Azide-Based Fuel Additives for Ionic Monopropellants

*† ‡ A key component of energetic ionic liquids used as monopropellants is the choice of the fuel which can be molecular non energetic compounds (i.e. thermodynamically stable) like alcohol, glycerol, glycine, or ionic energetic spec ies per se like TEAN (Triethanolammonium nitrate) used in LGP (Liquid Gun Propellant). Aqueous solution of energetic fuel ammonium azide (NH 4N3, AA), hydroxylammonium azide (NH 3OHN3, HAA) and hydrazinium azide (N2H5N3, AA) have been prepared by different ways; in aqueous solution through an original ion-exchange procedure using cationic exchange resins, and in solid state from sodium azide (NaN 3, SA). In this study we present only the results ob tained with AA and HAA. Binary AA-H2O and HAA- H 2O, and ternary stoichiometric mixtures HAN-AA-H2O, AN-AA-H2O, HAN-HAA-H2O and AN-HAA-H2O (HAN = NH 3OHNO 3, AN = NH 4NO 3) have been investigated for thermal and catalytic decompositio n using a thermal analysis apparatus. Ammonium azide shows only endothermic vaporization into ammonia and hydrogen azide with a decrease of the peak temperature on the surf ace of platinum-based catalyst. The presence of the oxidizer (HAN) leads to an acido-ba sic reaction between hydroxylammonium cation and azide ion, thus favoring the endothermic vaporization of a part of azide at low temperature. But no reaction was observed when blend ammonium nitrate and ammonium azide solutions have been used. For HAA, the same behavior as AA has been observed in thermal conditions; whereas, in the presence of the catalyst, HAA decomposes exothermally at room temperature. In the presence of HAN, the major reaction is the disproportionation of hydroxylammonium cation leading to the formation hydrogen azide and ammonium nitrate. Moreover, the presence of azide decreases strongly the activation energy of the ammonium nitrate decomposition, inducing AN to decompose more easily.