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Abstract: The performances of NEPE (Nitrate Ester Plasticized Polyether) propellants containing 1,1 diamino‐2,2‐dinitroethylene (FOX‐7) were evaluated by means of theoretical calculation, combustion, mechanical and sensitivity experiments. It was found that, by the replacement of Cyclotetramethylene tetranitramine (HMX) with FOX‐7 in NEPE propellants, the density (ρ) was maintained to be the same 1.80 g cm−3, whereas the combustion temperature (Tc) decreased from 3700 K to 3592 K. The meaN molecular weight of combustion gas (Mc) was slightly increased (from 27.28 to 27.48 g mol−1) and the theoretical specific impulse (Ispo) was decreased from 2615 to 2560 N s kg−1. The content of FOX‐7 was in the range of 0 % to 34 % in the formulation of NEPE propellant. It was also shown that the burning rate was increased along with the elevated pressure exponents from 0.44 to 0.48. Moreover, the tensile strength of the propellants at +20 °C and +50 °C was improved from 0.84 and 0.68 MPa to 1.06 MPa and 0.75 MPa, respectively, while the maximum elongation decreased from 64.1∼86.1 % to 32.5∼45.3 %. In terms of safety, the friction sensitivity of the propellant was improved (initiation probability decreases from 100 % to 88 % under pressure of 2.45 MPa) and the impact sensitivity (H50) increased from 6.74 N m to 9.31 N m (2.5 kg hammer). [ABSTRACT FROM AUTHOR]

The RDX, HMX, and AP are currently the most widely used energetic ingredients in composite solid propellants, since the newly developed energetic compounds are still unable to replace them due to various bottleneck technical problems. In order to improve their combustion efficiency and performance, a common alternative way is to utilize novel nano-sized energetic additives. There are a great many nanomaterials that have been developed in the past decades, which include nanometal particles, metal oxides, metal salts, metallic composites, organometallic compounds, energetic nanocatalysts, and carbon nanomaterials. These additives could increase both the decomposition and the burning rate as well as enhance the combustion efficiency of the corresponding solid propellants by changing the thermal conductivity, energy barrier of thermolysis, heat of reaction, and gas-phase reaction mechanisms of the main ingredients such as RDX, HMX, and AP. This review paper discusses and summarizes the effects of abovementioned nano additives on decomposition kinetics, reaction models, decomposition mechanisms and burning rates, pressure exponents, combustion wave structures, and flame propagation of RDX-, HMX-, and AP-based energetic compositions. The catalytic mechanisms associated with different types of nanomaterials are explained and clarified. Owing to their extremely large specific surface areas, nano-sized energetic additives have significant catalytic effects in both condensed and gas phases during decomposition and subsequent combustion via activation of the reactants and acceleration of their transition state formations. The flame structures of AP-based composite propellants under the effect of some nanoadditives are presented showing the enhanced burning characteristics and stabilized combustion process. [ABSTRACT FROM AUTHOR]

Abstract: The combustion efficiency of metallized propellants are investigated and compared to the corresponding blank propellant in order to evaluate the actual effect of the metals in solid rocket applications. The image analysis coupled with energy dispersive spectrometry (EDS) analysis on a scanning electron microscope (SEM) and quantitative X-ray diffraction analysis were applied to the characterization of the original metal particles such as aluminum (Al), magnesium (Mg), boron (B), nickel (Ni), and Mg–Al alloy (Mg/Al) and their condensed combustion products. Under the explored operating conditions, the results confirm that the metallized propellants show heterogeneous diffusing flame, with significant change in pressure sensitivity, and larger aggregation/agglomeration phenomena in combustion products than that of the blank propellant. Besides, the chemical reactions in condensed phase and gas phase which control the burning process and combustion efficiency of the double-base propellant containing different metal particles were systematically investigated and descriptions of the detailed reaction mechanisms from solid phase to liquid phase or to gas phase are also included. It was indicated that the combustion efficiency is favored by the activity and melting points of the metals. [Copyright &y& Elsevier]

Abstract: In order to evaluate the actual pros and cons in the use of new nitroamines for solid rocket applications, the combustion properties of double-base propellants containing nitrogen heterocyclic nitroamines such as RDX, TNAD, HMX and DNP are experimentally investigated by means of high-speed photography technique, thermogravimetry (TG) and differential scanning calorimetry (DSC). It was indicated that DNP and TNAD can yield a lower pressure exponent than that of RDX and HMX, especially, TNAD-CMDB can give plateau burning at higher pressure with higher burning rates (, ) than that of RDX and HMX. It was also concluded that the rate of change in space of the temperature gradient is negligible for these propellants and the rate of mass diffusion is assumed to be small compared with the rate of mass convection. Furthermore, the reaction of CH2O + NO2 → CO + NO + H2O is probably the most important one in the foam layer of the propellants containing nitrogen heterocyclic nitroamines and the thermodynamic phase transition consisting of both evaporation and condensation of NC, HMX, TNAD, RDX and DNP, are considered to provide a complete description of the mass transfer process. [Copyright &y& Elsevier]

In this paper, the dependences of the morphology, particle sizes, and compositions of the condensed combustion products (CCP) of modified double-base propellants (1,3,5-trimethylenetrinitramine (RDX) as oxidizer) on the chamber pressure (<35 MPa) and nickel inclusion have been evaluated under a practical rocket motor operation. It has been shown that higher pressure results in smaller average particle sizes of the CCPs. The CCPs of Ni-containing propellants have more diverse morphologies, including spherical particles, large layered structures, and small flakes coated on large particles depending on the pressure. The specific surface area (SSA) of CCPs is in the range of 2.49 to 3.24 m2 g−1 for propellants without nickel are less dependent on the pressure, whereas it is 1.22 to 3.81 Ni-based propellants. The C, N, O, Al, Cu, Pb, and Si are the major elements presented on the surfaces of the CCP particles of both propellants. The compositions of CCPs from Ni-propellant are much more diverse than another one, but only three or four major phases have been found for both propellants under any pressure. The metallic copper is presented in CCPs for both propellants when the chamber pressure is low. The lead salt as the catalyst has been transformed in to Pb(OH)Cl as the most common products of lead-based catalysts with pressure lower than 15 MPa. When pressure is higher than 5 MPa, the nickel-based CCPs has been found to contain one of the following crystalline phases: Pb2Ni(NO2)6, (NH4)2Ni(SO4)2·6H2O, C2H2NiO4·2H2O, and NiO, depending on the pressure. [ABSTRACT FROM AUTHOR]

To improve the ignition and combustion behaviors of Al, the strategy of interfacial modification using transition metals (TMs) for the Al/AP composites to produce the multi-layered core-shell structured Al@TMs@AP composite fuels is provided. The relevant Al-based composite fuels are fabricated using spray granulation method and their morphologies are characterized by SEM and TEM techniques. The ignition and combustion of the solid propellants prepared with the core-shell structured composite fuels are evaluated and compared with that of reference propellant formulated with typical compositions using laser ignition setup and combustion diagnostic system. Results indicate that the heats of reaction measured for the Al@TMs@AP contained propellants are increased by as high as 13%, suggesting the completeness in combustion of Al is greatly improved by construction of Al composites with the multi-layered core-shell structure. The ignition delay times are apparently shortened from 421 ms to 373 ms for the propellants with Al@TMs@AP involved, which proves that the promoted ignition of Al is achieved by surface modification with transition metals. Additionally, the significantly increased burning velocity is monitored for the Al@TMs@AP contained propellants at low-pressure regime leading to the corresponding pressure exponents to be reduced by more than 20%, which is beneficial to the stability in operation of solid rocket motors. At last, the higher combustion wave temperature and finer particle size in CCPs are observed for the propellants containing surface modified Al, and the plausible combustion mechanism is proposed based on the phase composition analysis for the CCPs of studied propellants. [ABSTRACT FROM AUTHOR]

• The combustion performance is significantly enhanced with the addition of integrated Al/oxidizers composites. • The burning rates of propellants can be well regulated in a wide range under 0.5–15 MPa with reduced pressure exponents. • The agglomeration of Al particles is greatly inhibited and the mechanism has been proposed and elucidated. Modulation of burning rates and inhibition of aluminum agglomeration in solid propellants have generated considerable research interest in the field of energetic materials. In this paper, integrated Al/oxidizer composites have been prepared by a spray-drying technique, which offer intimate contact between the fuel and oxidizers. The morphologies, thermal stability, density, heats of explosion and combustion performance of the resulted solid propellants containing these Al-based composites were systematically investigated, where the condensed combustion products (CCPs) analysis and the agglomeration behavior of Al particles have been focused. After well control of the Al/oxidizers structure, 9 % higher explosion heat, 58 % higher pressurization rate and 65 % stronger flame radiation intensity were achieved in comparison to the conventional solid propellants with the same formulation. The burn rate of the propellants can also be well controlled by using different type of Al/oxidizers composites, in the range of 3.6–5.9 mm s−1 under 0.5 MPa and 9.2–10.9 mm s−1 under 15 MPa. More importantly, very low burn rate pressure exponent of 0.1 within 0.5–15 MPa was obtained. Inspired by decreasing size of CCPs, the evolution of Al on the burning surface was studied and the agglomeration inhibition was observed, whose potential mechanism was then proposed and elucidated. [ABSTRACT FROM AUTHOR]

As a novel high energy fuel, aluminum hydride (AlH 3) has great potential in the field of solid propellants because of its high hydrogen capacity, which can significantly improve the specific impulse of solid propellants. In order to improve the stability of α-AlH 3 , hydrochloric acid has been used to stabilize AlH 3 and the stabilization mechanism has been investigated. Various characterization techniques including scanning electron microscopy, X-ray electron spectrometer, X-ray diffraction, thermal analysis, and vacuum stability test have been employed to investigate the morphology, crystal structure, thermal stability, and decomposition kinetics of raw and passivated α-AlH 3. The results showed that the honeycomb-like structures could be formed on the surface of α-AlH 3 after passivation. First of all, the initial decomposition temperatures of the passivated samples were slightly increased. In particular, for the optimized sample with 105 min passivation time (AlH 3 -105min), the initial decomposition temperature (173.4 °C) is increased by 5.6 °C. Moreover, the total decomposition time (1652 min) is improved by about 50% than that of the raw sample (1098 min). Besides, the decomposition activation energies (E a) of passivated samples are much higher than that of the raw sample (84.8 kJ mol−1), in which the optimized sample (AlH 3 -105min) reaches 107.1 kJ. mol−1. The decomposition kinetics model may change from 3-D nucleation and nucleus growth model to 2-D nucleation and nucleus growth model. It demonstrates the passivated samples have a lower decomposition rate and higher thermal stability. The stabilization mechanism is as follows: removing the impurities on the surface and accelerating the hydrolysis reaction of AlH 3 to generate complete and dense oxide layers. [Display omitted] • The stabilization of AlH 3 has been achieved by surface passivation in acidic media. • The activation energy of the optimized sample has been improved by 22.3 kJ. mol−1. • The optimized passivation time was determined by the decomposition activation energy. • The decomposition kinetics models and stabilization mechanisms have been proposed. [ABSTRACT FROM AUTHOR]

• Thermal reactivity of core–shell Al@AP and Al@AP/CuO composites were characterized. • The decomposition kinetics and gaseous products of composites were fully identified. • The Al@AP and Al@AP/CuO composites demonstrated better combustion performance. • Mutual interactions of Al@AP embedded with CuO under high temperature were clarified. Conventional solid propellants suffer from undesirable combustion performance due to the poor mass and heat transfer between metal fuels and oxidizers, as well as a lack of catalytic active sites between the catalyst and catalyzed objects. Embedding metal fuels and catalysts within the oxidizer has shown promise in improving the overall combustion performance of HTPB/AP/Al and HTPB/AP/RDX/Al composite solid propellants. However, the underlying mechanisms responsible for this enhancement remain to be further understood. In this study, we investigated the reactivities of core–shell Al@AP and Al@AP/CuO composites using thermal analysis and combustion diagnostic techniques. The results demonstrated that the decomposition of AP was promoted, as evidenced by a lower peak temperature (415.2–334.7 ℃), higher total heat release (116.4–720.8 J·g−1), a transition in the decomposition physical model from the random nucleation and 2D/3D growth of nuclei model to the auto-catalytic model, and increased generation of NO 2. Furthermore, the Al@AP/CuO propellant pellet exhibited a more stable flame without agglomeration, and the condensed combustion products (CCPs) contained a lower amount of unreacted Al compared to that of conventional mixtures. These findings highlighted the potential of core–shell Al@AP and Al@AP/CuO composites as replacements for discrete ingredients of solid propellants, thereby offering improved performance for next-generation propulsion systems. [ABSTRACT FROM AUTHOR]

Tailoring the combustion performance of propellant plays an important role in solid propellant design. Herein, we present that interfacial reaction (thermite reaction on Al surface) could be used for tuning the combustion performance of Al-based propellants. Two interfacial reactions included Al-based core-shell composites Al@PDA@CuO (Al@CuO) and Al@PDA@PVDF (Al@PVDF) were prepared and characterized. It is found that both Al@CuO and Al@PVDF have slightly decreased heat release and density, but significantly promote Al combustion, in comparison to the mechanically mixed ones without interfacial reaction. Experiments on ignition, combustion, agglomeration, and thermal property of those propellants containing core-shell Al-based composites have been carried out. The results show that both Al-CuO and Al-PVDF interfacial reactions could reduce the ignition delay time and improve the burn rate of propellant due to the low initial reaction temperature and generated high heat. In addition, it is also found that the interfacial reaction between Al and CuO could increase the size of condensed combustion products of the propellants due to the formation of AlCu 4. However, average condensed combustion product diameter of the propellant using Al@PVDF as the fuel is 0.47 µm, which is smaller than that of propellant using mechanically mixed Al/PVDF as the fuel (0.61 µm). This is a 23% decrease in agglomerate diameter compared with agglomerates formed from the propellant without interfacial reaction. These results reveal that different interfacial reaction may result in very different oxidation reaction mechanisms of Al that controls the combustion performances of the Al-based propellants. [ABSTRACT FROM AUTHOR]

Aluminum (Al) has been widely used in solid composite propellants (SCPs) to increase the specific impulse. However, Al always subjects to coalescence, sintering to large agglomerations during combustion of SCPs resulting in larger two-phase flow losses. Herein, core-shell μ-Al@M(IO 3) x composites have designed and synthesized as a replacement for micron-sized Al (μ-Al) in the Al/AP/RDX/HTPB propellant with tunable combustion behavior. The results show the thermal reactivity and heat releases of SCP are largely enhanced by using these novel metal-based composites. With the inclusion of μ-Al@EGCG@Fe(IO 3) 3 (EGCG: Epigallocatechin gallate), the major exothermic peak is reduced by 29.1 °C compared to the reference propellant with a heat release increase up to 5475 J g−1, exceeding that of the reference sample (86 J g−1 higher). The burn rates are increased with the inclusion of μ-Al@(MIO 3) x , while the pressure exponent is higher. The SCP-1 (0.3), SCP-2 (0.18) and SCP-4 (0.25) that have relatively low pressure exponent and high burn rates are good candidates for future applications. The major condensed combustion products (CCPs) of these SCPs are Al 2 O 3 , Al 2.81 O 3.56 N 0.44 , Al 4 C 3 , Al 2 OC, AlN and C 7 H 18 ClN. The agglomeration can be reduced with a minor inclusion of μ-Al@M(IO 3) x due to the enhanced interfacial reactions, and the average CCP sizes (0.5 μm for SCP-1 and SCP-4) are even smaller than that of initial μ-Al (1.2 μm). [ABSTRACT FROM AUTHOR]

• Interfacial control Al@HMX composites with graphene-based carbohydrazide complexes as catalysts are prepared via spray-drying technique. • Enhanced heat release, reaction efficiency and ignition process between Al and HMX are realized. • A more complete oxidation reaction of Al by HMX is verified by reducing unreacted Al and increasing content of submicron-sized condensed products. • The synergy of interfacial control and GO-based catalysts on the decomposition mechanism of HMX is proposed and discussed. The incomplete combustion of aluminum in solid propellants leads to a low-level energy release. As a promising strategy, fuel/oxidizer interfacial control is proved to be effective for enhancing their reaction efficiency and less environmental dependence. In this paper, in order to investigate the effect of interfacial control on the reaction efficiency of Al and HMX, spherical Al@HMX composites with polydopamine as interfacial layer were prepared via spray-drying technique. The morphology, structure, heat of reaction, thermal stability, condensed/gaseous products, decomposition kinetics as well as the ignition performance of the composites under the catalytic effects of graphene-based carbohydrazide complexes (GO-CHZ-M, M = Co2+ or Ni2+) were comprehensively investigated. Results showed that the heat of reaction of Al@HMX increased by 220 J g−1 compared to corresponding physical mixture (5655 J g−1), which was further increased to 6210 J g−1 in presence of minor GO-CHZ-Co (1 wt%) as a catalyst. Moreover, the thermal decomposition temperature of HMX was slightly increased in Al@HMX composites. Under the synergy of interfacial control and GO-based catalysts, the enhanced reaction efficiency of Al with HMX was observed and verified by a shorter ignition delay time (reduced from 126 to 71 ms) and the condensed products analysis, with decreasing unreacted Al content and increasing content of submicron-sized particles. Gaseous products investigation illustrated that there were two main decomposition pathways for Al@HMX composites: the C N scission (dominant) and N N scission, where the latter could be enhanced by GO-CHZ-M catalysts. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical properties of a typical four-component composite solid propellants with various designed Al/oxidizer interfaces have been studied. The Al/oxidizer interfacial control is mainly realized by using the core-shell composites AP@Al and Al@RDX with different particle sizes, where Al powder was coated with a thin layer of polydopamine (PDA) as the binding sites, so that the oxidizers could crystalize on it during a rapid spray granulation process. The stress-strain curves of the above propellants at different temperatures and different tensile rates have been obtained. The dependence of the loss factor on temperature was studied by using a dynamic thermomechanical analysis (DMA). It has been shown that the fracture elongation of the interfacial modified propellants can reach 51.81% at room temperature, which is 127.3% higher than that of the blank formulation under the same formulation. Moreover, the temperature and strain rate sensitivity of interfacial controlled HTPB propellants is much less than that of traditional ones. The microstructure of these propellants at the crack sites was investigated by scanning electron microscopy (SEM) supported with micro-area in-situ tensile CT scanning technology, to clarify their damage and failure mechanisms. • Two types of core-shell Al-based composite fuels and corresponding solid propellants have been prepared. • The fracture elongation of the interfacial controlled solid propellants was improved significantly. • The temperature and strain rate sensitivity of these propellants are much less than those of traditional ones. • The fracture mode and damage evolution mechanisms of these propellants have been clarified. [ABSTRACT FROM AUTHOR]

Nanoscale aluminium (nAl)-based composites find important applications in propellant, explosives and pyrotechnics, and the improved combustion efficiency is always desirable but challenging. A core-shell nAl@CuO composite with improved combustion performance was prepared by means of a biological interfacial layer, which is inspired by the fast polymerization and strong adhesion of juglone and tannic acid in walnut peel juice. It is found that interfacial layer contains phenolic hydroxyl and amino groups, which could interact with nAl and introduce the growth of CuO crystal, respectively. Obtained nAl@CuO shows higher stability but 1.2 times more heat release than that of the mechanically mixed nAl/CuO. In addition, nAl@CuO also has 5 times faster burning rate than the mechanically mixed one. It is believed that interfacial layer hindered the direct contact of reactants but improved mass transport/diffusion efficiency in nAl@CuO. Thus, Al based composites with higher stability and superior combustion efficiency could be obtained by this interfacial layer. [Display omitted] • Core-shell structured nAl based composites with superior combustion efficiency was prepared. • Walnut peel juice was used in the Al surface engineering as a simple and environmentally friendly method. • The CuO crystal was synthesized under the introduction of interfacial layer, forming core-shell structured nAl@CuO. • nAl@CuO has 1.2 times higher heat release and 5 times faster burning rate than nAl/CuO. [ABSTRACT FROM AUTHOR]

[Display omitted] • Homogeneous composites have been obtained by in-situ recrystallization method. • Stability of AlH 3 and reactivity of oxidizers in composites are both improved. • VST results indicate the involved mixture systems are all compatible. • Composites have higher flame radiation intensity and shorter ignition delay time. Aluminum hydride (AlH 3), as a promising fuel, has been utilized to improve the energy performance of propellants. Moreover, the inherent compatibility and mutual interaction between AlH 3 and the commonly used oxidizers of solid propellants are the basics of propellant formulation design. Herein, the homogenous composites of AlH 3 /oxidizer have been prepared by the in-situ recrystallization method, and then their thermal stability, compatibility, and ignition performance have been investigated. The initial decomposition temperatures (T i) of AlH 3 in composites are increased by at least 16 °C, whereas the thermal decomposition peak temperatures (T p) of involved oxidizers are lower than that of their pure state. The compatibility tests showed that AlH 3 is compatible with the mentioned oxidizers. In particular, the induction time of the dehydrogenation of AlH 3 in presence of these oxidizers is improved by almost 1.2 times that of raw AlH 3 , which means that the oxidizers have an unexpected strong stabilization effect on AlH 3 due to strong hydrogen bonding. Moreover, the optimized contents of AlH 3 in AlH 3 /HMX, AlH 3 /CL-20, and AlH 3 /AP composites have been determined to be 45 %, 40 %, and 33 %, which have the maximum flame temperatures of 1275.3, 1440.4, and 1616.8 °C, respectively. Besides, AlH 3 /CL-20 has the strongest flame radiation intensity (18.5 K) and shortest ignition delay time (32.2 ms) among the involved composites. [ABSTRACT FROM AUTHOR]

The preparation and energy release mechanism of catalyst-coated RDX: (A), diagram of preparation of catalyst-coated RDX based CPs; (B), Dependence of the burning rates (r, mm·s−1) on initial chamber pressures (P, 1–3 MPa) in Ar atmosphere under ambient initial temperature; (C), Flame temperature and burning time at 2 MPa for different CPs. [Display omitted] • High energy density and insensitive qy-RDX hybrid crystals is prepared. • The in-situ synthesis and coating of metal oxides as catalysts on qy-RDX results in greatly improved catalytic efficiency. • The pressure exponent of composite propellants was reduced by 50% by using only 10 wt% of catalyst-coated qy-RDX. High-energy solid propellants with lower pressure exponent, lower burn rate but with high combustion efficiency are usually desired. The use of catalysts in less amount but maintained high efficiency is essential for high-energy content and better combustion performances. The fine combination of catalyst with energetic fillers as oxidizer has been found to be a promising strategy to achieve this goal. In this paper, a widely used nitramine oxidizer, cyclotrimethylenetrinitramine (RDX) has been selected as a typical example, which was first intercalated for lower sensitivity and lower burn rate, and then it was coated with in-situ synthesized nanosized metal oxides as catalysts for lower pressure exponent using polydopamine as the interfacial binding layer. Two types of catalyst-coated hybrid RDX crystals (named as qy-RDX@Fe 2 O 3 and qy-RDX@CuO) have been prepared and characterized. It is found that the in-situ grafted nano-Fe 2 O 3 and CuO crystals have significant catalytic effect on qy-RDX, which increased the heat release of qy-RDX@Fe 2 O 3 and qy-RDX@CuO from 1747 J·g−1 to 2159 J·g−1 and 2133 J·g−1, respectively. The results show that both qy-RDX@Fe 2 O 3 and qy-RDX@CuO could reduce the ignition delay time and largely improve the burn rate of corresponding propellants at lower pressure (e.g. increased from 3.14 mm·s−1 to 5.50 mm·s−1 at 1 MPa) by coating only 0.13 wt% Fe 2 O 3 and 0.15 wt% CuO catalysts, resulting in much lower pressure exponent (from 0.32 to 0.15). In particular, the decomposition heat of propellant containing only 10 wt% of qy-RDX@CuO is 1.5 times higher than the reference blank sample, so that its flame temperature was increased from 1800 °C to 2400 °C due to higher combustion efficiency with more energy release. [ABSTRACT FROM AUTHOR]

• Composite propellants (CPs) containing insensitive high-energy qy-HMX have been prepared. • The qy-HMX-based CPs has 9.64% higher heat of explosion than HMX-based one. • The burn rate of CPs containing qy-HMX is 4.38 mm·s−1 at 3 MPa, 45.9% lower than that of corresponding HMX-based one. • The average particle size of the CCPs of qy-HMX-based CPs is 71.5% lower than that of HMX-based one. Two types of qy-HMX (insensitive HMX with improved energy density, numbered 1 and 2) have been used and studied as an ingredient of HTPB-based composite propellants (CPs), and the decomposition and combustion performances have been investigated. It has been shown that the main exothermic peak temperature of blank CPs containing 21 wt% of qy-HMX-1 is 258.9 °C, which is 4.7 °C higher than that of HMX-containing one, indicating improved thermostability. The corresponding heat of explosion for blank qy-HMX-2-based CPs was measured to be 5830 J∙g−1, which is 300 J∙g−1 higher than that of HMX-based one. Interestingly, the qy-HMX-2-based CPs has higher energy density than corresponding CL-20-based ones, but it has much lower burn rate under the same pressure, e.g. 4.38 mm∙s−1 at 3 MPa for the former vs. 9.03 mm∙s−1 for the latter. Under the effect of typical conventional catalysts such as nano-CuO and nano-Fe 2 O 3 , the qy-HMX-1-based CPs showed increased heat of explosion and higher burn rate. In addition, the particle sizes of condensed combustion products (CCPs) of CPs containing qy-HMX-2 are much smaller than that of HMX-based one, where the Al 4 C 3 was produced as its unique CCPs ingredient. [ABSTRACT FROM AUTHOR]

In this work, Si@NC/AP and Si@PVDF/CL-20 composites with different Si contents have been fabricated by spray-drying technique. The flame structure, ignition delay time and combustion process have been investigated. It has been shown that the ignition delay of Si-based fuel with 40 wt% of Si is the shortest. This means that oxygen balance and the catalytic effect of Si on the energetic composites are playing a dominant role during the combustion processes of these composites. The solid composite propellants (SCP, named as SCP-1 and SCP-2) contains two typical Si-based composites Si-80@NC/AP and Si-80@PVDF/CL-20 have been prepared for propellant applications. Their propellants containing the corresponding mechanical mixtures (named as SCP-3 and SCP-4) have been fabricated as a comparison. It has been observed that the cross sections of propellants containing Si-based composites are denser than that of the reference propellants. The burn rate of SCP-1 (with Si-80@NC/AP) and SCP-2 (with Si-80@PVDF/CL-20) are 5.74 and 5.10 mm s−1 at 2.0 MPa, respectively, which are lower than those of the reference samples SCP-3 (6.51 mm s−1) and SCP-4 (5.70 mm s−1). However, the pressure exponent of former is slightly lower than that of the latter. Moreover, the combustion products (CCPs) of SCP-1 and SCP-3 are more fluffy and smaller in particles size than those of SCP-2 and SCP-4. This indicates that the core-shell structured composites have much better combustion performances due to better heat and mass transfer between the oxidizers and Si as fuel. [ABSTRACT FROM AUTHOR]

Owing to the novel insensitive high-energy-density material 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide (ICM-102) has lower sensitivity and higher energy(see in Table S1, Supporting Information), it has great advantages in the application of low-vulnerability propellants. In this paper, the evaluation of ICM-102-containing composite propellants has been carried out, where the decomposition and combustion performances of these propellants have been comprehensively investigated. It has been shown that the main exothermic decomposition peak temperature can be increased from 235 ºC to 350 ºC, when 6 to 10 wt% of ICM-102 was used to replace RDX, but heat release rate was largely increased. Moreover, the burning rate of ICM-102 containing propellants at 3 MPa is in the range of 6.97–7.75 mm• s − 1, depending on its content. The pressure exponent (0.5–3 MPa) is between 0.34–0.44. Compared with the typical propellants with RDX, the burn rate and the flame temperature of ICM-102- containing propellants are higher. In addition, the particle size distributions of condensed combustion products of ICM-102 propellants are narrower and smaller than that of RDX-based one. It also shows that extra products such as aluminum carbide (Al20C) and aluminum oxide nitride (Al5O6N) were produced once ICM-102 was used. [ABSTRACT FROM AUTHOR]

The ignition and combustion characteristics of kerosene fuels containing polydopamine (PDA)-coated metastable intermixed composite (MIC) nano-aluminum (n-Al)/nano-copper oxide (CuO) are experimentally investigated, with a focus on the mass content of CuO in n-Al@PDA@CuO MICs. The total heat release of n-Al@PDA@CuO (2%) is found to be higher than that of the other n-Al@PDA@CuO samples. During the combustion of n-Al@PDA@CuO (2% and 5%)/kerosene droplets, a yellow flame appears around the agglomerate, which eventually evolves into a yellow light sphere with a diameter of around 5 mm after the kerosene flame extinguishes. Examination of the normalized droplet diameter curves and the morphology of combustion residues shows that the n-Al@PDA@CuO (2%)/kerosene droplet has the best all-around combustion characteristics. A mechanism is proposed for the enhancement of kerosene combustion by n-Al@PDA@CuO. Supporting data from thermogravimetry and differential scanning calorimetry (TG-DSC) measurements are presented. The findings and data in this study are expected to advance the development of new kerosene-based nanofluid fuels that meet the high energy demands of liquid propulsion systems. [ABSTRACT FROM AUTHOR]

• Recent advances on preparation/regeneration methods and processing techniques of high energy fuel (AlH 3) are summarized and discussed. • The detailed thermal decomposition properties and mechanisms under different conditions are elucidated. • The ignition and combustion properties and modifications methods are summarized and discussed for the first time. • Various challenges and future perspectives on the development of AlH 3 as high energy fuel have been proposed. As a novel energetic material, aluminum hydride (AlH 3) has attracted much attention because of its high hydrogen storage capacity and rapid dehydrogenation at low temperatures, which can be used as a promising energetic additive in solid propellants or in some other areas such as catalysts, fuel cell, and reducing agents. In particular, AlH 3 as a component of solid propellant may largely promote the specific impulse of rocket engines and effectively reducing the erosion of engine nozzles. This review focuses on the research results in synthesis/regeneration, thermal decomposition, oxidation, ignition and combustion characteristics, and stabilization of AlH 3 over the past decades. In particular, the stabilizing of AlH 3 is essential for the its application in solid propellants, where the most widely used strategies have been introduced and compared, based on which some suggestions regarding possible future research directions are proposed. [ABSTRACT FROM AUTHOR]

A phase manipulation of molybdenum disulfide strategy has been adopted for fast decomposition of AP and HMX with safety operation performance. • Li-ion assisted manipulation of MoS 2 made it into highly active 1T phase. • 1T-MoS 2 possessed enhanced active sites, electrical conductivity and porosity. • Intrinsic lamellar MoS 2 improved safety performances of AP and HMX. • Fast energy releasing of HMX and AP was gained using 1T-MoS 2 catalyst. Designing advanced component for synergistically achieving the safety performance and energy releasing of widely studied energetic materials (EMs) is of far-reaching significance in composite solid propellants. Herein, molybdenum disulfide with high-active 1T phase (1T-MoS 2) was engineered by a phase-manipulation strategy through chemical Li-intercalation from its original state (2H-MoS 2). The as-prepared 1T-MoS 2 was used for the improved safety and decomposition performances of two typical EMs (ammonium perchlorate: AP and 1,3,5,7-tetranittro-1,3,5,7-tetrazocane: HMX) in propellants. Lubricant 1T-MoS 2 endowed considerable advances in safety performance of EMs, with remarkably reduced the impact and friction sensitivity. Besides, fast energy-releasing performance with visibly lower activation energy was realized for AP@1T-MoS 2 and HMX@1T-MoS 2. In addition, large decomposition heats were simultaneously achieved. Computational studies disclosed this improvement could be attributed to the multi-coupling effect arising from the promoted electron transfer capability, strong affiliations of catalyst/burning products and the abundant actives sites of 1T-MoS 2 phase. Our results demonstrate substantial improvements in the synergistical design of safe and fast-decomposed AP and HMX complex for solid propellants. [ABSTRACT FROM AUTHOR]

• The pressure exponents (1–4 MPa) of Al@PDA@RDX based propellants are greatly decreased. • Steeper temperature profiles and smaller agglomeration sizes are obtained by fine interfacial control of fuel/oxidizer. • The primary combustion mechanism of Al@PDA@RDX based propellants is proposed. In this paper, micro-spherical Al@PDA@RDX composites with fine interfacial control have been fabricated by spray-drying technique, where poly-dopamine (PDA) is employed as a binding layer. These composites have been applied in HTPB/AP/RDX/Al propellants, which have the same theoretical formulation and hence identical specific impulse (I sp). However, these propellants differ in the interfacial structure due to different ways of assembling the ingredients, resulting in significant changes in their combustion performance. The thermal reactivity, burning rate, flame structure and the morphology of condensed combustion products (CCPs) of the prepared propellants have been investigated comprehensively. It has been shown that the pressure exponent (1–4 MPa) can be decreased from 0.236 to 0.024 (10 times lower) by the fine interfacial control, with more than 500 °C increase in flame temperature and 45.5% drop-off in the flame stand-off distance. In addition, the CCPs size distributions of the propellants have shown the enhanced interfacial interaction from Al@PDA@RDX composites can greatly inhibit the large-sized agglomeration of Al particles during the burning process. [ABSTRACT FROM AUTHOR]