P doped CoMoO4/RGO as an efficient hybrid catalyst for hydrogen evolution

Transition metal oxides, as newly earth-abundant and low-cost catalysts, have been regarded as promising materials for electrocatalytic oxygen evolution. However, they are rarely used as an electrocatalyst in hydrogen evolution reaction (HER) due to the poor HER activity. Herein, we present a facile two-step method to synthesize P doped CoMoO₄/RGO (P-CoMoO₄/RGO) with different atomic ratios of Co²⁺/Co³⁺ through a simple phosphorization strategy by changing the mass of NaH₂PO₂. The effective P-doping into CoMoO₄/RGO can modify the electronic properties and modulate the atomic ratio of Co²⁺/Co³⁺, which promotes the electron transfer and creates more activity sites. Therefore, the optimized P-CoMoO₄/RGO with a relatively larger atomic ratio of Co²⁺/Co³⁺ shows superior HER performances in alkaline media, which affords a current density of 10 mA cm⁻² at a small overpotential of 90 mV and a low Tafel slope of 62 mV dec⁻¹ along with having satisfactory long-term stability. This work provides a valuable route to enhance the HER activity of transition metal oxides.     

Model-based decoupling control for the thermal management system of proton exchange membrane fuel cells

As one of the most promising sustainable energy technologies available today, proton exchange membrane fuel cell (PEMFC) engines are becoming more and more popular in various applications, especially in transportation vehicles. However, the complexity and the severity of the vehicle operating conditions present challenges to control the temperature distribution in single cells and stack, which is an important factor influencing the performance and durability of PEMFC engines. It has been found that regulating the input and output coolant water temperature can improve the temperature distribution. Therefore, the control objective in this paper is regulating the input and output temperature of coolant water at the same time. Firstly, a coupled model of the thermal management system is established based on the physical structure of PEMFC engines. Then, in order to realize the simultaneous control of the inlet and outlet cooling water temperature of the PEMFC stack, a decoupling controller is proposed and its closed-loop stability is proved. Finally, based on the actual PEMFC engine platform, the effectiveness, accuracy and reliability of the proposed decoupling controller are tested. The experimental results show that with the proposed decoupling controller, the inlet and outlet temperatures of the PEMFC stack cooling water can be accurately controlled on-line. The temperature error range is less than 0.2 °C even under the dynamic current load conditions.     

Effect of hydroxyl and Mo doping on activity and carbon deposition resistance of hydroxyapatite supported NixMoy catalyst for syngas production via DRM reaction

The doping of the second metal Mo is expected to further enhance the carbon deposition resistance of Ni-based catalysts for syngas production via dry reforming of methane (DRM). In this study, the hydroxyapatite (HAP) was used as the support and a small Mo dosage was doped in the Ni-based catalysts to investigate the effect of intrinsic hydroxyl and Mo doping on the catalytic activity and carbon deposition resistance in DRM reaction. The catalyst characterization results show that both Ni and Mo are doped into the HAP structure with relatively uniform dispersion. The basic site strength of Ni4Mo0.2-HAP catalyst containing Mo is significantly higher than that of without Mo. The Mo dopant significantly improves the initial catalytic activity, but has minimal effect on the stability enhancement. Whether the catalyst is pre-reduced or not is crucial to the initial activity of the DRM reaction, the non-pre-reduced catalysts will go through a “self-activation” stage at the beginning of the reaction, where the “hydroxyl group” are proved to play as an “oxygen supply” for the partial oxidation of CH₄ or the oxidation of the carbon deposition in the initial stage. Only trace amount of carbon deposition is found after 100 h of DRM reaction on Ni3Mo0.2-HAP catalyst. The NiMo-HAP catalysts exhibit excellent initial activity and resistance to carbon deposition due to the synergistic effect of Ni–Mo alloy and hydroxyl groups in the hydroxyapatite support.     

热处理对Ti_(35)Zr_(30)Be_(27.5)Cu_(7.5)非晶合金压缩性能的影响

利用铜模铸造法获得了直径为2 mm的Ti35Zr30Be27.5Cu7.5块体非晶合金。采用X射线衍射(XRD)、扫描电镜(SEM)、差氏扫描量热仪(DSC)及压缩试验等方法研究了非晶合金的相结构、显微组织和热稳定性,以及热处理对其压缩强度及塑性的影响。结果表明:在553和583 K温度下分别保温5 h后,实验合金仍保持为非晶态;在613 K保温1 h后,有晶化相出现。Ti35Zr30Be27.5 Cu7.5非晶合金在583 K下保温1 h后其塑性变形量达到了6.57%,较热处理前提高了1倍,且保持了热处理前的强度,屈服强度和抗压强度分别为1921 MPa,2169 MPa。随着热处理温度的提高,非晶相含量减少,合金断裂强度、塑性变形量随之降低;同时合金断裂方式由韧性断裂转变为脆性断裂。     

The internal stress state in lamellar PST-crystals of the intermetallic alloy TiAl after compressive deformation

The microstructure of γ-based TiAl alloys often exhibits grains with an internal lamellar structure consisting of alternating γ-TiAl and α₂-Ti₃Al lamellae. Even in undeformed material, internal coherency stresses, due to the lattice misfit between the two phases and the tetragonality of the γ-phase are present. The goal of this work was to investigate the evolution of internal strains induced by compressive deformation of PST-specimens of the alloy TiAl at room temperature and at 800°C. The results of X-ray measurements of different peak profiles, performed with a special high-resolution double-crystal diffractometer are reported, which revealed the dependence of the deformation-induced internal strains on the orientation of the lamellar boundaries with respect to the axis of deformation.     

螺杆泵定子内螺旋曲面铣削指状铣刀的有限元分析

应用有限元方法,分析指状铣刀在铣削内螺旋曲面的情况下,刀具的内部应力、变形及其在随加工参数每齿进给量变化而变化的规律,并对指状铣刀的模态进行分析,为减少指状铣刀在加工过程中的非正常磨损现象,提高指状铣刀寿命,提供了优化方案,为优化加工工艺参数提供参考.     

基于Pro/E与ADAMS管道机器人设计仿真

针对ADAMS分析能力强大、建模功能弱的特点,运用Pro/E创建机器人虚拟样机,基于Pro/E与ADAMS对机器人进行联合仿真。主要介绍了联合仿真技术,指出样机导入过程中需要注意的关键问题,利用接口模块Mechanism/Pro对管道机器人进行了联合仿真,研究分析了机器人在管道内的运动特性,并对弹簧预紧力与样机驱动轮直径进行了优化。仿真结果表明,所设计的管道机器人能够满足设计指标要求,其结论可作为研制管道机器人物理样机的理论依据。     

The numerical analysis of the radial sleeve bearing with combined surface slip

In order to improve the carrying capacity and reduce the temperature rise in high speed and precise spindle systems, a combined surface radial sleeve bearing using the interfacial slip technique was discussed. An extended Reynolds equation was derived based on the modified slip length model considering the limiting shear stress. By means of the finite differential methods, the characteristic analysis and optimization of the slip region of the combined surface sleeve bearing were carried out, and it has been proved that there is still a considerable large load support in a parallel sliding gap. Comparing with the general journal bearing, the load capacity and end leakage rate of the combined surface sleeve bearing can be increased greatly and the load capacity can be increased by 1.75 times. The attitude angle, friction drag, temperature rise of the combined bearing can be decreased distinctly and the temperature rise can be decreased by 92.4%.     

Influence of grain boundary carbides on mechanical properties of high nitrogen austenitic stainless steel

Precipitation behavior of grain boundary carbides and its influence on mechanical properties and fracture mechanism of the high nitrogen austenitic stainless steel produced by different processing methods were studied. The simulation software Thermo-calc was applied to analyze the effects of element content on precipitation of carbides. The results show that hot-rolled plate has higher strength, but solution-treated one followed by water quenching has excellent combination of strength and ductility (toughness). M₂₃C₆ is the main precipitate and deteriorates the toughness of the steel obviously when it precipitates along grain boundaries. In this case, intergranular fracture is the predominant failure mechanism and the fracture surface is characterized by the shape of rock candy. The toughness at −40 °C is decreased by 53% when small amount of carbides precipitates during sand cooling process after solution treatment. The simulation results exhibit that with the decrease of C content, both the precipitation quantity and precipitation temperature of M₂₃C₆ decrease. Cr and N have no influence on precipitation quantity of M₂₃C₆, but the precipitation temperature will increase with the increase of Cr and the decrease of N.     

Unidirectional wavelength filtering characteristics of the two-dimensional triangular-lattice photonic crystal structures with elliptical defects

The unidirectional wavelength filtering characters of the two-dimensional triangular-lattice photonic crystal structures consisting of two waveguides and an elliptic defect are theoretically studied by the finite-difference time-domain method. Through designing the coupling regions between the elliptical defect and the adjacent waveguides, the unidirectional wavelength filtering is achieved owing to the modes’ match and mismatch between the elliptical defect and waveguides, which converts the incident fundamental even-symmetric modes to the higher order odd modes. Based on the abundant defective modes with different symmetries supported by the elliptical defect, this kind of wavelength filters can allow the unidirectional light propagation with inverse forward directions, and the bidirectional propagation through the same structure at different wavelengths.