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In this work, the preparation and combustion catalysis effects of Cu2O−PbO/GO and CuO−Bi2O3/GO nanocomposites were systematically investigated. It was shown that the burning rate of the DB propellants can be significantly enhanced by both the nanocomposite catalysts, with reduced pressure exponent. In particular, the Cu2O−PbO/GO induced a burn rate enhancement for DB propellant in pressure range of 2–14 MPa, with the maximum catalytic efficiency of 3.87 at 2 MPa. More interestingly, it resulted in "mesa" burning of DB propellant in the pressure range of 12–20 MPa (n=‐0.05). The CuO−Bi2O3/GO have the same effect with a burning rate increasing from 2.15 to 8.57 mm s−1 at 2 MPa. Similarly, for the RDX‐CMDB propellant, the GO‐based composites of Cu2O−PbO/GO and CuO−Bi2O3/GO showed evident catalytic activities. Plateau combustion was achieved in their presence, which is of great importance for practical applications. The catalysis effects of the two composites are closely related to the high dispersion of metal oxide particles and GO with excellent thermal conductivity. [ABSTRACT FROM AUTHOR]

Conceptually new cylindrical charges enveloped by Al foils have been designed and their thermobaric effects, due to simultaneous fragmentation and combustion of the foils, have been experimentally determined. The fragmentation processes of Al foil was supported by numerical simulations. It has been shown that the quasistatic pressures (QSP) for phlegmatized RDX (RDX ph ) enveloped with Al-coated plastic foils are higher than that of the pure RDX ph , due to combustion of these foil fragments in a thermobaric explosion. The QSP generated by Al–Ni foils enveloping RDX ph was found to be much lower than performance of other foils, possibly due to relatively inert nature of Ni. In a small detonation chamber, the charges of RDX ph /Al foil (RDX ph /Alf) produced even higher experimental maximum peak pressure (Δ p max ) than the charges that contained Al powder (Al p ). In a closed bunker, the impulse amplitudes of RDX ph enveloped by aluminized polyethylene (Al-PE) foils and RDX ph enveloped by 100 µm Alf (Alf100) charges are much lower than those of the other charges. It was found that the charges enveloped by Al foils have even larger Δ p max than that of RDX ph /Al p charges, indicating that the Alf could generate better blast performances than the Al p . The simulations indicate that the observed blast enhancement is dependent not on the thickness, but on the size of surrounding space. The thermobaric fire-ball generated by 40 g RDX/Alf charge could sustain combustion up to 40 ms, reaching a maximum radius of about 2.4 m. [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]

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 investigated by means of high-speed photography technique, Non-contact wavelet-based measurement of flame temperature distribution. The chemical reactions in different combustion zone which control the burning characteristics of the double-base propellant containing nitrogen heterocyclic nitroamines were systematically investigated and descriptions of the detailed thermal decomposition mechanisms from solid phase to liquid phase or to gas phase are also included. It was indicated that the thermodynamic phase transition consisting of both evaporation and condensation of NC+NG, HMX, TNAD, RDX and DNP, are considered to provide a complete description of the mass transfer process in the combustion of these double-base propellants, and the combustion mechanisms of them are mainly involved with the oxidation mechanism of the NO2, formaldehyde (CH2O) and hydrogen cyanide (HCN). The entire oxidation reaction rate might be dependent on the pressure of the combustion chamber and temperature of the gas phase. [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]

• 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]

Graphical abstract Highlights • Formulation of PVDF/CuO/Al is optimized on the basis of maximum heat of reaction. • Electrospinning is employed to fabricate high solid-loading MICs based on PVDF. • Electrospinning and doping of GO can improve the density, heat of reaction, etc. Abstract In this paper, the electrospinning technique has been employed to fabricate PVDF/CuO/Al nanocomposites, where the formulation was optimized on the basis of maximizing the reaction heat with increased efficiency. The graphene oxide (GO) has also been used as both lubricant and catalyst, which is well dispersed inside the PVDF matrix by the electrospinning process as well. It has been found that the smooth PVDF nano-fibers could be fabricated with GO content of 0.5 wt%, where the Al and CuO nanoparticles are also uniformly loaded. In comparison with the n-CuO/n-Al and PVDF/CuO/Al prepared by conventional mechanical mixing method, the GO-doped PVDF/CuO/Al nanocomposites via electrospinning improved heat of reaction, density as well as anti-oxidation capability. In addition, the electrospinning technique and doping of 0.5 wt% of GO can improve the reaction efficiency of PVDF/CuO/Al nanocomposites since they contribute to dispersion of components and homogeneous structure fabrication. [ABSTRACT FROM AUTHOR]

Development and molecular engineering of new highly-efficient energetic biocidal materials is a significant challenge and of a great importance. Until now this type of materials included mostly halogen-rich nano-thermites and iodine-rich organic materials. So far, no energetic coordination polymers were reported as precursors for combustion-generated biocidal agents. Here, we demonstrate for the first time the synthesis of uniquely-structured three-dimensional energetic coordination polymer ( ECP3 ) containing Zn metal centers and iodine- and nitrogen-rich bridging ligand ( 2 ). Upon its combustion, ECP3 is capable of generating gaseous reactive iodine species and elemental iodine-coated ZnO particles. ECP3 presents a novel approach for the design of efficient biocidal agents. [ABSTRACT FROM AUTHOR]

The combustion of metastable intermixed composites (MICs) containing fluoropolymers is yet still not well understood. In this study, five new Al/MO X /PVDF nanocomposites (MO X : WO 2 , WO 3 , CuO, Fe 2 O 3 , Bi 2 O 3) are prepared using a high-energy ball milling method. The thermal decomposition behaviors, combustion characteristics, and combustion products of the MICs are compared using TG-DSC, laser ignition test, and a multifunctional combustion diagnostic system. It is proved that PVDF efficiently promotes the energy release of conventional thermites. All five composites show a higher heat of reaction than Al/MO X in an argon environment by over 30%. Al/WO 3 /PVDF has the fastest combustion propagation speed in the confined combustor (72.5 mm⋅s−1). Due to the low boiling temperature and low thermal conductivity of the product, Al/Bi 2 O 3 /PVDF exhibits the lowest ignition delay (62 ms), the best pressure output performance (27.5 MPa⋅s−1), and the least product agglomeration (D 43 = 15.2 μm). Due to the highest heat of reaction (3829 J⋅g−1), Al/CuO/PVDF has the highest flame temperature (2544 °C). The combustion flame temperature of Al/MO X /PVDF nanocomposites is suggested to be controlled by the heat of reaction, the ignition delay is mainly controlled by the thermal conductivity of the material, and the main factor affecting the high pressure output is the boiling point of the combustion products. This study can provide a theoretical basis for the development and application of MICs. [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]

Recently fluoropolymers are of great interest as an oxidative binder and modifier in Al-based metastable intermixed composites (MICs) due to the high heat of reaction between Al-F and gas production characteristics. In this paper, Polytetrafluoroethylene (PTFE) and Polyvinylidene Fluoride (PVDF) have been incorporated into three typical Al-based MICs independently using CuO, Fe 2 O 3 , and Bi 2 O 3 as oxidizers, where the contents of Al to metal oxide are maintained optimum stoichiometric ratios. Heats of reaction have been measured by a bomb calorimeter for mechanically mixed MICs samples, from which the optimum fluoropolymer content has been determined using the maximum calorific values as the criteria. After that, the optimized formulations have been prepared by a spray drying method. The thermal behavior, combustion characteristics and pressurization features of the studied Al-based MICs were evaluated and compared with those without fluoropolymers. The experimental results showed that with a minor inclusion of fluoropolymers, the combustion heat was improved by 3.8% to 8.6% depending on the type of oxidizers, and the onset temperature of the exothermic reaction was observed to be decreased by 250 °C for Al/CuO, 200 °C for Al/Fe 2 O 3 and 16 °C for Al/Bi 2 O 3 with a higher reaction heat release, showing a higher reactivity. Besides, the maximum pressure and pressurization rate were both increased for the fluorine-containing MICs, whereas the burn rates under confinement were found to drop significantly by 72% to 91%. The AlF 3 , Cu-Al alloy, and Fe-Al alloy are found in the condensed combustion products (CCPs), and it tends to have smaller and more uniform particles. It probably results from the large difference in the energy and mass transfer process on the combustion surface when the gaseous phase products are generated. [ABSTRACT FROM AUTHOR]

In this paper, three nanocomposite fuels (Al/TMs@AP) including Al/Co@AP, Al/Ni@AP and Al/Ti@AP have been fabricated by a spray-drying technique. Their morphology, heat of reaction, ignition and combustion performances, as well as their condensed combustion products (CCPs) have been comprehensively investigated. The results suggested that the core-shell structured Al/TMs@AP has lower ignition delay and better combustion performances comparing to the corresponding mechanically mixed ones. The promoted thermal reactivity could be attributed to resulted intimate reactants contacts with shortened heat and mass transfer distance. Furthermore, the reactivity of Ti is higher than that of Co and Ni, so that a much more violent chemical reaction occurred for the Ti-containing composites, and thereby the combustion wave temperature was increased to 2136.6 °C and the particle size of the corresponding CCPs was reduced to as low as 170 nm. Moreover, the compositions of CCPs for Al/Ti/AP and Al/Ti@AP are quite different. The typical CCPs phases for Al/TMs@AP are dominated with Al x TM y O z and Al 5 O 6 N, whereas the CCPs of the other samples are dominated with transition metals oxides such as Co 3 O 4 , NiO and TiO 2 depending on the type of transition metals involved. [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]

• 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]

• ECs can enhance the combustion of Si/Ta. • Core-shell structure has some advantages compared with traditional mechanical mixing preparation method. • The reaction mechanism for ECs enhanced Si/Ta combustion was summarized. • Heat release efficiency of the composites could be well tuned by using different content and type of the ECs. This paper reports a group of new energetic materials (EMs) based on Si/Ta coated with recently developed high energetic composites (ECs), such as AP/NC and PVDF/CL-20. These Si/Ta-based nano-energetic composites have been prepared by both mechanical mixing method and an advanced technique of electrostatic self-assembly followed with a spray-drying process. The heat of reaction and combustion behavior of these novel Si/Ta@ECs composites, as well as the morphologies and compositions of their condensed combustion products (CCPs) have been comprehensively studied. It has been shown that the combustion efficiency of Si-Ta could be largely enhanced with the inclusion of two types of ECs. The maximum energy release was 18.39 kJ cm−3 of Si/Ta with the inclusion of ECs prepared by electrostatic self-assembly followed with spray-drying technique, which was 51.6% of the theoretical energy density of the pure Si/Ta and it is about 9.58 kJ cm−3 higher than the mechanically mixed one. It shows that the enhanced flame has improved luminosity and radiation due to increased energy content with higher reaction rate. The maximum flame-front propagation rate and the condensed phase reaction rate of Si/Ta with the addition of 10 wt% of ECs are 30.1 mm s−1 and 120.7 mg s−1, respectively. The maximum combustion wave temperature of Si/Ta-based composite was 2.4 times higher than that of pure Si/Ta without the ECs inclusion. The typical phase composition of the CCPs is composed of TaSi 2 , which is combined with a minor inclusion of Ta 2 O 5 , TaN 0.25 , TaC and Ta 5 Si 3. The two-step reaction mechanism includes the activation and propagation of the fast combustion wave of the ECs and the initiation of the post-burning reaction. [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]

[Display omitted] • The n-Al@PDA(1 h)/kerosene nanofluid fuel exhibits better stability than n-Al@PDA/kerosene nanofluid fuel. • PDA coating increases the combustion rate of n-Al/kerosene nanofluid droplets. • The role of PDA layer in the n-Al/kerosene nanofluid is revealed. • Mechanism of PDA in the combustion of n-Al@PDA/kerosene. In this experimental study, we examine the stability and combustion of a new nanofluid fuel created by mixing kerosene and nano-aluminum (n-Al) particles coated with polydopamine (PDA). Focus is placed on examining the effect of the PDA coating time, and hence the PDA film thickness, with the aid of a proposed heat transfer mechanism for the combustion of n-Al@PDA/kerosene droplets. The results indicate that n-Al@PDA(1 h)/kerosene (i.e. a PDA coating time of one hour), which remains stable for seven hours, exhibits better stability than all the other samples, but that the stability worsens as the PDA coating time increases. The ignition character of n-Al/kerosene nanofluid droplets is not quite sensitive to PDA layer. The combustion processes of n-Al/kerosene and n-Al@PDA/kerosene are remarkably similar, consisting of four distinct stages: ignition, classic combustion, vapor flame extinguishing, and Al droplet combustion. The burning intensity of n-Al agglomerates coated with PDA is stronger than that without PDA, with more black smoke generated and more n-Al particles expelled near the end of the n-Al burning stage. The combustion rates of kerosene droplets containing 5% n-Al@PDA(1 h) and 5% n-Al@PDA(2 h) are higher than other samples. The intensity of the emission spectra for the n-Al@PDA(2 h) agglomerates is the highest among all the samples. Taken together, these results indicate that, compared with uncoated n-Al/kerosene and other PDA-coated nanofluid fuels, n-Al@PDA(2 h)/kerosene exhibits superior ignition and combustion characteristics, opening new possibilities for tailoring Al-based nanofluid fuels. [ABSTRACT FROM AUTHOR]

Electrically controlled solid propellant (ECSP) is one promising solution for thrust adjustment and repeated ignition of conventional solid rocket motors (SRM). However, the widely studied ECSP based on hydroxylammonium nitrate (HAN) faces the problems of strong hygroscopicity and low thermal stability, which can lead to failure of ECSP. Inspired by polyethylene oxide-polyacrylonitrile (PEO-PAN) based solid polymer electrolyte, the new PEO-PAN based ion conductive energetic composites (ECs) have been designed and evaluated in this paper. The formulation was theoretically determined based on the energy content, and the samples were prepared by a conventional milling mixing method. The morphology, ionic conductivity, thermal reactivity, decomposition gaseous products and combustion behavior of these new ECs have been comprehensively studied. It has been shown that the initial decomposition temperature of PEO-PAN based ECs is around 243 °C with heat release of 1677.8–1873.9 J·g−1 depending on the oxidizer and polymer content. Meanwhile, the dependences of the ionic conductivity on the burning rate are evaluated. The results showed that the burning rate decreases as ionic conductivity increases. One of these ECs has a high ionic conductivity with a low burning rate under pressure, which is suitable for controllable ECSP. [ABSTRACT FROM AUTHOR]

• An Al-based MIC (EF@EMOF) was prepared via electrospinning combining with in situ growth technique. • Obtained MIC has significantly increased heat release and burning rate. • The etching reaction avoids the sintering and improves combustion efficiency. Combustion is a kind of reacting process involves fluid mechanics and chemical reactions at the same time. In the past decades, little attention has been paid to the improvement on the heat and mass transfer rate of EMs, especially for metastable intermixed composites (MICs). In this paper, an Al-based MIC (EF@EMOF) with modified chemical kinetics as well as improved heat and mass transfer rate was prepared by precisely designing the reaction process and introducing energetic metal organic frameworks (EMOF) with high specific surface area as the reactants. The overall reaction process includes the activation of n-Al by eliminating Al 2 O 3 , decomposition of EMOF producing metal oxide, followed by exothermic reactions between the activated n-Al with metal oxide and PVDF. Results show that obtained MIC has significantly increased heat release (3464 J g−1), burning rate (more than 5 times faster than that of mechanically mixed one), and improved combustion efficiency. Furthermore, it is found that the decomposition of EMOF as well as the etching reaction generates massive gas products on the interface layer which avoid the sintering and form lots of holes. Those holes, in return, provide new channels for the further reaction, thus significantly improving the energy output and chemical reaction kinetics. [ABSTRACT FROM AUTHOR]