关键词： Sol-gel processes   Perovskites   Ionic conductivity   Fuel cells  

摘要： The perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) is extensively utilized to yield remarkable cathode properties owing to its superior ion conductivity, high electrocatalytic activity, and low polarization resistance. In this work, BSCF in nanotube form is introduced into a pristine BSCF cathode (BSCF nanospherical powder), which enhanced the oxygen reduction reaction (ORR) and electrode stability. The specific surface area (15.02 m(2) g(-1)) and porosity (27%) of the cathode were improved by the combination of 10 wt% BSCF nanotubes with BSCF nanospherical powder when compared to the cell using the pristine BSCF cathode. The resultant heterostructured cathode demonstrated high ORR performance with the best area-specific resistance (ASR) value of 0.06 Omega cm(2) at 800 degrees C, corresponding to a 50% enhancement relative to the pristine BSCF cathode. The results demonstrate that introducing the BSCF nanotubes improved the performance of BSCF cathodes.

关键词： 基体强化   粉末冶金   显微结构   摩擦磨损  

摘要： 为了探讨不同含量的Sn、Ni、Cr元素对铜基粉末冶金摩擦材料性能及显微结构的影响,采用粉末冶金技术制备了4组铜基摩擦材料,分别测试材料的压缩强度、硬度和摩擦磨损性能及显微结构。研究结果表明:合金元素能强化基体,显著提高材料的力学性能。Ni能显著提高摩擦因数,但会导致磨损率较高。3%Sn的加入,提升了材料的耐磨损性能,降低对偶擦伤。Ni和Cr元素增强铜基材料的磨损机制主要为黏着磨损和犁沟效应,而其他材料的磨损机制主要为剥离磨损和犁沟效应的共同作用。

关键词： EBSD maps   Flow arm   Tool pin   Microstructure   Microhardness  

摘要： Frictional stir welding (FSW) generally experiences the forces Mode I axial metal flow and Mode II shear deformation around the rotating pin, along the welding direction to produce high-efficiency joints. The dissimilar FSW of AA6082/7075 joint was fabricated utilizing the process parameters such as rotational speed (R) of 900 rpm, travel speed (S) 90 mm/min, tilt angle (T) 2 degrees and plunge depth (t) 0.9 mm. Subsequently, the zone-wise EBSD and metal flow analyses were carried out and compared with the results of the microstructure and the microhardness. Distinct variations of Mode I and Mode II metal flow and fine grain formation in weld nugget have been shown here.

关键词： Metallic phase change materials   Form-stable   Thermal stability   DSC   Ball milling  

摘要： Phase change materials (PCMs) can store and release the latent heat associated with a phase transition, so they can be applied in thermal energy management and storage systems. Among them, form-stable (FS) PCMs can consist of two immiscible phases: an active phase, which undergoes the solid-liquid transition, and a matrix, which provides the structural properties and prevents leakage of the active phase when it is liquid. This experimental study focused on the characterization of a metallic FS-PCMs based on an Al-Sn alloy, obtained by powder metallurgy from ball-milled powders, compacted at room temperature and sintered at 200, 250 and 500 degrees C. The main properties that characterize PCMs are the temperature range over which transition occurs and the associated enthalpy, i.e. the stored energy. Differential scanning calorimetry (DSC) is one of the more suitable characterization techniques to evaluate these properties and so the thermal response of PCMs. To check thermal response and its stability, DSC tests including several thermal cycles were conducted. DSC analyses were performed also before and after several thermal cycles simulating possible operative conditions. Moreover, microstructural analysis, through scanning electron microscopy and X-ray diffraction, allowed to relate the thermal response variations to microstructural and mechanical changes.

关键词： RPC detectors   ion implantation   defects   diffusion   electrical conductivity   band gap energy  

摘要： Argon ions with energy of 1 MeV and 500 keV are implanted at various fluences into Asahi and Saint Gobain clear float glasses used for resistive plate chamber (RPC) detector fabrication. The decreased size of voids (V-f) in the selected glasses is interpreted as an increased short-range order of the glass structure at higher fluence of argon ion implantation. The increased local temperature influences the diffusion of argon ions via trapping in the silica glass voids for higher implantation fluence. The slight increase in bandgap energy (E-g) in the glass RPC detector materials at higher argon ion implantation fluence observed reduced electrical conductivity. The increased energy bandgap in the float glass RPC detector samples enhanced surface resistivity, consequently reducing the leakage current.

关键词： Cathode composite materials   Semantic segmentation   Microstructure features   Solid oxide fuel cells   Stereology  

摘要： Automated semantic segmentation is applied to the quantification of microstructural features in three-phase composite cathode materials of solid oxide fuel cells (SOFCs), i.e., GDC/LSC/Pore where GDC stands for Gd2O3-doped CeO2 and LSC for La0.6Sr0.4CoO3-delta. Our aim is to eliminate the tedious involvement of human experts and the associated errors. The high volume of image information sets is generated using automatic acquisition systems involving focused-ion beam scanning electron microscopy through a so-called slice-view procedure. Through the integration of semantic segmentation with image processing-assisted stereography tools, the following detailed microstructural features are quantitatively extracted automatically and objectively without any human involvement: size distribution, surface (or equivalently, volume) fraction, lengths of two-phase boundaries, and density of triple-phase boundaries based on two-dimensional images. The extracted two-dimensional information is connected with three-dimensional reconstruction analysis. The implications of semantic segmentation in SOFCs are discussed considering efficient analysis and design of high-performance electrode structures in energy-oriented devices.

关键词： 异质纳米复合   永磁体   微结构   磁性能   织构  

摘要： 采用高压热压缩变形技术对高能球磨的SmCo基非晶-纳米晶粉体与商用的Nd-Fe-B纳米晶粉体的混合物冷压块进行变形处理,成功制备出块体各向异性SmCo7/Nd2Fe14B异质纳米复合永磁体。通过X射线衍射仪(XRD)、透射电子显微镜(TEM)以及振动样品磁强计(VSM)对块体SmCo7/Nd2Fe14B异质纳米复合永磁体的微结构和磁性能进行分析研究得出:所制备磁体的微结构由SmCo7/Nd2Fe14B纳米晶区域组成,且SmCo7/Nd2Fe14B纳米晶具有沿其(00l)方向(平行于压力方向)的择优取向;磁体具有明显的磁各向异性,室温下沿压力方向具有16MGOe的最大磁能积;磁体具有较好的温度稳定性,其矫顽力温度系数β(RT-250℃)=-0.26%℃^-1。研究结果表明,所制备磁体具有较高的潜力,可应用于国防军工、轨道交通等科技领域。

关键词： latent heat   Field's metal   Wood's metal   thermal cycling   thermal stability   passive cooling  

摘要： Metallic phase change materials (mPCMs) have been demonstrated as potential passive cooling solution for pulse power applications. The possibility of integrating a metallic PCM directly on top of a heat source, reducing the thermal resistance between the device and the cooling system, could result in a significant improvement in thermal management for transient applications. However, many thermo-physical properties of these alloys are still unknown;furthermore, their microstructural stability with repetitive melting/solidification cycles is not warrant. In this work, we provide a series of potential mPCMs for thermal management of electronics operating on a wide range of application temperatures, followed by an experimental investigation of microstructural and thermo-physical stability of these materials under repetitive melting solidification cycles. The results of the effect of cyclic thermal loading of theses alloys on the melting behavior and latent heat of fusion are discussed. Thermal stability of 51.0wt % In-32.5wt %Bi-16.5wt %Sn and 50wt %Bi-26.7wt %Pb-13.3wt %Sn-10wt %Cd alloys, as potential midtemperature mPCM, has been evaluated. The results suggest that these mPCMs maintain their thermo-physical stability over large periods of thermal cycles.

关键词： Thin films   Plasma-enhanced chemical vapor deposition   Optical properties   Microstructural properties   Substrate material  

摘要： Plasma-enhanced chemical vapor deposition (PECVD) technique is well suited for fabricating optical filters with continuously variable refractive index profiles;however, it is not clear how the optical and microstructural properties of thin films differ when deposited on different substrates. Herein, silicon oxynitride films were deposited on silicon, fused silica, and glass substrates with two stoichiometric ratios by PECVD, using silane, ammonia and nitrous oxide gasses, to investigate the effects of the substrate used on the optical properties and microstructures of the films. All the deposited films were amorphous. Further, the types and amounts of Si-centered tetrahedral O-x-Si-N(y )bonds formed were based upon the substrates and stoichiometric ratios used;O-x-Si-N-y bonds with higher elemental nitrogen content were formed on Si substrates, which lead to obtaining higher refractive indices. The relationship between the surface roughness of the film and type of substrate was discussed. The extinction coefficients of all the films were very small, and the films exhibited low absorption. The refractive indices of the films formed on the different substrates had a maximum difference of 0.03. The deposition rates of the films increased in the order of fused silica, glass, and silicon.