Study on vapour dispersion and explosion from compressed hydrogen spill: Risk assessment on a hydrogen plant

Hydrogen produced from renewable resources is one of the cleanest fuels and could be used to store intermittent solar, wind and other energies. The main concern about using hydrogen is its hazards, such as high storage pressure, wide-range flammability, low mass density, and high diffusion. This study investigated the hazards of compressed hydrogen storage by developing a CFD model to understand the gas dispersion behaviour. The model was validated using the past experimental data and showed a good agreement, which could demonstrate the diffusion characteristics and gas stratification of a buoyant gas. A case study of an accidental release of compressed hydrogen from a storage tank was investigated to evaluate the risk of a hydrogen plant. A mathematical model of the jet spill was used to account for the choking effect from a high-pressure release to ensure the input velocity in CFD simulation is suitable for modelling gas dispersion using verified spatial and temporal scales, then the simulation results were used as inputs of vapour cloud explosions (VCEs) to investigate the potential overpressure effect. It was found the CFD model could predict a more reasonable flammable gas amount in cloud than using the bulk hydrogen release rate. The safety distance based on the overpressure prediction was reduced by 35%. The method proposed in this study can provide more validity for the consequence analysis as part of risk assessment.     

Impedance matching optimization of SiCf/Si3N4–SiOC composites for excellent microwave absorption properties

SiC fiber reinforced ceramic matrix composites (SiC_f-CMCs) are considered to be one of the most promising materials in the electromagnetic (EM) stealth of aero-engines, which is expected to achieve strong absorption and broad-band performance. Multiscale structural design was applied to SiC_f/Si₃N₄–SiOC composites by construction of micro/nanoscale heterogeneous interfaces and macro double-layer impedance matching structure. SiC_f/Si₃N₄–SiOC composites were fabricated by using SiC fibers with different conductivities and SiOC–Si₃N₄ matrices with gradient impedance structures to improve impedance matching effectively. Owing to its unique structure, SiC_f/Si₃N₄–SiOC composites (A3-composites) achieved excellent EM wave absorption performance with a minimum reflection coefficient (RC_min) of ?25.1 dB at 2.45 mm and an effective absorption bandwidth (EAB) of 4.0 GHz at 2.85 mm in X-band. Moreover, double-layer SiC_f/Si₃N₄–SiOC with an improved impedance matching structure obtained an RC_min of ?56.9 dB and an EAB of 4.2 GHz at 3.00 mm, which means it can absorb more than 90% of the EM waves in the whole X-band. The RC is less than ?8 dB at 2.6–2.8 mm from RT to 600 °C in the whole X-band, displaying excellent high-temperature absorption performance. The results provide a new design opinion for broad-band EM absorbing SiC_f-CMCs at high temperatures.     

Spin-state regulating of cobalt assisted by iron doping and coordination for enhanced oxygen evolution reaction

Customizing catalysts from the electronic structure, such as spin state, is an effective but challenging strategy for oxygen evolution reaction (OER). Herein, an ultrafine Co–Fe material highly dispersed on nitrogen carbide matrix is fabricated by coordination polymer and self-templating method to scrutinize the impact of spin state of Co on OER through Fe doping. The optimized catalyst shows boosted OER performance, which only requires overpotential of 333 mV at 10 mA cm^?2, outperforming other control samples and commercial RuO₂. The elevated local spin states of Co by Fe doping lead to charge transfer acceleration and fast generation of oxygenated intermediates, which is proved to account for the OER elevation. In addition, the long-term stability of Co–Fe material is guaranteed by the strong coordination of Co/Fe to the melamine-formaldehyde resin, which is used to adsorb metal ions, contributing to the high dispersion of active sites during the OER process.     

Synthesis and characterizations of highly responsive H2S sensor using p-type Co3O4 nanoparticles/nanorods mixed nanostructures

High-quality p-type semiconducting Co₃O₄ with mixed morphology of nanoparticles/nanorods are synthesized using a hydrothermal route for high response and selective hydrogen sulphide (H₂S) sensor application. XRD and Raman studies revealed the crystal structure and molecular bonding for obtained Co₃O_4, respectively. The nanoparticles/nanorods-like structures were confirmed for Co₃O₄ using FESEM and TEM analysis. The EDS and XPS spectra analysis were carried out for elemental composition and chemical atomic states of Co₃O₄. The Co₃O₄ sensor is investigated for gas sensing properties in dynamic conditions. The sensor exhibited the highest selectivity towards H₂S among various hydrogen-contained gases at 225 °C. The sensor revealed a high response of 357% and 44% for 100 and 10 ppm H₂S gas concentrations, respectively. The Co₃O₄ sensor exhibited a systematic dynamic resistance response for 100–10 ppm range H₂S gas. The excellent dynamic resistance repeatability of the sensor was shown towards 25 ppm H₂S gas. The response of Co₃O₄ sensor was investigated at different operating temperatures and H₂S concentrations. The sensor stability and H₂S sensing mechanism for the Co₃O₄ sensor have been reported. Highly uniform and mixed nanostructures of Co₃O₄ can be the potential sensor material for real-time high-performance H₂S sensor application.     

Chemically complex intermetallic alloys: A new frontier for innovative structural materials

Intermetallic materials are bestowed by diverse ordered superlattice structures together with many unusual properties. In particular, the advent of chemically complex intermetallic alloys (CCIMAs) has received considerable attention in recent years and offers a new paradigm to develop novel metallic materials for advanced structural applications. These newly emerged CCIMAs exhibit synergistic modulations of structural and chemical features, such as self-assembled long-range close-packed ordering, complex sublattice occupancy, and interfacial disordered nanoscale layer, potentially allowing for superb physical and mechanical properties that are unmatched in conventional metallic materials. In this paper, we critically review the historical developments and recent advances in ordered intermetallic materials from the simple binary to chemically complex alloy systems. We are focused on the unique multicomponent superlattice microstructures, nanoscale grain-boundary segregation, and disordering, as well as the various extraordinary mechanical and functional properties of these newly developed CCIMAs. Finally, perspectives on the future research orientation, challenges, and opportunities of this new frontier are provided.     

A high temperature and pressure framework for supercritical water electrolysis

Water electrolysis technologies aim to provide a significant increase in green hydrogen production efficiency. In this work, a framework was developed to explore the use of supercritical water for alkaline electrolysis. This framework was used to perform Arrhenius analysis as a function of potential, and to explore activation energies for sub- and supercritical water electrolysis. An analysis of the conductivity of solution unveiled a discontinuity in the trends between sub- and supercritical potassium hydroxide solution conductivity. Unlike prior work on supercritical water electrolysis, this work investigates trends in electrochemical parameters, the sources of these trends, and how they change between the sub- and supercritical regimes.     

Preparation of high-purity SiC ceramics with good plasma corrosion resistance by hot-pressing sintering

High-purity SiC ceramic devices are applied in semiconductor industry owing to their outstanding properties. Nevertheless, it is difficult to densify SiC ceramics without any sintering additive even by HP sintering. In this work, high-purity and dense SiC ceramics were fabricated by HP sintering with very low amounts of sintering aids. Residual B content was only 556 ppm and relative density was more than 99.5%. Furthermore, thermal conductivity of as-prepared SiC ceramics was improved from 155 W m^?1 K^?1 to 167 W m^?1 K^?1 by increasing holding time and their plasma corrosion resistance was promoted in the meantime. The as-prepared high-purity SiC ceramics have broad application prospects in the field of semiconductor industry.     

Effect of scandium and zirconium alloying on microstructure and gaseous hydrogen storage properties of YFe3

RM₃ compounds (R = rare earth metals, M = transition metals) have rarely been studied for gaseous hydrogen storage applications because of unfavorable thermodynamics. In this work, the hydrogen storage properties of a single-phase YFe₃ alloy were improved by non-stoichiometric composition and alloying with Sc and Zr. Only the Y_1.1–ySc_yFe₃ (y = 0.22, 0.33) alloys consist of a single rhombohedral phase. The Sc substitution for Y leads to the reduction in the unit cell volume of the YFe₃ phase, and thus significantly increases the dehydriding equilibrium pressure and decreases the dehydrogenation temperature. The alloy Y_0.77Sc_0.33Fe₃ delivers a decomposition enthalpy change of 33.54 kJ/mol and a lowest dehydrogenation temperature of 135 °C, in comparison with 38.99 kJ/mol and 165 °C for the alloy Y_1.1Fe₃. The Zr substitution causes a similar thermodynamic destabilization effect, but the composition and microstructure of Y–Zr–Fe alloys need to be further optimized.     

Sn-containing Si3N4-based composites for adaptive excellent friction and wear in a wide temperature range

Ceramic design based on reducing friction and wear-related failures in moving mechanical systems has gained tremendous attention due to increased demands for durability, reliability and energy conservation. However, only few materials can meet these requirements at high temperatures. Here, we designed and prepared a Sn-containing Si₃N₄-based composite, which displayed excellent tribological properties at high temperatures. The results showed that the friction coefficient and wear rate of the composites were reduced to 0.27 and 4.88 × 10^?6 mm³ N^?1 m^?1 in air at 800 °C. The wear mechanism of the sliding pairs at different temperatures was revealed via detailed analyses of the worn surfaces. In addition, the tribo-driven graphitization was detected on the wear surfaces and in the wear debris, and the carbon phase was identified by SEM, TEM, and Raman spectrum.