Synthesis And Ignition Performance Of A New High-energy Low-toxic Liquid Propellant

In the field of aerospace and military science, propellant is one of the key materials. The current choices of fuels are mainly concentrated on hydrazine and its derivatives, such as monomethyl hydrazine and unsymmetrical dimethylhydrazine. However, these hydrazine-based fuels are extremely toxic and carcinogenic, highly volatile, very sensitive to adiabatic compression and difficult to handle, thereby greatly increasing the handling and storage costs. Thus, exploration of alternative liquid hypergolic fuels that are environmentally benign yet exhibiting comparable properties and performance to hydrazine and its derivatives has become a hot spot in the field of space propulsion. In this thesis, we synthesized and characterized four classes of hypergolic liquid bipropellants fuels, their physicochemical properties and hypergolic reactivity were studied.In the first part, a class of [imidazolyl-amine-BH2]+-cation based ionic liquids were designed, synthesized and fully characterized. Their thermal properties, densities, viscosities, heats of formation, hypergolic reactivity were measured and studied in detail. The results showed that the strategy of incorporating reducing B-H bonds into the cations may be helpful for shortening the ignition delay (ID) times of ionic liquids; in contrast with bisimidazolium dihydroboronium-based ILs, these asymmetric monoimidazole dihydroboronium-based ILs exhibited improved properties with shorter ignition delay times, higher densities, and lower phase transition temperature probably due to the asymmetric structure of cation, thereby suggesting their potenail application in "green" liquid bipropellant fuels or formulations.In the second part, a class of super-base-derived hypergolic ionic liquid materials were designed, synthesized and fully characterized. Their thermal properties, densities, viscosities, heats of formation, hypergolic reactivity were studied in detail. The results showed that these new hypergolic ionic liquids derived from DBU and DBN frameworks showed an unexpected thermal stability of> 280? and quaternized DBN or DBU skeletons exhibited high chemical inertness due to the lacking of active hydrogen atoms in the structures. The conclusions are helpful for designing and exploring new hypergolic ionic liquid fuels with high thermal stability.In the third part, a class of N-heterocyclic carbene (NHC-borane) compounds were designed, synthesized and fully characterized. Their thermal properties, densities, viscosity, heat of formation, energy and hypergolic reactivity were measured and studied in detail. The results showed that these NHC-boranes exhibited high water stability and had no obvious chemical degradation after being stored in water for one month, thereby suggesting that this imidazolylidene-borane framework can play a role in stabilizing the{BH3} moiety like the cyano group to improve the water stability of {BH3}-containing structures. These NHC-borane compound exhibited fast spontaneous combustion on contact with white fuming nitric acid, among them the shortest ID time was 2 ms.In the fourth part, a class of imidazole-borane adducts was synthesized in a new synthetic pathway and fully characterized. The physicochemical properties and hypergolic reactivity were measured and fully studied. In the new synthetic pathway, the sodium borohydride instead of the toxic and hazardous borane were used for the synthsis of imidazole-borane adducts in one pot reaction. The results showed that these imidazole-borane adducts have some advantages including easy to produced, low cost, easy large-scale production and excellent hypergolic performance, highlighting their potential as hypergolic fuels or additives in bipropellant formulations.In summary, these results are helpful in design and application of new "green" hypergolic liquid propellant.