Study On Synthesis And Characterization Of Rich B-H Based Ionic Liquid Propellants

Hypergolic propellant,as the key power of rocket and space aircraft,is an important guarantee for the development of aviation and aerospace field.As the derivatives of hydrazine(the main component of hypergol)are volatile and highly carcinogenic substances with low volumetric energy density,the research shows the environmental and strategic importance in replacing the derivatives of hydrazine with hypergolic ionic liquids(ILs).In this paper,B-H cluster-based and mutil-azole B-H based hypergolic ILs,and green IL-IL bipropellants were synthesized.Some innovations and advances were made in the study of B-H based hypergolic ILs.The research contents are as follows:(1)Twelve B-H cluster based([B12H,2]2-and[B10H10]2-)hypergolic ILs were designed and synthesized.Compared with the conventional B-H based hypergolic ILs,the hydrothermal stability,density and ignition activity of the two ILs have been greatly improved.The thermal decomposition temperature(Td)of the compounds can reach higher than 200?,or even higher than 250?.The NMR tests and hydrolysis mechanism analysis showed that[B12H12]2-and[B10H10]2-had good water stability at room temperature.The densities of conventional B-H based ILs were relatively low(less than 1.0 g cm-3),while 12 kinds of ionic salts were more than 1.0 g cm-3,the highest of which was 1.18 g cm-3,indicating that the cluster structure was beneficial to increase the density of compounds.Most of the heats of formation(?Hf)of B-H cluster ions were positive.At the same oxidizer/fuel(O/F)ratio,the specific impulse(ISP)values were higher than that of UDMH.And B-H cluster based hypergolic ILs exhibited a wide range of O/F combinations resulting in high performance,which was advantageous for reducing propulsion performance loss and simplifying engine design.The ignition delay times of[B12H12]2-ion salts upon contact with HNO3 ranged from 4 to 16 ms.But it could not spontaneously ignite with N2O4.The ignition delay times of[B10H10]2-ionic salts upon contact with HNO3 reached to 1 ms.And it could spontaneously ignite upon contact with N2O4 and exhibited short ignition delay times(<10 ms).(2)Six[B6H7]-based ILs were designed and synthesized.The melting points of[B6H7]-ionic salts were lower than that of[B12H12]2-and[B10H]10]2-ionic salts.Four compounds were liquid at room temperature and belonged to the category of room temperature ILs.Such ILs also showed good hydrothermal stability.Because the cluster-like stacking units of[B6H7]-anions are small,the density of the ionic compounds is not significantly increased,but the ionic compounds with unsaturated groups can be denser than 1.0 g cm-3.The ?Hf values of[B6H7]-ions were all positive.At the same O/F ratio,the Isp values were higher than that of UDMH,and the O/F ratio with high specific impulse ranged from 50%to 80%,which is beneficial to reducing propulsion performance loss during operation and simplifying engine design.The ignition delay times of[B6H7]-ILs upon contact with HNO3 or N2O4 could reach 1 ms,which is the shortest ignition delay time so far.(3)Ten mutil-azole B-H based hypergolic ILs were designed and synthesized.The design of mutil-azole B-H based hypergolic ILs adopted the concept of anion-cation co-modification,which modifies anions and cations on both "ignition point" B-H groups and "energy point" azole groups simultaneously,overcoming the disadvantages of single anion-cation effect in the past.The transition temperature range of mutil-azole B-H based ionic liquid is-44.9--57.6?.The thermal stability of these ILs is good,and theTd of most ILs are around 250 ?.The densities of ILs were increased by the introduction of azole group,ranging from 1.07 to 1.16 g cm-3.The ?Hf values of ILs were increased by introducing azole groups.The ?Hf of the cations varied from 440.6 to 759.2 kJ·mol-1 and that of[BTzB]-was 24.3 kJ·mol-1.The AHf of[BTzB]--based ILs ranged from 83.1 to 390.2 kJ·mol-1.Because of the high viscosity,the ignition activity was limited,and the lowest value of the ignition delay time is 20 ms.The Isp values were about 260 s(oxidizer is HNO3).Because of their relatively high densities,the density specific impulse(plsp)performance is good,about 360 s·g·cm-3.(4)Nine IL-IL bipropellants were designed and synthesized.The concept of IL-IL bipropellant was proposed for the first time,aiming at greening propellant fuel and oxidizer.The IL oxidizers are a kind of Bronsted acidic ILs with NO3-as anion and imidazolium or triazolium as cation.The IL fuel is a class of[B6H7]--based ILs with excellent ignition activity.The IL oxidizers are superior to HNO3 and N2O4 in melting points(<80?)and thermal stabilities(>50?).The freezing points of IL fuels were slightly higher and the thermal stabilities were good(Tg>190?).The densities of IL oxidizers were around 1.5 g·cm-3,and the densities of IL fuels were greater than 0.9 g·cm-3.The ?Hf values of the three IL oxidizers are all negative,and that of the IL fuels are high(122.9-379.8 kJ·mol-1).The ISP of 9 kinds of hypergolic bipropellants varied from 182.5 to 204.0 s.The heats of combustion(?Hc)ranged from-2738.0 to-3011.0 J g-1.The change of ISP was consistent with the change of??Hc.Nine IL-IL combinations can spontaneously ignite,and IDs varied from 98 to 952 ms,except for 03/F2.Although IL-IL combinations still have many deficiencies in performance,this concept has some inspiration for the design of new green hypergolic bipropellant.