材料期刊网

STUDY OF THE NUCLEATION MECHANISM OF α-Al GRAINS AFTER ADDITION OF Al-Ti-B MASTER ALLOYS

X.F. Liu , X.F. Bian , X.G. Qi , M. Thompson and J.J Ma (Colledge of Materials Science and Engineering , Shandong University of Technology , Jinan 250061 , China)

金属学报(英文版)

Nucleation sites of α-Al grains after addition of an Al-Ti-B master alloy into pure aluminium have been investigated using EPMA. The results show that either TiAl3 or boride particales can nucleate α-Al grains. But the number of TiAl3 nucleants is reduced with the holding time prolonged and the boride-nuclei are increasing gradually. Based on these results, a new refining method, adding molten Al-Ti-B into commercially pure aluminium, which has a quicker and better refining efficiency is presented.

关键词: Al-Ti-B master alloy , null , null , null

原生QI成核中间相炭微球的结构

王成扬 , 姜卉 , 李鹏 , 郑嘉明

新型炭材料 doi:10.3969/j.issn.1007-8827.2000.04.003

以含有原生QI的煤沥青为原料,采用热缩聚方法制备出中间相炭微球.用扫描电子显微镜(SEM)观察了中间相炭微球的形貌和断面结构.经初步判断,在实验条件下原生QI成核煤沥青基中间相炭微球更倾向于"地球仪" 型结构.并对以QI为核形成中间相微球的过程进行了分析.

关键词: 原生喹啉不溶物 , 中间相炭微球 , 结构

煤沥青原料中QI含量对中间相有序生长的影响

黄爱华 , 金鸣林 , 李和兴 , 房永征

材料导报

试验是以2种含不同QI的煤沥青为原料,采用变径反应管进行热转化反应制备有序性中间相的研究.试验采用偏光显微镜和扫描电镜(SEM)观察了原料各反应阶段的微观结构,考察了QI对热转化过程中中间相有序生长的影响,分析了热转化过程中软化点及族组分的变化.结果表明:少量的喹啉不溶物含量不会阻碍中间相有序的发展.高QI(2.03%)原料易生成镶嵌结构的中间相体,高温处理后样品呈轴状、短纤维、层片松散的石墨化焦结构;含低QI(0.11%)的原料能生成较好的、大区域的中间相体,域结构的中间相体在外力导向和内部裂解气流的作用下容易生成有序的半焦,高温处理后呈大区域、片层紧密、有序性强的细纤维焦结构.同时研究发现,在热转化过程中可通过测定软化点(SP)和TI含量来确定中间相转化程度.软化点约低于250℃、TI为75%左右时为初始中间相区域体形成阶段、半焦生成的前期.

关键词: 煤沥青 , 热转化反应 , 喹啉不溶物 , 中间相

Explanations of the optical spectra and g factor for V3+ ions in ZnX (X = S, Se, Te) crystals

Physica B-Condensed Matter

This paper presents a cluster approach for the calculations of the absorption band positions and the g factor of d(2) tetrahedral cluster. In the approach, the different modifications of e and t(2) orbitals of d electrons and the contribution from the spin-orbit coupling of ligands to the EPR g factor due to the mixing of d(2) ions with the ligands are considered. The calculated band positions and g factor for ZnX : V3+ (X = S, Se, Te) crystals show good agreement with the observed values by using only two adjustable parameters. The contribution from the spin-orbit coupling of ligands to the g factor is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

关键词: crystal- and ligand-field theory;optical spectra;electron paramagnetic;resonance;spin-orbit coupling;V3+ ZnX (X = S, Se, Te);vanadium centers;znte crystals

INVESTIGATIONS ON THE g FACTORS AND THE SUPERHYPERFINE PARAMETERS FOR THE TETRAGONAL Pd(3+) CENTERS IN AgX (X = Cl, Br)

International Journal of Modern Physics B

The g factors and the superhyperfine parameters for the tetragonal Pd(3+) centers in AgX (X = Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a 4d(7) ion in tetragonally elongated octahedra In the calculations, the related molecular or coefficients and the unpaired spin densities of the ligands are determined quantitatively from the cluster approach in a uniform way. Both centers originate from substitutional Pd(3+) on Ag(+) site in AgX, with no charge compensator (silver vacancy) nearby. The [PdX(6)](3-) clusters suffer a relative elongation of 0.01 angstrom (or 0.06 angstrom) along [1 0 0] (or C(4)) axis for X = Cl (or Br) due to the Jahn-Teller effect The calculated g factors and the superhyperfine parameters based on the above Jahn-Teller elongations show good agreement with the experimental data.

关键词: Electron paramagnetic resonance;crystal and ligand fields;Pd(3+);AgCl;AgBr;transition-metal ions;epr spectroscopic investigations;electron-paramagnetic-resonance;atomic screening constants;laser-light;generation;color image-formation;silver bromide;superposition model;scf functions;agbr

Theoretical investigations of the g factors and the local structure for the trigonal Zr(3+) center in X-ray irradiated YSZ

Journal of Alloys and Compounds

The electron paramagnetic resonance (EPR) g factors g(parallel to) and gperpendicular to and the local structure for the trigonal Zr(3+) center in X-ray irradiated yttria-stabilized zirconia (YSZ) are theoretically investigated from the perturbation formulas of the g factors for a 4d(1) ion in trigonally distorted octahedra. Based on the studies, in this trigonal center (characterized as [ZrO(6)](9-) cluster associated with two oxygen vacancies V(o) along the [ 111] axis), the O(2-) ions in the ligand triangles are found to displace towards the neighbouring Vo by about 0.42 Angstrom due to the electrostatic attraction of the V(o). The above displacement is comparable with that (approximate to 0.36 Angstrom) obtained from neutron diffraction measurements and those (approximate to 0.24-0.37 Angstrom) based on the optical spectral analysis and crystal-field calculations in the previous works. Particularly, partial quenching of the spin-orbit (SO) coupling interaction (i.e., gamma(SO) approximate to 0.44) due to the dynamic Jahn-Teller effect (DJTE) and its influence on the g factors, which were ignored by the previous authors, are taken into account in the present 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-fields;and spin Hamiltonian;Zr(3+);yttria-stabilized zirconia (YSZ);oxide fuel-cells;paramagnetic-resonance spectra;yttria-stabilized;zirconia;spin-orbit interaction;single-crystals;electron traps;ions;epr;fabrication;impurity

Calculation of EPR parameters g factors for Ce3+ ion in YBa2Cu3O6+x superconductor

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

PVC／PP-g-MAH共混物X射线能谱微区分析

赵敏 , 姚子华 , 张荣珍 , 高俊刚

高分子材料科学与工程

用X射线能谱微区分析方法对PVC／PP-g-MA H共混物进行了研究,得到了共混物断面氯元素的面分布图,并对面分布图像进行了相分析,从 亚微观层次揭示了PVC／PP-g-MAH共混物的相结构。通过对元素面分布图的面积计算,研究 了共混组成与相容性的关系,并初步探讨了共混物力学性能与面分布的相关性。

关键词: X射线能谱 , 微区分析 , 面分布 , 相结构 , PV C/PP-g-MAH

Investigations of the g factors for the orthorhombic Co2+ center in YBa2Cu2.7Co0.3O7-x at room temperature

Physica C-Superconductivity and Its Applications

The anisotropic g factors g(x), g(y) and g(z) for the orthorhombic Co2+ center on the Cu(l) site in YBa2Cu2.7CO0.3O7-x at room temperature are theoretically investigated from the perturbation formulae of the g factors for a 3d(7) ion having low spin (S = 1/2) under octahedra with orthorhombic distortion. In these formulae, the contributions to the g factors from the orthorhombic crystal-fields as well as the ligand orbitals and spin-orbit coupling are taken into account based on the cluster approach. This center may be attributed to Co2+ located in a moderately compressed oxygen octahedron with additional orthorhombic distortion. The significant decline (characterized by the reduction factor y approximate to 0.13) of the energy separations due to the Jahn-Teller effect is suggested, by analyzing the experimental g factors. The calculated g factors based on the above contributions show good agreement with the observed values. In addition, the pronounced decrease in the intensity and the remarkable nonlinear increase in the g, of Co2+ EPR spectra as the temperature is lowered from room temperature to 150 K are also mentioned, in view of the opening of the spin gap due to antiferromagnetic interactions. (c) 2007 Elsevier B.V. All rights reserved.

关键词: electron paramagnetic resonance;crystal fields and spin hamiltonians;Co2+;YBa2Cu2.7Co0.3O7-x;atomic screening constants;d-orbital theory;paramagnetic-resonance;scf functions;spin gap;field;ions;0-less-than-or-equal-to-x-less-than-or-equal-to-0.30;yba2cu3o7-delta;la2-xsrxcuo4

Investigations on the EPR g factors for the six-coordianted Cu2+(1) site in YBa2Cu3O6+x

International Journal of Modern Physics B

The EPR g factors g(//) and g(perpendicular to) for the six-coordinated Cu2+(1) site in YBa2Cu3O6+x are theoretically investigated from the perturbation formulas for a 3d(9) ion in tetragonally elongated octahedra. The related tetragonal crystal-field parameters Ds and Dt are determined from the superposition model and the structural data for the Cu2+(1) site, by considering the effective elongation of the oxygen octahedron due to the Jahn-Teller effect of the Cu2+ cluster. Based on the calculations, the effective elongation (= 15%) of the ligand octahedron is obtained for the signals at 100K. As for the EPR signals at room temperature, the elongation declines to merely 4%, corresponding to the smaller anisotropy Delta g (=g(//) - g(perpendicular to)). The theoretical results for the g factors are in good agreement with the observed values, and the local tetragonal distortion due to the Jahn-Teller effect is discussed.

关键词: crystal fields and spin hamiltonians;electron paramagnetic resonance;Cu2+;YBa2Cu3O6+x;single-crystals;yba2cu3o7-delta;evolution;esr