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• New modified multimetal composite powder fuel with good performance. • Ignition experimental method for simulating air/H 2 O environments. • Quantitative analysis of the flame development process of image processing methods. Studying the ignition and combustion performances of modified aluminum-based metallic fuels in variable oxidizing atmospheres is highly important for large-scale space exploration. In this study, Al–B–Mg multi-metal composite powders (MMP) were prepared using the mechanical ball-milling method.It was coated respectively by ammonium perchlorate (AP), lithium perchlorate (LP), and potassium nitrate (KN) to obtain modified multi-metal composite powder fuels (AP@MMP, LP@MMP, and KN@MMP, respectively) by a recrystallization method. The samples were characterized and their thermal oxidation, ignition and combustion processes were investigated through a TG and laser-ignition experiment under Air/H 2 O environments. The results show that the MMP samples can potentially be called pure aluminum substitutes. All three samples exhibit fast ignition characteristics with ignition delay times of 2.95–6.75 ms in air. AP@MMP exhibits the highest ignition speed. The thermal oxidation, ignition, and combustion properties of all samples decayed with increasing water content in the atmosphere (Air→Air+H 2 O→H 2 O). AP@MMP exhibits a significantly more intense and stable combustion overall than LP@MMP and KN@MMP. This study expands the direction and application range of aluminum-based composite metal fuels, guiding their applications in Air/H 2 O environments. [ABSTRACT FROM AUTHOR]

The potential of the Al-F reaction in suppressing agglomeration during propellant combustion and enhancing combustion performance is investigated by introducing fluorinated graphene as a fluorinated oxidizer. Comparative analyses of ignition combustion and agglomeration behaviors are conducted on novel composite powders and propellant samples modified with varying contents of fluorinated graphene using laser and hot wire ignition visualization systems. Characterizing parameters such as characteristic spectra, flame grayscale, ignition delay time, combustion duration, and burning rate are measured during combustion at different pressures. Additionally, agglomerated particles are collected via quenching techniques under 7 MPa pressure to explore the influence mechanism of fluorinated graphene on agglomeration near the burning surface, and a comprehensive influence mechanism is proposed. Results indicate that fluorinated graphene promotes ammonium perchlorate decomposition, accelerates oxidizing gas release, and enhances thermal conduction at the burning surface. The reaction between Al and F decreases the formation of intermediates (AlO and Al 2 O), while the interaction of F with Al and Al 2 O 3 effectively inhibits the clustering of Al particles, replacing conventional oxidation reactions and resulting in a unique micro-explosion jetting phenomenon. The introduction of 15 % fluorinated graphene concentrates most product particles around 10 μm, enhancing energy release during combustion. Overall, this composite powder containing fluorinated graphene effectively improves the combustion performance of aluminum-containing composite propellants, inhibiting Al particle agglomeration and potentially reducing specific impulse loss in solid rocket motors. • Fluorinated graphene promotes advanced decomposition and combustion. • Composite particles increase the combustion intensity of Al-based propellants. • F-O competition reaction suppresses the formation of agglomerations. • Multi-factor induced micro-explosions in agglomerations. [ABSTRACT FROM AUTHOR]

The investigation of the primary combustion products of boron-based fuel-rich propellants is conducive to understanding the mechanism of the two-stage combustion process and provides important information for the prediction and organization of secondary combustion processes. The present investigation methods include numerical simulation and experimental analysis. The former deviates considerably from the actual conditions. The latter is currently a reliable and practical method, although it is difficult to quantify when the components are complex. In this work, SEM, LPSA, XRD, XPS, IC, ICP–MS, AAS, EDS, and chemical analysis methods were employed to qualitatively and quantitatively analyze the 3 solid products (aggregations, condensed-phase products, and flocculent products) at 1, 5, and 10 bar. GC, GC–MS, and IC combined with chemical tests were adopted to investigate the gaseous products (including chlorine-containing gas) for the first time. The solid products primarily included B 2 O 3 , B(HO) 3 , unburned boron, KB 5 O 8 (H 2 O) 4 , KCl, C, NH 4 Cl, NH 4 Mg(H 2 O) 6 Cl 3 , B 13 C 2 , Fe 3 O 4 , Mo, MgO, Mg(OH) 2 , MoO 3 , C 3 N 4 , BN, MgCO 3 (H 2 O) 3 (or MgCO 3), MoO 2 , Fe 4 (Fe(CN) 6) 3 , and FeB (or BFe 4), and the first 7 were dominant. The reaction degree of boron was less than 50 wt% (increasing with increasing pressure), indicating the significance of the secondary combustion process. The reacted boron was likely to react with O and C but not with N. The generated B 2 O 3 vapor easily combined with H 2 O to form B(HO) 3 or reacted with KCl (from the thermal decomposition of KP) and H 2 O to produce KB 5 O 8 (H 2 O) 4 after cooling. There was less B 13 C 2 (its content increased with increasing pressure, resulting in increases in particle size), since it was easily oxidized to generate B 2 O 3. NH 4 Cl was produced by the oxidation-reduction reaction between the NH 3 and HClO 4 released from large-sized AP, and some of it crystallized with MgCl 2 and H 2 O to form NH 4 Mg(H 2 O) 6 Cl 3. The gaseous products primarily included N 2 , H 2 , CO, CH 4 , CO 2 , C 2 H 4 , C 2 H 2 , HCl, C 4 H 6 , C 3 H 6 , Cl 2 , C 6 H 6 , and other hydrocarbons. N 2 and H 2 had the highest content. The N 2 content increased with increasing pressure, while the content of the combustible gases decreased, indicating that high pressure promotes the propellant reaction. The results also show that high pressure was conducive to the low-temperature decomposition of AP (producing more HCl and Cl 2) and the reaction of boron and hydrocarbons (generating more B 13 C 2), while it had an adverse effect on the C reaction (producing less CO x and mostly CO). Nevertheless, the increasing pressure had little effect on the combustion product components but did affect the content within the pressure range. • Solid/gaseous primary combustion products of boron-based propellants were quantified. • Twenty-two solid products and twelve main gases were detected. • Chlorine-containing gaseous products were investigated. • Main products' generating paths were analyzed. • Small pressure changes were observed to affect the content, not the product components. [ABSTRACT FROM AUTHOR]

Overcoming the difficulty of ignition and combustion of aluminium in water vapour is the key to being applied in underwater propellant applications. The effect of coating or blending 20 mass% ammonium perchlorate (namely, AP@Al or AP–Al samples) on the ignition and combustion of Al particles in a 1.0 MPa water vapour–Ar environment was investigated using a constant temperature pressurized combustion chamber and a CO 2 laser. The results show that the combustion of Al particles in a water vapour–Ar environment is a non-homogeneous reaction and that agglomeration processes of Al droplets are observed. The ignition and combustion properties of the AP@Al and AP–Al samples under water vapour were greatly improved due to the decomposition of AP for heat/oxygen (particularly, O 2 provided a new pathway for AlO(g) generation) supply and the effect of dispersed particles. The maximum pressure change and combustion temperature (T max) were increased significantly for the AP@Al and AP–Al samples combustion, while their ignition delay time (t i) and combustion time (t c) decreased remarkably. In addition, the coating form is more effective in the combustion-promoting effect of AP than the blending form. Interestingly, the increase in water vapour concentration is not conducive to the ignition and combustion of samples in this work. It is probably because the reaction system is lean-fuel where the excess water vapour absorbs some of the heat and prevents effective collisions among the radicals. In addition, the chemical equilibrium largely influences the combustion temperature, resulting in a conspicuous effect of changes in water vapour concentration on the T max values. The reaction interface largely influences the combustion reaction rate of Al, so changes in particle size have a significant effect on the t i and t c values. [ABSTRACT FROM AUTHOR]

Aluminum is a promising energy-containing material that can satisfy both aerospace and underwater thermodynamic propulsion systems. A high-temperature pressurized combustion chamber and a CO 2 laser were adopted to investigate the ignition and combustion characteristics of 2, 5, and 40 μm aluminum particles in a 1.0 MPa air–H 2 O–Ar mixed atmosphere (with varying O 2 and H 2 O concentrations). The combustion-promoting effect of the ammonium perchlorate-coated modification (namely, the AP@Al sample) was evaluated. The results show that Al melts and agglomerates into millimeter-sized droplets (covered with a gas-phase flame) after ignition, and its nonhomogeneous combustion is dominated by diffusion. The flame propagation is greatly enhanced by the AP combustion-promoting effect of oxygen/heat supply and particle dispersion, resulting in a significant decrease in the ignition delay time (t i , approximately 55–85%) and combustion time (t c , approximately 32–96%), whereas an extraordinary increase in the maximum combustion temperature (T max , approximately 170–224 K) and pressure changes (approximately 1.7–8.5 kPa, approximately 10.6–136.5 kPa/s) are also observed. Excess water vapor inhibits the flame propagation for AP@Al, viz. the flame area and number of ejected burning particles is decreased. The main factor affecting the combustion temperature is the oxidant rather than the particle size, which may be related to the small difference in the active aluminum content of the samples and the diffusion-controlled combustion mechanism. Due to the advantage of O 2 for oxidation and the diffusion rate, the gradual replacement of H 2 O by air (similar to conversion to a fuel-lean system) leads to a decrease in t i , whereas T max is increased for all the samples, and the t c and self-sustaining combustion time are increased for the Al samples, whereas t c is decreased for AP@Al samples for both the equal-molar oxidizing gas concentration and equivalence ratio of O 2 –H 2 O control groups in this work. Since O 2 creates a new pathway for AlO production, the ignition and combustion performance of Al and AP@Al samples is significantly improved when H 2 O is replaced by a small amount of air. [ABSTRACT FROM AUTHOR]

[Display omitted] • AlH 3 made Al–AlH 3 form a mushroom flame. • Replacing Al with AlH 3 decreased the combustion temperature but increased the combustion rate. • Inhibition of HTPB on O 2 adsorption and mass transfer suppressed the metallic particles' combustion. Aluminum hydride (alane, AlH 3) is a promising energetic material that can significantly increase the specific impulse of propellants while lowering the combustion temperature. In this work, a CO 2 laser was adopted to investigate the effect of α-AlH 3 content on the ignition and combustion characteristics of AlH 3 –Al, AlH 3 –ammonium perchlorate (AP), AlH 3 –Al–AP, and AlH 3 –Al–AP–hydroxyl-terminated polybutadiene (HTPB) mixtures (namely, samples D Al , D AP , T, and Q, respectively). The D Al samples formed a mushroom flame at the beginning of combustion due to the Kelvin-Helmholtz effect under the heat flow generated by the combustion of H 2 released from AlH 3. The rapid hydrogen release caused the flame to break away from the sample to form a "dark zone", whose height gradually shortened. The high AlH 3 content promoted the decomposition of HTPB to C 4 species, resulting in a "dark zone" for Q samples during ignition. The D AP and T samples combusted intensely with lower ignition delay time (t i) and combustion time (t c) and higher maximum combustion temperature (T max) than the other two samples due to the AP. The combustion temperatures of the mixed samples were effectively decreased, while the combustion rates were also accelerated by partially replacing Al with AlH 3. As the rate of AlH 3 :Al was increased from 1:3 to 3:1, the T max of the D Al , T, and Q samples decreased by 113, 276, and 128 K, respectively, whereas t c decreased by 16.18 %, 32.11 %, and 8.18 %, respectively. However, the t i of the Q samples increased with increasing AlH 3 , probably because a large amount of hydrogen release exacerbated the effect of the porous layer, thus hindering the escape of the gas phase products. In addition, only weak Al(g) characteristic emission spectra were observed during combustion, which is due to the HTPB adhesion largely inhibiting the combustion of metallic fuels. [ABSTRACT FROM AUTHOR]

Coating boron particles with materials having multiple mechanisms of action is a promising way to promote the ignition and combustion properties of boron. The differences in thermal oxidation properties and ignition combustion characteristics of micron-sized boron composite particles (namely, AP@B, FR@B, and GAP@B) coated with 20 wt% ammonium perchlorate (AP), fluoropolymer (FR), or glycidyl azide polymer (GAP) were comparatively investigated using TG–DSC and CO 2 laser ignition test systems. The results showed that the starting reaction temperature and activation energy of the composite particles were significantly reduced by the lower pyrolysis temperatures of the three modified materials. However, their oxidation phase lagged behind that of the original boron particles, most likely because the coating agglomerated 27% of the fine boron particles (<0.1 μm) into micron-sized particles. In addition, the slow heating approach did not allow the particles to reach the ignition temperature immediately and may indirectly aggravate the oxide layer thickness. Nevertheless, the coating modifier effectively promoted energy release (the heat release was increased by 93.76%, 28.65%, and 24.20% for FR@B, GAP@B, and AP@B, respectively). Generally, the ignition delay time (t i) decreases, whereas the combustion time (t c), self-sustaining combustion time (t f), maximum combustion temperature (T max) and burnout rate (α) increase after the coating of modified materials. First, AP decomposition produced O 2 and other gases to provide an oxidant for boron combustion and disperse the particles into space, which promotes extremely rapid energy release. Thus, the T max and α of AP@B were significantly enhanced. Second, FR pyrolysis gas production can vaporize B 2 O 3 and then promote the exposure of internal boron to react with oxygen. Thus, the t f and α of FR@B were significantly enhanced. However, the T max value was not the highest since the highest calorific value (up to 15,094 J•g−1) of FR@B is released at a slow rate. Finally, GAP can significantly shorten t i due to its lower activation energy, and this modification effect can be significantly improved by increasing the O 2 content. Since boron is characterized by high oxygen consumption, increasing the oxygen partial pressure can significantly promote ignition and combustion. The T max values of four samples in a mixed O 2 –N 2 environment under 1.0 MPa even exceeded the boiling point of B 2 O 3 , which is favorable for the reaction of internal boron with oxygen due to the gasification of the oxide layer at this time. [ABSTRACT FROM AUTHOR]

Abstract Introduction It is necessary to clearly understand construction accidents for preventing a rise in Chinese construction accidents and deaths. Better analysis methods are required for Chinese construction sector accidents. Methods Choosing and analyzing a typical construction accident based on four popular contemporary accident causation models: STAMP, AcciMap, HFACS, and the 2-4 Model. Then we evaluated the models' applicability to construction accidents, including their usability, reliability, and validity. Results STAMP addressed how complexity within the accident system influenced the accident development, and its output makes the responsibilities clearer for the accident. AcciMap described the entire system's failure, the entire accident's trajectory, and the relationship between them. AcciMap showed that the accident was a dynamic developing process, and this method has a high usability. The taxonomic nature of HFACS is an important feature that provides it with a high reliability. In the accident reviewed here, we found that poor management was a critical factor rather than the individual factor in the accident. The 2-4 Model provided detailed causes of the accident and established the relationship among the accident causes, the safety management system, and the safety culture. It also avoided capturing all of the complexity in the large sociotechnical system and revealed a dynamic analysis and developing process. We confirmed that it has a high usability and validity. Therefore, the 2-4Model is recommended for future Chinese construction accident analysis efforts. Practical Applications The study provides a useful, reliable, and effective analysis method for Chinese construction accidents. Highlights • STAMP, AcciMap, HFACS, and the 2-4Model, were comprehensively analyzed and applied to a typical construction accident. • We evaluated the four models' applicability to construction accidents, including their usability, reliability, and validity. • The 2-4 Model is recommended for future construction accident analysis efforts. [ABSTRACT FROM AUTHOR]

Aluminum hydride (AlH 3) is currently receiving considerable attention due to its potential to replace aluminum (Al) as a new metal fuel in solid propellants. In this study, simultaneous thermogravimetric analysis and differential scanning calorimetry and a laser ignition testing system were used to investigate the thermal oxidation and combustion characteristics of AlH 3 and Al. The combustion residues were then analyzed using a scanning electron microscope. Results show that the thermal oxidation processes of both AlH 3 and Al contain a mass loss stage and two mass gain stages. After dehydrogenation, AlH 3 exhibits a stepwise oxidation behavior that is similar to that of a similar sized Al, but has a much higher mass gain. The combustion process of Al can be divided into three stages, which correspond to the combustion of dispersed Al particles, formation of Al agglomerate and combustion of Al agglomerate, respectively. The combustion flame of AlH 3 is significantly different from that of Al, but their microscopic combustion behaviors are very similar. A unique flame delamination phenomenon exists in the early stage of AlH 3 flame development. AlH 3 has shorter ignition delay times and a larger combustion intensity than Al. The release and combustion of hydrogen changes the combustion environment of the remaining AlH 3 particles, leading to the appearance of an OH characteristic peak and increasing the production path of AlO. The morphology of combustion residues shows that the dehydrogenation of AlH 3 starts from the particle surface and then gradually expands towards its interior. • TG-DSC was used to contrastively study thermal oxidation properties of AlH 3 and Al. • Combustion flames, micro-combustion behaviors and emission spectra were analyzed. • Hydrogen plays a critical role in the combustion of AlH 3. • Dehydrogenation/passivation mechanism of AlH 3 was analyzed. [ABSTRACT FROM AUTHOR]

Impact injuries and fire risks generally coexist simultaneously in extreme environments. In this context, it is of great necessity to design impact resistant materials with both flame retardant performance and thermal stability. Here, a multi-functional flame retardant coating was prepared from the combination of silica sol (Si-sol), phytic acid (PA) and expandable graphite (EG) by graft modification with γ-propyl-trimethoxysilane (KH550). Subsequently, hierarchical composites were fabricated using one-pot foaming and brush coating method, where the carbon fiber cloth and coating served as the surface layer, while rigid polyurethane foams (RPUF) acted as the interlayer. The hierarchical structure endowed the RPUF composites with high compression resistance and impact resistance properties. Furthermore, the flame retardant coating could effectively reduce the values of peak heat release rate and peak smoke production rate of RPUF composites by 77.5% and 81.8%, respectively. Therefore, these RPUF composites can effectively prevent impact damage and achieve excellent flame retardancy, making them promising candidates as safety protective materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The energy release efficiency of boron (B)-containing fuel-rich solid propellants depends largely on the combustion behavior of the B particles contained therein. Here, the combustion process of B particles was first studied using a laser ignition testing system. Then, the combustion and agglomeration characteristics of B particles in a fuel-rich propellant were further investigated. To this end, a microtube burner was specially manufactured to mimic the secondary combustion of boron-containing propellant. Results show that the primary combustion intensity of the boron-containing propellant was relatively weak, and the combustion temperature was 1720±32 K. B particles would participate in the primary combustion reaction of the propellant, resulting in short time detection of the characteristic green flame and BO 2 spectrum. Severe self-conglomeration of B particles occurred on the propellant burning surface, forming irregular coral-like B particle conglomerates. The development of the quasi-secondary (the word "quasi" is added to highlight the difference between the experimental conditions and the actual conditions in engines) combustion flame showed that hot B particles were an important ignition source for the gaseous fuel and that the existence of excess gaseous fuel in the primary plume was an important prerequisite for self-sustaining combustion of B particles in air. The emission spectra of propellant quasi-secondary combustion were very similar to those of primary combustion, but the intensity was significantly increased. Microstructures of the combustion residues showed that the oxide layer on the surface of B particles played an important role during the formation of B conglomerates. Irregular B conglomerates detached from the propellant burning surface might further develop into spherical B agglomerates in the high-temperature secondary combustion flame zone. [ABSTRACT FROM AUTHOR]