable form, exist between 186 and 223 K. This novel application of adiabatic calorimetry allows one to determine the temperature dependence of the growth process of the metastable solid in only one experiment. The spontaneous evolution of the system temperature with time during the crystallisation process is modelled assuming a temperature dependence of the growth rate and using the Avrami-Kolmogorov assumption. The results suggest that the number of nuclei is constant during the growth process and that the crystallites grow with a constant shape in the undercooled liquid.