Catalytic synthesis of long NbS2 nanowire strands

Large-scale of long NbS₂ nanowire strands were successfully synthesized by a catalyzed transport reaction involving C₆₀. The strands have a diameter of 1–2 μm and length up to 0.5 mm, which are composed of single nanowire. The diameter of single nanowire is 1.6–20 nm. The products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Probable mechanisms for catalytic growth were proposed.     

Water-splitting properties of bi-phased TiO2 nanotube arrays subjected to high-temperature annealing

An extended study was conducted to correlate between morphological, crystalline phase conversion and the photoelectrochemical water-splitting properties of anodic TiO₂ nanotube arrays (TNTs) films annealed at elevated temperatures, starting from 450 °C to 850 °C. A distinct visualization was provided to support the effect of the high temperature annealing up to 850 °C on the photocurrent productivity of the TNTs films, which acted as photoanodes based on the crystalline anatase-rutile composition ratio. To assess the photoelectrochemical productivity for different annealed materials, several electrochemical techniques were utilized namely; electrochemical impedance spectroscopy (EIS), chronoamperometry and potentiodynamic polarization (PP). Results indicated that the crystalline bi-phased (anatase/rutile) TiO₂ nanotube arrays synergistically influenced the photoelectrochemical water splitting. It was found that the annealed TNTs film with bi-phase content composition (66% anatase and 34% rutile) at 650 °C exhibited maximum photoelectrochemical water-splitting properties with a significant applied bias photon-to-current conversion efficiency (ABPE%) of 0.41%. These results describe a promising target for the fabrication of high performance bi-phase crystalline (anatase and rutile) nanoporous TNTs for improving the photoelectrochemical water-splitting efficiency. Incident photon-to-electron conversion efficiency measurements (IPCE%) also showed the superiority of annealed sample at 650 °C (43.4%), which agrees with EIS, PP and ABPE% calculations.     

Online welding quality monitoring based on feature extraction of arc voltage signal

Arc sensing plays a significant role in the control and monitoring of welding quality for aluminum alloy pulsed gas touch argon welding (GTAW). A method for online quality monitoring was proposed based on the analysis of acquired arc voltage signal, through which two algorithms of feature extraction were developed in time and frequency domain, respectively. In time domain,the wavelet packet transform was carried out to eliminate the pulse interference of the feature parameter curve. In frequency domain, the other new algorithm was proposed based on the voltage power spectrum density (PSD) which was calculated by using the improved Welch algorithm and divided into five frequency bands before the statistic parameters were extracted. The correlation between the feature parameters in different frequency bands and welding defects were carefully analyzed to select a more sensitive one as the monitoring parameters. The proposed algorithms on this paper were verified to be capable of detecting lack of penetration, burn through, and the defect caused by lack of gas.     

醇盐水解法制备铝酸镧粉体

采用金属与醇直接反应制得金属醇盐，经水解、干燥、焙烧，最终制得LaAlO3粉体。实验证明，金属镧、铝与醇直接反应可制得镧铝双金属醇盐。经过TG、XRD、SEM分析可得知水解过程、相转变、晶粒大小等信息。油酸的加入可降低醇盐活性，可控制水解反应速度；在TG曲线上，到600℃左右，湿凝胶几乎停止失去结构水，凝胶趋于转化完全；XRD表明，在900℃条件下焙烧，可得到LaAlO3，且晶型发育较完好，且为立方相；焙烧温度到1000℃时，晶粒发育完善；由谢乐公式计算，晶粒尺寸为80nm左右；经SEM观察，粉体颗粒呈规则的立方体。     

In-situ reaction synthesis of porous Si2N2O-Si3N4 multiphase ceramics with low dielectric constant via silica poly-hollow microspheres

In the present work, a novel and facile process has been proposed to fabricate porous Si₂N₂O-Si₃N₄ multiphase ceramics with low dielectric constant (ε_r＜4.0). Since silica poly-hollow microspheres could serve as the source of SiO₂ and the pore-forming agent, they have been introduced into Si₃N₄ slurry through the gelcasting technique. This process is benefited from the liquid phase sintering reaction between SiO₂ and Si₃N₄ with the aid of sintering additives, leading to in-situ synthesis of Si₂N₂O phase and porous structure. The content of silica poly-hollow microspheres has great influence on the properties of the final products. It indicates that Si₂N₂O phase would become the major phase when the content of silica poly-hollow microspheres was above 25 wt%. Furthermore, the micromorphology results reveal that the content of pores with many smaller aggregate microspheres increases as microspheres amount rises. As a result, along with the addition of silica poly-hollow microspheres, the bulk density decreases to 1.32±0.01 g/cm³, and open porosity ranges from 28.4±0.4% to 52.0±0.5%. Porous Si₂N₂O-Si₃N₄ multiphase ceramics prepared with 25 wt% silica poly-hollow microspheres addition possess flexural strength of 42.3±3.8 MPa, low dielectric constant of 3.31 and loss tangent of 1.93×10⁻³. It turns out to be an effective method to fabricate porous Si₂N₂O-Si₃N₄ composites with excellent mechanical and dielectric properties, which could be applied to radome materials.     

Influence of Al2O3 on low-field spin-polarized tunneling magnetoresistance of (1 − x) La0.7Ca0.3MnO3 + x Al2O3 composites

In this study we report the effect of Al₂O₃ on the low field magnetoresistance (LFMR) of (1 ? x) La_0.7Ca_0.3MnO₃ + x Al₂O₃ composite synthesized through a solid-state reaction method combined with an energy milling method. Based upon a spin-polarized tunneling of conduction electrons at the grain boundaries, we have proposed a phenomenological model to explain the observed electrical transport behavior over the whole temperature range (5  300 K), especially the gradual drop of metal-insulator transition temperature (T_p = T_max) as a function of increasing Al₂O₃ content, while the ferromagnetic–paramagnetic transition temperature (T_C) remains almost constant (T_C = 250 K).     

B＋级钢壁厚对力学性能影响的研究

以铁路货车转向架主要铸件的材质B^＋级钢为研究对象,通过对不同壁厚B^＋级钢铸件进行标准拉伸、冲击试验,研究铸件壁厚变化对其力学性能的影响。结果发现B^＋级钢壁厚在14～50mm区间内,随着壁厚增加,铸造试块边缘的抗拉强度和冲击性能有缓慢增加的趋势,但并不明显;随着壁厚继续增加,铸造试块中心的抗拉强度和冲击性能明显降低,当壁厚达到50mm时,抗拉强度和冲击性能只有其对应边缘部位的30％左右。     

Mechanical characterization of sol-gel alumina-based ceramics with intragranular reinforcement of multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) have been widely considered for mechanical reinforcement of ceramic matrix composites. Nevertheless, the efficiency of this reinforcement strategy is under debate due to fabrication issues, such as a good homogenization or the location of the MWCNTs inside the matrix composite. Regarding this, the intragranular location of the MWCNTs has been deemed a crucial feature for optimizing the reinforcement compared to the typical intergranular placement achieved by conventional procedures. Recently, the sol-gel method has been reconsidered, as it promotes the intragranular placement of the MWCNTs. This work presents the mechanical characterization of these composites synthesized by the sol-gel method, where crack-bridging has been revealed as toughening mechanism. Finally, the conventional use of the bibliographical Young's modulus of pure alumina for the estimation of the fracture toughness is discussed, obtaining significant improvements of the fracture toughness when indentation measurements are treated by considering elastic moduli obtained by nanoindentation.     

Tunable band gap of NV co-doped Ca:TiO2B (CaTi5O11) for visible-light photocatalysis

Visible-light photocatalysis in layered perovskite CaTi₅O₁₁ is measured by band-gap tuning with co-doped anionic nitrogen (N) and cationic vanadium (V). The screening of hybrid density functional (HSE06) calculation reveals that strong Coulomb interaction between the dopants and other atoms makes NV co-doping energetically favorable and effective for narrowing the band gap. More importantly, co-doping can eliminate the impurity states to reduce the electron-hole combination and improve the efficiencies of photocatalysis, since the mono-doped N or V ion produces impurity near the Fermi level. The impurity state captures the photoexcitation-generated carriers and accelerates the recombination process of the electron-hole pairs, thus suppressing their photocatalytic performance. The alignment of the band edge position with respect to the water oxidation/reduction potential indicates that NV co-doped CaTi₅O₁₁ can act as a potential photocatalytic water catalyst. Co-doping is expected to be an effective way of improving the visible-light photocatalytic activity in layered perovskite due to the elimination of recombining the electron-hole pairs.     

基于惰性气体钨极保护焊受电弓用6082铝合金角接接头开裂分析

受电弓在组装时发现下臂主轴与吊耳所组成的角接接头近焊缝区出现表面裂纹,结合焊接结构和实际工艺,通过材料理化性能试验、T型接头裂纹敏感性分析、焊接接头裂纹断面宏观和微观检查,对裂纹产生的原因及机理进行了分析。结果表明：受电弓下臂主轴与吊耳的焊接接头近焊缝区开裂是由于热输入过大而引起的液化裂纹,而吊耳装配时的锤击导致该液化裂纹进一步扩展,形成了沿焊趾的开裂。最后提出了预防裂纹的措施,保证了产品的焊接质量。