Creep of polycrystalline SrCo0.8Fe0.2O3−δ

In this study, a series of compressive creep tests on rectangular specimens of SrCo_0.8Fe_0.2O_3−δ of grain sizes in the range of 2.4–6.8 μm was performed in air, covering a temperature range of 850–975°C and a stress range of 2–80 MPa. The stress exponent has been found to be close to unity in the 10–20 MPa stress range. The apparent activation energy assumes two different values, 471 kJ/mole below 925°C and 275 kJ/mole above 925°C. The microstructural observations of crept samples revealed equiaxed grains and negligible grain growth indicating a diffusion-accommodated grain switching mechanism. The logarithmic plot of strain rate vs inverse grain size has been found to be non-linear. A possible explanation for this behavior is discussed through the incorporation of a threshold stress. The possibility of estimating the lattice and grain-boundary diffusion coefficients from the data is discussed.     

Cr12MoV钢表面激光熔覆多层Ni基合金涂层的组织及性能

使用脉冲Nd:YAG激光器在Cr12MoV模具钢表面熔覆了Ni20Cr和Ni60A多层Ni基合金耐磨涂层,并使用X射线衍射仪、扫描电镜及能谱仪分析了涂层的物相和显微组织。同时运用显微维氏硬度计以及高速往复摩擦磨损试验机对比分析了涂层与基体的硬度及耐磨性。结果表明,采用Ni20Cr作为打底层的多层Ni基合金涂层,能有效改善涂层与基体的冶金结合,大大减少涂层中的裂纹、气孔等缺陷。涂层表面物相主要为g-(Fe, Ni)、FeNi₃、BNi₃、Cr₃C₂以及Ni-Cr-Fe;涂层底部至表面的组织为胞状树枝晶、柱状树枝晶、择优生长树枝晶以及等轴树枝晶。Ni60A涂层大大提高了Cr12MoV模具钢的表面硬度,涂层表面显微硬度最高可达到1000 HV0.2,是基体的1.6倍。Ni60A涂层耐磨损性能明显优于基体,较基体提高了2.0~3.3倍。在Cr12MoV模具钢表面激光熔覆多层Ni基合金涂层后,形成了Cr₃C₂、Ni-Cr-Fe等硬质相,可有效提高其表面的硬度和耐磨性,起到降低模具在使用过程中因摩擦磨损而报废的概率,从而进一步延长模具的使用寿命。     

5182铝合金表面硅烷涂层的制备与性能研究

目的提高5182铝合金表面耐蚀性能及其与漆膜的结合力。方法采用KH550硅烷试剂在5182铝合金表面制备硅烷涂层,同时探究不同浸泡时间、溶液pH值和固化温度对硅烷涂层结构和性能的影响,并优化硅烷涂层的制备工艺。采用扫描电子显微技术(SEM)、接触角试验仪和拉曼光谱研究硅烷涂层的结构和成分。采用电化学阻抗谱(EIS)技术评价涂层的耐蚀性能。采用涂层附着力自动划痕仪评价硅烷涂层对有机漆膜结合力的影响。结果浸泡时间180 s、溶液pH值11、固化温度90℃为5182铝合金表面硅烷涂层的最佳制备工艺,该工艺条件下制备的硅烷涂层均匀、致密地覆盖于铝合金基体表面,厚度约为100 nm。在Na_2B_4O_7×10H_2O和NaOH水溶液中,硅烷处理试样的低频阻抗值比未硅烷处理试样高约2个数量级,硅烷处理样品与漆膜的结合力明显优于未经过硅烷处理的试样。结论采用优化工艺制备的硅烷涂层能改善5182铝合金的耐蚀性能。当硅烷涂层作为中间层存在时,显著提高了有机涂层与合金基体的结合强度。     

强流脉冲电子束改性过程温度场数值模拟

强流脉冲电子束表面改性过程具有非稳态、有内热源的温度场特点,利用ANSYS软件对其温度场进行了数值模拟。以纯镁板材为实验材料,采用强流脉冲电子束装置对试样表面进行了脉冲次数为10次的辐照处理。建立了强流脉冲电子束表面改性过程内热源的一维物理模型,并在实验和理论基础上对电子束改性过程中的温度场演化进行了数值模拟。模拟结果显示,所建立的物理模型与实验结果较为吻合。     

One-step solvothermal synthesis of Fe3O4@Carbon composites and their application in removing of Cr (VI) and Congo red

Fe₃O₄ @C nano-adsorption was prepared by a simple one-step solvothermal synthesis method using Fe (NO₃)₃ 、cyclodextrin as raw materials, meanwhile urea as an alkali source. The obtained samples were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, and Brunauer-Emmett-Teller. The adsorption behavior of the Fe₃O₄@C toward Cr (VI) and Congo red was also studied. The core-shell structure Fe₃O₄@C exhibited large specific surface area of 112.91?m² g^?1. The prepared Fe₃O₄@C samples demonstrated typical ferromagnetic behavior and high removal capacity in removing the toxic Cr (VI) ions and organic pollutant CR from wastewater, together with facile magnetic separability and good recyclability. Equilibrium adsorption performance was conducted by using the Langmuir and Freundlich model and Freundlich model could simulate the adsorption process of Congo red and Cr (VI) better. The maximum adsorption capacity of Cr (VI) and Congo red was 33.35?mg?g^?1 and 262.72?mg?g^?1 by calculation.     

Hierarchical NiS decorated CuO@ZnFe2O4 nanoarrays as advanced photocathodes for hydrogen evolution reaction

Rationally designed architecture and smart components of catalysts can greatly accelerate the hydrogen evolution reaction in photoelectrochemical water splitting. Herein, hierarchical NiS quantum dots decorated CuO nanowires@ZnFe₂O₄ nanosheets core/shell nanoarrays were prepared by a viable multi-step synthesis approach. First, CuO nanowire arrays were prepared through the thermal treatment of copper mesh. Then, CuO@ZnO core/shell nanowire arrays were prepared via an impregnation-calcination process. Next, the CuO nanowire arrays with different ZnFe₂O₄ nanosheet contents were prepared through wet chemical reaction and subsequent thermal treatment. The further NiS quantum dots decoration was realized through a chemical bath deposition. The CuO nanowire arrays covered with ZnFe₂O₄ porous nanosheets not only offer abundant active sites to react with the electrolyte but also improve visible light utilization. Moreover, the hierarchical nanoarray structure provides a direct electron transport pathway with a graded interface for better charge flow. As a result, remarkably enhanced photoelectrochemical performance and excellent cycling stability were obtained for the CuO@ZnFe₂O₄ nanoarray photocathodes due to the synergistic effects of ideal components and hierarchical nanoarray structure. Additionally, the further NiS decoration makes CuO@ZnFe₂O₄ exhibit a significantly enhanced photocathodic current density.     

Calcium silicate-based catalytic filters for partial oxidation of methane and biogas mixtures: Preliminary results

Development and testing of catalytic filters for partial oxidation of methane to increase hydrogen production in a biomass gasification process constitute the subject of the present study. Nickel, iron and lanthanum were coated on calcium silicate filters via co-impregnation technique, and catalytic filters were characterized by ICP-MS, XPS, XRD, TEM, TGA, TPR and BET techniques. The influences of varying reaction temperature and addition of Fe or La to Ni-based catalytic filters on methane conversion, and hydrogen selectivity have been investigated in view of preliminary results obtained from reactions with 6% methane-nitrogen mixture, and catalytic filters were tested with model biogas mixtures at optimum reaction temperature of each filter which were 750 °C or 850 °C. Approximately 93% methane conversion was observed with nearly 6% methane-nitrogen mixture, and 97.5% methane conversion was obtained with model biogas containing CH₄ which is 6%, CO₂, CO, and N₂ at 750 °C. These results indicate that calcium silicate provides a suitable base material for catalytic filters for partial oxidation of methane and biogas containing methane.     

Performance optimization of hybrid hydrogen fuel cell-electric vehicles in real driving cycles

In this research study, a fuel cell-electric hybrid car is studied. This car includes an electric motor that is connected to a fuel cell and a complex which includes a battery pack and an Ultracapacitor. The assessment of this hybrid vehicle is conducted by using various driving cycles such as FTP-75 driving cycle, NEDC driving cycle and SFTP-SC03 driving cycle. Battery state of charge (SoC) and hydrogen fuel consumption are the effective parameters influencing the vehicle performance. For analysing the performance of this vehicle, an innovative computational model is considered. In this innovative computational model, an accurate control strategy is considered in order to control the power demand, staying the battery packs and the Ultracapacitor state of charge in a limited domain. Results show that in NEDC driving cycle, by means of using Ultracapacitor in this model, 3.3% reduction in fuel consumption and 20.2% decrease in the difference between initial and final State of Charge (SoC) in battery pack can be achieved. In addition, a robust regenerative braking control strategy is used in order to recover some parts of the wasted energy in braking driving modes.     

Effects of post-deposition annealing on different DLC films

Amorphous hydrogenated carbon films have been deposited by plasma-enhanced chemical vapour deposition at different process pressures and substrate temperatures, resulting in film properties ranging from polymer-like to diamond-like. The deposition parameter combinations were chosen by experimental design to enable the determination of both deposition pressure and deposition temperature effects on the annealing behaviour. The deposited films have then been annealed in vacuum at successively higher temperatures. Changes in optical band gap, internal stress, film thickness and infrared (IR) absorption spectra have been recorded to assess the influence of deposition parameters on the thermal stability of diamond-like carbon (DLC) and to identify temperature-induced modifications in the bonding structure. The results show a large variation in thermal stability between the different DLC films; samples deposited at low pressure display the greatest stability. The internal stress of the films starts decreasing at very low annealing temperature (<100 °C for the majority of samples), in most cases long before any decrease in the optical band gap can be detected. This is explained by a movement of hydrogen from sp² to sp³ sites as detected by IR measurements.