Defects and Diffusion in Metals, 2009

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Authors: Zheng Chen Qiu, Can Fang Xia, Li Qun Chen
Abstract: By the use of the first-principles method, based upon density functional theory, we investigated the effect of C upon the electronic structure of a kink on the ½[111](1¯10) edge dislocation in bcc iron. The results show that C has a tendency to segregate towards the kink. The structural energies of some atoms of interest in the kink with C are lower than those of corresponding atoms in the clean kink. Furthermore, the interactions between C and the neighboring Fe atoms are very strong due to the hybridization between the C 2p state and the Fe 3d4s4p states. We find that there exists some charge accumulations between C and the neighboring Fe atoms. The analysis of the electronic structure indicates that the introduction of C can stabilize the kink system and impede the sideways motion of the kink. The C induces a strong pinning effect on the ½[111](1¯10) edge dislocation and may result in solid solute hardening.
Authors: Amitava Ghorai
Abstract: Graphs of monovacancy formation energy ( ) versus the parameter, , of Ashcroft's empty-core model potential (AECMP) and nine different exchange and correlation functions (ECF) are shown for two different group-IIa divalent fcc metals (Ca and Sr) and seven group-VIII divalent fcc metals in an active valence state (γ-Fe, β-Co, Rh, Ir, Ni, Pd and Pt). The criterion used is that is greater than the Bohr radius. There is a systematic increase and decrease in the fitted value of , and the calculated value of , respectively, in going from one ECF to other, as follows: Sham
Authors: Emad A. Badawi, M.A. Abdel-Rahman, E.M. Hassen, M. Abdel-Rahman, M.O. Abdel-Hamed
Abstract: A description of positron annihilation spectroscopy (PAS) in solids is given in terms of a trapping model. Data are presented for a commercial AA1050 dilute alloy ingot, and fitted to a model allowing presentation in the form of Arrhenius plots. From whence the value of the activation enthalpy, , for thermal vacancies obtained by PAS for AlFeSi is found to be 0.860.18eV.
Authors: B.B. Jha, Barada Kanta Mishra, S.N. Ojha
Abstract: Frequency spectrum analysis of acoustic emission (AE) signal has been carried out during breakaway oxidation and internal cracking of oxide scales formed on 2.25Cr-1Mo steel. Three regions viz pre-breakaway, post-breakaway and internal cracking of scales have been distinguished based upon thermogravimetric analysis and SEM/EPMA observations. The frequency pattern of the AE signal obtained in three different regions shows three different characteristic features. Frequency spectra based upon the predominant frequencies have been correlated with the physical phenomena occurring during the course of oxidation.
Authors: Abhijeet Moon, R. Balasubramaniam
Abstract: Hydrogen diffusivity was estimated in three different eutectoid rail steels (C-Mn, Cu-Mo and Ni-Cu-Cr) at ambient temperatures using the technique of sub-surface microhardness profiling after cathodic hydrogen charging in 0.5mol/l sulphuric acid at a current density of 0.1A/cm2 for 24 hours. The increase in the concentration of hydrogen at a certain depth below the surface was related to the microhardness increase at this location as compared to the bulk value. The procedure used to obtain the diffusion coefficient of hydrogen from the microhardness profiles is discussed. The hydrogen diffusivity values in all of the rail steels were found to be similar (of the order of 10-13m2/sec). The estimated hydrogen diffusivity in the rail steel was lower than in pure iron (10-8m2/sec). Possible reasons for the difference are discussed.
Authors: A.N. Jannah, S.A. Halim, Abdullah Huda
Abstract: Here, Bi(Pb)-Sr-Ca-Cu-O thin films having superconducting properties have been fabricated using Nd-YAG pulsed laser ablation onto single-crystal MgO(100) substrates. The as-deposited film was found to be in an amorphous state. The crystalline structure appeared after the film was annealed in an oxygen environment. The XRD spectrum revealed epitaxial growth of BSCCO (2212) phase at annealing temperatures of 850°C, 860°C and 870°C. In the amorphous state, the microstructure of the films exhibited spherical clusters of various sizes. Upon annealing, plate-like and needle-like structures were observed. These structures fused into grains with a plate-like shape when the annealing temperature reached 870°C. This could be due to the diffusion and arrangement of the components that make up the 2212 phase at elevated temperature in an oxygen environment. The superconducting transition temperature, Tc, is highest for samples annealed at 870°C. The post-annealing procedures were carried out in the ablation chamber in order to minimize contamination.
Authors: Abdullah Huda, M.N. Norazia, S. Shaari, A.Amir Khadum
Abstract: The sol-gel method was used to obtain ZnO films doped with Sn at different annealing temperatures, 400°C, 500°C and 600°C. As a starting material, zinc acetate dehydrate was used, with 2-methoxyethanol and monoethanolamine as the solvent and stabilizer, respectively. The dopant source was tin chloride. The amounts of dopant in solution were Zn1-xSnxO: x = 0 and 5at.%. The proportion of dopant and Zn atoms are not the same in the film and in the solution. In other cases, the dopant proportion in the film is less than that in the solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV-VIS spectroscopy and Raman spectroscopy were used to study the structural, surface morphological and optical properties of the films and the molecular bonding of the ZnO, respectively. It was concluded that the dopant amount, as well as the annealing temperature, modifies the film growth process and consequently the microstructure and surface morphology as well as the optical properties.
Authors: Abdullah Huda, Ari Sulistyo Rini, Mohd. Zulfa Ya, Mohd Ambar Yarmo
Abstract: Titanium dioxide has been successfully synthesized via an evaporation-induced self-assembly method. Here, TiCl4 was chosen as a precursor and CTAB as a surfactant. The SEM images revealed that hydrochloric acid, added during reaction, obviously enlarges the particle size of TiO2 since a larger size was obtained. The X-ray diffraction (XRD) results confirmed the appearance of both the anatase and rutile structures of TiO2 after titania film was calcined at 450°C for 1 hour. The TEM results showed that the evaporation temperature had no significant impact upon the particle size of TiO2.
Authors: Abdullah Huda, P.A. Nugroho
Abstract: Porous nanoflake ZnO has been successfully synthesized via a pyrolitic process of chemical bath deposition (CBD). The latter produced nanoflakes of Zn5(CO3)2(OH)6 as an intermediate product, which transformed to ZnO at 300°C. The microstructure has been investigated by surface morphology observation using a scanning electron microscope (SEM) and crystal-structure analysis using X-ray diffraction (XRD). A random structure of 40nm-thick flakes, grown perpendicularly on the substrate, has been obtained.
Authors: Yue Xia Hu, Shao Yi Wu, Xue Feng Wang, Li Li Li
Abstract: The spin Hamiltonian parameters (anisotropic g-factors and the hyperfine structure constants) and defect structure for Pt3+ in MgO are theoretically investigated by using the perturbation formulas of these parameters for a 5d7 ion in a tetragonally elongated octahedron. This impurity center is attributed to substitutional Pt3+ on host Mg2+ sites, and the [PtO6]9 cluster suffers a relative elongation of 0.08Å along the C4 axis due to the Jahn-Teller effect. In the calculations, the contributions arising from the ligand orbital and spin-orbit coupling interactions and the Jahn-Teller elongation are taken into account using the cluster approach. The calculated spin Hamiltonian parameters based upon the above defect structure show good agreement with the observed values.

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