Experimental Observation of Hypergolic Ignition of Superbase-Derived Ionic Liquids

The hypergolic ignition behaviors of four newly synthesized ionic liquids with dicyanamide anion (ionic liquids 1 and 3) and cyanoborohydride anion (ionic liquids 2 and 4) were experimentally investigated. The results showed that successful hypergolic ignition of both group ionic liquids were achieved with white fuming nitric acid and red fuming nitric acid. Two distinct flame initiation processes illustrated by several stages were observed for each group of ionic liquids. Specifically, the ionic liquid 1 drop showed immerging, exploding, and ignition: the drop immerged and reacted with the oxidizers underneath the liquid surface, producing gas vapor and white foam like intermediates on the surface; then, the surface exploded by fast accumulation of heat and vapor underneath, followed by flame kernels formation in the adjacent gas phase. The ionic liquid 2 drop showed bouncing and igniting: it just created a crater on the oxidizer surface and then sat on the Leidenfrost vapor layer generated by impaction and reaction. Ionic liquids 3 and 4 showed a similar flame initiation process, respectively, to that of ionic liquids 1 and 2. Furthermore, the explosion delay time and ignition delay time of the four ionic liquids were recorded, both the previous and present experimental repeatabilities were analyzed, and it was shown that heat loss control was important to the experimental repeatability.