要約

Hypergols (fuel and oxidizer that ignite on contact) are useful for space propulsion since reaction can be initiated or terminated by opening or closing appropriate valves. Hypergolic liquid propellants are strongly preferred over solid fuels or oxidizers since they show excellent hypergolic ignition and low ignition delay time, high specific impulse, and better thrust control. Hydrazine, and its methylsubstituted derivatives, are fuels of choice based on favorable combustion characteristics, and high specific impulse. However, these positive properties are diminished by many drawbacks including the volatility of these fuels which, because of their carcinogenic and toxic nature, require costly handling procedures to meet environmental requirements during manufacture, storage, shipping, and application. Based on these unattractive properties, chemists worldwide have been catalyzed to develop alternative environmentally friendly hypergolic ionic liquid propellants as fuels. Anions of these salts, which include dicyanamide, dicyanoborate, cyanoborate, azide, nitrate, aluminum borohydride, nitrocyanamide, etc., appear to play the major role in determining hypergolic properties. Although cations play a lesser role, they are most frequently nitrogen-containing alkyl and aromatic species, e.g., substituted alkyl ammonium, imidazolium, imidazolium-substituted with alkyl, vinyl, propargyl, etc. New stable, dense, storable oxidizers are needed in order to address dependably the demands for energetic systems that are on call 24/7 since the typical oxidizers are likely to be cryogens, unstable liquids, or corrosive substances. Stable room temperature oxidizers that possess positive chlorine or bromine atoms, e.g., azo bis (bromochloro FOX), exhibit appropriate properties when reacted with fuels. There is a strong need to design and synthesize compounds to be used as long-term storable oxidizers or as stable electron-rich fuels.