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ε-CL-20 is currently the most powerful commercially available explosive, but its high mechanical sensitivity and low phase stability limit its broad applications. In order to reduce the sensitivity of ε-CL-20, cross-linked graphene oxide (GO), using triaminoguanidine–glyoxal polymer (TAGP) as the bridging agent, was prepared in the ε-CL-20 solution, which could constrain the nano-sized ε-CL-20 crystals following a conventional solvent–nonsolvent in situ crystallization method. It was shown that the polymorphic transition temperature of the assembled CL-20/GO–TAGP crystals increased by about 36.0 °C at a maximum level compared with pristine ε-CL-20, and the polymorphic transformation temperature varied depending on the content of the cross-linked GO. Moreover, the heats of formation for the resulting modified products such as CL-20-2 (950.0 kJ kg−1) and CL-20-4 (848.3 kJ kg−1) were 26.9% and 13.3% higher than that of pure ε-CL-20 (748.9 kJ kg−1), respectively. The measured density of assembled CL-20 crystals was almost unchanged as 2.01 g cm−3 under a certain condition. The impact and friction sensitivities of the modified samples, such as CL-20-1, CL-20-3, and CL-20-6, were obviously reduced. More importantly, two of the assembled products even showed a certain improvement in specific impulse and detonation performance. [ABSTRACT FROM AUTHOR]

Co-crystallization of cyclic nitramines with sterically crowded molecules, i.e., ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20) with cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), is very difficult, but the co-agglomeration (slurry method) of their mixed micro-co-particles gives very good results. CL-20 is present in these co-agglomerates (CACs) in its β-form. Besides the medium of co-agglomeration, also the molar ratio is very important; it is possible to obtain β-CL-20/BCHMX (molar 1.8/1.0) with the impact sensitivity of 14.9 J. The density of these CACs approaches 99.6% of the density of the β-CL-20 crystals. Based on the application of the Raman, FTIR and PXRD techniques, it has been proved that the agglomeration of CL-20/BCHMX micro-co-particles leads to the formation of CACs mostly with the properties of co-crystals (CCs). This also seems to be confirmed by the relationships between the heat of formation and ring-deformation vibrations (in plane) and between the impact sensitivity and the difference in the asymmetric NO2 stretching vibrations in pure CL-20 and its CACs. The CACs studied have lower detonation energies than would be consistent with the percentage of individual coformers in these crystals. An examination of the most sensitive CACs (1.2 J) as a detonator primer has shown the absence of its required acceleration capabilities in the given detonator design. A comparison with literature data and our unpublished preliminary results indicates that the CACs and CCs of this type could have potential beneficial applications in propellants. [ABSTRACT FROM AUTHOR]

The surface functionalization of graphene oxide (GO) is always attractive in improving certain properties of the polymer. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyl-trimethoxysilane (SPTES) have been used to make silane functionalized graphene oxides (SiGOs). The APTES-grafted GO (NH-SiGO), SPTES-grafted GO (SH-SiGO) and pure GO have been separately introduced into the nitrocellulose (NC) matrix. The morphology, thermal properties and energetic properties of the prepared nanocomposites (NH-SiGO and SH-SiGO) were investigated comprehensively. It is shown that the presence of GO and SiGOs have different influences on the thermal reactivity of NC with various contents, and NH-SiGO with 0.5 wt% content showed better catalytic performance on the thermal decomposition of NC than others and showed prominently higher efficiency in improving its heat of combustion. Adding 0.5 wt% of NH-SiGO to NC may decrease its decomposition temperature from 202.1 °C to 196.6 °C, and the residue was decreased from 10.61 wt% to 3.95 wt%, respectively. One isoconversional kinetic method was exploited to determine the kinetic parameters of NC and its nanocomposites. It was found that NH-SiGO had a strong catalytic action on the thermal decomposition of NC-based nanocomposites for which the activation energy and the pre-exponential factor were considerably lowered, while SH-SiGO exhibited an inverse effect. The heat of combustion from NC/GO/0.5, NC/NH-SiGO/0.5 and NC/SH-SiGO/0.5 were determined as 11 249.5, 11 675.1 and 11 491.5 J g−1, respectively, which are higher than that of the pure NC (10 908.4 J g−1). From the combustion process of NC/NH-SiGO/0.5, it was shown that the nanocomposite was combusted completely. [ABSTRACT FROM AUTHOR]

The combination of Energetic Ionic Liquid (EIL) "green" fuels and high test peroxide (>90% H2O2; HTP), as a "green" oxidizer, is a very promising platform for the development of fully "green" bipropellants for space exploration. In this work, two new "tandem-action" promoters – [FcCH2N(CH3)3+]2[Cu2I42−] (P1) and [FcCH2N(CH3)3+]n[Cu2I3−]n (P2) – and two reference "single-action" promoters, [FcCH2N(CH3)3+][H3BCN−] (P3) and [CH3N(CH2CH3)3+]n[Cu2I3−]n (P4), were prepared, comprehensively characterized and evaluated for their ability to significantly shorten the Ignition Delay (ID) times of hypergolic reactions between a series of EILs and H2O2. These promoters exhibited high solubility and long-term chemical stability in a typical EIL fuel – 1-ethyl-3-methylimidazolium dicyanamide (F1). Upon screening the performance of promoter–EIL formulations, the best ID result of 31 ms was observed for the combination of 1-ethyl-3-methylimidazolium cyanoborohydride (F2) fuel and promoter P2 (10 wt%), with H2O2 (95%), whereas an ID time of 58 ms was observed for the F2/P2 formulation with commercially available H2O2 (70%), respectively. Remarkably, the latter formulation remained fully homogeneous even at −40 °C, and showed an ID time of 66 ms at this temperature with H2O2 (95%), indicating the advantages of our approach for the development of novel fully "green" bipropellants. [ABSTRACT FROM AUTHOR]

High energy density is always a key goal in the development of energy storage or energetic materials (EMs). Apart from exploring novel EMs with high chemical energy, it is also desirable for traditional EMs to be assembled at a higher density. It has been shown that a molecular level compression effect occurs due to the stacking of 2D triaminoguanidine–glyoxal polymer (TAGP) layers, resulting in a higher density packing of HMX molecules with changed conformation (qy-HMX). The qy-HMX crystal formed under compression in the solvent has a unit cell parameter very close to that of a reported system observed under a pressure of 0.2 GPa. This shows that the qy-HMX molecules are trapped in the TAGP layers, resulting in a higher density (e.g. 2.13 g cm−3), heat of formation and better stability. Certain types of constrained qy-HMX crystals are free from defects, where no polymorphic transition and melting point are observed upon heating. Experiments and relevant calculations show that the best resulted hybrid HMX crystal has a detonation velocity of 10.40 km s−1 and pressure of 53.9 GPa, respectively. Its ground specific impulse reaches about 292 s, much better than that of CL-20, making it a promising propellant component for use in future space explorations. [ABSTRACT FROM AUTHOR]

In this work, we prepared and comprehensively characterized four novel iodocuprate-containing ionic liquids, CuILs 1–4. In addition to their interesting molecular structures and physical properties CuILs exhibited capability to efficiently promote hypergolic reactions between boron-containing [EMIM+][H3BCN−] and [MIM]·[BH3] fuels and a highly concentrated H2O2 (95%) oxidizer. The most promising promoter CuIL 3 has the decomposition temperature well above the decomposition temperature of the fuels, was stable in promoter-in-fuel mixtures for weeks and showed ignition delay times down to 14 ms. We believe that further development of our new iodocuprate ionic liquids can lead to promising “green” H2O2-based bipropellant systems for space applications. [ABSTRACT FROM AUTHOR]

A number of energetic ionic liquids (EILs) have been reported as promising hydrazine-replacement fuels for hypergolic rocket propulsion. However, most of these EILs were ignited using corrosive and hazardous concentrated fuming nitric acid. Very significant efforts were recently made to utilize “rocket grade” highly concentrated H2O2 (＞90%) as a “green” alternative to fuming nitric acid and N2O4 oxidizers. Although “rocket grade” H2O2 is more challenging to use and less safe for storage than commercially available H2O2 (70%), the latter is not considered as a viable oxidizer for hypergolic propulsion. In this work, we focused on the development of novel iodine-rich promoters, capable of initiating hypergolic ignition reactions between a typical EIL fuel – 3-ethyl-1-methyl-1H-imidazol-3-ium cyanotrihydroborate – and H2O2. Among the prepared and evaluated promoters, the top performing [FcCH2NEtMe2+]2[B12I122−] compound 5 showed ignition delay times of 45 ms in the reaction of the tested EIL with H2O2 (70%) and 17 ms with H2O2 (95%). We believe that these findings provide a platform for the development and utilization of commercially available H2O2 as a potential “green” oxidizer for rocket propulsion. [ABSTRACT FROM AUTHOR]

The thermochemical ablation of insulation material caused by slag deposition in solid rocket motors has increasingly attracted researchers’ attention. Understanding the ablation mechanism and the ability to calculate reaction kinetics parameters determine the height of the thermal protection design for advanced solid rocket motors. In this work, the interaction of the Al2O3–C system is determined through static ablation experiments. Using X-ray diffraction, HSC thermodynamic software, and a thermogravimetric analyser, the carbon thermal reduction of alumina is analysed and the reaction mechanism and physical model are obtained. Isothermal experiments at 1700–1850 °C and mathematical analysis provide the kinetic parameters of the overall and step-by-step reactions. The results show that the overall reaction of the Al2O3–C system involves three steps. The overall reaction kinetics are described by the contracting area model R2 with apparent activation and frequency factors estimated as 254.5 kJ mol−1 and 5.5 × 106 min−1, respectively. The distribution reaction kinetics of steps 1 and 2 are described by the first-order chemical reaction control model (F1) and that of step 3 is described by the one-dimensional diffusion control model (D1). The corresponding activation energies are 107.9 kJ mol−1, 240.3 kJ mol−1, and 567.5 kJ mol−1, and frequency factors are 625.94 min−1, 8.3 × 105 min−1, and 1.6 × 1014 min−1, respectively. [ABSTRACT FROM AUTHOR]

In this work, inspired by the strong chemical adhesion of mussels, a facile and noncovalent in situ polymerization of dopamine approach has been employed to coat 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals. The resultant polydopamine (PDA) coated TATB (pTATB) core–shell particles are subjected to in-depth characterizations. It has been demonstrated that a dense graphite-like structure PDA is uniformly coated on the surfaces of TATB crystals. By optimization of the reaction time, pH value and temperature, the morphology and thickness of the PDA layer on TATB crystals were finely controlled on a nanometer scale. Then, the pTATB was further used as the solid filler of a typical polymer bonded explosive (PBX). It has been shown that the PBX containing pTATB exhibited significantly improved tensile and compression strength or strain, and creep resistance, due to the strong interfacial interactions at the PDA interlayer. Moreover, the mechanical properties could be further improved by using more PDA content. This work demonstrates an effective and fundamental surface modification method to enhance the interfacial interaction between crystalline particles and binders, resulting in improved mechanical properties. [ABSTRACT FROM AUTHOR]

A new member of the 2D carbon–nitrogen-rich family of nanomaterials was synthesized by polycondensation of triamino-guanidine hydrochloride with glyoxal. The obtained polymer (TAGP) has a carbon-to-nitrogen ratio of 3 : 4, identical to a ratio found in carbon nitrides. Our analysis showed that TAGP has a layered 2D network-type structure. TAGP is dispersible in polar organic solvents and forms stable complexes with various transition metal ions (TAGP–Ms). TAGP and most TAGP–Ms were found to exhibit properties of insensitive Energetic Materials (EMs), where TAGP shows a very low sensitivity to impact (Im = 71.7 J) and to friction (＞352.8 N). TAGP has also higher nitrogen content than all currently used energetic polymers, including glycidyl azide polymer [GAP], poly(3-nitrato-methyl-3-methyloxetane) [poly-NIMMO], and poly(glycidyl nitrate) [poly-GLYN]. Velocity of detonation of TAGP (6657 m s−1) was calculated to be significantly higher than that of azide-containing GAP and comparable to that of the nitrate ester-based poly-GLYN. In our perspective, TAGP is also an example of a modular and combinatorial approach in which high nitrogen-content aminoguanidine derivatives, reacted with amine-reactive low-carbon-content or energetic crosslinkers, can produce novel energetic polymers with tuneable properties and performance. The properties of the aminoguanidine-based EPs could be even further modified and tuned by coordination of transition metal ions. Our novel TAGP and TAGP–M energetic nanomaterials have great potential to be used in solid propellants and in energetic formulations and composites as new generation energetic binders and combustion catalysts. [ABSTRACT FROM AUTHOR]

In this research, a group of new energetic coordination nanomaterials (CNMs) based on functionalized graphene oxide sheets (FGS) have been designed and characterized. GO was first functionalized with N-rich energetic ligands such as triaminoguanidine (TAG), and then the resulting FGS was coordinated with metal ions to prepare energetic CNMs with high thermostability and insensitivity to mechanical stimuli. The density of GO–TAG–Cu(ii)/Cu(i) is as high as 3.14 g cm−3, while it has a Tp of 495 °C and VoD of 7723 m s−1 by using 40 wt% ammonium perchlorate as the oxidant. These insensitive (Im ＞ 81 J) and highly thermostable energetic CNMs in combination with oxidizers are good candidate ingredients of low-vulnerability solid propellants and charges of deep-well perforating guns. [ABSTRACT FROM AUTHOR]

The thermal behavior, decomposition kinetics and mechanisms of 1-amino-1-(tetrazol-5-yldiazenyl) guanidine (tetrazene) and 2-(tetrazol-5-yldiazenyl) guanidine (MTX-1) have been investigated using DSC, TG techniques, and quantum chemical calculations. It has been found that MTX-1 is much more stable than tetrazene and MTX-1, and both of them decompose in three steps with different kinetic parameters. Tetrazene is melted-dehydrated at 128.4 °C with a heat absorption of 50 J g−1 and then it starts to decompose at around 118.6 °C with a peak temperature of 126.3 °C covered by a heat release of 1037 J g−1 at a heating rate of 1.0 °C min−1, while MTX-1 starts at 167.7 °C with a main peak of 191.1 °C covered by a heat change of 1829 J g−1 under the same conditions. The activation energy is almost the same for their first decomposition steps (225 kJ mol−1), which are controlled by a three dimensional nucleation and growth model (A3). The mechanisms of the rate-limiting steps are supported by quantum chemical calculations. They could undergo a similar rate-limiting chemical process producing 1H-tetrazole and N2 for both cases, while the former also produces aminocyanamide and the latter produces cyanamide. [ABSTRACT FROM AUTHOR]

The surface functionalization of graphene oxide (GO) is always attractive in improving certain properties of the polymer. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyl-trimethoxysilane (SPTES) have been used to make silane functionalized graphene oxides (SiGOs). The APTES-grafted GO (NH-SiGO), SPTES-grafted GO (SH-SiGO) and pure GO have been separately introduced into the nitrocellulose (NC) matrix. The morphology, thermal properties and energetic properties of the prepared nanocomposites (NH-SiGO and SH-SiGO) were investigated comprehensively. It is shown that the presence of GO and SiGOs have different influences on the thermal reactivity of NC with various contents, and NH-SiGO with 0.5 wt% content showed better catalytic performance on the thermal decomposition of NC than others and showed prominently higher efficiency in improving its heat of combustion. Adding 0.5 wt% of NH-SiGO to NC may decrease its decomposition temperature from 202.1 °C to 196.6 °C, and the residue was decreased from 10.61 wt% to 3.95 wt%, respectively. One isoconversional kinetic method was exploited to determine the kinetic parameters of NC and its nanocomposites. It was found that NH-SiGO had a strong catalytic action on the thermal decomposition of NC-based nanocomposites for which the activation energy and the pre-exponential factor were considerably lowered, while SH-SiGO exhibited an inverse effect. The heat of combustion from NC/GO/0.5, NC/NH-SiGO/0.5 and NC/SH-SiGO/0.5 were determined as 11 249.5, 11 675.1 and 11 491.5 J g -1 , respectively, which are higher than that of the pure NC (10 908.4 J g -1 ). From the combustion process of NC/NH-SiGO/0.5, it was shown that the nanocomposite was combusted completely.

The thermochemical ablation of insulation material caused by slag deposition in solid rocket motors has increasingly attracted researchers' attention. Understanding the ablation mechanism and the ability to calculate reaction kinetics parameters determine the height of the thermal protection design for advanced solid rocket motors. In this work, the interaction of the Al 2 O 3 -C system is determined through static ablation experiments. Using X-ray diffraction, HSC thermodynamic software, and a thermogravimetric analyser, the carbon thermal reduction of alumina is analysed and the reaction mechanism and physical model are obtained. Isothermal experiments at 1700-1850 °C and mathematical analysis provide the kinetic parameters of the overall and step-by-step reactions. The results show that the overall reaction of the Al 2 O 3 -C system involves three steps. The overall reaction kinetics are described by the contracting area model R2 with apparent activation and frequency factors estimated as 254.5 kJ mol -1 and 5.5 × 10 6 min -1 , respectively. The distribution reaction kinetics of steps 1 and 2 are described by the first-order chemical reaction control model (F1) and that of step 3 is described by the one-dimensional diffusion control model (D1). The corresponding activation energies are 107.9 kJ mol -1 , 240.3 kJ mol -1 , and 567.5 kJ mol -1 , and frequency factors are 625.94 min -1 , 8.3 × 10 5 min -1 , and 1.6 × 10 14 min -1 , respectively.