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The employment of burning rate suppressants in the solid rocket propellant formulation is long known. Different research activities have been conducted to well understand the mechanism of suppression, but literature about the action of oxamide (OXA) and azodicarbonamide (ADA) on the thermal decomposition of composite propellant is still scarce. The focus of this study is on investigating the effect of burning rate suppressants on the thermal behavior and decomposition kinetics of composite solid propellants. Thermogravimetric analysis (TG) and differential thermal analysis have been used to identify the changes in the thermal and kinetic behaviors of coolant-based propellants. Two main decomposition stages were observed. It was found that OXA played an inhibition effect on both stages, whereas the ADA acts as a catalyst in the first stage and as coolant in the second one. The activation energy dependent on the conversion rate was estimated by two model-free integral methods: Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) based on the TG data obtained at different heating rates. The mechanism of action of coolants on the decomposition of solid propellants was confirmed by the kinetic investigation as well.

In this paper, the thermal decomposition characteristics and mechanical sensitivity of ETPE propellant were characterized by differential scanning calorimeter (DSC), vacuum stability tester (VST), impact sensitivity tester and friction sensitivity tester, and the main factors affecting the safety performance of ETPE propellant were studied. The results show that ETPE propellant has good thermal stability under 185°C. The combustion activation energy of ETPE propellant is slightly lower than that of HTPB propellant. By using 100°C heating method, the net added gas of ETPE propellant is 0.81ml/g, which meets the evaluation standard of stability qualification, and the propellant did not spontaneously combust under various high temperature test conditions. By reducing the amount of fine AP and controlling the amount of RDX, it is conducive to reducing the probability of the “hot spot” generated by the propellant under the external excitation energy, reducing the mechanical sensitivity of propellant and improving the safety performance of propellant.

By conducting slow cook-off tests on solid composite propellants, the combustion response characteristics of propellants under different casing materials were investigated. Propellant slow cook-off combustion experiments were designed and carried out. Combining the morphological changes of propellant thermal decomposition weight loss with theories of material mechanics and heat transfer, the heat transfer process and physical state of the propellant before ignition were examined to explore their effects on after ignition reaction intensity. The results indicated that the reaction intensity varied with different casing materials. When the casing material is 45# steel, spontaneous ignition occurred at 214.88, with a slider speed of 14.83 m/s, classifying the reaction as deflagration. For 2A12 aluminum casing material, spontaneous ignition occurred at 199.13, with a slider speed of 0.71 m/s, classifying the reaction as combustion. When the casing material is carbon fiber composite, the reaction was classified as combustion. Different casing materials influence the reaction intensity through their thermal physical parameters and casing constraint strength, providing guidance for the selection and design of casing materials and constraints in slow cook-off combustion of motors.

In order to improve the mechanical and combustion properties of composite solid propellant, the CuO@AP with core–shell structure was prepared by solvent–nonsolvent recrystallization method, and it was applied to AP/HTPB composite solid propellant. The thermal decomposition properties, sensitivity properties and tensile properties of CuO@AP propellant were studied and compared with ultrafine AP propellant, ultrafine spherical AP propellant and the mixture of CuO and AP (CuO/AP) propellant. The results show that the E a of ultrafine spherical AP propellant is 8.16% lower than that of ultrafine AP propellant with the same particle size, and the rate constant increases by 13.64%; the E a of the CuO@AP propellant is 23.63% lower than that of CuO/AP propellant with ultrafine AP of the same particle size, and the rate constant increases by 172.7%. What’s more, the catalytic effect of CuO@AP is obviously better than that of CuO/AP. The impact sensitivity of ultrafine spherical AP propellant is 29.61% lower than that of ultrafine AP propellant with the same particle size, and the ε b is increased by 51.35%. The impact sensitivity of the CuO@AP propellant is 25.38% lower than that of CuO/AP propellant with ultrafine AP of the same particle size, and the ε b is increased by 63.76%. The above shows that the CuO@AP composite particles with core–shell structure have potential application prospects in AP/HTPB propellant.

In this paper, the HTPB propellant of a solid rocket motor was taken as the research object. Considering the effect of temperature on the propellant, various types of tests were carried out to study the damage law of the propellant at the macroscopic scale. The aging of HTPB propellant under temperature loading is mainly manifested as oxidative cross-linking of the binder network. The greater the cross-linking degree of the specimen is, the smaller the maximum elongation of the propellant is. Under constant strain load, some AP particles will be dehumidified, and at room temperature, AP particles will decompose slowly, resulting in an increase in strength and a decrease in elongation. The aging of HTPB propellant under constant strain loading at high temperatures is manifested as oxidation cross-linking of the binder network, ε m of propellant declines, and σ m of propellant is reduced.

A simple and linear integral method which uses multiple heating schedules to evaluate the kinetic parameters has been proposed by Trache–Abdelaziz–Siouani (TAS). This approach is based on the combination of the iterative modified Coats–Redfern equation with the kinetic compensation parameters (ln A = aE + b). The suggested method was applied to experimental non-isothermal data obtained from the literature for decomposition of gun propellant containing the mixed ester of triethylene glycol dinitrate and nitroglycerin studied by differential scanning calorimeter at two different pressures (0.1 and 2 MPa). This method leads to consistent pre-exponential factor and kinetic model with those obtained from the accurate approximation of Tang et al. using the activation energy derived from either the integral nonlinear Vyazovkin procedure or the Friedman’s differential method. These kinetic parameters are reliable with those obtained by two integral linear (iterative Kissinger–Akahira–Sunose and iterative Flynn–Wall–Ozawa) methods as well. The superiority of TAS method is due to the possibility of obtaining all the kinetic parameters in an objective manner with a reasonable computation time.

The excellent thermal decomposition efficiency of ammonium perchlorate (AP) is of great importance for obtaining propellant with fast specific impulse. In this study, four CuM x O y catalysts, including M = Fe, Ni, Co, and Zn, were synthesized and then used for catalyzing AP decomposition and hydroxyl-terminated polybutadiene (HTPB)-based solid propellant combustion. The existed synergistic effect in CuM x O y catalysts improved the catalytic activity and the most active CuZnO catalyst decreased the AP high-temperature decomposition temperature (HTD) from 412.5 to 289.4 °C. Kinetic studies indicated that CuM x O y catalysts inhibited the conversion of N 2 O to a fully oxidized product and decreased the activation energy ( E a ) in HTD to concentrate AP decomposition to significantly decrease the heat loss, thereby increasing their decomposition efficiency. When applying the CuM x O y catalysts in the HTPB (hydroxyl-terminated polybutadiene)-based solid propellant, a faster burning rate and stronger optical emission spectrum were obtained. The CuM x O y catalyst is a potential additive for the preparation of outstanding combustion solid propellants. Graphical abstract

To improve the reinforcement effect between a binder and high solid filler in a propellant formula, grafting the bonding group into the binder to form a neutral polymeric is a practically novel approach to improving the interface properties of the propellant. In this work, a glycidyl azide polyol energetic thermoplastic elastomer binder with a –CN bonding group (GAP–ETPE) was synthesized, and the mechanical and thermal decomposition mechanism of GAP–ETPE with Hexogeon (RDX) model propellants were studied. The stress–strain results indicated that the tensile strength and strain of GAP–ETPE/RDX model propellants were 6.43 MPa and 32.1%, respectively. DMA data showed that the storage modulus (E’) of the GAP–ETPE/RDX model propellants could increase the glass transition temperature (Tg) values, those were shifted to higher temperature with the increase in filler RDX percentages. TG/DTG showed the four decomposition stages of the decomposition process of the GAP–ETPE/RDX model propellants, and the thermal decomposition equation was constructed. These efforts provide a novel method to improve GAP–ETPE/RDX propellants mechanical property, and the thermal decomposition behavior of GAP–ETPE/RDX propellants also provided technical support for the study of propellant combustion characteristics.

Ammonium perchlorate (AP), which has the advantages of high oxygen content, good thermal and chemical stability, and no solid residue after thermal decomposition, is considered to be the most widely used oxidiser for solid propellant applications. However, the high mechanical sensitivity, moisture absorption, and thermal decomposition temperature of AP seriously affect the performance of the solid propellant. In this paper, we systematically review the research progress of the improvement of desensitization, anti-hygroscopicity, and thermal decomposition performance by surface coating of AP. At the same time, the surface coating methods are focusing on electrospray technology, reduced pressure distillation, ultrasonic synthesis, liquid phase deposition, supercritical fluid, intermittent spray coating, and electrostatic self-assembly coating method. Among above, intermittent spray coating and liquid phase deposition method are the preferred surface coating method due to their uniformity of coating, ease of adhesion and good performance enhancement. It is expected that the research on surface coating and performance enhancement of AP can greatly promote the innovation and development of AP in the field of high burning rate solid propellant.

Ammonium perchlorate (AP), as the most commonly used oxidizer in composite solid propellants, achieving its rapid decomposition at lower temperatures, is one of the key items used to improve propellant performance. Copper-based catalysts, due to their good performance in promoting AP decomposition and improving propellant combustion characteristics, are currently one of the most widely used catalyst types. However, the catalytic performance of copper-based catalysts for the decomposition of ammonium perchlorate, including the decomposition products, changes in the kinetic process during the decomposition, and the combustion process needs further research and clarification in terms of the influencing factors and mechanisms. Based on this question, to further analyze the essence of copper-based catalysts and the decomposition mechanism of CuO-catalyzed ammonium perchlorate, as well as its relationship with particle size, this paper compared and studied the effects of two different particle size CuO catalysts (small-diameter CuO-S and large-diameter CuO-L) on the thermal decomposition and combustion performance of AP. The results indicate that the decomposition of AP catalyzed by CuO mainly includes two stages: the initial low-temperature decomposition stage accelerated by the electron transfer mechanism and the subsequent second stage accelerated by the adsorption and conversion of intermediates by the catalyst. The two stages are controlled by different properties and are related to the particle size of the catalyst. This work provides in-depth research on CuO catalysts for the thermal decomposition of AP.