Concentration and Pressure Effects on the Decomposition Rate of Aqueous Hydroxylammonium Nitrate Solutionsa

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Abstract
— Decomposition experiments have been performed on liquid propellants consisting of mixtures of hydroxylammonium nitrate (HAN) and water. Electric discharge initiation was used to produce a propagating, exothermic decomposition wave front, which was then observed by cineshadowgraphy. Experiments were conducted on quiescent HAN-water mixtures of 3.12 to 13.00M HAN in a 1.8 x 1.0mm rectangular strand burner over pressures of 6 to 34 MPa. A lean propagation limit was found to exist at a concentration of between 3.12 and 5.10 M HAN. Measured overall decomposition rates decreased with increased pressure in an unstable manner with instabilities ranging in size from tens of micrometers to the burner width. It was found that the overall decomposition rates were a function of both the HAN concentration and the density ratio, ϱproduct/ϱreactant (which is proportional to pressure), across the decomposition wave. This density ratio ettect is interpreted as affecting the hydrodynamic stability of the decomposition wave front. Low-density ratios ( < 0.10-0.12) are associated with pronounced meniscus decomposition fronts and overall decomposition rates dependent primarily on density ratio. Large density ratios (> 0.15) are associated with flatter decomposition fronts and density ratios (and hence pressure) independent decomposition rates. The importance of hydrodynamics on the overall decomposition rate has been attributed to the importance of condensed phase reactions in HAN-water mixtures.