Search Results (87)

Elastomeric ablative coatings are essential for protecting solid rocket motor (SRM) combustion chambers from extreme thermal and erosive environments, and their performance is governed by both material composition and processing strategy. This review examines the main elastomer systems used for SRM insulation, including ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), hydroxyl-terminated polybutadiene (HTPB), polyurethane (PU), silicone-based compounds, and related hybrids, and discusses how their rheological behavior, cure kinetics, thermal stability, and ablation mechanisms affect manufacturability and in-service performance. A comprehensive assessment of coating technologies is presented, covering casting, molding, centrifugal forming, spraying, automated deposition, and emerging additive-manufacturing approaches for complex geometries. Emphasis is placed on processing parameters that control adhesion to metallic substrates, layer uniformity, defect formation, and thermomechanical integrity under high-heat-flux exposure. The review integrates current knowledge on how material choice, surface preparation, and application sequence collectively determine insulation efficiency under operational SRM conditions. Practical aspects such as scalability, compatibility with complex chamber architectures, and integration with quality-control tools are highlighted. By comparing the capabilities and limitations of different materials and technologies, the study identifies key development trends and outlines remaining challenges for improving the durability, structural robustness, and ablation resistance of next-generation elastomeric coatings for SRMs. Full article

Hydroxyl-terminated polybutadiene (HTPB) is widely studied and the most used prepolymer for the binder system of composite solid propellants. A suitable functionalization of HTPB with energetic groups greatly improves the performance of the propellant. Therefore, the nitration of HTPB plays an essential role in the obtaining of high-energy binders. Among the reported methods, the nitration of HTPB using nitryl iodide (NO₂I) was distinguished as the most preferable due to the facilitated synthesis and product purity. However, the thus established synthesis is long and laborious; therefore, in the present work we focus our attention on the improved procedure using ultrasonic conditions. The resulted nitro-HTPB was characterized using FTIR, ¹H NMR, GPC, and DSC analyses. Also, based on the recorded IR-spectra a ratiometric analysis for determining the nitration rate was established, which could replace the expensive and time-consuming NMR analysis that was used. Full article

Hydroxyl-terminated polybutadiene (HTPB) is widely used in polyurethane binders, adhesives, and elastomers, but its low polarity and unsaturated backbone limit adhesion and long-term stability. Epoxidation presents a promising approach to addressing these limitations. However, most prior studies have focused on high-cis polybutadiene (PB), and systematic tuning of epoxidation in industrial low-cis HTPB has not been thoroughly examined. In this work, the epoxidation conversion of low-cis HTPB was systematically controlled by varying the equivalent amount of 3-chloroperbenzoic acid (m-CPBA). Conversion was governed solely by oxidant stoichiometry, while reaction time, concentration, and temperature had minimal effect, consistent with rapid, mixing-controlled epoxidation. Selective modification of 1,4-cis and 1,4-trans units enabled direct evaluation of how epoxidation degree influences polyurethane network formation and performance. Polyurethanes derived from epoxidized HTPB (EHTPB-PU) exhibited a clear correlation between epoxidation degree and network formation. Mechanical, adhesion, and chemical-resistance measurements revealed optimal performance at 10% epoxidation, where polarity and network compactness are effectively balanced. At this level, polyurethanes showed enhanced tensile strength, broad substrate adhesion, and increased resistance to acidic, basic, polar, and nonpolar environments, along with reduced water uptake. These results identify moderate epoxidation as a practical and efficient strategy for improving HTPB-based polyurethane materials. Full article

Hemorrhagic septicemia (HS) is a fulminant bovine disease across Asia and Africa, yet Pasteurella multocida (P. multocida) isolated from yak is poorly reported. We isolated strain NQ01 from a fatal HS case in Xizang, China and identified it as P. multocida B:2 by morphology, Gram stain, and PCR (kmt1⁺, bcbD⁺, LPS L2). NQO1 formed smooth, non-hemolytic colonies. After Gram staining, the cells appeared as red rods with bipolar staining. Antimicrobial testing showed broad susceptibility to β-lactams, aminoglycosides, tetracyclines, fluoroquinolones, midecamycin, florfenicol, polymyxin, and vancomycin, with resistance to metronidazole, trimethoprim sulfamethoxazole, and clindamycin. Streptomycin and ofloxacin had intermediate activity. In mice, the intraperitoneal and intranasal LD₅₀ values were 40.64 CFU/mL and 9.53 × 10⁶ CFU/mL, respectively. The intranasal fatal cases were characterized by bacteremia with multifocal disseminated intravascular coagulation involving lung, liver, and spleen. The complete genome comprises a single 2.33 Mb chromosome (40.47% GC, 2115 CDS, no plasmids) with only one resistance gene (Eco_EFTu_PLV) and 28 virulence genes spanning adhesion (tadA, rcpA, ppdD, pilB, tuf/tufA, htpB, PM_RS00430, PM_RS00425, PM_RS08640), immune modulation (lpxB/C/D, msbB, manB, rfaE/F, gmhA/lpcA, kdsA, pgi, wecA, galE, bexD’, ABZJ_RS06285, ABD1_RS00310), and nutritional/metabolic factor (hgbA, hemR, hemN), plus a YadA-like factor. Phylogenetically, NQ01 clusters with regional B:2 bovine/yak isolates. Collectively, these data define NQ01 as a highly virulent, low-resistance yak isolate and a practical model for natural-route HS pathogenesis and targeted control in high-altitude pastoral settings yaks. Full article

This study investigates the influence of selected combustion rate catalysts on the ballistic, physicochemical, and mechanical properties of non-isocyanate heterogeneous solid rocket propellants. Methods for curing prepolymers and modifying hydroxyl-terminated polybutadiene (HTPB) to obtain carboxyl-terminated polybutadiene (CTPB) and its epoxidized derivative (EHTPB) are discussed. The initial stage involved the synthesis of CTPB and EHTPB. The obtained compounds were analyzed for viscosity, comparing their properties to those of the base polymer HTPB. FTIR spectra of the synthesized compounds were recorded. Crosslinking systems were formulated based on the synthesized substances and tested for tensile strength. The final stage consisted of preparing solid heterogeneous rocket propellants containing selected catalysts—catocene and iron nanopowder—and evaluating their burning rate, hardness, and density. The results of the rocket propellant tests indicate that both catalysts perform effectively in the proposed system. Significantly higher burning rates were achieved compared to the catalyst-free formulation. The addition of 1% catocene resulted in a 2.5-fold increase in burning rate. Even better performance was observed with iron nanopowder—1% addition led to an almost threefold increase in burning rate. Neither catalyst significantly affected the hardness of the propellant; all samples exhibited hardness values in the range of 71–76 Shore A. Increasing the catocene content led to a decrease in the final propellant density, whereas the addition of iron nanopowder increased the density relative to the base formulation. Full article

In this study, we explored the evolution of mechanical properties in hydroxyl-terminated polybutadiene (HTPB) propellants under fatigue loading by performing fatigue tests with varying maximum stresses and cycle numbers, followed by uniaxial tensile tests on post-fatigue specimens. Residual elongation was used as a key parameter to characterize mechanical behavior, while scanning electron microscopy (SEM) provided insights into the mesostructural morphological changes that occur under different loading conditions, revealing the mechanisms responsible for variations in mechanical properties. The results show that, as the number of loading cycles increases, residual elongation decreases, with three distinct phases of decline—slow change, gradual decline, and rapid deterioration—depending on the stress levels. SEM analysis identified damage mechanisms such as “dewetting” and particle fragmentation at the mesostructural level, which compromise the material’s structural integrity, leading to reduced residual elongation. A novel aspect of this study is the application of Williams–Landel–Ferry (WLF) theory to construct a master curve describing residual elongation decay. This approach enabled the development of a generalized model to predict the material’s degradation under fatigue loading, with experimental validation of the fitted evolution model, offering a new and effective method for assessing the long-term performance of HTPB propellants. Full article

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

Composite solid propellants, which serve as the core energetic materials in aerospace and military propulsion systems, necessitate tailored enhancement of their mechanical properties to ensure operational safety and stability. A critical challenge involves elucidating the interfacial interactions among the multiple propellant components (≥6 components, including the polymer binder HTPB, curing agent IPDI, oxidizer particles AP/Al, bonding agents MAPO/T313, plasticizer DOS, etc.) and their influence on crosslinked network formation. In this study, we propose an integrated computational framework that combines coarse-grained simulations with reactive force fields to investigate these complex interactions at the molecular level. Our approach successfully elucidates the two-step reaction mechanism propagating along the AP interface in multicomponent propellants, comprising interfacial self-polymerization of bonding agents followed by the participation of curing agents in crosslinked network formation. Furthermore, we assess the mechanical performance through tensile simulations, systematically investigating both defect formation near the interface and the influence of key parameters, including the self-polymerization time, HTPB chain length, and IPDI content. Our results indicate that the rational selection of parameters enables the optimization of mechanical properties (e.g., ~20% synchronous improvement in tensile modulus and strength, achieved by selecting a side-chain ratio of 20%, a DOS molar ratio of 2.5%, a MAPO:T313 ratio of 1:2, a self-polymerization MAPO time of 260 ns, etc.). Overall, this study provides molecular-level insights into the structure–property relationships of composite propellants and offers a valuable computational framework for guided formulation optimization in propellant manufacturing. Full article

To investigate the aging behavior of HTPB composite solid propellant under constant strain conditions, this study analyzed the aging patterns of the propellant’s maximum elongation at four temperatures (323.15 K–343.15 K) and five strain levels (0–18%) using thermal–mechanical coupled accelerated aging tests. The results show that the maximum elongation initially increases, then decreases under constant strain conditions. To measure the mechanical work-induced decrease in the activation motor, we created a modified Arrhenius model with a strain correction factor based on empirical observations. The acceleration coefficient of a solid motor grain at the accelerated aging temperature (323.15 K) in comparison to the long-term storage temperature (293.15 K) was found to be 20.08 through finite element analysis. This means 206.80 days at the accelerated aging temperature is equivalent to 10 years at the long-term storage temperature. 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

Many factors and their mutual interaction between catalysts and AP/HTPB composite solid propellant induce the complexity in the combustion. Among them, we prepared two Fe-based MOFs as catalysts and investigated their catalytic effects and mechanism on the decomposition AP, HTPB and AP/HTPB complex by TG-DSC and TG-IR. The results show that both Fe-based MOFs exhibit catalytic effects on the decomposition of all samples. Specifically, in the AP/HTPB/MOFs composite system, a synergistic effect between MOFs and HTPB is observed, substantially accelerating the decomposition of both AP and HTPB, which makes the HTD temperature of AP advance approximately 100 °C, beyond what would be expected from each component acting independently. Mechanistic studies demonstrate that Fe₂O₃@C produced by the decomposition of Fe-based MOF uses the decomposition products of HTPB as a bridge to accelerate the overflow of NH₃ on the surface of AP, thereby allowing AP to decompose rapidly at a lower temperature and also accelerating the decomposition of HTPB. Moreover, its influence on the combustion performance of AP-based composite propellants was studied and the combustion rate increased by 20%. This research provides the new directions for designing and applying of Fe-based MOFs materials in HTPB-based solid propellent. Full article

The solution combustion method is widely used because of its simple operation and ability to produce porous structures. The chemical composition and morphological structure of the material can be regulated by different oxidiser-to-fuel ratios (φ). In this work, AlCo₂O₄ derived “Al” catalytic materials were successfully synthesised by adjusting the fuel-to-oxidiser ratio using a one-step solution combustion method. On the one hand, the aluminium nanoparticles act as a part of the metal fuel in the composite solid propellant and, at the same time, serve as a catalytic material. In contrast, the thermal decomposition performance of AP was significantly improved by the synergistic catalysis of AlCo₂O₄. Among the samples prepared under different fuel ratios, considering all aspects (high-temperature decomposition temperature, activation energy, and decomposition heat) comprehensively, the AlCo₂O₄ prepared with φ = 0.5 had a more excellent catalytic effect on AP thermal decomposition, and the T_HTD of AP was reduced to 285.4 °C, which is 188.08 °C lower. The activation energy of the thermal decomposition of AP was also significantly reduced (from 296.14 kJ/mol to 211.67 kJ/mol). In addition, the ignition delay time of AlCo₂O₄-AP/HTPB was drastically shortened to 9 ms from 28 ms after the addition of 7% AlCo₂O₄ derived “Al” catalytic materials. Composite solid propellants have shown great potential for application. 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 substitution of aluminum powder with highly reactive ultrafine aluminum-based metal fuels has a significant impact on the energy release of aluminum-containing energetic materials because of their excellent energy density and combustion performances. A series of ultrafine spherical Al-Mg alloy fuels with different contents of magnesium were prepared by close-coupled gas atomization technology. The properties of Al-Mg alloy powders of 13~15 μm were tested by SEM, TG-DSC, and laser ignition experiments. Results show that alloying with magnesium can significantly enhance thermal oxidation and combustion performance, leading to more oxidation weight gains and higher combustion heat release. HMX-based castable explosives with the same content of Al and the novel Al-Mg alloy were made and tested. Results show that the detonation performances of HMX/Al-Mg alloy/HTPB are better than HMX/Al/HTPB. Compared to the HMX/Al/HTPB explosive, the detonation heat of HMX/ Al-Mg alloy/HTPB was increased by 200 kJ/kg, the energy release efficiency was enhanced from 80.55% to 83.19%, the detonation velocity was increased by 114 m/s, and the shock wave overpressure at 5 m was increased by 83%. This research provides a new type of composite metal fuel for improving the combustion performance of Al powder. Full article