Contribution of the concept of simple solutions to calculation of the stoichiometric activity coefficients and density of ternary mixtures of hydroxylammonium or hydrazinium nitrate with nitric acid and water

Abstract

Binary data (water activity as a function of the molal concentration) at 25°C for the principal anti-nitrous compounds used in nitric acid aqueous media—hydrazinium nitrate (HDZN) and hydroxylammonium nitrate (HAN)—are determined by direct water activity measurements. Density variations at 25°C are also established. Ternary systems involving these nitrate salts and nitric acid are studied from the standpoint of simple solution theory. It is observed that the system HDZN–HNO3–H2O does not exhibit simple behaviour, which is due to the acid–base equilibrium involving HDZN and HNO3 (i.e., N2H62+ formation). On the other hand, the system HAN–HNO3–H2O which does not undergo major chemical interactions follows satisfactorily the simple solution rule as long as the water activity is higher than 0.84. For ternary simple solutions it is possible to predict activity coefficients for each component by applying the Zdanovskii–Stokes–Robinson rule and the Mikulin relationship.