SOLID-LIQUID EQUILIBRIA AND MODELING OF THE BINARY-SYSTEMS WATER-METHYLHYDRAZINE AND WATER-1,1-DIMETHYLHYDRAZINE

Solid-liquid equilibria of the system water-methylhydrazine are invest igated by direct thermal analysis on heating. Three liquidus curves ca n be observed corresponding to ice, methylhydrazine and a stable congr uently melting methylhydrazine monohydrate. Another metastable form of monohydrate can be observed, its transformation into the stable form being monotropic. A model deduced from the study of the water-alkylhyd razines vapor-liquid equilibria and representing strong interactions b etween molecules as chemical associations, allows, using the van Laar relation, to reproduce correctly all the liquidus curves. This modelin g is justified by the evolution of Raman spectra of the liquid phase. The crystal structure of pure methylhydrazine, determined at 179 K by X-ray diffraction on a single crystal, is favorable to the existence o f strong interactions between methylhydrazine molecules. The model is also used to reproduce the system water-1,1-dimethylhydrazine.