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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]

• 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]

• The chemical interactions between three typical pyrotechnics with cellulose as packing material have been studied. • The cellulose would interact with B/KNO 3 with exothermic reactions during the pyrolysis. • It is difficult for Mg/PTFE to undergo self-sustainable combustion at ambient pressure in presence of cellulose. • The cellulose has little effect on the flame temperature and reaction pathways of B/KNO 3. In order to study the effect of cellulose shell on the thermal behavior including pyrolysis gaseous products, ignition and combustion characteristics of typical pyrotechnics, three composites of pyrotechnics/cellulose were prepared in this paper. Various characterization techniques were used to investigate the prepared composites and their combustion condensed products (CCPs), including scanning electron microscopy (SEM), simultaneous thermal analysis (DSC-TG-FTIR), X-ray diffraction (XRD), bomb calorimetry, and home-made combustion diagnostic system. The results showed that the overall heat release of the black powder and Mg/PTFE decreased from 3108 J·g−1 and 1157.4 J·g−1 to 1045.4 J·g−1 and 810.4 J·g−1 in the presence of 33.3% cellulose, respectively. Moreover, the FTIR spectra showed that the cellulose did not change the reaction pathways of black powder and Mg/PTFE, which mainly include H 2 O, CO 2 , NO 2 for the black powder, and HF, H 2 O, CO 2 , CF 2 for Mg/PTFE. However, the condensed products of cellulose would interact with B/KNO 3 at a higher temperature, so that the heat release was largely increased by 339%. The cellulose has obviously impact on the energy release rate of Mg/PTFE in comparison to the other two composites. Moreover, the negative impact on ignition of Mg/PTFE composite is significant, when the content of cellulose reaches over 33.3%, resulting in difficult self-sustainable combustion at ambient pressure. The cellulose can largely reduce the maximum flame temperature of the black powder and Mg/PTFE, whereas it has little effect on B/KNO 3. The CCPs of the involved igniting pyrotechnics and their cellulose-based composites have different phases due to their strong thermal interactions with cellulose. [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]

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]

• There graphene-based transition metal coordination polymers have been evaluated as the energetic catalysts in Al-based composites. • These catalysts are well doped in the PVDF/AP matrix as the oxidizer shell of Al-based composites prepared by a spray drying method. • The high energy level but low burn rate has been achieved for the Al@PVDF/AP in presence of these graphene-based catalysts. In this paper, energetic combustion catalysts doped core–shell Al@PVDF/AP composites have been fabricated via a spray-drying method, where three kinds of graphene-based energetic coordination polymers (GECPs, GO-CHZ-Co, GO-CHZ-Ni and GO-CHZ-Cu) are employed. These composites have been characterized comprehensively in terms of morphologies, thermal decomposition behaviors, energy density, combustion performances and condensed combustion products (CCPs). The results show that the GO-CHZ-Co and GO-CHZ-Cu could increases the heat of explosion for Al@PVDF/AP composites from 6885.2 J·g−1 to 7491.0 J·g−1 and 7390.1 J·g−1, respectively, which are 8.8 % and 7.3 % higher than the blank reference samples. Moreover, the burn rates for these composites decrease when GO-CHZ-Co or GO-CHZ-Ni is included, indicating that these composites are promising candidates with improved energy density even unusually with decreased burn rates. [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]

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]

• 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]