材料期刊网

Numerical Simulation of Columnar to Equiaxed Transition for Directionally Solidified Ti-44Al Alloy

H.F. Wang , J.J. Guo , G.F. Mi , null , null , null , null , null , null , null , null

金属学报(英文版)

Solute diffusion controlled solidification model was applied to simulate the columnar to equiaxed transition (CET) during directional solidification of of TiAl alloys. The simulation results showed that the solutal interactions from growing equiaxed grains play an important role on CET, which can render a large fraction of seeds inactive. The effects of the applied temperature gradient and pulling speed, the equiaxed seed spacing and nucleation undercooling on the CET are investigated in present simulation. It indicated that the columnar branch spacing depends not only on the temperature gradient and the pulling speed, but also number of the seeds, a spacing adjustment can occur through initiation of seeds that develop into new columnar grains. The dependence of the CET on the temperature gradient and pulling speed, qualitatively agrees with the analytical CET model of Hunt.

关键词: TiAl alloys , null , null

Studies of the g factors for the tetragonally elongated and compressed CuIIN6 octahedra in image omitted (MI = K, Rb, Cs; MII = Ca, Sr, Ba, Pb) crystals

Philosophical Magazine

The EPR g factors, g// and g perpendicular to, of tetragonally elongated and compressed CuIIN6 octahedral clusters (with the ground states |dx2 - y2 > and |dz2 >, respectively) in [image omitted] (MI = K, Rb, Cs; MII = Ca, Sr, Ba, Pb) crystals were calculated using a two-mechanism model. In the model, the contributions to the g-shifts, gi (= gi - gs, where i = // or perpendicular to; gs approximate to 2.0023 is the free-ion g value), from both the crystal-field (CF) mechanism related to CF excited states and the charge-transfer (CT) mechanism related to CT excited states, which is neglected in the widely-used CF theory, were considered. For the CF mechanism, two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), were applied. The CF parameters used were calculated from the superposition model, in which the structural data for CuIIN6 clusters in [image omitted] crystals were measured exactly by X-ray diffraction. The calculated g factors for both the tetragonally elongated and compressed CuIIN6 octahedra are in reasonable agreement with the experimental values. For the strongly covalent CuIIN6 clusters in crystals with different ground states, both the PTM and CDM can be applied to calculate the g-shifts, [image omitted], arising from the CF mechanism, but exact and reasonable calculations of g factors should take both CF and CT mechanisms into account.

关键词: crystal field;electron paramagnetic resonance;octahedral cluster;charge transfer;spin-hamiltonian parameters;atomic screening constants;jahn-teller;distortion;temperature-dependence;lead hexanitrocuprate(ii);2-mechanism model;scf functions;br crystals;complexes;bands

G(f)/HA-CS复合材料的制备及性能研究

沈基显 , 黄剑锋 , 曹丽云 , 曾燮榕 , 熊信柏

稀有金属材料与工程

以羟基磷灰石-壳聚糖(HA-CS)为基体,玻璃纤维G(f)为增强相,采用原位杂化法制备短玻璃纤维增强HA-CS基生物复合材料.研究交联剂、羟基磷灰石含量和玻璃纤维含量对复合材料性能的影响.采用红外吸收光谱、扫描电子显微镜和万能材料试验机对材料的结构和性能进行表征.结果表明:原位杂化法能制备性能较好的复合材料;用戊二醛交联改性复合材料可以明显增加其韧性和弯曲强度,使复合材料抗弯曲强度提高16%;当CS/HA=10/1(质量比)和玻璃纤维含量为1.5%时复合材料抗折强度达到极大值84.47 MPa;随玻璃纤维含量的增加,复合材料的断裂面由平整向多层断裂变化,材料的韧性有所提高.

关键词: G(f)/HA-CS复合材料 , 玻璃纤维 , 交联剂 , 弯曲强度

Theoretical studies of g factors and defect structures for cubic, tetragonal, and orthorhombic Fe+ Centers in alkali halides MX (M = Li, Na; X = F, Cl)

Communications in Theoretical Physics

The EPR g factors for cubic, tetragonal and orthorhombic Fe+ centers in alkali halides MX (M = Li, Na; X = F, Cl) are calculated from second-order perturbation formulas of g factors based on cluster approach for 3d(7) ions in three symmetries. From calculations, the g factors of these Fe+ centers in MX crystals are reasonably explained and the defect structural data for the tetragonal and orthorhombic Fe+ centers are estimated. The results are discussed.

关键词: crystal;and ligand-field theory;electron paramagnetic resonance;defect structure;atomic screening constants;spin-orbit interaction;superposition model;resonance-spectra;epr parameters;crystal-field;scf functions;ions;co2+

Investigations of EPR g Factors and Rhombic Distortion for the Rhombic Cu2+ Centers in K2Zn1-x Cu (x) F-4 Crystals at Low Temperature

Applied Magnetic Resonance

The electron paramagnetic resonance g factors g (i) (i = x, y, z) of two rhombic Cu2+ centers, Cu2+(II) and Cu2+(III), in K2Zn1-x Cu (x) F-4 crystals found at low temperature are calculated from the complete diagonalization (of energy matrix) method based on the cluster approach. The calculations show that the ground state wave function of the two rhombically compressed Cu2+ centers is with a small admixture of . The rhombic distortions for both Cu2+ centers are obtained from the calculations. The results are discussed.

关键词: electron-paramagnetic-resonance;atomic screening constants;hyperfine;parameters;gyromagnetic factor;spin resonance;scf functions;field;copper(ii);dependence;spectra

Cu对MI(NiAlMnCoCu)5.1贮氢合金电化学性能的影响

林玉芳 , 李蓉 , 张羊换 , 陈梅艳 , 王新林

功能材料

研究了Cu含量对MINi3.9-xCoo.4 Al0.2 Mno.6Cux贮氢合金的电化学性能的影响.实验发现:随着Cu含量x从0增加至0.3,合金的活化性能仍保持在2～3次;但合金的最大放电容量从344mAh/g下降到310mAh/g;高倍率放电性能均在81%以上;合金的循环寿命随着Cu含量的增加而有所提高的.实验表明,合金中加入适量的Cu,可有效的改善舍金的循环寿命.

关键词: 贮氢合金 , Cu含量 , 电化学性能

金属有机骨架材料MI L-53对氯代甲烷的吸附?

王铭扬 , 田凤鸣 , 周林 , 张兴华 , 陈云琳

功能材料 doi:10.3969/j.issn.1001-9731.2016.05.011

采用水热法合成了金属-有机骨架材料 MIL-53(Al,Fe,Cr),并用 X射线衍射(XRD)、氮气吸/脱附等进行了测试表征.利用固定床吸附试验装置和气相色谱测定了在298 K,101 kPa 时,MIL-53(Al,Fe,Cr)对二氯甲烷、三氯甲烷的吸附情况.结果表明,二氯甲烷比三氯甲烷更易被MIL-53(Al,Fe,Cr)吸附,且 MIL-53(Al)对氯代甲烷的吸附能力最强,MIL-53(Cr)次之,MIL-53(Fe)最弱,MIL-53(Al)对二氯甲烷和三氯甲烷的吸附量最高分别可达16．88和7．11 mmol/g.实验结果与巨正则系综蒙特卡洛(GCMC)模拟结果一致.

关键词: 金属有机骨架 , MIL-5 3 , 吸附 , 氯代 , 挥发性有机物(VOCs)

Investigations of the EPR g factors for Er3+ in CaMoO4

Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences

The electron paramagnetic resonance (EPR) g factors g(parallel to) and g(perpendicular to) for Er3+ in CaMoO4 are theo retically investigated by using the perturbation formulas of the g factors for a 4f(11) ion in tetragonal symmetry. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various states are considered. The crystal-field parameters for the tetragonally distorted tetrahedra are determined by using the superposition model and the structural data of the impurity Er3+ on the host Ca2+ site in CaMoO4. The calculated g factors agree with the. observed values. The validity of the results is discussed.

关键词: electron paramagnetic resonance (EPR);crystal- and spin Hamiltonians;Er3+;CaMoO4;electron-paramagnetic-resonance;superposition-model;molybdate;crystals;calcium molybdate;ion;spectroscopy;parameters;tungstate;liyf4

A Novel Topological Index F* and Its Correlation With Standard Formaton Enthalpies of ABn(g) Molecules

武汉理工大学学报-材料科学版(英文版)

关键词:

ANISOTROPY OF THE G-FACTOR FOR NI2+ AND NI3+ IONS IN THE TETRAGONAL PHASE OF SRTIO3

Physica B-Condensed Matter

In this paper, a simple and uniform expression for calculating the anisotropy of the g factor (characterized by DELTAg = g(perpendicular-to) - g(parallel-to)) for 3d(n) ions in the tetragonal phase of the perovskite structure from the spin-lattice coupling coefficients F11 and F12 in the cubic phase has been proposed by introducing a release factor k. From this expression, the values of DELTAg for Ni2+(3d8) and Ni3+ (3d7) ions in the tetragonal phase of a SrTiO3 Crystal are studied. It is found that for SrTiO3:Ni2+, the observed isotropy of the g factor (DELTAg = 0) is due to the too small value of (F11 - F12) and for SrTiO3: Ni3+, the contribution to DELTAg from the elongation of the octahedron around the Ni3+ ion is important in the case of T near the transition temperature T(c).

关键词: lattice coupling-coefficients;cubic symmetry;fij