The valorization of coal gangue is of great significance for achieving clean and efficient utilization of coal. To lower the sintering temperature of high-alumina coal gangue (HACG), red mud (RM) was used as a fluxing agent to prepare high-strength ceramsite. The sintering mechanism was revealed and the sintering parameters including the sample proportion, sample particle size, sintering temperature, and sintering residence time were optimized. The optimal parameters were: HACG-to-RM mass ratio: 50:50, sample particle size: 125 mu m, sintering temperature: 1150 degrees C, and sintering residence time: 20 min, yielding the ceramsite with compressive strength of 228 MPa, 1-hour water absorption of 3.19%, and an apparent density of 2.68 g/cm3. Sintering mechanism analysis revealed that the Na from the RM reacted with the Si and Al from HACG to generate low-melting-point mineral (sodium feldspar), which is attributed to formation of liquid phase during sintering. However, excessive RM leads to inordinate liquid phase and reduced refractory crystal framework (mullite), which is detrimental to the performance of ceramsites. Furthermore, a substantial portion of the carbon in coal gangue serves as a heat source for the sintering process through combustion under an oxidative atmosphere, while a small fraction of carbon reacts with iron oxide at high temperatures to generate gas for pore. A suitable particle size distribution facilitates the mass transfer of the liquid phase within the pores and enhances the degree of densification of ceramsite. Finally, the heavy metal leaching concentrations of optimal performance ceramsite complied with the standard limits. These results can provide theoretical guidance for the preparation of high-strength ceramsite based on coal gangue and red mud.
The exploration of dual-medium electrocatalysts with robust adaptability and stability in both fresh and seawater is of paramount importance for advancing hydrogen energy. Herein, Fe-3(PO4)(2)@Ni7S6-Co3S4/NF was fabricated by combining hydrothermal synthesis and electrodeposition. Benefiting from the synergistic electronic modulation and interfacial coupling effects, the as-prepared catalyst exhibits exceptional oxygen evolution reaction (OER) performance: in fresh water, it requires overpotentials as low as 211 and 250 mV to reach 10 and 100 mA cm(-2), correspondingly, while maintaining stability for 200h; in seawater, it achieves overpotentials of 230 and 273 mV at identical current densities accompanied by negligible activity decay over 200 h of continuous operation. This activity originates from sulfidation modulating the electronic structures of Ni/Co, enhancing conductivity. Meanwhile, heterogeneous interfaces between Fe-3(PO4)(2) and the sulfide matrix facilitate charge transfer and improve stability and desirable operational stability in alkaline seawater. This work offers insights for developing non-precious metal catalysts with high adaptability toward efficient and durable water oxidation in diverse aqueous electrolytes.
Trimethylolethane trinitrate (TMETN) is a promising insensitive nitrate ester plasticizer for replacing highly sensitive nitroglycerin (NG), but its high-temperature ignition behavior, pyrolysis chemistry, and detailed condensed-phase decomposition mechanism remain insufficiently understood. In this work, the ignition, pyrolysis, and thermal decomposition mechanism of TMETN were systematically investigated by combining highpressure shock tube experiments, ReaxFF reactive molecular dynamics (ReaxFF MD) simulations, and high-level quantum chemical calculations. Ignition delay times (IDTs) were measured at 5, 10, and 20 bar in Ar and Ar/O2 atmospheres, and 14 major gaseous pyrolysis products were identified under high-temperature and high-pressure conditions. ReaxFF MD simulations were performed to analyze the temporal evolution of key intermediates and final products, while quantum chemical calculations were carried out to clarify the thermodynamic and kinetic preference between NO2 and HONO elimination pathways. The results show that: (1) TMETN ignition exhibits a strong pressure dependence. In Ar, the measured IDTs decrease from 0.78-0.876 ms at 5 bar to 0.52-0.609 ms at 10 bar and 0.23-0.301 ms at 20 bar; in Ar/O2, the IDTs decrease from 0.734-0.832 ms at 5 bar to 0.493-0.580 ms at 10 bar and 0.208-0.273 ms at 20 bar. (2) As the temperature increases, the concentrations of hydrocarbon products increase, whereas those of oxygen-containing intermediates such as methanol and formaldehyde decrease, indicating that higher temperatures promote the deep cracking and secondary decomposition of TMETN. (3) ReaxFF MD simulations capture the temperature-dependent evolution trends of representative products and reveal that O-NO2 bond cleavage accompanied by NO2 release dominates the initial decomposition stage of TMETN. (4) Quantum chemical calculations further demonstrate that NO2 elimination is generally more favorable than the competing HONO elimination pathway in terms of reaction barriers, reaction enthalpies, and temperature-dependent rate constants. These results indicate that the thermal decomposition of TMETN is mainly initiated by nitrate ester bond cleavage, followed by NOx/HONO-related secondary reactions and the formation of stable small-molecule products such as N2, CO2, and H2O. This work provides quantitative ignition data and a cross-scale mechanistic interpretation of TMETN thermal decomposition, offering a theoretical basis for kinetic model development and the safe application of insensitive energetic plasticizers.
The rational design and exploration of cost-effective nickel iron layered double hydroxides (NiFe-LDH) for highperformance oxygen evolution reaction (OER) catalysts still remain a grand challenge. Herein, the sea urchin-like Bi-doped NiFe-LDH structure was synthesized via a one-step corrosion of nickel foam. The resulting Bi-doped NiFe-LDH catalyst demands an overpotential of merely 228 mV to deliver a current density of 10 mA cm-2 for OER in 1.0 M KOH electrolyte. When employed as the anode in an overall water-splitting device with Pt/C as cathode, the assembled NiFeBi0.1-LDH || Pt/C cell achieved 10 mA cm-2 current density at a cell voltage of 1.53 V. The enhanced electrocatalytic performance is mainly attributed to the synergistic effect between morphological reconstruction and electronic state modulation induced by Bi doping.
To characterize pressure evolution, rigid-body motion, and structural response during projectile water entry, vertical-entry tests were conducted on a flat-nosed cylindrical projectile at 16–35 m/s. A light-gas gun, nose-center pressure sensor, non-contact full-field 3D strain measurement system (VIC-3D), and multichannel strain measurements provided synchronized pressure, kinematic, and structural data.Although the formation and evolution of the air cushion were not directly observed in this study, a mechanism by which air cushioning influences the pressure on the projectile during water entry was inferred from extensive previous research on air-cushioning effects and the nose-center pressure measurements obtained in the present study. Air-cushion compression, collapse, and liquid contact governed early pressure development. Peak nose-center pressure increased non-linearly with velocity, whereas air-cushion-induced pressure reduction weakened. Although the local center pressure does not represent end-face load distribution, its duration agreed with those of end-face loading and the acceleration pulse.A three-dimensional point-cloud rigid-body fitting method was proposed to obtain displacement, velocity, acceleration, and can also be used to precisely capture the various attitude angles caused by the experiment error in the vertical entry experiment, including the water-entry angle, attack angle (AOA), and axis deviation angle, etc. Fitting residuals, point matching, and published-data comparisons confirmed stable motion identification. The processed velocity and acceleration histories were physically consistent; both the initial negative and first positive acceleration peaks increased linearly with entry velocity.For case (l), low-order circumferential modal-tendency indices and joint axial–circumferential coupling criteria indicated that structural response was concentrated in 0.2–72.2 kHz. The low-frequency M0 response showed Poisson-type synchronous coupling, whereas the enhanced M1 bending response during initial impact showed bending shell-vibration-type coupling. The response then evolved into mixed ringing decay; near-tail response retained low-frequency dominance but had much lower energy. This work provides a framework for impact-load characterization, motion-attitude identification, and structural-dynamics analysis during projectile water entry.
