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[Display omitted] • Pomegranate-structured TEACM/AP/Al/catalysts/NC thermal expansion and contraction solid propellant mesoparticles (ECSPPs) were prepared. • The burning rate temperature coefficient (δ p) of ECSPPs are significantly lower than that of non-TEACM-contained mesoparticle at −40 ∼ 50 ℃. • At −30 ∼ 0 ℃, paraffin wax reduces the δ p of the solid propellant by 77.1 % at 3 MPa and 80.9 % at 5 MPa. • The tight packaging of temperature-sensitive AP with TEACM structurally reduces the δ p. How to reduce or eliminate the influence of initial ambient temperature on the interior ballistic of solid propellant (SP) has always been a technical bottleneck, and little progress has been made in recent years. The research of solid propellants with low burning rate temperature coefficient (δ p) mainly focuses on the use of temperature insensitive oxidants, but rarely from microstructure. In this work, cellulose acetate (CA), dioctyl adipate (DOA) and paraffin wax (PW) with high coefficient of linear thermal expansion were coupled with solid propellant energetic mesoparticle (SPP)-ammonium perchlorate (AP)/Al/CoWO 4 -reduced graphene oxide (rGO)/nitrocellulose(NC) through electrospray granulation method to form thermal expansion and contraction solid propellant mesoparticles (ECSPPs): CA-SPP, DOA-SPP and PW-SPP, followed by being used in solid propellants (SPs): SP-Co, SP-CA, SP-DOA and SP-PW. It suggests that recrystallized nano-AP is tightly packaged with efficient catalyst CoWO 4 -rGO, significantly improving the decomposition efficiency of AP and reaction efficiency of Al-AP to reduce the temperature-sensitivity of AP. For ECSPPs, PW significantly reduces the temperature sensitivity of AP which decrease the δ p of PW-SPP by 68.5 % at -40 ∼ 0 ℃. Compared with SP-Co, the δ p of SP-DOA and SP-PW at 3 MPa and −30 ∼ 0 ℃ are reduced by 20.7 % and 77.1 %, and the δ p of SP-CA, SP-DOA, SP-PW at 5 MPa and −30 ∼ 0 ℃ are reduced by 36.9 %, 35.3 %, 80.9 %. Thus, PW exhibits the optimal reduction effect on temperature sensitivity of AP, as a consequence of ECSPPs compensating for the burning surface through morphological changes in the microstructure with initial temperature. This study provides a novel strategy for reducing the δ p structurally through compensation for the burning surface. [ABSTRACT FROM AUTHOR]

The electrically controlled solid propellant (ECSP) has many advantages that are not available with traditional propellants, such as multiple start/stop operations and controllable thrust. In this research, conductive graphite (C) was employed as an additive to hydroxylammonium nitrate (HAN)‐based ECSPs to enhance electrical conductivity and thermal conductivity, and the influences of C on the burning characteristics of ECSPs were investigated by some characterization methods. The addition of 5 % C increases the electrical conductivity and thermal conductivity by 13.2 % and 18.9 %, while reduces the theoretical specific impulse (Isp) and adiabatic flame temperature (Tf) by 7.9 % and 18.4 %. C acting as electric and heat energy transfer media was demonstrated by TG‐DSC. ECSPs containing 1 %, 3 %, and 5 % C reinforce the burning rate by 11.4 %, 25.6 %, 35.9 % and mass loss by 6.9 %, 22.3 %, 47.8 % at 200 V; and enhance the burning rate by 39.2 %, 62.4 %, 104.9 %, and mass loss by 46.7 %, 84.7 %, 200.1 % at 0.6 MPa. This can be explained by the fact that the increase in electrical conductivity promotes the electrochemical decomposition rate of the ionic oxidizer in ECSPs at atmospheric pressure (0.1 MPa) and the rise in thermal conductivity promotes the heat transfer to the unburned zone of the propellant under high pressure (0.2 MPa∼0.6 MPa). [ABSTRACT FROM AUTHOR]

• A previously unreported porous layer mechanism of AlH 3 enhancing combustion was proposed. • A 50 μm thick porous layer when combustion was evaluated by SEM, thermo-analysis and a new simplified calculation method. • A new model predicting the overlapping process of AlH 3 dehydrogenation and Al oxidation in air atmosphere was developed. Although the motivation of AlH 3 enhancing combustion were recognized in many research, the promotion mechanism have been rarely explored. Herein, a previously unreported porous layer mechanism when combustion were determined in HTPB/AlH 3 fuels by SEM, thermo-analysis and a new simplified calculation method, owing to rapidly released gas phase H 2 from AlH 3 dehydrogenation exposing in melting layer. 5/10% 40–80 μm and 10% 80–200 μm AlH 3 -HTPB formulas show the regression rate increase by, 25.7%, 29.0% and 43.0% at Gox = 350 kg/m2·s, while by 57.2%, 42.0% and 44.2% enhancement at Gox = 150 kg/m2·s. The low AlH 3 content (≤ 10%) promotes the regression rate obviously, while excess AlH 3 content (≥ 20%) promotes slightly as a result of comprehensive factors combined by energy release, a certain porous layer mechanism, aggregated Al 2 O 3 attached on the burning surface and the blocking effect of the gaseous released H 2. A new model predicting the overlapping process of AlH 3 dehydrogenation and Al oxidation in air atmosphere was developed by superimposing AlH 3 dehydrogenation simulation and corresponding separated Al oxidation simulation. A 1.5th Avrami-Erofeev (A–E) simulation was proposed for Al passivation weight gain between 420 and 520 K with an activation energy of 124.92 kJ/mol and the pre-exponential of 10^12.35. [ABSTRACT FROM AUTHOR]

• M x WO y -rGO/Al nanothermites were fabricated by in situ and self-assembly methods. • The M x WO y -rGO/Al nanothermites present a dense layer stacked structure. • The energy release of the nanothermites can reach about 3000 J·g−1. • The nanothermites present outstanding combustion and catalytic performance. The development of nanothermites with high energy release rate is an important direction to the combustion catalysts in solid propellants. Herein, the bimetallic composite oxides (MgWO 4 , CoWO 4 and Bi 2 WO 6) were compounded with GO through an in situ solvothermal method, followed by self-assembly with Al nanoparticles in an organic solvent to obtain a new type of nanothermites. The structure, heat release and ignition performance of MgWO 4 -rGO/Al, CoWO 4 -rGO/Al and Bi 2 WO 6 -rGO/Al and their catalytic performances on several energetic materials were investigated. All prepared samples present a dense layer stacked structure. The heat outputs of MgWO 4 -rGO/Al, CoWO 4 -rGO/Al and Bi 2 WO 6 -rGO/Al nanothermites reach 2763.8, 3094.1 and 2853.6 J·g−1 respectively, which are significantly larger than those of Al/CuO (2070.0 J·g−1), Al/Fe 2 O 3 (2088.0 J·g−1), GO/Al/Bi 2 O 3 (1421.0 ± 12.0 J·g−1) and M x WO y /Al without GO. The enhanced performance may be ascribed to the unique structure of bimetallic composite oxides and GO, and uniform compact structure of nanothermites. CoWO 4 -rGO/Al exhibits a higher combustion heat release (3094.1 J·g−1), shorter ignition delay time (11.0 ms) and burning time (50.0 ± 2.0 ms), the minimum time of reaching the maximum flame area (20.0 ± 2.0 ms) and the maximum flame propagation speed (7.3 ± 0.7 m·s−1), demonstrating outstanding exothermic and combustion properties. The DSC results show that MgWO 4 -rGO/Al, CoWO 4 -rGO/Al and Bi 2 WO 6 -rGO/Al nanothermites reduce the peak temperature of AP (406.5 °C) by 23.8, 62.2 and 25.5 °C, and RDX by 3.2, 4.5 and 3.3 °C, respectively. This study will provide a new strategy of combustion catalysts utilizing the synergistic effects of energization and nanometerization. [ABSTRACT FROM AUTHOR]

The low regression rates for hydroxyl-terminated polybutadiene (HTPB)-based solid fuels and poor mechanical properties for the alternative paraffin-based liquefying fuels make today hybrid rocket engines far from the outstanding accomplishments of solid motors and liquid engines. In this paper, a survey is conducted of several innovative methods under test to improve solid fuel properties, which include self-disintegration fuel structure (SDFS)/paraffin fuels, paraffin fuels with better mechanical properties, high thermal conductivity fuels and porous layer combustion fuels. In particular, concerning HTPB, new results about diverse insert and low-energy polymer particles enhancing the combustion properties of HTPB are presented. Compared to pure HTPB, regression rate can be increased up to 21% by adding particles of polymers such as 5% polyethylene or 10% oleamide. Concerning paraffin, new results about self-disintegrating composite fuels incorporating Magnesium particles (MgP) point out that 15% 1 μm- or 100 μm-MgP formulations increase regression rates by 163.2% or 82.1% respectively, at 335 kg/m2·s oxygen flux, compared to pure paraffin. Overall, composite solid fuels featuring self-disintegration structure appear the most promising innovative technique, since they allow separating the matrix regression from the combustion of the filler grains. Yet, the investigated methods are at their initial stage. Substantial work of refinement in this paper is for producing solid fuels to fulfill the needs of hybrid rocket propulsion. [ABSTRACT FROM AUTHOR]

In order to develop a usable low-cost nanocomposite with better catalytic performances for solid propellants, the CuFe 2 O 4 /g-C 3 N 4 nanocomposite commonly used in photocatalysis was first used as combustion catalysis. CuFe 2 O 4 /g-C 3 N 4 nanocomposite was designed and successfully prepared by in situ solvothermal method. And the synergistic effect of CuFe 2 O 4 nanoparticles and g-C 3 N 4 on the thermal decomposition of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and ammonium perchlorate (AP) and their catalytic decomposition mechanisms were analyzed systematically. The results indicate that g-C 3 N 4 -based combustion catalyst exhibits better catalytic decomposition effect on AP and RDX compared to bulk g-C 3 N 4 and related GO-based catalysts (CuFe 2 O 4 /GO). CuFe 2 O 4 /g-C 3 N 4 nanocomposites shift the decomposition of RDX to a lower temperature with the increase of g-C 3 N 4 content, while present the opposite trend for AP. Besides, the thermal decomposition stages and related products of AP and RDX probed by thermogravimetry-mass spectrometry (TG-MS) reveal that CuFe 2 O 4 /g-C 3 N 4 catalyst reduces their decomposition temperatures, changes their decomposition processes and presents a better catalytic decomposition effect on AP and RDX. Thus, nano g-C 3 N 4 -based metal composite oxides used as combustion catalysts will be a more viable strategy in the field of solid propellants. [Display omitted] • CuFe 2 O 4 /g-C 3 N 4 nanocomposite was first used as combustion catalyst of solid propellants. • CuFe 2 O 4 /g-C 3 N 4 presents better catalytic decomposition effect on AP and RDX than that of single g-C 3 N 4 and CuFe 2 O 4 /GO. • CuFe 2 O 4 /g-C 3 N 4 accelerates the decomposition reaction and changes decomposition mechanism. • This work will provide a new strategy for the design of nano combustion catalysts in solid propellants. [ABSTRACT FROM AUTHOR]

In the controllable combustion field, hydroxyl ammonium nitrate (HAN)-based electrically controlled solid propellants (ECSPs) is of growing interest in green fuels with safety, throttle- ability and at-will on-off capability. However, the current research is confined to the ignition characteristics and ablation process of basic ECSP formulations (75 wt% HAN ionic liquid oxidizer, 5 wt% ammonium nitrate co-oxidizer and 20 wt% polyvinyl alcohol binder), rather than working in functional additives. Herein, multiwall carbon nanotubes (MWCNT) and nano/micro aluminum powders were introduced in ECSPs, facilitating electrical conductivity and energy release. It indicates that the homogeneous dispersed MWCNT in polyvinyl alcohol (PVA) microspheres, preparing by the micro-segmented flow method, results in a 9.8% increase in electrical conductivity of the ECSPs. At 0.5 MPa, ECSPs containing 1%, 3% and 5% 5 µm aluminum powder reinforce the burning rate by 38.0%, 186.3%, 214.7% and mass ablation by 10.7%, 95.2%, 175.6% at 200 V, yet the large heat release by excess aluminum powder shifts the non-self-sustaining combustion of ECSPs to self-sustaining combustion at high pressure (above 0.8 MPa). The mechanism of promoting ECSPs combustion by liberating aluminum-nitric acid (released by HAN ionization) reaction were proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new CuX-WO 3 /Biochar composite was designed and successfully constructed. • Biochar is used as a combustion catalyst. • Catalytic mechanism was inferred by DFT calculations combined with a series of characterizations. • CuX-WO 3 /Biochar has high catalytic activity for thermal decomposition of AP, RDX and TKX-50. • CuX-WO 3 /Biochar optimizes combustion performance of RDX and TKX-50. To develop efficient combustion catalyst for solid propellants, a novel WO 3 -based composite (CuX-WO 3 /Biochar) was designed by the method of doping and loading. As a dopant, Cu has the advantages of producing multiple bands, inhibiting grain growth and restraining exciton–exciton collisions. Meanwhile, biochar is cheap and available as a carrier, which can effectively inhibit the agglomeration of nanomaterials. Therefore, in this work, Cu-doped WO 3 nanoparticles were uniformly anchored on surface of biochar by in-situ solvothermal reaction combined calcination method, which significantly increased the surface-active area, and was firstly applied to catalytic decomposition and laser ignition of ammonium perchlorate (AP), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 5,5′-bistetrazole-1,1′-diolate (TKX-50). With the introduction of CuX-WO 3 /Biochar, decomposition peak temperature of AP, RDX and TKX-50 diminished by 97.0, 6.7 and 37.9℃, and activation energy decreased by 14.4, 93.5 and 22.6 kJ mol−1, respectively. Simultaneously, flame brightness, flame area and flame propagation speed during combustion of RDX and TKX-50 were evidently improved after CuX-WO 3 /Biochar was added. Finally, electron transfer mechanism of catalytic thermal decomposition of energetic materials was deduced based on Density Functional Theory (DFT) calculation and characterization analysis. This study will provide a new insight into development of combustion catalysts. [ABSTRACT FROM AUTHOR]

In order to solve the unclear problems of structure and composition for 2,4-dihydroxybenzoic acid (2,4-DHBA) copper salt (β -Cu), a new insoluble ternary copper (Ⅱ) complex of 2,4-DHBA ([Cu(C 12 H 8 N 2) 2 (C 7 H 5 O 4)](C 7 H 5 O 4)) was designed and synthesized in water. The ternary complex crystallizes in the monoclinic system with the space group P2 1 /n. The central Cu2+ is coordinated with four nitrogen atoms from two 1,10-phenanthroline ligands and one carboxyl oxygen atom from a 2,4-DHBA anion. The other 2,4-DHBA anion does not participate in coordination and only provides the action of balance charge. In addition, compared with β -Cu, no water molecules exist in the ternary complex. The thermal stability of the ternary complex was investigated, as well as its catalytic decomposition activity on AP and RDX. With the addition of the ternary complex, the exothermic decomposition peak temperatures of AP and RDX were reduced from 406.5 to 353.9 ​°C, and 242.3 to 181.4 ​°C respectively, and the apparent activation energies were reduced from 293.1 to 207.4 ​kJ ​mol−1, and 239.6 to 177.5 ​kJ ​mol−1, respectively. Moreover, the addition of the ternary complex has greatly improved the heat release of AP and RDX. The catalytic decomposition performance of the new ternary complex on AP and RDX is much better than that of the traditional β -Cu. Moreover, the new copper (Ⅱ) complex completely changed the thermal decomposition process of RDX from melting decomposition to direct solid phase decomposition, and such catalytic effect is uncommon. Therefore, the new ternary copper (Ⅱ) complex presents a better potential application for modified double-base propellant of RDX. A new insoluble ternary copper complex of 2,4-DHBA was designed, synthesized, structurally characterized, and its properties tested. The catalytic decomposition performance of the ternary copper complex on AP and RDX is much better than that of the traditional β -Cu. [Display omitted] • A new ternary copper (Ⅱ) complex of 2,4-dihydroxybenzoic acid was designed and synthesized in water. • The central Cu2+ is coordinated with four nitrogen atoms of two 1,10-phenanthroline ligands and one carboxyl oxygen atom of a 2,4-DHBA anion. The other 2,4-DHBA anion does not participate in coordination and only provides the action of balance charge. • The ternary complex exhibits outstanding catalytic effect on AP and RDX, and its catalytic performance is better than that of traditional β -Cu. • The new ternary copper complex presents a better potential application for modified double-base propellant of RDX. [ABSTRACT FROM AUTHOR]