Inert Gas Research Articles

Synthesis of Hybrid Tin-Based Perovskite Microcrystals for LED Applications.

Considerable focus on tin-based perovskites lies on substitution to leadhalide perovskites for the fabrication of eco-friendly optoelectronic devices.The major concern related to tin-based perovskite devices are mainly thestability and the efficiency. However, thinking on the final commercializationscope, other considerations such as precursor stability and cost are majorfactors to carry about. In this regard, this work presents a robust and facilesynthesis of 2D A2SnX4 (A = 4-fluorophenethylammonium(4-FPEA); X = I, Br, I/Br) and 3D FASnI3 perovskite microcrystals followinga developed synthesis strategy with low-cost starting materials. In thisdeveloped methodology, acetic acid is used as a solvent, which helps to protectfrom water by making a hydrophobic network over the perovskite surface, andhence provides sufficient ambient and long-term inert atmosphere stability ofthe microcrystals. Further, the microcrystals are recrystallized in thin filmsfor LED application, allowing the fabrication of orange, near-infrared and purered emitting LEDs. The two-step recrystallized devices show better performanceand stability in comparison to the reference devices made by using commercialprecursors. Importantly, the developed synthesis methodology is defined as ageneric method for the preparation of varieties of hybrid tin-based perovskitesmicrocrystals and application in optoelectronic devices.

Synthesis of Hybrid Tin-Based Perovskite Microcrystals for LED Applications.

Considerable focus on tin-based perovskites lies on substitution to leadhalide perovskites for the fabrication of eco-friendly optoelectronic devices.The major concern related to tin-based perovskite devices are mainly thestability and the efficiency. However, thinking on the final commercializationscope, other considerations such as precursor stability and cost are majorfactors to carry about. In this regard, this work presents a robust and facilesynthesis of 2D A2SnX4 (A = 4-fluorophenethylammonium(4-FPEA); X = I, Br, I/Br) and 3D FASnI3 perovskite microcrystals followinga developed synthesis strategy with low-cost starting materials. In thisdeveloped methodology, acetic acid is used as a solvent, which helps to protectfrom water by making a hydrophobic network over the perovskite surface, andhence provides sufficient ambient and long-term inert atmosphere stability ofthe microcrystals. Further, the microcrystals are recrystallized in thin filmsfor LED application, allowing the fabrication of orange, near-infrared and purered emitting LEDs. The two-step recrystallized devices show better performanceand stability in comparison to the reference devices made by using commercialprecursors. Importantly, the developed synthesis methodology is defined as ageneric method for the preparation of varieties of hybrid tin-based perovskitesmicrocrystals and application in optoelectronic devices.

Microstructure and properties of metal inert gas welded joints in a novel Al–Mg–Zn–Er–Zr alloy

Metal inert gas (MIG) welding of a novel Al-5.82Mg-0.61Zn-0.14Er-0.11Zr alloy was performed using ER5E61 and ER5B71 filler wires. The effect of the two filler wires on microstructures and mechanical properties of MIG welded joints was investigated. The study shows that fully penetrated joints are obtained by MIG welding process filled with ER5E61 and ER5B71 wires. Compared with ER5B71, the weld metal (WM) with ER5E61 exhibits a coarse structure and high solid solution of Mg and Mn elements. After the tensile test, the WM with ER5E61 and ER5B71 wires is composed of elongated coarse grains with a higher proportion of low angle grain boundaries (LAGBs). In addition, the lattice rotation occurring within the grains, indicating that single grain has an unevenly plastic deformation after the tensile test. The average microhardness of the WM is 83.4 HV and 82.9 HV for ER5E61 and ER5B71 wire, which is the lowest microhardness in the MIG welded joint. The average ultimate tensile strength (UTS) and elongation index (EI) of the MIG joints are 327.7 MPa and 8.5% for ER5E61 wire, and 314.3 MPa and 8.2% for ER5B71 wire, suggesting the MIG welded joint with ER5E61 wire achieves a good combination of strength and ductility. Quantitative assessments of the effects of different strengthening mechanisms on the strength reveal that dislocation strengthening and solid solute strengthening are the main factors to obtain a higher strength of welded joints with ER5E61.

Dependence of the Fluidizing Condition on Operating Parameters for Sorption-Enhanced Methanol Synthesis Catalyst and Adsorbent

The fluidization of two different solids was investigated by varying the temperature and pressure conditions and the fluidizing gas. The solids are a novel catalyst and a water sorbent that could be used to perform sorption-enhanced methanol synthesis; the operating conditions were selected accordingly to this process. The aim of this investigation was to find an expression for predicting the minimum fluidization conditions of a methanol synthesis catalyst and an adsorbent in the presence of their process stream and operating conditions. The findings of this study highlighted how umf (STP) decreases with a rise in temperature and increases with a rise in pressure, according to other works in the literature with different solids. Furthermore, the type of gas was found to influence the minimum fluidization velocity significantly. The experimental results agreed well with a theoretical expression of the minimum fluidization velocity adjusted for temperature, pressure, and viscosity. The choice of the expression for viscosity calculation in the case of gas mixtures was found to be of key importance. These results will be useful for researchers aiming to calculate the minimum fluidization velocity of a catalyst or other solids under reaction conditions using results obtained at ambient conditions with air or inert gas.

Molten salt biomass torrefaction – A sensitivity analysis of process conditions

Biomass is an abundant renewable resource that can be upgraded via torrefaction. Molten salts catalyze the torrefaction reaction, creating enhanced products for fuel and soil amendment purposes at lower temperatures than inert gas torrefaction. The objective of this study is to elucidate the main effects of molten salt torrefaction process conditions on ponderosa pine (Pinus ponderosa) and cave in rock switchgrass (Panicum virgatum) in a binary salt blend of lithium nitrate and potassium nitrate using a Plackett-Burman screening analysis. The investigated process conditions include sweep gas, temperature, salt to biomass ratio (S-B ratio), residence time, and lithium content. The metrics used to evaluate torrefaction severity include mass yields, chemical composition (lignin, cellulose, hemicellulose, extractives), higher heating value (HHV), carbon and nitrogen content, pH, and water sorption. The results show that switchgrass is more severely torrefied through molten salt torrefaction than pine at the same process conditions. For example, switchgrass mass yields are on average 23.3 % lower than pine mass yields across the test conditions. For both feedstocks, the most impactful process conditions are temperature, time, and lithium content in that order with some exceptions. For instance, the effect of temperature, time and lithium content on HHV are, respectively, 3.4×, 2.3×, and 1.7× larger than the next largest process condition for pine, whereas for switchgrass, these values are 3.6×, 2.7×, and 1×. Particle size, sweep gas, and S-B ratio have minor effects depending on the metric, but are overall not significant compared to temperature. The data suggests that an inert gaseous environment need not be maintained to facilitate molten salt torrefaction. Additionally, molten salt torrefaction can produce torrefied biomass with slightly different characteristics than inert gas torrefaction.

Comparison between Mechanical Properties and Joint Performance of AA 2024-T351 Aluminum Alloy Welded by Friction Stir Welding, Metal Inert Gas and Tungsten Inert Gas Processes.

The aim of this work is to study joining Al 2024-T3 alloy plates with different welding procedures. Aluminum alloy AA 2024-T351 is especially used in the aerospace industry. Aluminum plates are welded by the TIG and MIG fusion welding process, as well as by the solid-state welding process, friction stir welding (FSW), which has recently become very important in aluminum and alloy welding. For welding AA2024-T35 with MIG and TIG fusion processes, the filler material ER 4043-AlSi5 was chosen because of reduced cracking. Different methods were used to evaluate the quality of the produced joints, including macro- and microstructure evaluation, in addition to hardness and tensile tests. The ultimate tensile strength (UTS) of the FSW sample was found to be 80% higher than that of MIG and TIG samples. The average hardness value of the weld zone of metal for the MIG- and TIG-produced AA2024-T3511 butt joints showed a significant decrease compared to the hardness of the base metal AA2024-T351 by 50%, while for FSW joints, in the nugget zone, the hardness is about 10% lower relative to the base metal AA2024-T3511.

Sprint interval training in the postpartum period maintains the enhanced cardiac output of pregnancy: A case study.

During pregnancy an increased cardiac output ( ) and blood volume (BV) occur to support fetal growth. Increased and BV also occur during chronic endurance exercise training and benefit performance. We investigated if sprint interval training (SIT) undertaken early postpartum maintains the elevated and BV of pregnancy and benefits performance. The participant, a competitive field hockey player and former cyclist, visited our laboratory at 2weeks of gestation (baseline) and postpartum pre-, mid- and post-intervention (PPpre, PPmid and PPpost). Delivery was uncomplicated and she felt ready to start the SIT programme 5weeks postpartum. Inert gas rebreathing was used to measure peak exercise ( peak); was measured with a metabolic cart; and postpartum haematological values were measured with carbon monoxide rebreathing. The 18 SIT sessions progressed from four to eight sprints at 130% of peak power output. peak increased from baseline at all postpartum time points (baseline 16.2 vs. 17.5, 16.8 and 17.2L/min at PPpre, PPmid and PPpost, respectively). Relative remained below baseline values at all postpartum measurements (baseline 44.9 vs. 41.0, 42.3 and 42.5mL/kg/min at PPpre, PPmid and PPpost, respectively) whereas absolute rapidly reached baseline values postpartum (baseline 3.19 vs. 3.12, 3.23 and 3.18L/min at PPpre, PPmid and PPpost, respectively). Postpartum BV (5257, 4271 and 5214mL at PPpre, PPmid and PPpost, respectively) and Hbmass (654, 525 and 641g at PPpre, PPmid and PPpost, respectively) were similar between PPpre and PPpost but decreased alongside peak at PPmid. Peak power was returned to pre-pregnancy values by intervention end (302 vs. 303W, baseline vs. PPpost). These findings show that SIT undertaken early postpartumdefends the elevated peak of pregnancy and rapidly returns absolute and peak power to baseline levels. HIGHLIGHTS: What is the central question of this study? Can the enhanced cardiac output of pregnancy be maintained with strenous exercise training undertaken early postpartum. What is the main finding and its importance? Baseline values of absolute oxygen consumption, peak power output and peak exercise cardiac outputcan be regained rapidly or surpassed following 6weeks of sprint interval training postpartum. Sprint interval training can be used by endurance trained females to safely resume training early postpartum, allowing a rapid and efficient return to baseline fitness levels.

Time‐Resolved Mechanistic Depiction of Photoinduced CO2 Reduction Catalysis on a Urea‐Modified Iron Porphyrin

AbstractThe development of functional artificial photosynthetic devices relies on the understanding of mechanistic aspects involved in specialized photocatalysts. Modified iron porphyrins have long been explored as efficient catalysts for the light‐induced reduction of carbon dioxide (CO2) towards solar fuels. In spite of the advancements in homogeneous catalysis, the development of the next generation of catalysts requires a complete understanding of the fundamental photoinduced processes taking place prior to and after activation of the substrate by the catalyst. In this work, we employ a state‐of‐the‐art nanosecond optical transient absorption spectroscopic setup with a double excitation capability to induce charge accumulation and trigger the reduction of CO2 to carbon monoxide (CO). Our biomimetic system is composed of a urea‐modified iron(III) tetraphenylporphyrin (UrFeIII) catalyst, the prototypical [Ru(bpy)3]2+ (bpy=2,2’‐bipyridine) used as a photosensitizer, and sodium ascorbate as an electron donor. Under inert atmosphere, we show that two electrons can be successively accumulated on the catalyst as the fates of the photogenerated UrFeII and UrFeI reduced species are tracked. In the presence of CO2, the catalytic cycle is kick‐started providing further evidence on CO2 activation by the UrFe catalyst in its formal FeI oxidation state.

Vacuum sintering of the self-developed Chang’E-5 lunar regolith simulant

The utilization of in-situ lunar resources through the additive manufacturing of lunar regolith (LR) has attracted considerable interest. Sintering of LR is considered a promising method for lunar construction due to its high utilization rate and excellent service stability. However, numerous studies have been carried out on Apollo series LRs with similar chemical compositions in air or inert gas atmospheres. The effects of the lunar ultra-high vacuum conditions and the complex chemical composition of LRs on the sintering process require extensive investigation. In this study, a self-developed Chang’E-5 lunar regolith simulant (LRS) with a high-Fe content was used as the only raw material to investigate its potential applicability for future lunar construction in vacuum environment. The effects of sintering temperature on the microstructure, linear shrinkage, bulk density, weight loss ratio, and mechanical and thermal expansion properties were investigated. The results show that the linear shrinkage and weight loss ratio increase with increasing sintering temperature. However, the bulk density and unconfined compressive strength (USC) initially increase and then decrease, with the sample sintered at 1075℃ giving the highest bulk density of 2.10 ± 0.03 g/cm3 and a USC of 31.19 ± 1.96 MPa. This is attributed to the transformation of the sample sintered at 1090℃ into a semi-porous material with many cracks. Furthermore, the mechanism of pore and crack formation was revealed. The coefficient of thermal expansion (CET) of the sintered samples is approximately 7×10–6°C−1, which maintains a good service stability after cyclic temperature stress from room temperature up to 200°C. Both the USC and CET of the sample sintered at 1075℃ are superior to those of common terrestrial concrete materials. This indicates that the vacuum sintering process appears feasible for the production of building materials with sufficient mechanical strength and thermal durability for lunar base construction.

NiO thin films fabricated using spray-pyrolysis technique: structural and optical characterization and ultrafast charge dynamics studies

Nickel (II) oxide, NiO, is a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displays antiferromagnetic order at room temperature. NiO has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the fabrication of polycrystalline NiO using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. The composition and structure of the NiO thin films were then studied using x-ray diffraction, and atomic force and scanning electron microscopies (SEM). The phononic and magnonic properties of the NiO thin films were also studied via Raman spectroscopy, and the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that the NiO samples display the same phonon and magnon excitations expected for single crystal NiO at room temperature, and that electron dynamics in our system is like those of previously reported NiO mono- and polycrystalline systems synthesized using different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthesize strongly correlated materials for a large set of applications.

Preliminary strategy and product analysis of microwave pyrolysis of waste printed circuit board

AbstractIn this study, microwave pyrolysis of waste printed circuit boards (WPCBs) was carried out in an inert atmosphere, and the effects of pyrolysis temperature and nitrogen flow rate on the yield and composition of pyrolysis products were investigated. With the increase of pyrolysis temperature, the yield of liquid product increases gradually, and the yield of solid product decreases gradually. At 600°C, the yield of each phase tends to be stable. When the temperature continues to rise, the content of H2 and CO decreases, and the content of C6 ~ C9 in the liquid product decreases. Microwave heating promotes the pyrolysis of brominated epoxy resin, which helps to improve the recovery rate of valuable substances and reduce the environmental impact of waste treatment. This study demonstrates that the microwave pyrolysis of WPCBs in nitrogen atmosphere has great potential in the green recovery process.

Microwave-Assisted Pyrolysis of Carbon Fiber-Reinforced Polymers and Optimization Using the Box-Behnken Response Surface Methodology Tool.

This article introduces an eco-friendly method for the reclamation of carbon fiber-reinforced polymers (CFRP). The research project involved numerous experiments using microwave-assisted pyrolysis (MAP) to explore a range of factors, such as the inert gas flow, the power level, the On/Off frequency of rotation, and the reaction duration. To design the experiments, the three-level Box-Behnken optimization tool was employed. To determine the individual and combined effects of the input parameters on the thermal decomposition of the resin, the data were analyzed using least-squares variance adjustment. The results demonstrate that the models developed in this study were successful in predicting the direct parameters of influence in the microwave-assisted decomposition of CFRPs. An optimal set of operating conditions was found to be the maximum nitrogen flow (2.9 L/min) and the maximum operating experimental power (914 W). In addition, it was observed that the reactor vessel's On/Off rotation frequency and that increasing the reaction time beyond 6 min had no significant influence on the resin elimination percentage when compared to the two other parameters, i.e., power and carrier gas flow rate. Consequently, the above-mentioned conditions resulted in a maximum resin elimination percentage of 79.6%. Following successful MAP, various post-pyrolysis treatments were employed. These included mechanical abrasion using quartz sand, chemical dissolution, thermal oxidative treatment using a microwave (MW) applicator and thermal oxidative treatment in a conventional furnace. Among these post-treatment techniques, thermal oxidation and chemical dissolution were found to be the most efficient methods, eliminating 100% of the carbon black content on the surface of the recovered carbon fibers. Finally, SEM evaluations and XPS analysis were conducted to compare the surface morphology and elementary constitution of the recovered carbon fibers with virgin carbon fibers.

Narcotic Nitrogen Effects Persist after a Simulated Deep Dive

Background and Objectives: Scuba divers often experience persistent inert gas narcosis (IGN) even after surfacing. This study aimed to test the hypothesis that breathing oxygen (O2) before surfacing can reduce postdive IGN. Materials and Methods: A group of 58 experienced divers underwent a 5 min dive at a depth of 50 m in a multi-place hyperbaric chamber. They were decompressed using air (air group). Another group of 28 divers (O2 group) breathed 100% O2 during the end of decompression. Prior to and after the dive, all participants performed the Sharpened Romberg test (SRT) and a modified tweezers test. Results: In the air group, the number of positive SRT results increased postdive (47% vs. 67%), indicating a greater impairment in the vestibular system (Cohen’s d = 0.41). In the O2 group, the percentage of positive SRT results remained constant at 68% both before and after the dive. In terms of the modified tweezers test, the air group showed no significant change in the number of picked beads (40 ± 9 vs. 39 ± 7), while the O2 group demonstrated an increase (36 ± 7 vs. 44 ± 10) (Cohen’s d = 0.34). Conclusion: The results reveal that the SRT revealed a negative effect of nitrogen (N2) on the vestibular system in the air group. The increased number of beads picked in the O2 group can be attributed to the learning effect, which was hindered in the air group. Consistent with our hypothesis, breathing O2 during decompression appears to reduce postdive IGN.

Laser synthesis of oxide nanoparticles with controlled gas condensation

In this work, the oxide nanopowders of Al2O3, ZrO2, Y2O3, Gd2O3, CeO2, and SiO2 were synthesized by CW CO2 laser vaporization technique with controlled gas condensation in an inert atmosphere. Methods for controlling the size of the resulting nanoparticles by adjusting the gas composition and pressure during the vaporization process have been demonstrated. The potential for producing ultrasmall oxide nanoparticles with dimensions less than 5 nm has been shown. The size distribution of nanoparticles taken from different parts of the evaporation-condensation tract was studied using scanning (SEM) and transmission (TEM) electron microscopy methods. The effect of synthesis conditions (pressure and composition of the inert gas) on characteristics of the nanoparticles is discussed. Using a wide class of simple oxides as the example, it is shown that the powders synthesized by the laser method consist of three types of particles: target spherical particles with a diameter of 3–20 nm (more than 98%), larger spherical particles with a diameter of 50–200 nm, and shapeless large particles with sizes more than 200 nm. The possibility of separating large particles from the main particles using the original labyrinth system for gas pumping is shown. The obtained particles with controlled sizes can be effectively used in various applications, in particular, for the preparation of catalysts and adsorbents.

Structural modification of CNT-C xerogel through synthesis parameters

This study focuses on the synthesis of porous carbonaceous structures by drying resorcinol-formaldehyde (RF) gels under ambient conditions and then carbonizing them in an inert atmosphere. This avoids the expensive drying processes like supercritical drying or freeze drying. However, drying under ambient conditions does cause structural shrinkage and a reduction in porosity and specific surface area. Therefore, the goal of this study was to compensate for these structural degradations by adjusting other synthesis and process parameters, such as solvent exchange, drying condition, content of water, catalyst, and CNT in the gel. In the present study, different organic solvents such as t-butanol, ethanol, and acetone were used to replace the water in the hydrogels at a certain R/F molar ratio (1:2). The experimental results showed that t-butanol, with its low surface tension, resulted in a structure with a high specific surface area and pore volume. Regarding the catalyst dosage, by changing the R/C molar ratio between 71 and 849, the best structural properties were obtained using R/C∼200. Increasing the water content from 15 to 30 mL led to a decrease in specific surface area and pore volume. Drying the gel at an oven temperature of 85 °C resulted in the highest specific surface area, pore volume, and mean pore diameter. Increasing the dosage of carbon nanotubes (CNTs) in the range of 20–150 mg led to an increase in total pore volume and mean pore diameter. The results of this work can be a step forward towards the industrialization of these materials in various applications.

Revisiting biomass compositions determination using thermogravimetric analysis and independent parallel reaction model

The determination of biomass composition via thermogravimetric analysis (TGA) has been a subject of considerable interest for many years. The current work proposes a revised workflow for determining the amounts of cellulose, hemicellulose, and lignin in biomass by combining TGA under an inert atmosphere with analyses of extractives and ash. An independent parallel reaction (IPR) model used for the deconvolution of the derivative thermogravimetry data was improved by constraining model parameters, i.e., thermal decomposition kinetic parameters and char fractions of cellulose, hemicellulose, and lignin, with values compiled from the literature using statistical analysis. The workflow is developed and demonstrated using cellulose and starch mixtures and then applied to biomass with varying levels of ash, including pine, birch, and oak wood, switchgrass, and pine bark. Using extractive-free biomass in the new TGA-IPR workflow improved the composition results compared with untreated biomass. The compositions determined by this method agreed well with values reported in the literature (within approx. 8 wt%) for the tested samples. The results demonstrate improved biomass composition accuracy using an accessible and rapid TGA-based approach.

Venting Particle-induced Arc of Lithium-ion Batteries During the Thermal Runaway

Thermal runaway of lithium-ion batteries will release a large amount of particles with elevated temperature and high velocity, probably resulting in arc failures. In this study, we adopted an 117Ah fully-charged prismatic battery with Li(Ni0.8Co0.1Mn0.1)O2 cathode to collect the vented particles in an inert atmosphere after thermal runaway. All settled particles were classified into six groups to investigate the influence of electrode spacing, particle size and load resistance on the critical breakdown voltage as well as arc characteristics. As a result, a novel breakdown arc failure called venting particle-induced arc was firstly revealed and verified in the battery system. These settled particles significantly decrease the critical breakdown voltage for arc failure. The critical breakdown voltage exhibits a positively quadratic correlation with electrode spacing within 1–8mm, while it is negatively correlated with particle sizes. Furthermore, a critical voltage map for breakdown arc under various particle sizes and electrode spacing was proposed. The results provide guidance to electrical hazards prevention in the battery system.

On the role of hydrogen inhibition in gas-phase methane pyrolysis for carbon capture and hydrogen production in a tubular flow reactor

The thermal pyrolysis of methane allows an economically competitive hydrogen production without direct CO2 emissions. Although several mechanisms for the process have already been proposed, especially the inhibitory effect of hydrogen as well as the process operation at increased pressure have not yet been fully clarified. In this context, the present work investigates the influence of hydrogen and argon as inert gas on product composition, methane conversion, and hydrogen selectivity as a function of temperature (1000 °C to 1600 °C), residence time (1s to 7s), molar dilution ratio (1:1 to 4:1), and pressure (1bar to 4bar) in a high-temperature reactor. Within the scope of this work, total differences in CH4 conversion of up to 50% could be observed at equal process parameters between an argon and hydrogen dilution, underlining the potential impact of diluents on the overall process. Moreover, increasing the pressure from 1bar to 4bar reduces the formation of byproducts significantly for both H2 and Ar as diluent, however with different mechanistic characteristics. The most remarkable difference is the formation of propylene that exclusively takes place in argon-diluted reaction gas mixtures. This occurrence persists unabated, even under elevated pressures and temperatures reaching as high as 1600 °C. We ascribe this phenomenon to the interaction of methyl and ethyl radicals, establishing it as an impasse to further reactions leading to the formation of solid products. Herewith, the study provides novel insights from a reaction engineering perspective as well as from a process development perspective and clarifies the role of the dilution gases hydrogen and argon on the methane pyrolysis reaction.

Experimental studies of confined detonations of plasticized high explosives in inert and reactive atmospheres

When explosives detonate in a confined space, repeated boundary reflections result in complex shock interactions and the formation of a uniform quasi-static pressure (QSP). For fuel-rich explosives, mixing of partially oxidized detonation products with an oxygen-rich atmosphere results in a further energy release through rapid secondary combustion or ‘afterburn’. While empirical formulae and thermochemical modelling approaches have been developed to predict QSP, a lack of high-fidelity experimental data means questions remain around the deterministic quality of confined explosions, and the magnitude and mechanisms of afterburn reactions. This article presents experimental data for RDX- and PETN-based plastic explosives, demonstrating the high repeatability of the QSP generated in a sealed chamber using pressure transducers and high-speed infrared thermometry. Detonations in air, nitrogen and argon atmospheres are used to identify the contribution of afterburn to total QSP, to estimate the duration of afterburn reactions and to speculate on the flame temperature associated with this mechanism. Computational fluid dynamic modelling of the experiments was also able to accurately predict these effects. Understanding and quantifying explosions in complex environments are critical for the design of effective protective structures: the mechanisms described here provide a significant step towards the development of fast-running engineering models for internal blast events.

Ultrafine-grained refractory high-entropy alloy with oxygen control and high mechanical performance

Grain boundary engineering plays a significant role in the improvement of strength and plasticity of alloys. However, in refractory high-entropy alloys, the susceptibility of grain boundaries to oxygen presents a bottleneck in achieving high mechanical performance. Creating a large number of clean grain boundaries in refractory high-entropy alloys is a challenge. In this study, an ultrafine-grained (UFG) NbMoTaW alloy with high grain-boundary cohesion was prepared by powder metallurgy, taking advantages of rapid hot-pressing sintering and full-process inert atmosphere protection from powder synthesis to sintering. By oxygen control and an increase in the proportion of grain boundaries, the segregation of oxygen and formation of oxides at grain boundaries were strongly mitigated, thus the intrinsic high cohesion of the interfaces was preserved. Compared to the coarse-grained alloys prepared by arc-melting and those sintered by traditional powder metallurgy methods, the UFG NbMoTaW alloy demonstrated simultaneously increased strength and plasticity at ambient temperature. The highly cohesive grain boundaries not only reduce brittle fractures effectively but also promote intragranular deformation. Consequently, the UFG NbMoTaW alloy achieved a high yield strength even at elevated temperatures, with a remarkable performance of 1117 MPa at 1200 °C. This work provides a feasible solution for producing refractory high-entropy alloys with low impurity content, refined microstructure, and excellent mechanical performance.