QIAO Lijie LIU Rui XIAO Jimei University of Science and Technology Beijing
,
Beijing
,
China
金属学报(英文版)
The effects of stress components on nucleation sites and propagation directions of stress cor- rosion cracks in brass were investigated with specimens under mode Ⅱ and mode Ⅲ loadings. The results indicated that under mode Ⅱ loading,stress corrosion cracks nucleated on the site with maximum normal stress component and propagated along the plane perpendieular to the maximum normal stress,under mode Ⅲ loading,the stress corrosion crack was not evident on the 45°plane due to the general corrosion in aqueous solution with high NH_4OH concentra- tion,while stress corroded in aqueous solution with low NH_4OH concentration, numerous cracks with spacings of 10—150μm were found on the 45°plane with maximum normal stress and no stress corrosion cracks was observed on the plane with maximum shear stress.
关键词:
stress corrosion cracking
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null
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null
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null
Environmental Science & Technology
TiO(2) photocatalytic oxidation (PCO) of As(III) in the normal air-saturated aqueous solutions has been widely studied. Yet no consensus has been achieved on the mechanism whether superoxide is the main oxidant, although many approaches have been taken. (Photo)electrochemical method can minimize changes to TiO(2) surface and could therefore not alter the normal mechanism. In this Article, both this approach and As(III) oxidation kinetic measurements were performed to clarify the disputed mechanism. Under a sufficient cathodic bias potential, the dark oxidation of As(III) by superoxide could occur, but both the reaction rate and the columbic efficiency were rather low, suggesting that it is a weak oxidant. However, under UV light, both the reaction rate and the columbic efficiency were greatly enhanced even at potentials negative enough to eliminate photohole participation, indicating that more efficient oxidants than superoxide were produced. Under UV illumination and enough positive potential where superoxide was absent, the As(III) oxidation was the most highly efficient. The columbic efficiency of photoholes was much higher than that of superoxide. In the normal aerated aqueous solutions and at open circuit, although the total contribution of superoxide and its derivates to the PCO of As(III) was considerably high (up to 43%), it was not more than that of photohole (57%). In addition, the reported various approaches taken to elucidate the mechanism were discussed, and the resulting disputes can be clarified by these findings. It was demonstrated that (photo)electrochemical method could provide direct and undisputed evidence to reveal the truth mechanics issues.
关键词:
nanocrystalline titanium-dioxide;mechanism involving superoxides;alternative electron-acceptors;hydrogen-peroxide;film electrodes;as(iii);adsorption;photooxidation;recombination;arsenic(iii)
Condensed Matter Physics
The (63)Cu Knight shifts and g factors for the normal state of YBa(2)Cu(3)O(7) in tetragonal phase are theoretically studied in a uniform way from the high (fourth-) order perturbation formulas of these parameters for a 3d(9) ion under tetragonally elongated octahedra. The calculations are quantitatively correlated with the local structure of the Cu(2+) (2) site in YBa(2)Cu(3)O(7). The theoretical results show good agreement with the observed values, and the improvements are achieved by adopting fewer adjustable parameters as compared to the previous works. It is found that the significant anisotropy of the Knight shifts is mainly attributed to the anisotropy of the g factors due to the orbital interactions.
关键词:
electron paramagnetic resonance;nuclear magnetic resonance;Knight;Shift;(63)CU;YBa(2)Cu(3)O(7)
Journal of Materials Chemistry
We have investigated the electronic structure and chemical bonding properties of Ti3GeC2 by performing ab initio pseudopotential total-energy calculations. Our results show that the crystal structure of Ti3GeC2 is a characteristic zigzag chain of Ti-C-Ti-C-Ti-Ge, running parallel to the c-axis. The chemical bonding in Ti3GeC2 is anisotropic and metallic-covalent-ionic in nature with significant contributions from metallic and covalent bonds, which result in the combination of metallic and ceramic properties in Ti3GeC2.
关键词:
ti3sic2;pseudopotentials;ceramics
Acta Materialia
By use of the linear-combination-of-atomic-orbital (LCAO) method for a cluster model, we study the alloying effect on chemical bonding in TiH2 systems. In order to verify that the cluster model is suitable for describing the crystal behavior. the electronic structures in pure dihydrides. such as ScH2, TiH2, VH2, YH2, ZrH2 and NbH2 are calculated. Good agreement of the variant trend of the metal-hydrogen interaction with that of the enthalpy of formation for each pure dihydride is found, and the ionic and covalent contributions to the metal-hydrogen interaction are evaluated quantitatively as a reference for judging their contributions in the alloyed TiH2. The alloying effect on the ionic interaction of alloyed TiH2 is somewhat weaker than that on the covalent interaction. It is found that hydrogen makes a stronger covalent bond with the weaker hydride forming elements and hydride non-forming elements rather than the stronger hydride forming elements if there exist Ti atoms in the neighborhood in the alloyed TiH2. This trend can be understood by the orbital bonding analysis. The energy interval and orbital overlap contributions to the interaction between metal and hydrogen atoms are discussed qualitatively. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
关键词:
bonding;ab initio calculation;hydrides;electronic structure;electronic-structure;intermetallic hydride;hydrogen storage;binding-energy;band-structure;zirconium;dihydrides;clusters;niobium;systems
SUN Wenqiang
,
CAI Jiuju
,
MAO Hujun
,
GUAN Duojiao
钢铁研究学报(英文版)
As the largest energy consuming manufacturing sector and one of the most important sources of carbon dioxide (CO2) emissions, the China′s iron and steel industry has paid attention to the study of changing trend and influencing factors of CO2 emissions from energy use. The logarithmic mean Divisia index (LMDI) technique is used to decompose total change in CO2 emissions into four factors: emission factor effect, energy structure effect, energy consumption effect, and steel production effect. The results show that the steel production effect is the major factor which is responsible for the rise in CO2 emissions; whereas the energy consumption effect contributes most to the reduction in CO2 emissions. And the emission factor effect makes a weak negative contribution to the increase of CO2 emissions. To find out the detailed relationship between change in energy consumption or steel production and change in CO2 emissions, the correlation equations are also proposed.
关键词:
CO2 emissions
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energy use
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LMDI technique
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steel production
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energy consumption
American Mineralogist
A natural high-pressure phase of titanium oxide with alpha-PbO2-structure has been found in omphacite from coesite-bearing eclogite at Shima in the Dabie Mountains, China. High-resolution transmission electron microscope observations have revealed an orthorhombic lattice, corresponding to alpha-PbO2-type TiO2, with cell parameters a = 0.461 nm, b = 0.540 nm, c = 0.497 nm and space group Pbcn. It occurs as nanometer-thick (< 2 nm) lamellae between multiple twinned rutile crystals, providing additional evidence of very high-pressure, metamorphism at 7 GPa, 900 degrees C. This implies subduction of continental material to a depth of more than 200 kilometers. alpha-PbO-type TiO2 could be an extremely useful index mineral for ultrahigh-pressure.
关键词:
high-pressure phase;ries crater;rutile;polymorph;titanium
Applied Physics Letters
The magnetocaloric effect (MCE) at the antiferromagnetic (AF) to ferromagnetic (F) phase transition in Mn1.05Ni0.85Ge and CrO1.86F0.14, and the MCE at the F-AF transition in Tb3Co have been investigated. Mn1.05Ni0.85Ge and CrO1.86F0.14 are found to exhibit the inverse MCE whereas the MCE of Tb3Co is normal. For these compounds, the dependence of the transition temperature on the applied magnetic field B has been studied. A thermodynamical analysis is presented of the sign of the magnetic-entropy change in these three compounds which are representatives of two different types of B-T diagrams. Other possible B-T diagrams are discussed and the analysis is extended to AF-F and F-AF phase transitions reported in literature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729122]
关键词:
Y.T. Liu
,
X.J. Guan
,
X.M. Shen
,
X.F. Ma
,
L.J.Wang
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null
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null
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null
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null
金属学报(英文版)
The microstructures and their kinetics of normal
grain growth are simulated using different Monte Carlo (MC)
algorithms. Compared with the relative figures and the theoretical
normal grain growth exponents of n=0.5, the effects of some
factors of MC algorithm, i.e. the lattice types, the methods of
selecting lattice sites, and the neighbors selection for energy
calculations, on the simulation results of grain growth are studied.
Two methods of regression were compared, and the three-parameter
nonlinear regression is much more suitable for fitting the grain
growth kinetics. A better model with appropriate factors included
triangular lattice, the attempted site randomly selected, and the
first and second nearest neighbors for energy calculations is
obtained.
关键词:
Grain growth
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null
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null
