Achieving both large piezoelectric constant and high Curie temperature in BiFeO3-PbTiO3-BaTiO3 solid solution

The high-temperature and high-performance piezoelectric ceramics are required urgently in the petrochemical, automotive, and aerospace industries. In this work, the (0.85-x)BiFeO₃-xPbTiO₃-0.15BaTiO₃ (BF-PT-BT, x = 0.21, 0.22, 0.23, 0.24 and 0.25) piezoelectric ceramics with both high Curie temperature and large piezoelectric constant d₃₃ were presented. X-ray diffraction analysis shows that BF-PT-BT ceramics exhibit dominant perovskite structure with the coexistence of tetragonal (T) and rhombohedral (R) phases. The c/a ratio, Curie temperature, piezoelectric constant, dielectric constant and loss of the BF-PT-BT ceramics for x = 0.23 are 1.06, 546 °C, 222 pC/N, 545 and 0.013, respectively. Room temperature piezoelectric constant of BF-PT-BT ceramics is much higher than those of PbTiO₃, PbNb₂O₆ and other ABO₃ perovskite compounds (BaZrO₃, Bi(Zn, Ti)O₃, PbZrO₃ and Pb(Mg, Nb)O₃) modified ternary BiFeO₃-PbTiO₃ ceramics with similar Curie temperatures. The piezoelectric constant is almost unchanged after BF-PT-BT ceramics was annealed at 450 °C for 30 min, which is due to the stable switched non-180° domain and transformed R phase by annealing treatment.     

Formation and properties of high entropy oxides in Co-Cr-Fe-Mg-Mn-Ni-O system: Novel (Cr,Fe,Mg,Mn,Ni)3O4 and (Co,Cr,Fe,Mg,Mn)3O4 high entropy spinels

Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)₃O₄, (Co,Cr,Fe,Mg,Mn)₃O₄ and (Cr,Fe,Mg,Mn,Ni)₃O₄ are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient.     

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.     

Impacts of the subsurface storage of natural gas and hydrogen mixtures

The subsurface storage of hydrogen (H₂) provides a potential solution for load-balancing of the intermittent electricity production from renewable energy sources. In such technical concept, surplus electricity is used to power electrolyzers that produce H₂, which is then stored in subsurface formations to be used at times when renewable electricity is not available. Blending H₂ with natural gas (NG) for injection into depleted gas/oil reservoirs, which are already used for NG storage, is considered a good option due to the lower initial capital cost and investment needed, and potential lower operating costs. In this study, the potential impact of storing a mixture of H₂ and NG in an existing NG storage field was investigated. Relevant reservoir, caprock and cement samples from a NG storage formation in California were characterized with respect to their permeability, porosity, surface area, mineralogy and other structural characteristics, before and after undergoing 3-month incubation experiments with H₂/NG gas mixtures at relevant temperature and pressure conditions. The results indicated relatively small changes in porosity and mineralogy due to incubation. However, the observed changes in permeability were more dramatic. In addition, polymeric materials, similar to those used in NG storage operations were also incubated, and their dimensions were measured before and after incubation. These measurements indicated swelling due to the exposure to H₂. However, direct evidence of geochemical reactions involving H₂ was not observed.     

Exploring the biomechanics of walking and crowd “flow”

Crowd movement simulation models are generally based on aggregated speed and flow data collected more than 50 years ago. There appears to be no validated modelling capability to include the impact of recent and future changes in population demographics, resulting from an ageing population and increasing obesity rates. New analytical approaches and data gathering are required to successfully model crowd movement and safety for current and future generations. This study carried out (a) a review of the primary components of crowd movement, demographics and analytical techniques, (b) prototype experiments to investigate age-related aspects of space and potential points of contact and (c) a new predictive model for crowd flow analysis based on pedestrian biomechanics and anthropometric data. The model uses the physical space taken up by the biomechanical walking process and the spatial buffer between points of potential contact with other pedestrians to predict the speed of movement at different levels of congestion. The new analytical model was used to predict single file speeds (for people with different demographics in congested space), which compared well with published experimental data. The next steps for model development for wider “flows” and additional experiments to provide data sets for wider demographics are also proposed.     

塔山矿新型27 mm高强玻璃钢锚杆技术应用

由于塔山矿回采巷道均为放顶煤开采，矿压显现明显，巷道断面大，在回采过程中尾顺槽围岩变形量大，致使使用传统普通玻璃钢锚杆支护时出现杆体被拉断、杆体尾部被剪断等支护失效现象。为了解决上述问题，采用新型27 mm高强玻璃钢锚杆对塔山矿8112工作面进行试验。试验结果表明，在保证采掘安全的前提下，使用新型锚杆取代普通锚杆，可以大大提高巷道支护的稳定性，节约巷道支护成本，保证施工工期正常完成，同时提高工作面回采效率。采用新型锚杆后，使巷道支护兼具安全、经济双重效益，同时对全矿井以及其他所有同类型矿井类似回采巷道，具有积极的推广和借鉴意义。     

GIS气体高压开关在阳煤五矿变电站的应用

针对阳煤五矿广场变电站的高压开关老化问题,为了保证安全性,采用了GIS气体的高压绝缘开关进行了改造。在改造后,变电站的安全性得到了显著提高,设备运行可以节省成本200多万元。     

Cd-substituted Mg composites with dual-equivalent permeability and permittivity for high-frequency miniaturization antennas

Spinel Mg ferrites Mg_1-xCd_xCo_0.05Fe_1.95O₄ (x=0.0, 0.2, 0.3 and 0.4) as potential agents for the miniaturization of high frequency antennas are presented. All the synthesized compositions were experimentally revealed to possess pure spinel phase. Dual-equivalent permeability and permittivity (μ'≈26, ε'≈25, x=0.3 and μ'≈29, ε'≈28, x=0.4) from 5 to 100 MHz can be achieved by introducing Cd²⁺ ions, yielding large miniaturization factors of up to 25 and 28. To figure out the effects of Cd²⁺ ions substitution on magnetic and dielectric properties, the change in microstructure is mainly investigated. Meanwhile, enhanced magnetic properties including upward saturation magnetization (Ms) (approximately 47.60 emu/g) and reduced coercivity (approximately 54.22 Oe) are obtained due to increased grain size and denser microstructure arrangements reflected from scanning electron microscopy images. With low magnitude order of magnetic and dielectric losses factors (tanδ_ε reaches 10^-4, tanδ_μ reaches 10^-2), the composites can potentially exhibit high operating efficiencies at high frequencies.     

Ti-48Al-2Nb-2Cr合金热变形行为及本构关系研究

采用Gleeble-1500热力模拟机对铸态Ti-48Al-2Nb-2Cr合金进行高温变形热压缩试验,变形温度范围为1050~1200℃,应变速率范围为0.001~0.1s^-1,压缩变形量为60%。研究该合金高温变形温度和应变速率与流变应力之间的关系,计算了合金激活能,并建立了Ti-48Al-2Nb-2Cr合金的Arrhenius本构模型和多元线性回归的本构模型。结果表明,该合金的激活能随温度升高和应变速率增大而增大;Arrhenius本构模型的相关系数为0.98228,平均相对误差为9.97%,相对误差在10%以内的点只占62.0%;而采用多元线性回归本构模型的相关系数为0.99566,平均相对误差为4.76%,相对误差在10%以内的点占92.6%,本构精度较高。     

A one-pot sealed ammonia self-etching strategy to synthesis of N-defective g-C3N4 for enhanced visible-light photocatalytic hydrogen

Photocatalytic hydrogen (H₂) evolution from water is considered as a prospective approach, which can convert inexhaustible solar energy into chemical energy to alleviate energy crisis and environmental problems. Herein, the N-defective g-C₃N₄ with porous structure was firstly synthesized in a sealed crucible by one-step thermal polymerization method. The experimental data showed that the yield of the catalyst was obviously increased under sealing condition. Moreover, the N-defective g-C₃N₄ prepared from urea precursor under sealed condition reached an optimum photocatalytic H₂ production rate of 597.4 μmol/h and an apparent quantum efficiency of 15.6% at wavelength of 420 nm. This enhanced photocatalytic H₂ production performance is mainly ascribed to the introduction of N-defects, which not only extended of the visible light absorption, but also acted as the electron trap centers to suppress the recombination of the photogenerated electron and hole pairs. This work offers one-step facile strategy for the introduction of N-defects to prepare N-defective g-C₃N₄ with superior photocatalytic activity, which is also a great substitute for the high-energy consuming and complicated synthetic routes.