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The flexible control in burning rate and stable combustion of solid propellants over a broad range of pressures essentially determine the performance of solid rocket motors. The nanoscale metals and their oxides are usually utilized as the traditional burn rate modifiers in adjusting the combustion behaviors of solid propellants, but the energy characteristics of propellants are greatly compromised owing to the inert nature of additives used. In this paper, a series of metal complexes of triaminoguanidine-glyoxal polymer (TAGP-Ms) with high nitrogen content were synthesized and employed as energetic burn rate inhibitors in tunning the combustion properties of composite modified double-based (CMDB) propellants. The influences of prepared TAGP-Ms on the thermal decomposition and combustion of CMDB propellants were comprehensively investigated based on thermal analysis technique and combustion characterization methods. It was found that the peak temperatures of the second exotherm displayed for the propellants containing TAGP-Ms inhibitors were significantly increased by more than 30°C (except for TAGP-Cu), indicating the TAGP-Ms is capable of suppressing the thermal decomposition of CMDB propellants. More importantly, the heat releases of CMDB propellants were substantially enhanced by 16%~34% determined by DSC analysis. In comparison to the blank reference, the energetic TAGP-Ms inhibitors could promote the heat of combustion for the involved CMDB propellants by 5%~9%. The burning rates of CMDB propellants were notably reduced over a wide range of pressures by adding TAGP-Ms, whereas the calculated pressure exponents at pressures ranging from 10 to ~ 22 MPa appear to be relatively high due to the accelerated HMX decomposition. The measured combustion wave temperatures suggest that the CMDB propellants with TAGP-Ms undergo a three-stage combustion process with the highest temperatures in the range of 2160 ~ 2230°C. [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 incorporation of Al nanoparticles (Al NPs) into 1,3,5-trinitro1,3,5-triazinane (RDX) can catalyze its thermal decomposition and reduce the pressure exponent (n) of solid propellants. However, the underlying reaction mechanism at a deeper level remains unclear. In this study, the reaction processes of Al NPs catalyzing the thermal decomposition of RDX under different initial pressures were investigated by utilizing the ReaxFF molecular dynamics (ReaxFF-MD) simulations combined with DFT calculations, and the influence mechanism of Al NPs on the pressure sensitivity of RDX thermal decomposition was revealed from various perspectives. In the initial stage of the reaction, unlike the nitro group dissociation observed in pure RDX, the incorporation of Al NPs alters the initial decomposition pathway of RDX, making it more easily adsorbed on the surface of Al and enhancing the early-stage decomposition rate. Furthermore, Al NPs exhibit higher catalytic activity in low-pressure systems. In the later stage, because of the massive adsorption of free radicals generated from RDX decomposition on the surface of Al NPs, the decomposition rate of RDX decreases significantly, especially in high-pressure systems. Consequently, Al NPs synergistically reduce the pressure sensitivity of the RDX thermal decomposition from two different perspectives. Compared to traditional experimental research or single RDX simulation studies, this work further explores the interaction between Al and RDX from a microscopic perspective, addressing the gap in the field of the influence mechanisms of Al NPs on the pressure sensitivity of RDX thermal decomposition. It also establishes a theoretical foundation for the practical application of Al@RDX fuels. [Display omitted] • Al NPs largely reduces the activation energy of RDX decomposition at low pressures. • The initial decomposition pathway of RDX in the initial stage is altered by Al NPs. • Impact mechanism of Al NPs on pressure sensitivity of RDX decomposition was revealed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Promotion effect of CuO on the LTD stage of AP weakens at higher pressure due to more physically adsorbed NH 3 on the AP surface. • The T HTD of the Al@AP-CuO changes little in higher pressure due to the limited effect of more NH 3 and other species accumulated on the CuO surface. • The reasons of CuO of reducing the burning rate pressure index of Al@AP propellants is obtained. • CuO can regulate the oxidation of NH 3 to control the burning rate. Burning rate modulation is a crucial but challenging technology for designing solid propellants. The core–shell structured Al@AP and Al@AP/CuO were prepared and their thermal reaction properties were investigated at different pressures. The precise catalytic mechanism of doped CuO in oxidizer and the key reason for its burning rate modulating effect on solid propellants were elucidated by combining DFT calculations. The *NH 4 ClO 4 on the CuO (1 1 1) surface is more likely to undergo a dehydrogenation reaction first. The large difference in activation energy between *NH 4 ClO 4 →*NH 3 +*ClO 4 +*H and *NH 4 ClO 4 → NH 3 + HClO 4 explains the reasons that CuO can reduce the ignition delay of the Al@AP. CuO promotes the decomposition of the AP@Al at the low- and high-temperature decomposition (LTD and HTD) stage. For the Al@AP-CuO, the temperature of the high-temperature decomposition peak (THTD) does not shift to the lower temperature range with increasing pressure. These results are responsible for a reduction of pressure exponent in the presence of minor CuO as reported in the literature. CuO can facilitate the transformation process *NH 3 →*NH 2 on the CuO (1 1 1) surface at low-temperature and low-pressure conditions. However, at high-temperature and high-pressure conditions, it can inhibit the reaction *NH 2 →*NH→*N, so the burning rate of solid propellants can be controlled. [ABSTRACT FROM AUTHOR]

• Al/oxidizer composites integrated with energetic coordination polymers as catalyst are prepared. • The ignition and combustion of propellants are enhanced under the synergistic effects of Al/oxidizer interfacial control and the catalysts. • The burning rates of propellants can be well controlled in a wide range and lowered pressure exponent is achieving. The control of burning rate pressure sensitivity is essential for stable and reliable combustion of solid propellants. It has been proved that the combustion behavior of propellants can be effectively tuned by interfacial control of Al/oxidizers. In this work, core-shell Al-based composites, using oxidizers such as ammonium perchlorate (AP) and cyclotetramethylene tetranitramine (HMX) as the shell layer, have been prepared with a well-controlled location of graphene-based carbohydrazide complexes (GO-CHZ-M, M = Co2+ or Ni2+) as the catalysts. The catalysts can be located inside HMX or embedded on the surface of AP particles. The decomposition of AP and HMX could be greatly promoted with a trace amount of catalyst. Under the synergistic effects of Al/oxidizer interfacial control and GO-CHZ-M, the ignition delay time is shortened by >48 % with increased in flame radiation. More importantly, the burning rate (r) and pressure exponent (n) of the solid propellants are effectively regulated in a wide range. In particular, the use of Al@HMX/Co results in a lowered n of 0.29 within 1∼20 MPa compared to 0.79 for the blank reference sample. The agglomeration of Al particles during combustion was also inhibited due to the micro-explosion effect of Al@HMX composites. The innovative approaches of integrating Al/HMX/AP composites and precise catalysis of graphene-based energetic catalysts in solid propellants have successfully achieved, regarding the modulation of the burning rates and pressure sensitivity. Moreover, the effect of catalyst location on the ignition delay and burning rates has also been studied thoroughly and clarified. This paper provides new insight into the regulation of combustion performance of solid propellants, with improved reaction efficiency and maintained energy density. [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]