Search Results (26)

Hydroxyl-terminated-polybutadiene (HTPB)-based composite solid propellants are extensively used in aerospace and defense applications due to their high energy density, thermal stability, and processability. However, the presence of highly sensitive energetic components in their formulations leads to a significant risk of accidental ignition under electrostatic discharge, posing serious safety concerns during storage, transportation, and handling. To address this issue, this study explores the prediction of electrostatic sensitivity in HTPB propellants using machine learning techniques. A dataset comprising 18 experimental formulations was employed to train and evaluate six machine learning models. Among them, the Random Forest (RF) model achieved the highest predictive accuracy (R² = 0.9681), demonstrating a strong generalization capability through leave-one-out cross-validation. Feature importance analysis using SHAP and Gini index methods revealed that aluminum, catalyst, and ammonium perchlorate were the most influential factors. These findings provide a data-driven approach for accurately predicting electrostatic sensitivity and offer valuable guidance for the rational design and safety optimization of HTPB-based propellant formulations. Full article

To improve the combustion performance of boron powder, a method was developed for synthesizing boron–magnesium–titanium (B-Mg-Ti) ternary composite powders with controlled metal content. Boron–magnesium (B-Mg) base materials were first prepared via electrical explosion, followed by the incorporation of titanium powder at varying mass fractions (1 wt.%, 3 wt.%, 5 wt.%, and 7 wt.%) through mechanical ball milling. Field emission scanning electron microscopy (FE-SEM) revealed that the addition of titanium promoted a more uniform dispersion of magnesium within the boron agglomerates. Moreover, nanoscale titanium particles were observed to be embedded on the particle surfaces, confirming successful microscale composite formation. Particle size distribution was measured using a Malvern 3000 laser particle size analyzer, and results showed that the particle size of the ternary composites decreased gradually with increasing titanium content. Specific surface area was determined via the Brunauer–Emmett–Teller (BET) method, with all samples exhibiting values greater than 15 m²/g, indicating good surface reactivity. Furthermore, the rheological behavior of the B-Mg-Ti composite powders, when combined with terminal hydroxyl polybutadiene (HTPB)—a typical binder in solid propellants—was evaluated. Viscosity measurements were conducted using a rotational rheometer at constant temperatures of 20 °C and 70 °C. The results demonstrated a marked decrease in viscosity with increasing titanium content, suggesting that titanium incorporation enhances the flowability of the composite powders. This study systematically evaluated the influence of titanium content on the structural and physicochemical properties of B-Mg-Ti composite powders, thereby providing a valuable experimental foundation for the optimized design of boron-based combustion systems and the enhancement of their processing and application performance. Full article

The curing reaction of hydroxyl-terminated polybutadiene (HTPB) solid propellant slurry alters its internal molecular structure, leading to variations in rheological properties. This study investigates the evolution of the rheological behaviour of HTPB propellant slurry during the curing process. Rheological parameters of the slurry at different curing stages were measured using a rotational rheometer, and its time-dependent rheological characteristics were systematically analysed. Building upon the Herschel–Bulkley–Papanastasiou (HBP) viscosity model, a temporal variable was innovatively incorporated to extend the model into the time domain, resulting in the development of the Herschel–Bulkley–Papanastasiou–Wang (HBPW) constitutive viscosity model. Model parameters were determined through experimental data, and the accuracy of the HBPW model was rigorously validated by comparing numerical simulations with experimental results. The findings demonstrate that the HBPW model effectively captures the viscosity variation patterns of HTPB propellant slurry with respect to both shear rate and curing time, exhibiting a minimal discrepancy of 1.7525% between simulations and experimental data. This work establishes a novel theoretical framework for analysing the rheological properties of HTPB propellant slurry, providing a scientific foundation for optimised propellant formulation design and processing techniques. Full article

Ionizing radiations are responsible for bond scission, radical formation, and oxidative degradation of polymer matrices. This study focuses on the effects of gamma irradiation on solid propellant binders, targeting a comprehensive chemical and mechanical characterization of different formulations. Samples were produced either by conventional methods based on hydroxyl-terminated polybutadiene and standard polyaddition reaction using isocyanates, or innovative approaches involving UV-driven radical curing. The samples were irradiated for comparison and to study their evolution as a function of three absorbed doses (25, 45, 130 kGy) for preliminary characterization studies, using a 60-Co gamma source. Samples were irradiated in air at uncontrolled room temperature. The coupling of spectroscopy techniques (Fourier transform infrared—FTIR, Raman and electron paramagnetic resonance—EPR) and dynamic mechanical analysis (DMA) highlighted the key role of antioxidant agents in tailoring mechanical changes in the binder phase. The absence of antioxidants enhances radical formation, oxidation, and cross-linking. These processes lead to progressively increased rigidity and reduced flexibility as a function of the absorbed dose. Complex interactions between photocured components largely influence radical stabilization and material degradation. These findings provide valuable insights for designing novel radiation-resistant binders, enabling the development of solid propellants tailored for reliable, long-term permanence in space, and advancing the knowledge on the applicability of 3D-printed propellants. Full article

This study employed an in-situ displacement technique to eliminate the oxide layer present on the surface of micron aluminum (μAl). Utilizing the exposed metallic aluminum, we facilitated the displacement of copper and nickel nanoparticles. These nanoparticles, approximately 90 nanometers in size, were densely adhered to the surface of the μAl particles. The elemental composition and structural characteristics of the composite particles were meticulously analyzed using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Vibrating Sample Magnetometry (VSM), and X-Ray Photoelectron Spectroscopy (XPS). Subsequently, thermal analysis and combustion performance assessments were conducted to elucidate the catalytic effects of the composite particles ([nCu+nNi]/μAl) on the thermal decomposition and combustion efficiency of ammonium perchlorate (AP). The results elucidate that the nanoparticles immobilized on the surface of μAl are unequivocally metallic copper (nCu) and metallic nickel (nNi). Following the application of nCu and nNi, the oxidation reaction of μAl accelerated by nearly 400 °C; furthermore, the incorporation of [nCu+nNi]/μAl raised the thermal decomposition peak temperature of AP by approximately 130 °C. Notably, the thermal decomposition activation energy of raw AP reached as high as 241.7 kJ/mol; however, upon doping with [nCu+nNi]/μAl, this activation energy significantly diminished to 161.4 kJ/mol. The findings of the combustion experiments revealed that both the raw AP and the AP modified solely with μAl were impervious to ignition via the hot wire method. In contrast, the AP doped with [nCu+nNi]/μAl demonstrated pronounced combustion characteristics, achieving an impressive peak flame temperature of 1851 °C. These results substantiate that the nCu and nNi, when deposited on the surface of μAl, not only facilitate the oxidation and combustion of μAl but also significantly enhance the thermal decomposition and combustion dynamics of ammonium perchlorate. Consequently, the [nCu+nNi]/μAl composite shows considerable promise for application in high-burn-rate hydroxyl-terminated polybutadiene (HTPB) propellants. Full article

The effect of the process aid “OPS” on the rheological properties of hydroxyl-terminated polybutadiene propellant was investigated by formulating different components of high-solid-content slurry, and the change in slurry viscosity with shear rate, surface morphology of solid-phase particles, and contact angle of the relevant interfaces were characterized. The results showed that the polyalkene polyamine surfactant OPS could significantly reduce the apparent viscosity and enhance the rheological properties of the slurry, to up to a 30% reduction, and the effect was achieved by adjusting the interfacial properties of the aluminum powder and the binder system. With the addition of 0.1% OPS, the contact angle of the interface between the aluminum powder and the binder was obviously reduced, from 97° to 30°, and the wetting was significantly enhanced, so it was judged that the OPS was suitable for HTPB-based composite propellants. Full article

To enhance both the mechanical properties of hydroxyl-terminated polybutadiene (HTPB) binder and the combustion efficiency of aluminized propellants, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol (OFHD) was employed as a chain extender to impart mechanical regulation to the HTPB binder. Mechanical testing showed that the mechanical properties of fluoride-modified HTPB polyurethane (FPU) were significantly improved: the peak tensile strength of the optimized samples reached 1.99 MPa, and the elongation at break attained 486%. The structural characterization of the FPUs was conducted using Fourier transform infrared (FTIR) spectroscopy. Thermogravimetry-mass spectrometer (TG-MS) analysis revealed that the initial thermal decomposition temperature of the FPU shifted from 170 °C to 162 °C, accompanied by the release of fluorine-containing fragments during decomposition. Analysis of the combustion residue indicated that the addition of OFHD can reduce the agglomeration of aluminum (Al) powder in aluminized propellants. Dynamic pressure characteristics results showed an augmented pressurization rate under argon and oxygen atmospheres, increased by 18.67% and 37.29%, respectively. Heat release tests indicated that the aluminized propellants with the addition of OFHD had a higher combustion heat, being increased by 6.57%. The binder system is expected to be applied in aluminized propellants to improve the mechanical properties and combustion efficiency of Al powder. Full article

The process of solid propellant production, which is the most widely used high-energy material, has garnered significant attention from researchers. However, there have been relatively few studies on its processing, due to the unique nature of the casting process. This paper aims to further analyze the pouring process of the propellant slurry. Initially, we obtained a sample of the propellant slurry and measured its rheological parameters using a rotary rheometer. From the analysis of the experimental results, we derived the viscosity parameters and the yield values of the propellant slurry. Subsequently, we simulated the pouring process, setting the slurry parameters based on the data obtained from the rheological measurement experiment. The simulation results demonstrated that the flower plate significantly impacts upon the cutting and separating effect on the slurry during pouring. Upon leaving the flower plate, the slurry descends onto the core mold platform under the influence of gravity, gradually flowing along the edge of the core mold. Although there may be some small voids in the pouring process, the voids will disappear completely at the end of pouring. A comparison with the actual pouring situation revealed a higher consistency between the simulation results and reality, thus establishing the reliability of the simulation method as a reference for analyzing the pouring process. Full article

A gas–solid-coupled sandwich combustion model was established for ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) composite propellant. Numerical simulations were conducted to investigate the influence of the content of AP and the relative position of the coarse AP on the flame structure and the burning rate of the propellant. The results indicated that the overall AP mass fraction has a significant effect on the gas-phase flame temperature and burning rate, and there exists an optimal oxygen-to-fuel ratio that maximizes the burning rate. As the mass fraction of fine AP increased, the premixed flame above the binder matrix gradually took over the dominance of the diffusion flame, and the intensity of the diffusion flame near the interface of coarse AP and binder matrix also increased, resulting in a significant increase in the burning rate. As the mass fraction of fine AP increases from 0% to 70.0%, the average surface temperature increases from 937 K to 1026 K, and the burning rate rises from 0.9 cm/s to 2.7 cm/s. The location of the coarse AP causes the flame tilts to the side with less binder matrix, but it had little effect on the burn rate of the propellant. Full article

The aim of this article is to compare rocket propellants containing a traditional binder (hydroxyl-terminated polybutadiene) and an energetic binder (glycidyl azide polymer), as well as a perchlorate oxidising agent and a “green” one, i.e., ammonium perchlorate and phase-stabilised ammonium nitrate. We have outlined the effects of individual substances on the sensitivity parameters and decomposition temperature of the produced solid propellants. The linear combustion velocity was determined using electrical methods. Heats of combustion for the propellant samples and the thermal decomposition features of the utilised binders were investigated via differential scanning calorimetry (DSC). Activation energy values for the energetic decomposition of the propellants were determined via the Kissinger method, based on DSC measurements at varied heating rates. Full article

To investigate the structural effects of the mechanical heterogeneity of Hydroxyl-terminated polybutadiene (HTPB) propellant grain under ignition pressurization, a gradient finite element method was proposed to evaluate its structural integrity. The heterogeneous mechanical properties of the propellant grain were constructed and assessed. The results demonstrate that the mechanical properties of the propellant grain are spatially variable when taking into account the effect of the load. The range of variation in the mechanical properties is related to the size of the load and its effect on the mechanical properties of the propellant. Two key parameters that affect the mechanical response of the grain are the non-uniform distribution of the modulus and the damage strain threshold. An increase in the propellant modulus leads to an increase in the stress response and a decrease in the strain response of the propellant grain under ignition pressurization. Meanwhile, an increase in the damage strain threshold improves the propellant’s modulus in the linear elastic stage in a disguised form. This also leads to an increase in the stress response and a decrease in the strain response when the strain response exceeds the damage strain threshold. The safety factor, based on the equivalent strain failure criterion of the grain, directly depends on both the strain response of the propellant grain and the maximum elongation of the propellant. Furthermore, the change in the safety factor of two propellant grains is primarily affected by the maximum elongation of the propellant. Full article

To examine the interactions between two binder systems—hydroxyl-terminated polybutadiene (HTPB) and hydroxyl-terminated block copolyether prepolymer (HTPE)—as well as between these binders and ammonium perchlorate (AP) at various temperatures for their susceptibility to varying degrees of thermal damage treatment, the thermal characteristics and combustion interactions of the HTPB and HTPE binder systems, HTPB/AP and HTPE/AP mixtures, and HTPB/AP/Al and HTPE/AP/Al propellants were studied. The results showed that the first and second weight loss decomposition peak temperatures of the HTPB binder were, respectively, 85.34 and 55.74 °C higher than the HTPE binder. The HTPE binder decomposed more easily than the HTPB binder. The microstructure showed that the HTPB binder became brittle and cracked when heated, while the HTPE binder liquefied when heated. The combustion characteristic index, S, and the difference between calculated and experimental mass damage, ΔW, indicated that the components interacted. The original S index of the HTPB/AP mixture was 3.34 × 10⁻⁸; S first decreased and then increased to 4.24 × 10⁻⁸ with the sampling temperature. Its combustion was initially mild, then intensified. The original S index of the HTPE/AP mixture was 3.78 × 10⁻⁸; S increased and then decreased to 2.78 × 10⁻⁸ with the increasing sampling temperature. Its combustion was initially rapid, then slowed. Under high-temperature conditions, the HTPB/AP/Al propellants combusted more intensely than the HTPE/AP/Al propellants, and its components interacted more strongly. A heated HTPE/AP mixture acted as a barrier, reducing the responsiveness of solid propellants. Full article

Boron powder is a kind of metal fuel with high gravimetric and volumetric calorific values, which has been widely used in military fields such as solid propellants, high-energy explosives, and pyrotechnics. However, the easily formed liquid oxide layer can adhere to the surface of boron powder and react with the hydroxyl (-OH) group of hydroxyl-terminated polybutadiene (HTPB) binder to form a gel layer that is detrimental to propellant processing and restricts the complete oxidation of boron powder. Therefore, to improve the combustion efficiency of boron powder, the ignition and combustion mechanisms of boron powder have been studied, and surface coating modification strategies have been developed by researchers worldwide, aiming to optimize the surface properties, improve the reaction activity, and promote the energy release of boron powder. In this review, recent studies on the ignition and combustion mechanisms of boron powder are discussed. Moreover, the reported boron powder coating materials are classified according to the chemical structure and reaction mechanism. Additionally, the mechanisms and characteristics of different coating materials are summarized, and the mechanism diagrams of fluoride and metal oxide are provided. Furthermore, promising directions for modification methods and the potential application prospects of boron powder are also proposed. Full article

A solid rocket motor (SRM) is a rocket engine that uses a fuel/oxidizer mixture in a solid state; the most commonly employed propellants are Hydroxyl-Terminated Polybutadiene (HTPB) as the fuel and ammonium/potassium perchlorate as the oxidizer. To increase the flight range of this kind of vehicle, the weight has to be reduced as much as possible. A possible element that can be worked on is the coating of the combustion chamber: the skirt. The aim of this paper is to investigate the behavior of a cylindrical skirt subjected to internal pressure load and axial thrust and to compare the performance of a skirt made of a standard steel for aeronautics purposes with a carbon-fiber-reinforced composite skirt. The motor test case is taken from the ONERA C1xb and the flowfield is simulated with an axisymmetric k-ω turbulence model. The carbon-fiber-reinforced composite skirt is a cylindrical shell with a symmetric and balanced layup [90/0/45/−45]s. To check composite layer integrity, Hashin’s failure criteria were adopted while linearized buckling methods were used to assess the buckling behavior of the skirt. The composite layup was modeled by adopting the classical laminate theory. Full article

Catalytic hybrid rocket motors using hydrogen peroxide (HP) are easy and efficient to achieve multiple starts and stops, and hydroxyl-terminated polybutadiene (HTPB) grains are commonly used due to their excellent mechanical properties. The low regression rate of HTPB grains limits the application of hybrid rocket motors. Furthermore, the addition of solid aluminum particles can effectively improve the regression rate and performance of hybrid rocket motors. However, the experimental results of a high mass fraction of aluminum and hydrogen peroxide available at present are not sufficient. In this research, the impact of a high mass fraction of aluminum on the motor performance and ablation rate of nozzles is studied experimentally. A solution of 95% hydrogen peroxide and HTPB with an aluminum additive are adopted as propellants. The variation in the axial regression rate of the grains is obtained by computed tomography (CT) scans and pre-test parameter measurements. The instantaneous regression rate method is adopted to obtain the real-time regression rate of the motor. The surface appearance and composition of the front and the end of the grains after the tests are analyzed by electron microscopy. Carbon ceramic and tungsten-bronze nozzles are used to explore the effect of a high mass fraction of aluminum on nozzle ablation. The experimental results show that the addition of aluminum raises the specific impulse and decreases the optimal oxygen-to-fuel ratio of the propellant combination. The high mass fraction of the aluminum particles has a severe ablative effect on carbon ceramic nozzles, while the effect on tungsten-bronze nozzles is minimal for a hot test lasting four to five seconds. Our results can provide experimental guidance for the application of a high mass fraction of aluminum and hydrogen peroxide hybrid rocket motor. Full article