J.C. Wang
,
Z.M. Zhang and G.C. Yang State Key Labortory of Solidification Processing
,
Northwestern Polytecnical University
,
Xi'an 710072
,
China
金属学报(英文版)
Taking three kinds of metal-matrix composites (MMCS) (laminated composites, fibers reinforced MMCs, and particle-reinforced MMCs)as examples, the recent develop ments in modeling the damping behaviors of MMCs are extensively reviewed. The damping mechanisms of different kinds of composites are quite different, and therefore, the analytical of numerical methods for different kinds of MMCs are also quite different. This will he shown in this extensive review. Furthermore, the directions of future developments in modeling the damping behavior of MMCs are also presented.
关键词:
modeling
,
null
,
null
Intermetallics
The phase transformation of alumina formed during oxidation of beta-NiAl coating prepared on M38G alloy by pack cementation was investigated. Oxidation experiments were conducted at 950 degrees C for various times from 2 to 180 min. The phase composition and microstructure of the oxide scales were investigated by using glancing angle XRD, AFM and SEM. The results showed that at the initial oxidation stage needle-like theta-Al2O3 was formed and then it covered the sample surface rapidly. The formation of alpha-Al2O3 grains beneath the theta-Al2O3 layer was favored by depletion of Al in the beta-NiAl coating during oxidation. alpha-Al2O3 preferred growing on the top (ridge) of beta-NiAl grains, which resulted in the formation of net-like alpha-Al2O3 inner layer. With increasing time, theta-Al2O3 transformed to alpha-Al2O3 gradually. After 180 min oxidation, most of alpha-Al2O3 grains transformed into alpha-Al2O3. A mechanism of excessive voids' formation at the oxide/coating interface was also proposed in this paper. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
nickel aluminides, based on NiAl;oxidation;phase transformations;coatings, intermetallic and otherwise;high-temperature oxidation;theta-alpha-al2o3 transformation;behavior;coatings;superalloy;transition;layers
Communications in Theoretical Physics
By using the theory of pressure-induced shifts and the eigenfunctions at normal and various pressures obtained from the diagonalization of the complete d(3) energy matrix adopting C-3v symmetry, g factors of the ground state of ruby and their pressure-induced shifts have been calculated. The results are in very good agreement with the experimental data. For the precise calculation of properties of the ground state, it is necessary to take into account the effects of all the excited states by the diagonalization of the complete energy matrix.
关键词:
crystal fields;g factors;ruby;high-pressure effects
Physics Letters A
In a magnetic system, consistent with Griffiths analyticity requirements one can parameterize the equation of state near criticality by writing H = r(beta delta)h(theta), T = rt(theta) and the magnetization M = r(beta)m(theta), where T is measured from the critical temperature. For the insulating ferromagnet CrBr(3), the experimental data of Ho and Litster [J.T. Ho, J.D. Litster, Phys. Rev. Lett. 22 (1969) 6031 is well fitted by m(theta) as a linear function of theta [P. Schofield, J.D. Litster, J.T Ho, Phys. Rev. Lett. 23 (1969) 1098]. Also Ho and Litster give beta = 0.368, gamma = 1.215 and delta = 4.3. Those critical experiments are very close to the recent 31) king results of Zhang [Z.D. Zhang, Philos. Mag. 87 (2007) 5309], namely beta = 3/8, gamma = 5/4 and delta = 13/3. We therefore predict that m(theta) will be proportional to theta as a fingerprint of the 3D Ising Hamiltonian. (C) 2009 Elsevier B.V. All rights reserved.
关键词:
Critical-point effects;Critical exponents;Ising model;Criticality;Ferromagnet;Magnetic equation of state;critical exponents
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
The microstructural evolution during solidification and subsequent solid-state transformation of AISI 304 stainless steel is studied by directional solidification and quenching methods in this paper. The phase transformation sequence in the steel directionally solidified is that the precipitation of primary ferritic dendrites, ferrite-austenite eutectic reaction, and the direct formation of austenite occur in sequence during the directional solidification of the austenitic stainless steel. At the eutectic reaction stage, plenty of columnar and cellular eutectic colonies composed of the coupled growth of lamellar ferrite and austenite take place. During the course of subsequent solid-state transformation, austenite grows into ferrite gradually, resulting in the disappearing of eutectic colonies and thinning of primary ferritic dendrites, and dendrite cores of primary ferrite are retained as the final skeletal ferrite in the final microstructure. (c) 2006 Elsevier B.V. All rights reserved.
关键词:
austenitic stainless steel;directional solidification;eutectic colony;austenitic stainless-steel;cr-ni alloys;sequence;welds
刘亚男
,
王瑞霞
,
杨正坤
,
杜虹
,
姜一帆
,
申丛丛
,
梁况
,
徐安武
催化学报
doi:10.1016/S1872-2067(15)60985-8
随着科学技术的不断进步和经济的快速发展,人类对自然资源的需求量越来越大,在开发利用自然资源的同时,大量的有机污染物也随之进入自然环境.这些物质不仅污染环境、破坏生态,更对人类的生活和健康带来了巨大的威胁.研究证实,半导体光催化剂在光照条件下可以破坏有机污染物的分子结构,最终将其氧化降解成CO2、H2O或其它不会对环境产生二次污染的小分子,从而净化水质.近年来,有关光催化降解有机污染物的报道日益增多. ZnO作为一种广泛研究的光催化降解材料,因其无毒、低成本和高效等特点而具有一定的应用前景.但是ZnO较大的禁带宽度(3.24 eV)导致其只能吸收紫外光部分,而对可见光的吸收效率很小,极大地制约了其实际应用.除此之外, ZnO受光激发产生的电子-空穴分离效率较低、光催化过程中的光腐蚀严重也是制约其实际应用的重要因素.为了提高ZnO的光催化活性和稳定性,本文合成了用g-C3N4修饰的氧空位型ZnO(g-C3N4/Vo-ZnO)复合催化剂,在有效调控ZnO半导体能带结构的同时,通过负载一定量的g-C3N4以降低光生电子-空穴对的复合速率和反应过程中ZnO的光腐蚀,增强催化剂的光催化活性和稳定性.本文首先合成前驱体Zn(OH)F,然后焙烧三聚氰胺和Zn(OH)F的混合物得到g-C3N4/Vo-ZnO复合催化剂,并采用电子顺磁共振波谱(EPR)、紫外-可见光谱(UV-vis)、高分辨透射电镜(HRTEM)和傅里叶变换红外光谱(FT-IR)等表征了它们的结构及其性质. EPR结果表明,ZnO焙烧后具有一定浓度的氧空位,导致其禁带宽度由3.24 eV降至3.09 eV,因而提高了ZnO对可见光的吸收效率. UV-vis结果显示, Vo-ZnO复合g-C3N4后对可见光的吸收显著增强. HRTEM和FT-IR结果均表明, g-C3N4纳米片和Vo-ZnO颗粒之间通过共价键形成了强耦合,这对g-C3N4/Vo-ZnO复合催化剂中光生载流子的传送和光生电子-空穴对的有效分离起到重要作用.可见光催化降解甲基橙(MO)和腐殖酸(HA)的实验进一步证明, g-C3N4/Vo-ZnO复合材料具有较好的光催化活性,优于单一的g-C3N4或Vo-ZnO材料.同时还发现, g-C3N4的负载量对光催化活性有显著影响,当氮化碳的负载量为1 wt%时,所制材料具有最高的光催化活性：可见光照射60 min后,MO降解率可达到93%, HA降解率为80%.复合材料光催化活性的增强一方面是因为氧空位的形成减小了ZnO的禁带宽度,使得ZnO对可见光的吸收能力大大增强；另一方面, g-C3N4和Vo-ZnO的能带符合了Z型催化机理所需的有效能带匹配,使得光生电子-空穴对得到了有效的分离,从而提高了光催化活性.降解MO的循环实验表明, g-C3N4/Vo-ZnO催化剂具有很好的稳定性且不容易发生光腐蚀.与此同时,我们对比了用不同方法制备的g-C3N4/ZnO材料的催化性能.结果显示,本文制备的g-C3N4/Vo-ZnO复合材料具有更好的降解效率.总体而言,对于降解有机污染物, g-C3N4/Vo-ZnO可能是一个更为有效可行的催化体系.此外,本文也为设计与制备其他新型光催化剂提供了一条新的思路.
关键词:
氧空位氧化锌
,
石墨化氮化碳
,
复合光催化剂
,
光降解
,
Z型
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
Communications in Theoretical Physics
By using the wavefunctions obtained from diagonalizing the complete d(3) energy matrix at normal and various pressures, the g factor of the ground state of SrTiO3:Cr3+ and its pressure-induced shift have been microscopically calculated. Only by taking the local strains around Cr3+ in SrTiO3:Cr3+ (which are about twice the bulk ones) and corresponding P-chi dependence, can we obtain a good agreement between the calculated result of pressure-induced shift of ground-state g factor and the experimental one. The physical origins of this pressure-induced shift have been explained. It is found that the change of Dq(-1) with pressure makes main contribution to the pressure-induced shift of ground-state g factor of SrTiO3:Cr3+. By using the wavefunctions obtained from diagonalizing the complete d3 energy matrix at normal pressure, the relevant matrix elements and accordingly strain-induced splittings of t(2)(3) E-2 and t(2)(3) (4)A(2) of SrTiO3:Cr3+ have been calculated. The important results of Y-c, Z(c), P-c and Q(c) have also been evaluated. It is the admixtures of basic wavefunctions resulted from the spin-orbit interaction and/or Coulomb interaction and/or Kramers degeneracy that make the strain-induced splittings of the levels nonzero. It is found that there are nonvanishing matrix elements of operators T2 xi, T2 eta and T2 zeta between wavefunctions with positive M-s and those with negative M-s', which have important effects on the strain-induced splittings of the levels.
关键词:
crystal fields;energy spectrum;g factors;high-pressure effect;strain-induced splitting;theoretical calculations;ruby;crystal
