Synthesis And Characterization Of Hypergolic Metal-Coordination Ionic Liquids

Propellants are the core power for rockets and aerospacecrafts,whcih play a vital role in the development of space industry.The traditional fuels of hypergolic propellants such as hydrazine and its derivatives are toxic and carcinogenic,so that it is urgent to design the green alternatives.As the potential next-generation propellant fuels,hypergolic ionic liquids?HILs?have been recognized with low melting point,wide liquid range,high thermal stability,and so on.However,most of HILs possess undesired ignition delay times,which is a significant parameter in evaluating the fuels.Herein,a new family of hypergolic metal-cioordination ILs with superior hypergolicity were prepared by the addition of catalytic metal ions.The contents are as follows:Six B₁₂H₁₂₂^-based metal(Cu²⁺,Ni²⁺,Zn²⁺)complexes were designed and prepared.The results showed that the six metal complexes are all solid at room temperature with melting points ranging from 196.7 to 269.3 ?,which is partly due to the structural symmetry.As to thermal stabilities,these complexes possessed decomposition temperatures>220 ?,and[Ni?C₅H₆N₂?₆]B₁₂H₁₂ gave the highest decomposition temperatures of 286.3 ?.Their densities are all much higher than those of hydrazine-based fuels ranging from 1.215 to 1.264 g cm^-3.Among them,[Cu?C₅H₆N₂?₄]B₁₂H₁₂ exhibited the highest density of 1.264 g cm^-3.The results of hypergolic tests showed that[Cu?C₅H₆N₂?₄]B₁₂H₁₂ and[Ni?C₅H₆N₂?₆]B₁₂H₁₂ had ultra-short ignition delay times?1 ms?,and the main contribution to the ignition delay times came from the favorable catalytic effect of metal ions.Five N?CN?₂^--based Cu²⁺ complexes were designed and prepared.The results showed that melting points of 57.5-133.6 ?,decomposition temperatures of 200-282 ? and densities of 1.10-1.31 g cm^-3.Among them,melting points and densities decrease with the increase of the side chain length.These complexes were added to some N?CN?₂^--based HILs with the propotions ranging from 1.0-5.0%.Their ignition delay times were measured,showing the desirable hypergolicity.For example,1-allyl-3-methylimidazolium dicyanamide indicated the inferior hypergolicity?tid:43 ms?,while it gave a very fast ignition delay time as short as 6 ms after adding 5%[Cu?C6H8N2?4][N?CN?2]2.In short,B,2H,2₂^--based metal(Cu²⁺,Ni²⁺,Zn²⁺)complexes and N?CN?₂^--based Cu²⁺ complexes were obtained from the idea of enhancing hypergolicity.The structures,phase transition temperatures,thermal stabilities,densities and hypergolicity of these complexes were measured?or calculated?,and fully dicussed.The results verified the feasibility of enhancing the HILs hypergolicity by the introduction of favorable metal ions.