Electrocatalytic performance of copper selenide as structural phase dependent for hydrogen evolution reaction

A cost-effective, efficient and stable electrocatalyst is a remarkable and significant prospect for hydrogen evolution reaction. By adjusting the copper contents, the Hexagonal and Tetragonal phases of the copper selenide have been synthesized using the solvo-hydrothermal process. Hexagonal phased-based copper selenide has exhibited a greater current density than the Tetragonal phase. However, the augmented structure, lower Gibbs Free energy, greater electrical conductivity and electrochemical surface promoted the electrocatalytic behavior of Hexa-CuSe-1.04 nanosheets. Hexa-CuSe-1.04 nanosheets exhibit a good overpotential of 61 mV at the state of art current density of 10 mAcm⁻² along with Tafel slope of 59 mV dec⁻¹ in 1 M KOH, which is better than the other Hexagonal phase structure, Hexa-CuSe-1.67 nanosheets and Tetra-Cu₂Se-1.30 phase of the copper selenides. The electrocatalyst Hexa-CuSe-1.04 maintains the current density for a long duration and exhibits a similar linear sweep voltammetry curve in 1 M KOH during the chronoamperometry test. Moreover, Hexa-CuSe-1.04 nanosheets show a good Tafel slope of 26 mV dec⁻¹ with a good turnover frequency of 72.40 m s⁻¹ in 0.5 M H₂SO₄ and follow the Tafel phenomenon. Optimized density functional theory reveals that Hexa-CuSe-1.04 exhibits the lower Gibbs of 1.04 eV, free energy, which promotes the desorption and recombination process of the active hydrogen atoms at the active sites and enhanced the hydrogen evolution process. All results indicate the leading potential application of the Hexagonal phase of Hexa-CuSe-1.04 for hydrogen evolution reaction.     

Lead characterisation by an objective evaluation method

A new algorithm for characterising macro-lead is introduced. The algorithm is based on a two-dimensional discrete Fourier transformation of the data set measured by a standard roughness system or a form-tester with a surface texture probe. A data pre-processing ensures the elimination of an eventually radial run out of the work piece. The lead parameters which are relevant to leak-tightness are derived from the position of the most significant peak in the frequency domain and a reconstructed deterministic surface.     

First-principles prediction of structural,electronic and optical properties of alkali metals AM4BN3H10 hydrides

To explore the high storage capacity of hydrogen storage material, the structural feature and hydrogenated mechanism of Li₄BN₃H₁₀ alkali metal hydrides are studied by using the first-principles calculations. The calculated result predicts that the Li₄BN₃H₁₀ and Rh₄BN₃H₁₀ are thermodynamic and dynamical stabilities according to the phonon dispersion and thermodynamic model. Essentially, the hydrogen storage mechanism of AM₄BN₃H₁₀ hydride mainly depends on the formation of [BH₄] group and [NH₂] group. Compared to LiBH₄, the hybridization between the B atom and H atom in [BH₄] group and between the N atom and H atom in [NH₂] group can store a lot of hydrogen. However, the dehydrogenation of AM₄BN₃H₁₀ hydride prefers to [BH₄] group rather than the [NH₂] group. The narrow band gap is beneficial to hydrogen release in AM₄BN₃H₁₀ hydride. Therefore, the Rb₄BN₃H₁₀ has better hydrogen release properties in comparison to the Li₄BN₃H₁₀ and Na₄BN₃H₁₀. Therefore, we believe that the AM₄BN₃H₁₀ hydride is a promising hydrogen storage material with the high hydrogen storage capacity.     

Experiment and numerical simulation of the influence mechanism of kinetic factors on rapid growth of KDP crystal

A series of KDP crystals at different rotation speeds ranging from 9 to 120 rpm were grown by rapid growth method. The results fully demonstrate that rotation speed as a key kinetic parameter has a great influence on the whole crystallization process. Moreover, an important characteristic has been proved that the growth rates along X and Z-direction increase with the increase of rotation speed lower than 100 rpm, while the rates of X-direction are always greater than Z-direction. Combined with numerical simulation method, the correlations of solution stability with kinetic factors including rotation speed, crystal size and growth platform are explored in detail. During the crystallization process, the thickness of boundary layer decrease and a higher flow rate is caused with the increase of rotation speed below 100 rpm, and the generation of inclusions at lower speed may be associated with the slower flow rate of growth solution. The stability of solution gradually decreases as the rotation speed ranges from 100 to 120 rpm. Furthermore, the computed results of R_e imply that reducing rotation speed as increasing of crystal size may be an effective method to obtain high-quality and large-scale KDP crystal by rapid growth technique. Comparing to the growing platform with four columns, the platform with two circular connecting columns play an active role in influencing the growth rate of KDP crystal, especially in axial direction.     

轧辊表面残余应力测试方法的对比试验研究

轧辊体积大且辊面状态又不好,尤其是热轧辊的表面常有氧化膜和微裂纹,在测量时又不能损伤轧辊表面,因此,轧辊残余应力的测量较困难.为验证临界折射纵波法测轧辊表面残余应力的准确性,用超声波法、X射线法和盲孔法对同一试件进行了应力测量.对这3种测量方法所测得的结果进行比较后,评价超声波法的可靠性和有效性.试验结果显示:临界折射纵波法测试的应力值与X射线衍射法和盲孔法测试的结果具有较好的一致性.     

Investigation into the flow behavior of high-temperature ash and low-temperature ash of high calcium coal

The flow behavior of high-temperature ash (HTA) and low-temperature ash (LTA) of high calcium coal in the heating process was investigated systematically. By means of the heating stage microscope, the behavioral changes of samples were studied visually. The composition and mineral matters transformations of HTA and LTA samples were analyzed by X-ray fluorescence and X-ray diffraction. The results show that the original composition of HTA sample is different from that of LTA sample. In addition, the HTA and LTA samples experience the shrinkage, fusion and spreading processes in succession. However, the volume change of HTA sample is different from that of LTA sample. The volume of LTA sample shows a slow change at the temperature lower than 800 °C, while the volume of HTA sample is unchanged. In the temperature range of 800°C–1100 °C, the remarkable shrinkage of HTA and LTA samples are demonstrated. The formation of srebrodolskite and gehlenite attributes to this volume change. Moreover, the sharp shrinkage of HTA and LTA samples is indicated at 1100°C–1300 °C. This is caused by the formation of eutectics. Because of the diverse content and species of mineral matters in LTA sample, the volume change of LTA sample is more remarkable than that of HTA sample. The maximal shrinkages of LTA and HTA sample are 57% and 53%, respectively.     

基于自适应调频模态追踪方法的铣削颤振识别

在铣削加工工程中,产生颤振,严重影响产品的加工精度和表面质量。为了有效避免铣削过程中发生颤振,提出了基于自适应调频模态追踪(adaptive chirp mode pursuit, ACMP)的铣削颤振监测和识别方法。该方法综合考虑了振动信号的带宽和微弱特性,ACMP在递归框架中逐个捕获信号模式,在该算法中,不需要输入信号模式的个数,而是可以通过评估残差信号的能量来学习,这样就可以避免由于分解层数不确定带来的模态混叠或者过度分解的问题。首先使用仿真信号验证了该算法对颤振信号具有很高的识别精度;然后基于现场的铣削实验数据证明该方法及时有效地对颤振进行识别;最后从ACMP处理后的信号中提取功率谱熵值作为颤振识别特征。该方法解决了经验模态分解(empirical mode decomposition, EMD)算法的模态混合和伪分量问题,又降低了变分模态分解(variational mode decomposition, VMD)的精度不稳定的影响,可以准确快速地识别到颤振,对提高加工质量具有重要意义。     

新型无刷直流电机结构设计与性能分析

针对物联网通讯技术对微纳卫星提出的高性能、低成本的需求,提出了一种新型双圈磁钢无刷直流电机结构动量轮,介绍了其结构和工作原理。采用有限元法对气隙磁密进行仿真分析,结果表明,双圈构型电机气隙磁密和有效气隙磁密平均值均优于传统方案,气隙平顶宽度从传统方案的90°拓宽到120°,有效的提升了力矩输出性能。通过对无控制器状态下两种电机转速特性分析,验证双圈构型电机具有更优的动态和抗干扰性能;基于该结构设计了转速闭环PID控制系统并进行仿真分析,结果表明双圈构型电机在空载状态及突加负载两种情况下,电机达到稳定转速的时间和达到稳定转矩的时间均优于传统结构电机,且新型结构电机的脉动幅值降低约46.5%,可实现电机的高精度稳速控制。     

Alumina ceramic tool material with enhanced properties through the addition of bionic prepared nano SiC@graphene

Graphene-coated SiC nanoparticles containing graphene floating bands (SiC@G) were prepared by a liquid-phase laser irradiation technique, and SiC@G nanoparticles with high dispersivity were incorporated into an Al₂O₃ matrix. An Al₂O₃-based composite ceramic tool was prepared by spark plasma sintering (SPS), and the effects of SiC@G nanoparticles on the mechanical and cutting properties and microstructure of the materials were further investigated. Analysis of the cross-sectional morphology shows that SiC@G nanoparticles containing graphene floating bands were homogeneously dispersed in the composite, which resulted in tighter bonds between the Al₂O₃ particles. This particular core-shell structure increased the contact area between the graphene and the matrix due to the formation of a graphene 3D mesh by extrusion, which enhanced the difficulty of relative sliding of graphene. Second, this special core-shell structure also made the crack propagation path more tortuous, further increasing the energy consumed in the fracture process, which is conducive to improving the mechanical properties of ceramic tools. The addition of SiC@G nanoparticles improves the mechanical properties of Al₂O₃-based composite ceramic tools. The fracture toughness (7.2 Mpa·m^1/2) and flexural strength (709 MPa) increased by 75.6% and 28.7%, respectively. Cutting experiments with Al₂O₃/SiC/G composite ceramic tool and Al₂O₃/SiC@G composite ceramic tools on 40Cr hardened steel were performed. The results prove that the addition of SiC@G nanoparticles improves the cutting life by 18.1% and reduces the cutting force and friction coefficient by 6.3% and 14.8%, respectively.