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37 pages, 4320 KiB  
Article
Proof of Concept for Enhanced Sugar Yields and Inhibitors Reduction from Aspen Biomass via Novel, Single-Step Nitrogen Explosive Decompression (NED 3.0) Pretreatment Method
by Damaris Okafor, Lisandra Rocha-Meneses, Vahur Rooni and Timo Kikas
Energies 2025, 18(15), 4026; https://doi.org/10.3390/en18154026 - 29 Jul 2025
Viewed by 236
Abstract
The transition to sustainable energy sources has intensified interest in lignocellulosic biomass (LCB) as a feedstock for second-generation biofuels. However, the inherent structural recalcitrance of LCB requires the utilization of an effective pretreatment to enhance enzymatic hydrolysis and subsequent fermentation yields. This manuscript [...] Read more.
The transition to sustainable energy sources has intensified interest in lignocellulosic biomass (LCB) as a feedstock for second-generation biofuels. However, the inherent structural recalcitrance of LCB requires the utilization of an effective pretreatment to enhance enzymatic hydrolysis and subsequent fermentation yields. This manuscript presents a novel, single-step, and optimized nitrogen explosive decompression system (NED 3.0) designed to address the critical limitations of earlier NED versions by enabling the in situ removal of inhibitory compounds from biomass slurry and fermentation inefficiency at elevated temperatures, thereby reducing or eliminating the need for post-treatment detoxification. Aspen wood (Populus tremula) was pretreated by NED 3.0 at 200 °C, followed by enzymatic hydrolysis and fermentation. The analytical results confirmed substantial reductions in common fermentation inhibitors, such as acetic acid (up to 2.18 g/100 g dry biomass) and furfural (0.18 g/100 g dry biomass), during early filtrate recovery. Hydrolysate analysis revealed a glucose yield of 26.41 g/100 g dry biomass, corresponding to a hydrolysis efficiency of 41.3%. Fermentation yielded up to 8.05 g ethanol/100 g dry biomass and achieved a fermentation efficiency of 59.8%. Inhibitor concentrations in both hydrolysate and fermentation broth remained within tolerable limits, allowing for effective glucose release and sustained fermentation performance. Compared with earlier NED configurations, the optimized system improved sugar recovery and ethanol production. These findings confirm the operational advantages of NED 3.0, including reduced inhibitory stress, simplified process integration, and chemical-free operation, underscoring its potential for scalability in line with the EU Green Deal for bioethanol production from woody biomass. Full article
(This article belongs to the Section A4: Bio-Energy)
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27 pages, 5196 KiB  
Article
Impact of Hydrogen Release on Accidental Consequences in Deep-Sea Floating Photovoltaic Hydrogen Production Platforms
by Kan Wang, Jiahui Mi, Hao Wang, Xiaolei Liu and Tingting Shi
Hydrogen 2025, 6(3), 52; https://doi.org/10.3390/hydrogen6030052 - 29 Jul 2025
Viewed by 230
Abstract
Hydrogen is a potential key component of a carbon-neutral energy carrier and an input to marine industrial processes. This study examines the consequences of coupled hydrogen release and marine environmental factors during floating photovoltaic hydrogen production (FPHP) system failures. A validated three-dimensional numerical [...] Read more.
Hydrogen is a potential key component of a carbon-neutral energy carrier and an input to marine industrial processes. This study examines the consequences of coupled hydrogen release and marine environmental factors during floating photovoltaic hydrogen production (FPHP) system failures. A validated three-dimensional numerical model of FPHP comprehensively characterizes hydrogen leakage dynamics under varied rupture diameters (25, 50, 100 mm), transient release duration, dispersion patterns, and wind intensity effects (0–20 m/s sea-level velocities) on hydrogen–air vapor clouds. FLACS-generated data establish the concentration–dispersion distance relationship, with numerical validation confirming predictive accuracy for hydrogen storage tank failures. The results indicate that the wind velocity and rupture size significantly influence the explosion risk; 100 mm ruptures elevate the explosion risk, producing vapor clouds that are 40–65% larger than 25 mm and 50 mm cases. Meanwhile, increased wind velocities (>10 m/s) accelerate hydrogen dilution, reducing the high-concentration cloud volume by 70–84%. Hydrogen jet orientation governs the spatial overpressure distribution in unconfined spaces, leading to considerable shockwave consequence variability. Photovoltaic modules and inverters of FPHP demonstrate maximum vulnerability to overpressure effects; these key findings can be used in the design of offshore platform safety. This study reveals fundamental accident characteristics for FPHP reliability assessment and provides critical insights for safety reinforcement strategies in maritime hydrogen applications. Full article
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15 pages, 3645 KiB  
Article
PVP-Regulated Self-Assembly of High-Strength Micrometer-Scale Al/CuO/AP Energetic Microspheres with Enhanced Reactivity
by Xuyang Wu, Hongbao Wang, Chenglong Jiao, Benbo Zhao, Shixiong Sun and Yunjun Luo
Polymers 2025, 17(14), 1994; https://doi.org/10.3390/polym17141994 - 21 Jul 2025
Viewed by 248
Abstract
Al-based nanocomposite energetic materials have broad application prospects in explosives and propellants, owing to their excellent energy release efficiency. However, their insufficient reliability, poor stability, and difficulty of formation limit their practical application. This study employed self-assembly using a hydrophilic polymer polyvinylpyrrolidone (PVP) [...] Read more.
Al-based nanocomposite energetic materials have broad application prospects in explosives and propellants, owing to their excellent energy release efficiency. However, their insufficient reliability, poor stability, and difficulty of formation limit their practical application. This study employed self-assembly using a hydrophilic polymer polyvinylpyrrolidone (PVP) together with nano-aluminum powder (Al), copper oxide (CuO), and ammonium perchlorate (AP) to obtain high-strength and high-activity composite micrometer-sized microspheres. The influence of PVP concentration on the mechanical behavior of Al/AP composite microspheres was systematically investigated, and Al was replaced with ultrasonically dispersed Al/CuO to explore the mechanism of action of PVP in the system and the catalytic behavior of CuO. PVP significantly enhanced the interfacial bonding strength. The Al/AP/5%PVP microspheres achieved a strength of 8.4 MPa under 40% compressive strain, representing a 365% increase relative to Al/AP. The Al/CuO/AP/5%PVP microspheres achieved a strength of 10.2 MPa, representing a 309% increase relative to Al/CuO. The mechanical properties of the composite microspheres were improved by more than threefold, and their thermal reactivities were also higher. This study provides a new method for the controlled preparation of high-strength, high-activity, micrometer-sized energetic microspheres. These materials are expected to be applied in composite solid propellants to enhance their combustion efficiency. Full article
(This article belongs to the Special Issue Eco-Friendly Polymeric Coatings and Adhesive Technology, 2nd Edition)
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16 pages, 3629 KiB  
Article
Influence of Mg/Al Coating on the Ignition and Combustion Behavior of Boron Powder
by Yanjun Wang, Yueguang Yu, Xin Zhang and Siyuan Zhang
Coatings 2025, 15(7), 828; https://doi.org/10.3390/coatings15070828 - 16 Jul 2025
Viewed by 259
Abstract
Amorphous boron powder, as a high-energy fuel, is widely used in the energy sector. However, its ignition and combustion difficulties have long limited its performance in propellants, explosives, and pyrotechnics. In this study, Mg/Al-coated boron powder with enhanced combustion properties was synthesized using [...] Read more.
Amorphous boron powder, as a high-energy fuel, is widely used in the energy sector. However, its ignition and combustion difficulties have long limited its performance in propellants, explosives, and pyrotechnics. In this study, Mg/Al-coated boron powder with enhanced combustion properties was synthesized using the electrical explosion method. To investigate the effect of Mg/Al coating on the ignition and combustion behavior of boron powder, four samples with different Mg/Al coating contents (4 wt.%, 6 wt.%, 8 wt.%, and 10 wt.%) were prepared. Compared with raw B95 boron powder, the coated powders showed a significant reduction in particle size (from 2.9 μm to 0.2–0.3 μm) and a marked increase in specific surface area (from 10.37 m2/g to over 20 m2/g). The Mg/Al coating formed a uniform layer on the boron surface, which reduced the ignition delay time from 143 ms to 40–50 ms and significantly improved the combustion rate, combustion pressure, and combustion calorific value. These results demonstrate that Mg/Al coating effectively promotes rapid ignition and sustained combustion of boron particles. Furthermore, with the increasing Mg/Al content, the ignition delay time decreased progressively, while the combustion rate, combustion pressure, and heat release increased accordingly, reaching optimal values at 8 wt.% Mg/Al. An analysis of the combustion residues revealed that both Mg and Al reacted with boron oxide to form new multicomponent compounds, which reduced the barrier effect of the oxide layer on oxygen diffusion into the boron core, thereby facilitating continuous combustion and high heat release. This work innovatively employs the electrical explosion method to prepare dual-metal-coated boron powders and, for the first time, reveals the synergistic promotion effect of Mg and Al coatings on the ignition and combustion performance of boron. The results provide both experimental data and theoretical support for the high-energy release and practical application of boron-based fuels. Full article
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12 pages, 9217 KiB  
Article
Nonlinearity in Turbulent Diffusion as a Possible Cause of Stellar Flares
by Elena Popova
Astronomy 2025, 4(3), 12; https://doi.org/10.3390/astronomy4030012 - 7 Jul 2025
Viewed by 233
Abstract
Extremely powerful flares releasing energy well above 1032 erg are rare compared to the typical manifestations of solar activity, which are already being routinely monitored by the existing Space Weather network—with some level of predictability. However, much less is known about the [...] Read more.
Extremely powerful flares releasing energy well above 1032 erg are rare compared to the typical manifestations of solar activity, which are already being routinely monitored by the existing Space Weather network—with some level of predictability. However, much less is known about the mechanisms behind such rare events (like the well-documented Carrington event of 1859) or about hypothetical superflares that could exceed current energy estimates by several orders of magnitude. We propose a model based on the nonlinear suppression of turbulent diffusion with increasing magnetic field, which ultimately leads to the random occurrence of regions with a magnetic field amplitude significantly exceeding the magnetic field amplitude in a regular cycle. This is similar to the mechanism of a local “explosion of an overheated boiler”. Such regions can be correlated with flares. In our model, flares have different powers. Full article
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22 pages, 6616 KiB  
Article
Study on Vertical Propagation of Power Parameters in RC Frame Under Internal Explosion
by Junrun Li, Yonggang Lu, Haibin Miao, Hengwei Xu, Xiaowei Feng and Yixin Yuan
Buildings 2025, 15(12), 2080; https://doi.org/10.3390/buildings15122080 - 17 Jun 2025
Viewed by 198
Abstract
The roof slab, as a critical component for partitioning the vertical space within RC frame structures, can effectively mitigate the propagation of shock waves and reduce damage levels in adjacent rooms. This study employed finite element (FE) modeling to investigate the vertical propagation [...] Read more.
The roof slab, as a critical component for partitioning the vertical space within RC frame structures, can effectively mitigate the propagation of shock waves and reduce damage levels in adjacent rooms. This study employed finite element (FE) modeling to investigate the vertical propagation of blast waves and roof ejection velocity in RC frames. The model’s reliability was verified by reconstructing internal explosion tests on RC frames and close-in explosion tests on masonry walls. On this basis, two typical single-room RC frame structures that are vertically adjacent were designed, and numerical simulations of the internal explosion were conducted under four explosive equivalents and four venting coefficients. The propagation of shock waves, load characteristics in the vertically adjacent room, and the dynamic response of roof slabs were examined. The results show that shock waves propagated to the vertically adjacent room decreased by approximately two orders of magnitude for peak overpressure and one order of magnitude for impulse due to the obstruction of shock waves by roof slabs, respectively, compared to the source explosion room. For larger venting coefficients, abundant energy was released through the venting openings, making it difficult to form a quasi-static pressure with a long duration inside the source explosion room. In addition to the shock wave, the explosive ejection of roof slabs in the explosion source room will further exacerbate the damage to the vertically adjacent room. Peak overpressure and impulse propagated to the vertically adjacent room were reduced significantly by the increase in the venting coefficient, resulting in an attenuation of structural damage. Finally, empirical models incorporating the venting coefficient were established to characterize the attenuation coefficients of power parameters, demonstrating the predictive capability for peak overpressure, impulse, and roof ejection velocity in both the explosion source room and the vertically adjacent room. Full article
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31 pages, 4555 KiB  
Article
The Roles of Transcrustal Magma- and Fluid-Conducting Faults in the Formation of Mineral Deposits
by Farida Issatayeva, Auez Abetov, Gulzada Umirova, Aigerim Abdullina, Zhanibek Mustafin and Oleksii Karpenko
Geosciences 2025, 15(6), 190; https://doi.org/10.3390/geosciences15060190 - 22 May 2025
Viewed by 601
Abstract
In this article, we consider the roles of transcrustal magma- and fluid-conducting faults (TCMFCFs) in the formation of mineral deposits, showing the importance of deep sources of heat and hydrothermal solutions in the genesis and history of deposit formation. As a result of [...] Read more.
In this article, we consider the roles of transcrustal magma- and fluid-conducting faults (TCMFCFs) in the formation of mineral deposits, showing the importance of deep sources of heat and hydrothermal solutions in the genesis and history of deposit formation. As a result of the impact on the lithosphere of mantle plumes rising along TCMFCFs, intense block deformations and tectonic movements are generated; rift systems, and volcanic–plutonic belts spatially combined with them, are formed; and intrusive bodies are introduced. These processes cause epithermal ore formation as a consequence of the impact of mantle plumes rising along TCMFCF to the lithosphere. At hydrocarbon fields, they play extremely important roles in conductive and convective heat, as well as in mass transfer to the area of hydrocarbon generation, determining the relationship between the processes of lithogenesis and tectogenesis, and activating the generation of hydrocarbons from oil and gas source rock. Detection of TCMFCFs was carried out using MMSS (the method of microseismic sounding) and MTSM (the magnetotelluric sounding method), in combination with other geological and geophysical data. Practical examples are provided for mineral deposits where subvertical transcrustal columns of increased permeability, traced to considerable depths, have been found; the nature of these unique structures is related to faults of pre-Paleozoic emplacement, which determined the fragmentation of the sub-crystalline structure of the Earth and later, while developing, inherited the conditions of volumetric fluid dynamics, where the residual forms of functioning of fluid-conducting thermohydrocolumns are granitoid batholiths and other magmatic bodies. Experimental modeling of deep processes allowed us to identify the quantum character of crystal structure interactions of minerals with “inert” gases under elevated thermobaric conditions. The roles of helium, nitrogen, and hydrogen in changing the physical properties of rocks, in accordance with their intrastructural diffusion, has been clarified; as a result of low-energy impact, stress fields are formed in the solid rock skeleton, the structures and textures of rocks are rearranged, and general porosity develops. As the pressure increases, energetic interactions intensify, leading to deformations, phase transitions, and the formation of chemical bonds under the conditions of an unstable geological environment, instability which grows with increasing gas saturation, pressure, and temperature. The processes of heat and mass transfer through TCMFCFs to the Earth’s surface occur in stages, accompanied by a release of energy that can manifest as explosions on the surface, in coal and ore mines, and during earthquakes and volcanic eruptions. Full article
(This article belongs to the Section Geophysics)
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16 pages, 1716 KiB  
Review
Immunological Avalanches in Renal Immune Diseases
by Davide Viggiano, Pietro Iulianiello, Antonio Mancini, Candida Iacuzzo, Luca Apicella, Renata Angela Di Pietro, Sarah Hamzeh, Giovanna Cacciola, Eugenio Lippiello, Andrea Gigliotti, Carmine Secondulfo, Giancarlo Bilancio and Giuseppe Gigliotti
Biomedicines 2025, 13(4), 1003; https://doi.org/10.3390/biomedicines13041003 - 21 Apr 2025
Viewed by 630
Abstract
The complex nature of immune system behavior in both autoimmune diseases and transplant rejection can be understood through the lens of avalanche dynamics in critical-point systems. This paper introduces the concept of the “immunological avalanche” as a framework for understanding unpredictable patterns of [...] Read more.
The complex nature of immune system behavior in both autoimmune diseases and transplant rejection can be understood through the lens of avalanche dynamics in critical-point systems. This paper introduces the concept of the “immunological avalanche” as a framework for understanding unpredictable patterns of immune activity in both contexts. Just as avalanches represent sudden releases of accumulated potential energy, immune responses exhibit periods of apparent stability followed by explosive flares triggered by seemingly minor stimuli. The model presented here draws parallels between immune system behavior and other complex systems such as earthquakes, forest fires, and neuronal activity, where localized events can propagate into large-scale disruptions. In autoimmune conditions like systemic lupus erythematosus (SLE), which affects multiple organ systems including the kidneys in approximately 50% of patients, these dynamics manifest as alternating periods of remission and flares. Similarly, in transplant recipients, the immune system exhibits metastable behavior under constant allograft stimulation. This critical-point dynamics framework is characterized by threshold-dependent activation, positive feedback loops, and dynamic non-linearity. In autoimmune diseases, triggers such as UV light exposure, infections, or stress can initiate cascading immune responses. In transplant patients, longitudinal analysis reveals how monitoring oscillatory patterns in blood parameters and biological age markers can predict rejection risk. In a preliminary study on kidney transplant, all measured variables showed temporal instability. Proteinuria exhibited precise log–log linearity in power law analysis, confirming near-critical-point system behavior. Two distinct dynamic patterns emerged: large oscillations in eGFR, proteinuria, or biological age predicted declining function, while small oscillations indicated stability. During avalanche events, biological age increased dramatically, with partial reversal leaving persistent elevation after acute episodes. Understanding these dynamics has important implications for therapeutic approaches in both contexts. Key findings suggest that monitoring parameter oscillations, rather than absolute values, better indicates system instability and potential avalanche events. Additionally, biological age calculations provide valuable prognostic information, while proteinuria measurements offer efficient sampling for system dynamics assessment. This conceptual model provides a unifying framework for understanding the pathogenesis of both autoimmune and transplant-related immune responses, potentially leading to new perspectives in disease management and rejection prediction. Full article
(This article belongs to the Section Immunology and Immunotherapy)
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15 pages, 7958 KiB  
Article
Laboratory Study on Rockburst Control by Step Method in Deep Tunnel
by Chao Ren, Xiaoming Sun, Dongqiao Liu and Jinkun Yang
Appl. Sci. 2025, 15(7), 3853; https://doi.org/10.3390/app15073853 - 1 Apr 2025
Viewed by 317
Abstract
In terms of rockburst control technology, it is generally believed that optimizing the section design and adopting the step method can effectively suppress the occurrence of rockburst, but there is no literature to explain the reasons for adopting this method from the experimental [...] Read more.
In terms of rockburst control technology, it is generally believed that optimizing the section design and adopting the step method can effectively suppress the occurrence of rockburst, but there is no literature to explain the reasons for adopting this method from the experimental point of view. In addition, compared with the application of support, this method can achieve the effect of not increasing the construction process, not affecting the progress of the project and reducing the project cost. In view of this, the Gaoloushan deep-buried tunnel with rockburst was taken as the research object in this paper. Firstly, the excavation scheme based on the step method was proposed, and its explosion-proof effect was verified again. The experimental results showed that the step method could be essentially regarded as the transformation of surrounding rock by reasonably distributing explosives and reducing the working section. The beneficial effects of this method were as follows: the release intensity of absolute energy was slowed down, the way of energy release was changed; the stress condition of surrounding rock was improved; the path of the continuous supplement of strain energy in the original rockburst area was cut off; and the energy accumulation degree of surrounding rock was reduced, so that the accumulated energy in the rock mass did not exceed its energy storage limit at the location where the rockburst should have occurred. The reduced high energy was released in an orderly manner and induced the rock failure process, forming a fracture zone and a plastic zone. In the process of expansion, the fracture zone and plastic zone further reduced the stress concentration of the surrounding rock and deteriorated the mechanical properties of the surrounding rock. The stress concentration zone was transferred to the deeper surrounding rock outside the unloading relaxation zone, and part of the elastic energy accumulated in the surrounding rock was released. The strain energy could be distributed and dissipated, and the effect of energy safety and slow release was achieved. Full article
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17 pages, 4802 KiB  
Article
The Effects of HMX and CL-20-Based Co-Particles on the Ignition and Combustion Performances of Aluminum Powders
by Zhihua Xue, Weimeng Zhang, Ruixuan Xu, Sulan Yang and Qilong Yan
Aerospace 2025, 12(4), 272; https://doi.org/10.3390/aerospace12040272 - 24 Mar 2025
Viewed by 1418
Abstract
Energetic co-particles have been proven effective in balancing high-energy and safety performance, which might be used as insensitive oxidizers in solid propellants. In this work, the high temperature interactions between several co-particles and aluminum (Al) powders in the presence of ammonium perchlorate (AP) [...] Read more.
Energetic co-particles have been proven effective in balancing high-energy and safety performance, which might be used as insensitive oxidizers in solid propellants. In this work, the high temperature interactions between several co-particles and aluminum (Al) powders in the presence of ammonium perchlorate (AP) have been studied. The co-particles are based on octogen (HMX) and hexanitrohexaazaisowurtzitane (CL-20), with balanced energy content and safety performance. They are used to combine with Al and AP to form either binary or ternary systems. Their energy release rate during decomposition and combustion have been fully evaluated. Due to the intimate contact between components in co-particles, the binary/ternary systems exhibit superior reaction efficiency compared to relevant mechanical mixtures with the same formulations. These novel energetic systems have maximum two times higher pressurization rate, 10% higher heat of explosion, 53.8% higher flame propagation rate, and much shorter ignition delay than the corresponding normal mixtures. For both HMX- and CL-20-based co-particle systems, the median size of condensed combustion products (CCPs) is smaller than those of the mechanical mixtures, with higher content of Al2O3. This indicates that co-particles have advantages in improving combustion efficiency of Al particles by eliminating their agglomeration. Full article
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12 pages, 5153 KiB  
Article
Preparation of CL-20 with Controllable Particle Size Using Microfluidic Technology
by Zihao Zhang, Jin Yu, Yujia Wen, Hanyu Jiang, Siyu Xu, Yubao Shao, Ergang Yao, Heng Li and Fengqi Zhao
Molecules 2025, 30(5), 1176; https://doi.org/10.3390/molecules30051176 - 6 Mar 2025
Cited by 1 | Viewed by 1102
Abstract
As a typical high-energy-density material, the sensitivity of CL-20 severely limits its application in explosives and propellants. Adjusting its structure at the microscopic level can effectively solve such problems. In this study, a microfluidic recrystallization technique was used to prepare ε-CL-20 with three [...] Read more.
As a typical high-energy-density material, the sensitivity of CL-20 severely limits its application in explosives and propellants. Adjusting its structure at the microscopic level can effectively solve such problems. In this study, a microfluidic recrystallization technique was used to prepare ε-CL-20 with three different particle sizes, with narrow particle size distributions (D50 = 2.77 μm, 17.22 μm and 50.35 μm). The prepared samples had fewer surface defects compared to the raw material. As the particle size decreased, the density of CL-20 increased and its impact sensitivity was significantly reduced. The activation energy of the CL-20 prepared using microfluidic technology increased with increases in particle size. Laser ignition experiments revealed that smaller CL-20 particles had the highest energy release efficiency, while larger particles exhibited a higher energy density and more stable energy release. The combustion performance and safety of CL-20 can be effectively improved by improving the crystal size distribution and surface morphology. Controllable preparation of multiple particle sizes of CL-20 was achieved using microfluidic recrystallization technology, which provides a reference for the preparation of multiple particle sizes of other energetic materials. Full article
(This article belongs to the Section Materials Chemistry)
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11 pages, 5046 KiB  
Article
Coulomb Effect of Intermediate Products of Core–Shell SiO2@Al Nanothermite
by Jinping Zhang, Yuanhong Chu, Fei Wang, Shan Yuan, Minghui Tan, Hui Fu and Yu Jia
Molecules 2025, 30(4), 932; https://doi.org/10.3390/molecules30040932 - 17 Feb 2025
Viewed by 575
Abstract
Nanothermites as high-energy-density and high-reaction-rate materials have important applications in civil and military fields. Nevertheless, it is difficult to detect all intermediates and products using conventional experimental methods. In this work, the reaction process of core-shell SiO2@Al nanoparticles under adiabatic conditions [...] Read more.
Nanothermites as high-energy-density and high-reaction-rate materials have important applications in civil and military fields. Nevertheless, it is difficult to detect all intermediates and products using conventional experimental methods. In this work, the reaction process of core-shell SiO2@Al nanoparticles under adiabatic conditions was investigated through molecular dynamics simulations using a reactive force field (ReaxFF). In the microcanonical ensemble, the redox reaction of SiO2@Al nanothermite becomes explosive due to the huge energy release during Al-O bond formation. The gaseous products are mainly the intermediate products Al5O and Al4O as well as the final products Al2O, AlO, Si and Al. Analyses of the steric charge distributions and evolution show that the Coulomb effect causes the number of intermediates Al5O (0.32|e|) to increase to the maximum, then slowly decrease and remain stable. But the tetrahedral Al4O cluster is almost charge-neutral, at −0.05|e|, and the number remained almost constant. This work is expected to provide deeper insights into the complex reaction mechanism of nanothermite. Full article
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17 pages, 11556 KiB  
Article
Simulation Tests on Granite Pillar Rockburst
by Xinmu Xu, Peng Zeng, Kui Zhao, Daxing Lei, Liangfeng Xiong, Cong Gong and Yifan Chen
Appl. Sci. 2025, 15(4), 2087; https://doi.org/10.3390/app15042087 - 17 Feb 2025
Viewed by 411
Abstract
Parallelepipeds specimens were made to further investigate the rockburst occurrence mechanism of ore pillars in underground mining units. The investigation was carried out with uniaxial compression systems and real-time testing systems, such as stress, video, and acoustic emission, combined with digital image correlation [...] Read more.
Parallelepipeds specimens were made to further investigate the rockburst occurrence mechanism of ore pillars in underground mining units. The investigation was carried out with uniaxial compression systems and real-time testing systems, such as stress, video, and acoustic emission, combined with digital image correlation (DIC) and SEM electron microscope scanning technology, to systematically analyze the evolution of rockburst of ore pillars, strain field characteristics, acoustic emission characteristics, mesoscopic characteristics of the rockburst fracture, morphology of the bursting crater, and debris characteristics. The findings demonstrate that the pillar’s rockburst process went through four stages, including the calm period, the particle ejection period, the block spalling period, and the full collapse period. According to DIC digital image correlation technology, the development of cracks in the rock is not obvious during the calm period, but during the small particle ejection and block spalling periods, the microcracks started to form and expand more quickly and eventually reached the critical surface of the rock, resulting in the formation of a complete macro-rockburst rupture zone. During stage I of the test, the rate of acoustic emission events and energy was relatively low; from stages II to IV, the rate gradually increased; and in stage V, the rate of acoustic emission events and energy reached its maximum value at the precise moment the rock exploded, releasing all of its stored energy. The specimen pit section primarily exhibits shear damage and the fracture exhibits shear fracture morphology, while the ejecta body primarily exhibits tensile damage and the fracture exhibits tensile fracture morphology. The location of the explosion pit is distributed on the left and right sides of the middle pillar of the specimen, and the shape is a deep “V”. The majority of the rockburst debris is greater than 5 mm, and it mostly takes the shape of thin plates, which is comparable to the field rockburst debris’s shape features. Full article
(This article belongs to the Special Issue Recent Advances in Rock Mass Engineering)
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20 pages, 9964 KiB  
Article
Damage Behaviour and Fractal Characteristics of Underground Openings Under True Triaxial Loading
by Yunfeng Wu, Peng Li, Xiaolou Chi, Baokun Zhou, Erhui Zhang, Youdong Zhu and Changhong Li
Fractal Fract. 2025, 9(2), 121; https://doi.org/10.3390/fractalfract9020121 - 15 Feb 2025
Viewed by 663
Abstract
In the context of advancements in deep resource development and underground space utilisation, deep underground engineering faces the challenge of investigating the mechanical behaviour of rocks under high-stress conditions. The present study is based on a gold mine, and the bulk ore taken [...] Read more.
In the context of advancements in deep resource development and underground space utilisation, deep underground engineering faces the challenge of investigating the mechanical behaviour of rocks under high-stress conditions. The present study is based on a gold mine, and the bulk ore taken from the mine perimeter rock was processed into two sets of specimens containing semicircular arched roadways with half and full penetrations. The tests were carried out using a true triaxial rock test system. The results indicate that the true triaxial stress–strain curve included stages such as compression density, linear elasticity, yielding, and destructive destabilisation following the peak; the yield point was more pronounced than that in uniaxial and conventional triaxial tests; and the peak stress and strain of the semi-excavation were higher than those of the full excavation. Furthermore, full excavation led to greater deformation along the σ3 direction. The acoustic emission energy showed a sudden increase during the unloading stage, then fluctuated and increased with increasing stress until significant destabilisation occurred. Additionally, increased burial stress in the half-excavation decreased the proportion of tension cracks and shear cracks. Conversely, in semi-excavation, the proportion of tensile cracks decreased, while that of shear cracks increased. However, the opposite was observed in full excavation. In terms of fractal dimension, semi-excavation fragmentation due to stress concentration followed a power distribution, while the mass fragmentation in full excavation followed a random distribution due to uniform stress release. Furthermore, the specimen strength was positively correlated with fragmentation degree, and primary defects also influenced this degree. This study provides a crucial foundation for predicting and preventing rock explosions in deep underground engineering. Full article
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14 pages, 7114 KiB  
Article
Preparation of Ultrafine Spherical Al-Mg Alloy and Its Energy Release Characteristics in Explosives
by Junhui Liu, Jie Yao, Zichao Wang, Wei Liu, Jianxin Nie and Shi Yan
Metals 2025, 15(2), 202; https://doi.org/10.3390/met15020202 - 14 Feb 2025
Viewed by 986
Abstract
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 [...] Read more.
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
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