Y.T. Liu
,
X.J. Guan
,
X.M. Shen
,
X.F. Ma
,
L.J.Wang
,
null
,
null
,
null
,
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
,
null
,
null
Materials Letters
beta-quartz, stable at room temperature and under normal pressure, is obtained by high-pressure quenching, using an all-silicon ZSM-5 zeolite as the reaction precursor and characterized by means of X-ray diffraction.
关键词:
Science and Engineering of Composite Materials
The impact toughness of normal bamboo, reformed bamboo and reformed bamboo reinforced composites was studied comparatively by using a computerized Automatic Impact Testing System. It is found that the impact toughness of normal bamboo is dependent on the direction of the impact load. If the impact load is applied in the radial direction of the bamboo culm, the specimen impacted on the pith-ring has a much higher impact toughness than those impacted on the rind side. The impact toughness of reformed bamboo is somewhat lower than that of normal bamboo when most static mechanical properties are increased. The experimental results reveal that one of the technical parameters of reformed bamboo, the compressive ratio, is closely related to its impact toughness. However, the composition of reformed bamboo with glass fabric and aluminum sheets can improve the impact properties of reformed bamboo composites to a satisfactory extent while maintaining the superiority of their static mechanical properties.
关键词:
reformed bamboo;impact toughness;dynamic fracture
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:
Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms
Evolutions of angular distributions and surface composition profiles of a sputtered Pt0.5Cu0.5 alloy were simulated under 1 keV Ar ion bombardment at normal incidence, with the help of a dynamic Monte Carlo program including preferential sputtering and BIGS (bombardment-induced Gibbsian segregation) processes etc. It is found during the PtCu alloy sputtering that the Cu enrichment in the near-normal direction is regularly transformed into the Pt one as the Ar ion fluence increases. Below a low fluence of about 1.7 ions/cm2, Cu is preferentially ejected in the near-normal direction; above 1.7 ions/cm2, on the other hand, Pt is preferentially ejected in the near-normal direction instead of Cu. Effects of preferential sputtering and BIGS processes on enrichment transformation between Cu and Pt elements in the near-normal direction are also discussed.
关键词:
bombardment-induced segregation;monte-carlo simulation;surface;segregation;cu;implantation;depth
Jun ZHANG
,
Qian LIU
,
Lin WANG
材料科学技术（英文）
Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative information available on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the present paper, the effect of coarse aggregate size (single grade of 5～10, 10～16, 16～20 and 20～25 mm) on stress-crack opening (σ-ω) relation in normal and high strength concretes (compressive strength of 40 and 80 MPa, respectively) was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. The result shows that coarse aggregate size and cement matrix strength significantly influence the shape ofσ-ω curve. For a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensile strength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-ωcurve. By contrast, in high strength concrete, the effect of aggregate size on σ-ω relation almost vanishes. A similar σ-ω relation is obtained for the concrete except for the case of 20～25 mm coarse aggregate size. The stress drop after the peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, the smaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increase with increasing coarse aggregate size in both normal and high strength concretes.
关键词:
Aggregate size
,
null
,
null
,
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)
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
,
null
,
null
,
null
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)
