Q. Gao
,
X.J. Yang and G.Z. Kang(Department of Applied Mechanics and Engineering
,
Southwest Jiaotong University
,
Chengdu 610031
,
China )
金属学报(英文版)
An experimental investigation was cawted out of the cyclic saturated kinematic hardening of the solution treatment stainless steel 316L subjected to cyclic loading for seveml strain paths, such as uniaxial cycling, cireulan elliPtic, diamond, rectangular shapes. The evoluting tndectories of back stresses in deviatoric stress space were obtained, and the evolution of back stress mtes during cyclic saturuted loading was analyzed under the assumption that the yield sudece rudius at cyclic saturation is constant and the direction of plastic stmin rute coincides with the one of the out normal vector Of the yield sudece. Some significant results were obtained.
关键词:
stainless steel 316L
,
null
,
null
Journal of Physics D-Applied Physics
The dynamic aspects of linear elastic fracture mechanics applied to dielectric breakdown are studied. In the same direction as the fracture mechanics analogue for dielectric breakdown described previously by some researchers, this paper develops the intrinsic, rate-dependent bond breakdown micromechanism to account for the dynamic process of dielectric breakdown. The formulae of conducting microcrack growth rate and lifetime prediction are derived and applied to the experimental data of SiO2 films.
关键词:
sio2-films;oxides
Optical Materials
The perturbation formulas of the EPR g factors g,, g and g. for a 4f(11) 1 ion in orthorhombic symmetry are established. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various states are taken into account. The above formulas are applied to the orthorhombic Er3+ centers in YAG, YGG and LuGG garnets. By analyzing their g factors, we find that the polar angles theta(j)(') of the impurity-ligand bonds related to the Z axis of the crystals in these Er3+ centers are smaller than the host angles theta(j) in pure crystals, whereas the azimuthal angles, related to the X axis in the impurity centers are larger than the corresponding phi(j) in the hosts. The g factors and their anisotropies Delta g [= g(z) - (g(x) + g(y))/2] and delta g (= g(x) - g(y)) for Er3+ in the garnets based on the above local structural parameters are in good agreement with the observed values. In addition, the angular distortions Delta theta (= theta(j)(') - theta(j)) or Delta phi (= phi(j)(') - phi(j)) obtained by analyzing the EPR data in this work are different from Delta theta(2), or Delta phi(2) (for only the second set of ligands, i.e., j = 2) based on the superposition model crystal-field analysis in the previous work. The validity of the results is discussed. (c) 2004 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance (EPR);defect structure;crystal-field;and spin hamiltonians;Er3+;garnets
International Journal of Modern Physics B
The perturbation formulae of EPR parameters g factors g(x), g(y) and g(z) for the lowest Kramers doublet of 4f(1) ion in orthorhombic symmetry are established. In these formulae, the contributions of the covalency effects, the admixture between J = 7/2 and J = 5/2 states as well as the second-order perturbation (which is not considered in the previous works) via crystal-field and orbital angular momentum interactions are all included. According to these formulae, and by using the superposition model, the g-factors g., g(y) and g(z) for Ce3+ center in YBa2CU3O6+x superconductor are calculated. The results are discussed.
关键词:
YBa2Cu3O6+x;EPR;superposition model;Ce3+;crystal-field
何科林
,
谢君
,
罗杏宜
,
温九青
,
马松
,
李鑫
,
方岳平
,
张向超
催化学报
doi:10.1016/S1872-2067(17)62759-1
光催化技术是目前解决能源和环境问题最具前景的手段之一,因此寻找高效光催化剂已成为光催化技术的研究热点.而在众多半导体催化剂中,廉价、环保且性能稳定的g-C3N4光催化剂在太阳光开发利用方面尤其引人关注.然而,由于g-C3N4的比表面小,活性位点少,以及光生电子/空穴对易复合等不足,严重导致其较低的光催化量子效率.因此,构造Z型体系和负载助催化剂等策略被广泛应用于提高g-C3N4光催化效率.在过去几年中,TiO2,Bi2WO6,WO3,Bi2MoO6,Ag3PO4和ZnO已经被成功证实可以与g-C3N4耦合而构造Z型光催化剂体系.其中,WO3/g-C3N4光催化剂体系,具有可见光活性的WO3导带中的光生电子和g-C3N4价带中的光生空穴容易实现Z型复合,从而保留了WO3的强氧化能力和g-C3N4的高还原能力,最终大幅度提高了整个体系的光催化活性.在g-C3N4的各种产氢助催化剂中,由于常用的Pt,Ag和Au等贵金属的高成本和低储量等问题严重限制了它们的实际应用,所以近年来各种非贵金属助催化剂(包括纳米碳,Ni,NiS,Ni(OH)2,WS2和MoS2等)得到了广泛的关注.我们采取廉价且丰富的Ni(OH)x助催化剂修饰g-C3N4/WO3耦合形成的Z型体系,开发出廉价高效的WO3/g-C3N4/Ni(OH)x三元产氢光催化体系.在该三元体系中,Ni(OH)x和WO3分别用于促进g-C3N4导带上光生电子和价带的光生空穴的分离及利用,从而使得高能的g-C3N4的光生电子在Ni(OH)x富集并应用于光催化产氢,而高能的WO3的光生空穴被应用于氧化牺牲剂三乙醇胺,最终实现了整个体系的高效光催化产氢活性及稳定性.我们通过直接焙烧钨酸铵和硫脲制备出WO3纳米棒/g-C3N4,并采用原位光沉积方法将Ni(OH)x纳米颗粒负载到WO3/g-C3N4上.随后,我们采取X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、X射线光电子能谱分析(XPS)和比表面和孔径分布等表征手段来研究光催化剂的结构与形貌;采取紫外-可见漫反射表征方法来研究其光学性能;采取荧光光谱,阻抗和瞬态光电流曲线等表征手段来测试光催化剂的电荷分离性能;采取极化曲线和电子自旋共振谱等表征手段来证明光催化机理;采取光催化分解水产氢的性能测试来研究光催化剂的光催化活性与稳定性.XRD,HRTEM和XPS表征结果,表明WO3为有缺陷的正交晶系的晶体,直径为20–40纳米棒且均匀嵌入在g-C3N4纳米片上;Ni(OH)x为Ni(OH)2与Ni的混合物,其Ni(OH)2与Ni的摩尔比为97.4 : 2.6,Ni(OH)x粒径为20–50 nm且均匀分散在g-C3N4纳米片上,WO3/g-C3N4/Ni(OH)x催化剂界面之间结合牢固,其中WO3和Ni(OH)x均匀分布在g-C3N4上.紫外-可见漫反射表征结果表明,随着缺陷WO3的负载量增加,复合体系的吸收边与g-C3N4相比产生明显的红移,而加入Ni(OH)x助催化剂使得催化剂体系的颜色由黄变黑,明显地增加了可见光的吸收.荧光光谱,阻抗和瞬态光电流曲线结果表明,WO3和Ni(OH)x的加入能有效地促进光生电子/空穴的分离.极化曲线结果表明,掺入WO3和Ni(OH)x能降低g-C3N4的析氢过电位,从而提高光催化剂表面的产氢动力学.?O2?和?OH 电子自旋共振谱表明成功形成了WO3/g-C3N4 耦合Z 型体系.光催化分解水产氢的性能测试表明,20%WO3/g-C3N4/4.8%Ni(OH)x产氢效率最高(576 μmol/(g?h)),分别是g-C3N4/4.8%Ni(OH)x,20%WO3/g-C3N4和纯g-C3N4的5.7,10.8和230倍.上述结果充分证明,Ni(OH)x助催化剂修饰和g-C3N4/WO3 Z型异质结产生了极好的协同效应,最终实现了三元体系的极高的光催化产氢活性.
关键词:
光催化产氢
,
稳定的Ni(OH)x催化剂
,
g-C3N4
,
Z型体系
,
异质结
Journal of Alloys and Compounds
The EPR g factors g(x), g(y) and g(z) and the local structures for the orthorhombic Nd3+ centers in YAG, YGG and LuGG garnets are studied by using the perturbation formulas of the g factors for a 43 ion in orthorhombic symmetry. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various energy levels are considered. Based on the analyses of the g factors, we find that the polar angles theta'(j) of the impurity-ligand bonds related to the Z-axis of the crystals in these Nd3+ centers are smaller than the host angles theta(j) in pure crystals, whereas the azimuthal angles phi'(j) related to the X-axis in the impurity centers are larger than the corresponding phi(j) in the hosts. The calculated g factors, particularly their anisotropies Delta g [= g(z) - (g(x) + g(y))/2] and delta g (= g(x) - g(y)) for Nd3+ in the gamets based on the above local angles show reasonable agreement with the observed values. (c) 2004 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance (EPR);defect structure;crystal-field;and spin hamiltonians;Nd3+;garnets;crystal-field;substituted garnets;superposition-model;magnetic-properties;neodymium;laser;parameters;calcium;cerium;ion
杜龙
,
矫桂琼
,
黄涛
,
赵龙
,
黄峰
复合材料学报
doi:10.3321/j.issn:1000-3851.2007.06.024
通过不同Z-pin角度(15°和25°)和夹芯厚度(8mm和12.7mm)的X状Z-pin增强泡沫夹层材料的剪切性能试验,与相同材料同尺寸的未增强件进行对比,考察X状Z-pin对泡沫夹层结构的增强作用.试验结果表明,X状Z-pin增强使材料的剪切强度和刚度都有较大幅度的提高;同时,Z-pin的加入使该结构具有与传统泡沫夹层材料不同的剪切破坏形式.在此基础上,结合空间网架结构和等效夹杂方法,提出了X状Z-pin增强泡沫夹层结构剪切刚度模型,计算结果与试验值符合良好.结果表明,X状Z-pin增强不仅能大幅度提高泡沫夹层结构的剪切性能,并具有良好的可设计性,可以通过改变Z-pin角度和材料等改变其力学性能.
关键词:
夹层结构
,
Z-pin增强
,
剪切性能
Materials Science & Engineering C-Biomimetic Materials Sensors and Systems
Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.
关键词:
bamboo;bast fiber;biomimetics;engineering composites
