Y修饰CuO/ZrO_2催化剂高效催化水煤气变换反应制氢

采用水热法制备了具有不同Y掺杂量的单分散ZrO_2纳米粒子(n(Y)/n(Y+Zr)=0-5%),并以其为载体采用沉积-沉淀法制得CuO/ZrO_2催化剂;考察了富氢气氛下上述催化剂的水煤气变换反应(WGS)催化性能。结果表明,掺杂Y后催化剂的活性明显提高,其中,载体掺杂2%Y的催化剂具有最佳的催化活性,在270℃时的CO转化率高达91.4%,明显高于研究较多的CuO/ZnO和CuO/CeO_2催化剂。X射线粉末衍射、N_2物理吸附-脱附、N_2O滴定、扫描电镜和CO程序升温还原等表征结果表明,Y~(3+)掺入了ZrO_2的晶格并对催化剂的结构和还原性能产生直接影响。Y助剂的引入一方面促进了CuO在ZrO_2表面的分散,提高了催化剂表面活性Cu-[O]-Zr物种的含量;另一方面,改善了催化剂的颗粒单分散性和织构性能。载体掺杂2%Y助剂的样品具有较高的Cu-[O]-Zr物种含量、较佳的颗粒单分散性和织构性能,且其表面的Cu-[O]-Zr物种和活性羟基具有较佳的还原性能,因而表现出较高的催化活性     

具确定弱区域正交各向异性薄板的弹塑性屈曲分析

基于弹塑性力学和损伤理论,建立了一个与应力球张量有关的具损伤正交各向异性材料的混合硬化屈服准则,该准则无量纲化后与各向同性材料的Mises准则同构,在此基础上,建立了正交各向异性材料的增量型和全量型弹塑性损伤本构方程,并以具确定弱区域正交各向异性矩形薄板为例,根据屈曲时的能量准则和全量理论,以等效塑性应变为内变量,对其弹塑性屈曲问题进行了分析,讨论了几何参数和弱区域对正交各向异性薄板弹塑性屈曲临界应力的影响.     

Multi-scale finite element analyses of sheet metals by using SEM-EBSD measured crystallographic RVE models

In this study, two multi-scale analyses codes are newly developed by combining a homogenization algorithm and an elastic/crystalline viscoplastic finite element (FE) method (Nakamachi, E., 1988. A finite element simulation of the sheet metal forming process. Int. J. Numer. Meth. Eng. 25, 283–292; Nakamachi, E., Dong, X., 1996. Elastic/crystalline viscoplastic finite element analysis of dynamic deformation of sheet metal. Int. J. Computer-Aided Eng. Software 13, 308–326; Nakamachi, E., Dong, X., 1997. Study of texture effect on sheet failure in a limit dome height test by using elastic/crystalline viscoplastic finite element analysis. J. Appl. Mech. Trans. ASME(E) 64, 519–524; Nakamachi, E., 1998. Elastic/crystalline viscoplastic finite element modeling based on hardening–softening evaluation equation. In: Proc. of the 6th NUMIFORM, pp. 315–321; Nakamachi, E., Hiraiwa, K., Morimoto, H., Harimoto, M., 2000a. Elastic/crystalline viscoplastic finite element analyses of single- and poly-crystal sheet deformations and their experimental verification. Int. J. Plasticity 16, 1419–1441; Nakamachi, E., Xie, C.L., Harimoto, M., 2000b. Drawability assessment of BCC steel sheet by using elastic/crystalline viscoplastic finite element analyses. Int. J. Mech. Sci. 43, 631–652); (1) a “semi-implicit” finite element (FE) code and (2) a “dynamic explicit” FE code. These were applied to predict the plastic strain induced yield loci and the formability of sheet metal in the macro scale, and simultaneously the crystal texture and hardening evolutions in the micro scale. The isotropic and kinematical hardening laws are employed in the crystalline plasticity constitutive equation. For the multi-scale structure, two-scales are considered. One is a microscopic polycrystal structure and the other a macroscopic elastic plastic continuum. We measure crystal morphologies by using the SEM-EBSD apparatus with a unit of about 3.8 μm voxel, and define a three dimensional (3D) representative volume element (RVE) for the micro polycrystal structure, which satisfy the periodicity condition of crystal orientation distribution. A “micro” finite element modeling technique is newly established to minimize the total number of finite elements in the micro scale. Next, the “semi-implicit” crystallographic homogenization FE code, which employs the SEM-EBSD measured RVE, is applied to the 99.9% pure-iron uni-axial tensile problem to predict the texture evolution and the subsequent yield loci in the various strain paths. These “semi implicit” results reveal that the plastic strain induced anisotropy in the micro and macro levels can be predicted by our FE analyses. The kinematical hardening law leads a distinct plastic strain induced anisotropy. Our “dynamic-explicit” FE code is applied to simulate the limit dome height (LDH) test problem of the mild steel DQSK, the high strength steel HSLA and the aluminum alloy AL6022 sheet metals, which were adopted as the NUMISHEET2005 Benchmark sheet metals (Smith, L.M., Pourboghrat, F., Yoon, J.-W., Stoughton, T.B., 2005. NUMISHEET2005. In: Proc. of 6th Int. Conf. Numerical Simulation of 3D Sheet Metal Forming Processes, PART A and B(Benchmark), pp. 409–451) to estimate formability. The “dynamic explicit” results reveal that the initial crystal orientation distribution has a large affects to a plastic strain induced texture and anisotropic hardening evolutions and sheet formability.     

Axisymmetric thermoelastoplastic stress-strain state of flexible laminated transversely isotropic shells

The paper presents a technique for numerical analysis of the elastoplastic stress-strain state of flexible laminated shells of revolution made of isotropic and transversely isotropic materials and subjected to axisymmetric loading and heating. The technique is based on the Kirchhoff-Love hypotheses for the whole laminate. The deformation of the isotropic materials is described using the theory of deformation along paths of small curvature. The deformation of the transversely isotropic material is described using the flow theory with isotropic hardening. The process of loading is divided into steps at each of which the stress-strain state is determined by the method of successive approximations. A numerical example is given __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 12, pp. 76–86, December, 2006.     

Thermoelastoplastic axisymmetric stress-strain state of laminated orthotropic shells

A method is proposed for the numerical analysis of the thermoelastoplastic stress-strain state of laminated shells of revolution, made of isotropic and orthotropic materials, under axisymmetric loading. The method is based on the Kirchhoff-Love hypotheses for a layer stack, the theory of deformation along paths of small curvature for isotropic materials, and Hills theory of flow with isotropic hardening for orthotropic materials. The problem is solved by the method of successive approximations. A numerical example is given.__________Translated from Prikladnaya Mekhanika, Vol. 40, No. 12, pp. 84–91, December 2004.     

扭转冷作硬化的试验研究及分析

扭转冷作硬化技术，能产生充分的塑性变形，从而使试件后继屈服极限和极限载荷比拉伸冷作硬化有大幅度提高。本文从试验研究和理论分析两个方面深入研究了这一问题，引出了有益的结果。     

Adsorption CO2 on the perfect and oxygen vacancy defect surfaces of anatase TiO2 and its photocatalytic mechanism of conversion to CO

The adsorption energies for physisorption and the most stable chemisorption of CO₂ on the neutral charge of perfect anatase [TiO₂] (0 0 1) are −9.03 and −24.66 kcal/mol on the spin-unpolarized and −12.98 and −26.19 kcal/mol on the spin-polarized surface. The small activation barriers of 1.67 kcal/mol on the spin-unpolarized surface and of 6.66 kcal/mol on the spin-unpolarized surface were obtained. The adsorption mechanism of CO₂ on the oxygen vacancy defect [TiO₂ + V_O] surface of anatase TiO₂ using density functional theory calculations was investigated. The energetically preferred conversion of CO₂ to CO was found either on the spin-unpolarized or spin-polarized surfaces of oxygen vacancy defect surface [TiO₂ + V_O] as photocatalyst.     

Oxygen deficiency effect on resistive switching characteristics of copper oxide thin films

In this Letter, bilayered Cu₂O/CuO thin films were grown on Nb doped SrTiO₃ (Nb:STO) substrates by plasma assisted molecular beam epitaxy. The current-voltage characteristics of Pt/Cu₂O/CuO/Nb:STO devices show reproducible and pronounced current-voltage hysteresis which was induced by the CuO/Nb:STO junctions. By comparing the current-voltage curves of the bilayered and single-layered CuO thin films, we attribute the prominent switching behavior to the oxygen-vacancies-mediated-carriers-trapped-detrapped process with the aid of the applied forward (reversed) bias voltage.     

利用透射电镜衬度像变化判定位错环类型及注氢纯铁中形成的位错环分析

本文分两部分,第一部分研究了利用透射电镜衬度像变化判定材料中位错环类型的方法,即采用所谓inside-outside方法来判断位错环为空位型位错环或间隙型位错环. 第二部分讨论了加速器注氢纯铁在673—773 K时效后形成的位错环的类型. 关键词： 透射电镜 空位型位错环 间隙型位错环 氢     

Achieving high strength and high ductility in nanostructured metals: Experiment and modelling

Engineering nanostructures in metallic materials such as nanograins and nanotwins can promote plastic performance significantly. Nano/ultrafine-grained metals embedded in coarse grains called bimodal metals and nanotwinned polycrystalline metals have been proved to possess extensively improved yield strength whilst keeping good ductility. This paper will present an experimental study on nanostructured stainless steel prepared by surface mechanical attrition treatment (SMAT) with surface impacts of lower strain rate (10 s^?1–10³ s^?1) and higher strain rate (10⁴ s^?1–10⁵ s^?1). Microstructure transition has been observed from the original γ-austenite coarse grains to α′-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins in the ultrafine/coarse grained austenite phase for higher strain rates. Meanwhile, we will further address the mechanism-based plastic models to describe the yield strength, strain hardening and ductility in nanostructured metals with bimodal grain size distribution and nanotwinned polycrystalline metals. The proposed theoretical models can comprehensively describe the plastic deformation in these two kinds of nanostructured metals and excellent agreement is achieved between the numerical and experimental results. These models can be utilized to optimize the strength and ductility in nanostructured metals by controlling the size and distribution of nanostructures.