THERMODYNAMIC PROPERTIES OF GASES IN PROPELLANTS. SOLUBILITY OF HE, N2, AND AR IN HYDRAZINE, METHYLHYDRAZINE, AND UNSYMMETRICAL DIMETHYLHYDRAZINE

Solubilities of He, N2, and Ar in liquid hydrazine, methylhydrazine, and unsymmetrical dimethylhydrazine were measured at various pressures and temperatures. The results show that Henry's law is obeyed and the standard change of Gibbs energy is linear in temperature. The standard heat of solution and the entropy of solution were obtained, and the Gibbs energy was expressed as a linear function of temperature. The change in the solubility of a chosen gas from one solvent to another has been correlated by using the Lennard-Jones 6-12 potential with the assumption that the solute interacts with a hard core studded with H atoms. The functional forms of (Gibbs energy) = (heat of solution) - T(entropy of solution) for He, N2, and Ar in symmetrical dimethylhydrazine have been obtained from such correlations, and the method is shown to be useful for similar gas-liquid systems. It is shown that (a) the changes in the solubilities follow the changes in the dipole moments of liquids and (b) the entropy of solution varies linearly with the logarithm of mol fractions of solutes in methylhydrazine and in unsymmetrical dimethylhydrazine but not of solutes in hydrazine.