Defect and Diffusion Forum Vols. 312-315

Abstract: The solid polymer electrolyte films consisting of polyacrylonitrile (PAN) as the host polymer, lithium triflate (LiCF3SO3) and sodium triflate (NaCF3SO3) as dopant salts were prepared by the solution cast technique. The pure PAN film was prepared as a reference. The films were characterized using a.c. impedance spectroscopy. At room temperature, the highest conductivity for the sample from the (PAN+LiCF3SO3) system and the (PAN+NaCF3SO3) system is 3.04 x 10-4 Scm-1 and 7.13 x 10-4 Scm-1, respectively. The temperature dependence of ionic conductivity for the highest conducting film from both systems follows the Arrhenius equation in the temperature range of 303 K to 353 K. The frequency dependence of ionic conductivity, , complex permittivity, *, and complex electrical modulus, M* were studied at different temperatures. The ionic conductivity and the dielectric behavior are described in terms of ion diffusion and polarization.

Abstract: In this paper, the transport properties of Hg0.8Cd0.2Te have been investigated at 77 K using the hydrodynamic model. We remarked that ionized impurity scattering mechanism plays a dominant role in this material at low electric field. The drift velocity, mean energy and drift mobility are determined as functions of the electric field strength. Comparison is made with Monte Carlo calculations and experimental results. The obtained velocity-field curve is in good agreement with reported experimental data.

Abstract: The modified Redlich-Kister approximation of the composition dependent intrinsic diffusivities in the multicomponent solid solution is presented. The effective computation method (the inverse problem) combines the Hierarchical Genetic Strategy with real number encoding (HGS-FP) with the modified Redlich-Kister approximation. The Cu–Ni–Fe alloys at 1271 K are analyzed. We show that the measured intrinsic diffusivities, the estimated from available diffusivity data and calculated by inverse method are in agreement. The presented method may become a very effective tool when the diffusion multiple technique is considered.

Abstract: In situ monitoring of surface processes and understanding of growth processes are important in achieving precise control of crystal growth. Therefore, many surface monitoring techniques are used during crystal growth by molecular beam epitaxy (MBE). The most popular is reflection high-energy electron diffraction (RHEED) and photoemission current which provides information on the morphology during the growing surface. The photoemission oscillation technique has been successfully used in situ to monitor the growth of materials and to control the thickness as well as the roughness of the deposited layer. In this paper, we report results of atomic scale simulations used to study the dynamics of homoepitaxial growth of GaAs(001) β2(2x4) reconstructed surface and, in particular, the RHEED oscillations of the photoemission current.

Abstract: Recently, several metal oxide nanomaterials have been deposited on the surface of electrodes and investigated for the reduction/ oxidation and detection of some biological materials. Electrochemical Sensors with high surface area and porosity are important components in an irresistible wealth of systems for various applications. An electrochemical sensor for the sensitive determination of parabromophenol (PBP) was synthesized based on the nano-SiO2 film-modified electrode. Owing to the exceptional properties of nano-SiO2 such as successfully minimized transport limitations, huge surface area, strong adsorptive ability, subtle electronic properties and catalytic ability, the electrochemical oxidation signal of PBP significantly increases at the nano- SiO2/GC electrochemical sensor, suggesting that nano-SiO2 film exhibits obvious enhancement effect to the determination of PBP. Based on this, a sensitive electrochemical method was developed for the determination of PBP.

Abstract: In this investigation, we focus on the glass formation and crystallization process of Ag, Au pure metals as well as Ag-20%Au, Ag-50%Au, and Ag-80%Au (Atoms%) random alloys at the nanoscale. The thermodynamic properties such as solidification temperature and cohesive energy were calculated in the NVT ensemble by the molecular dynamics (MD) simulation technique. The Quantum Sutton-Chen (Q-SC) potential was used to study phase transition and thermal properties of nanoparticles. The temperature dependence of energy was calculated at various concentration of Au. Moreover, the solidification of pure nanoparticles, Ag, Au, and Ag-x%Au nanoalloys were studied at different cooling rates. Our molecular dynamics simulation results show glass structure at fast cooling rates while crystallization at a slow cooling rate. Moreover, the obtained results show that the solidification temperature decreases with decreasing nanoparticle size.

Abstract: Amorphous alloys Ni64Zr36 and Ni36Zr64 structure and hydrogen mobility are researched by the molecular dynamics method. The analysis of structure factors and partial distribution functions of atoms revealed hydrogen affects the short order parameters of the disordered systems. Diffusion coefficients of hydrogen are shown to depend on its concentration.

Abstract: Wax deposition continues to be a relevant problem for petroleum production and transportation pipelines. This viscous and waxy flow is theoretically modelled with a simple conservation equation system, by expressing the wax layer thickness as function of time and duct length. The flow parameters are written, depending on these independent variables but also on the Reynolds and the Peclet numbers, where effect of latent heat on the wax layer thickness deposit is investigated. A numerical simulation of the flow, for two practical cases, is performed in order to predict the pipeline obstruction.

Abstract: TiO2 nanoparticles were synthesized from a triethylene glycol solution of titanium isopropoxide (Ti(O-iPr)4) by refluxing at 270°C for 12 hrs. The as-prepared sample was heated at 600 °C for 3 hrs in order to study the thermal stability of the sample. The X-ray diffraction patterns of the samples were well indexed to the anatase phase. The field emission TEM images show uniform spherical morphologies with average sizes of 25 nm. The electrochemical measurements revealed that the discharge capacities of the heated sample exhibited high capacities and good rate performances without capacity fading during extended cycles, due to their electrochemically beneficial highly crystalline structures, nano-sized particles, and uniform distribution.

Abstract: ECAP (Equal Channel Angular Pressing) is one of the useful methods of Severe Plastic Deformation (SPD) to reach ultrafine grain size. ECAP was carried out on Al-Fe-Si alloy. All grains stretched along the ECAP direction. Samples were ECAPed for one pass into an ECAP mold with two equal channels (1 cm × 1 cm) with 90o between them. After ECAP, specimens were heat treated (semisolided) for different times and temperatures for achieving globular grains. Optical microscopy has been used to evaluate the microstructure. By ECAP and semisolid processes, the structure becomes fine and globular. The kinetic grain growth has been studied for this alloy by the calculation of the D = Ktn equation and log(D)-log(t) curves.