Hypergolic Properties of Solvated Lithium, Sodium, and Calcium in Liquid Anhydrous Ammonia

Liquid anhydrous ammonia reacts violently when placed in contact with white-fuming nitric acid (WFNA) but does not produce a flame. However, adding small amounts ([Formula: see text]) of lithium or sodium to ammonia to form a solvated electron solution makes ammonia hypergolic with WFNA. Adding small amounts of calcium ([Formula: see text]) to ammonia makes a mildly pyrophoric solution in air. The relative ignition delay between lithium–liquid-anhydrous-ammonia (LiLAA) and sodium–liquid-anhydrous-ammonia (NaLAA) solutions was experimentally determined. Kinetic calculations employing alkali metal and ammonia combustion mechanisms validated experimentally observed trends. The difference in ignition delay between lithium and sodium solutions was attributed to the strength of their respective -O and -OH bonds, which promote the formation of radicals and affect ignition delay. Thermodynamic calculations indicated that nonsolvated mixtures of lithium or calcium with ammonia increased specific impulse by several seconds in a WFNA-operated motor. However, mixtures with sodium decreased specific impulse by several seconds. Importantly, certain key thermodynamic properties of solvated electron solutions are still unknown, and combustion-related calculations are likely inaccurate. The use of these solutions in practical applications is currently very limited, as their metastable nature prevents feasible storage and would require modified engines that make the solution in situ.