Tianlin Liu

Towards Safer Rocket Fuels: Hypergolic Imidazolylidene-Borane Compounds as Replacements for Hydrazine Derivatives

Currently, toxic and volatile hydrazine derivatives are still the main fuel choices for liquid bipropellants, especially in some traditional rocket propulsion systems. Therefore, the search for safer hypergolic fuels as replacements for hydrazine derivatives has been one of the most challenging tasks. In this study, six imidazolylidene-borane compounds with zwitterionic structure have been synthesized and characterized, and their hypergolic reactivity has been studied. As expected, these compounds exhibited fast spontaneous combustion upon contact with white fuming nitric acid (WFNA). Among them, compound 5 showed excellent integrated properties including wide liquid operating range (-70-160 °C), superior loading density (0.99 g cm(-3) ), ultrafast ignition delay times with WFNA (15 ms), and high specific impulse (303.5 s), suggesting promising application potential as safer hypergolic fuels in liquid bipropellant formulations.

Fluorescent heterometallic MOFs: tunable framework charges and application for explosives detection

A series of three-dimensional fluorescent heterometallic MOFs based on rod- and cluster-like building blocks were readily prepared under solvothermal conditions. Among them, compounds 1–4 were constructed from rod-like building blocks {Cd–O–M}n (M = Na, K, Na–K, and Mg) and BDC2− ligands, featuring right-hand and left-hand channels with a cap topology. The framework charges of 1–4 can be tuned from negative to neutral via a strategy of changing the secondary metal centre (Na+, Na+–K+, K+ and Mg2+). It is worth noting that the rod-like building block of compound 2 contained three types of metal ion centres (Cd2+, Na+ and K+). Different from compounds 1–4, the topology of 5 changed from a cap net to a 610 net in the presence of Ca2+ as a secondary metal centre. Interestingly, the anionic framework of 5 features two types of linear trinuclear clusters as the building blocks, i.e. {Cd2CaO17} and {Cd2CaO16}, which are relatively rare in known heterometallic open frameworks. Moreover, fluorescent compound 5 with a microporous structure displayed sensing properties towards some nitro-containing compounds, suggesting its potential application as a fluorescent sensor for the sensitive detection of explosives.

Nitrato-Functionalized Task-Specific Ionic Liquids as Attractive Hypergolic Rocket Fuels

Hypergolic ionic liquids (HILs) as potential replacements for hydrazine derivatives have attracted increasing interest over the last decade. Previous studies on HILs have mostly concentrated on the anionic innovations of ionic liquids to shorten the ignition delay (ID) time, but little attention has been paid to cationic modifications and their structure-property relationships. In this work, we present a new strategy of cationic functionalization by introducing the energetic nitrato group into the cationic units of HILs. Interestingly, the introduction of oxygen-rich nitrato groups into the cationic structure significantly improved the combustion performance of HILs with larger flame diameters and duration times. The density-specific impulse (ρIsp ) of these novel HILs are all above 279.0 s g cm-3 , much higher than that of UDMH (215.7 s g cm-3 ). In addition, the densities of these HILs are in the range of 1.22-1.39 g cm-3 , which is much higher than that of UDMH (0.79 g cm-3 ), showing their higher loading capacity than hydrazine-derived fuels in a propellant tank. This promising strategy of introducing nitrato groups into the cationic structures has provided a new platform for developing high-performing HILs with improved combustion properties.

Towards N-alkylimidazole-borane-based hypergolic fuels

Over the past few decades, toxic and highly volatile hydrazine derivatives have been the main fuel choices for liquid bipropellants, especially in traditional hypergolic rocket engines. The search for new hypergolic fuels as replacements for hydrazine derivatives is of great interest to researchers. In this study, a series of N-alkylimidazole borane compounds has been synthesized and characterized. Interestingly, these compounds display promising applications as potential hypergolic fuels owing to their excellent physiochemical properties including low melting points, high thermal stability, low viscosities, and unique hypergolic reactivity. Compared with popular hypergolic ionic liquids, the cost-effective and scaling-up advantages of these materials highlight their promising potential as high-performance fuels in liquid bipropellant formulations.

Green primary energetic materials based on N-(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)nitramide

In this study, a series of high-energy-density materials (1·2H2O–9) based on N-(3-nitro-1-(trinitromethyl)-1,2,4-triazol-5-yl)nitramide were synthesized and structurally characterized using 1H NMR, 13C NMR, IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The crystal results demonstrated that potassium 3-nitro-5-(nitroimino)-1-(trinitromethyl)-1,2,4-triazolate hydrate (2·H2O) exhibits an infinite two-dimensional (2D) metal–organic framework (MOF) containing the coordination group NO2 and metal cation K+. Additionally, this 2D MOF exhibited a high oxygen content (46.41%) and a positive oxygen balance (14.77%). Heats of formation and the detonation properties of the newly prepared compounds were calculated using the Gaussian 09 and EXPLO 5 programs, respectively. Energetic evaluation indicated that these compounds demonstrate good detonation performances, all of which outperform traditional primary explosives mercury fulminate, lead azide, 2-diazo-4,6-dinitrophenol, and in some cases, even exceed the performance of high explosive RDX. Therefore, the high detonation parameters of the compounds enable these potential primary explosives to trigger the whole detonation easily. Furthermore, several attractive properties, such as an excellent density (2.00 g cm−3), an impact sensitivity of 2 J, a friction sensitivity of 32 N, and a low amount of toxic detonation products, make 2·H2O an eco-friendly primary explosive.

Rational Design and Facile Synthesis of Boranophosphate Ionic Liquids as Hypergolic Rocket Fuels

The design and synthesis of new hypergolic ionic liquids (HILs) as replacements for toxic hydrazine derivatives have been the focus of current academic research in the field of liquid bipropellant fuels. In most cases, however, the requirements of excellent ignition performances, good hydrolytic stabilities, and low synthetic costs are often contradictory, which makes the development of high-performance HILs an enormous challenge. Here, we show how a fuel-rich boranophosphate ion was rationally designed and used to synthesize a series of high-performance HILs with excellent comprehensive properties. In the design strategy, we introduced the {BH3 } moiety into the boranophosphate ion for improving the self-ignition property, whereas the complexation of boron and phosphite was used to improve the hydrolytic activity of the borohydride species. As a result, these boranophosphate HILs exhibited wide liquid operating ranges (>220 °C), high densities (1.00-1.10 g cm-3 ), good hydrolytic stabilities, and short ignition delay times (2.3-9.7 milliseconds) with white fuming nitric acid (WFNA) as the oxidizer. More importantly, these boranophosphate HILs could be readily prepared in high yields from commercial phosphite esters, avoiding complex and time-consuming synthetic routes. This work offers an effective strategy of designing boranophosphate HILs towards safer and greener hypergolic fuels for liquid bipropellant applications.