Defect and Diffusion Forum Vols. 312-315

Abstract: Mg-based alloys are prospective materials for reversible hydrogen storage in the form of metallic hydrides. Usually, hydrogen saturation is carried out at high temperatures and high hydrogen pressures. This is the reason for the high cost of metallic hydrides in comparison with other hydrogen storage methods. Electrochemical hydriding, on the other hand, can be realized at room temperature. Moreover, this process does not need any hydrogen atmosphere. In the presented work, electrochemical hydriding of several Mg-Ni-Mm-based alloys (Mm = mishmetal) is performed. Hydriding efficiency, mechanism and kinetics are described. It is shown that the additions of Ni, Mm and the formation of eutectic structures support hydriding of alloys.

Abstract: Diffusion bonding of sialon and 7.5%-Cr Ferritic Steel (FS) in as-received and nitrided condition was studied. Decomposition of sialon and interdiffusion of elements between the sialon and the steel were observed. The interdiffusion of elements produced reaction layers at the joint. The steel moved into the decomposition part of the sialon and replaced the decomposed sialon in this part. Diffusion of silicon into the steel resulted in the silicon-diffusion layer. FeSi2 was formed in the reaction layer when Si in the decomposition part of the sialon reacted with Fe. The use of nitrided steel in the diffusion bonding had suppressed the formation of the FeSi2 in the layer.

Abstract: In this study, nanostructured composite coatings of hydroxyapatite (HA)/ 30wt% yttria stabilized zirconia (YSZ) coatings containing 0, 3, 5, and 8 mol% Y2O3 (namely; HA-0YSZ, HA-3YSZ, HA-5YSZ, and HA-8YSZ) were successfully synthesized using the sol-gel method. The crystallite size of the coating was about ~44-58 nm for tetragonal and cubic zirconia grain size and 75-87 nm for hydroxyapatite grain size. Crack-free and homogeneous HA-YSZ composite coatings were obtained with no observable defects. The uniform distribution of zirconia particles in a composite would be highly beneficial for obtaining homogeneous coatings of HA-YSZ film and would hinder grain growth of HA phase during calcinations. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than pure HA coatings.

Abstract: The effects of synthesis temperature on the quality and quantity of vertically aligned carbon nanotubes (VACNT) were studied using high resolution scanning electron microscopy, and micro-Raman spectroscopy. The VACNT was synthesized by Fe catalytic decomposition of palm oil deposited on silicon substrate by thermal chemical vapour deposition method. The analysis shows that the growth rate increases from 3.8 to 5.5 µm/min as the temperature was increased from 750 to 800°C. The nanotube diameters were observed bigger at low temperature range. Smaller and uniform diameter (~15 nm) was found at 750°C and the increment in diameter size was seen at higher temperature range. Smaller graphite Raman “G” peak width, low ID/IG ratio (~0.52) indicated higher crystallinity of the nanotube and moderate I2D1/ I2D2 ratio for second order Raman peak was also detected at synthesis temperature of 750°C. These results indicated that the optimum synthesis temperature for higher quality VACNT production was at 750°C.

Abstract: Carbon nanotubes (CNTs) were fabricated from palm oil using the thermal chemical vapor deposition technique utilizing a two furnace system. The effect of precursor vaporization temperature of the first furnace, in the range of 300-600°C was systematically studied with the synthesis temperature (second furnace) fixed at 750°C for a total time of 30 min. The samples were characterized using field emission scanning electron microscopy and micro-Raman spectroscopy. CNTs of various packing densities and diameters were synthesized with the varying precursor vaporization temperature. Based on micro-Raman measurements nanotube defect level and the presence of SWCNT were dependent on the vaporization temperature. Vertically aligned CNTs (VACNTs) were found to grow within the vaporization temperature range of 400-500°C, with well graphitized and higher yield obtained at 450°C with excellent lateral alignment, uniform nanotubes diameter (~15 nm), orientation and distribution within the CNT bundles. At vaporization temperatures of 300-350°C and 500-600°C, lower growth rate, bigger nanotubes diameter and higher ID/IG ratio were observed which indicated lower nanotubes quality that produced at both temperature ranges.

Abstract: Optical techniques have a long tradition in flow visualization, allowing both qualitative and quantitative analysis. In particular, speckle photography, introduced in 1968, has been extensively used. The aim of this work is to discuss speckle-based deflection techniques in the investigation of diffusion phenomena in liquids.

Abstract: To understand the role of annealing conditions on the segregation and selective oxidation phenomena, Fe 2Mn 2Si 0.8Cr (all in wt.%) model alloy was investigated. The samples were annealed at 820°C in N2-5%H2 forming gas atmospheres over a wide range of dew pints (-80 to 0°C) with dwelling time of 1 to 5 minutes. At all dew points, the strong chemical interaction between Mn and Si causes the formation of manganese silicates. External oxidation of Mn, Si and Cr were decreased at the higher dew points. Increasing the dwelling time shows an extended oxidation front i.e. pronounced external/internal oxidation of Mn, Si and Cr. Basically, the present work addresses the two stages of oxidation front.

Abstract: A three dimensional conductive field is analyzed and solved by means of the COMSOL Multiphysics code. The investigated work-pieces are made up of a simple brick-type solid. A laser source with combined donut-Gaussian distributions is considered moving with a constant velocity along motion direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while finite width (2ly) and thickness (s) are considered. Thermal properties are considered temperature dependent and the materials are considered isotropic. Surface heat losses toward the ambient are taken into account. Several convective heat flux values on the upper surface, with corresponding Biot numbers, and Peclet numbers are considered with negligible radiative heat losses.Results are presented in terms of profile temperatures to evaluate the effect of impinging jet.

Abstract: Twin elliptic inclined tandem jets are emitted within an oncoming cooler crossflow. The jets contain a non reactive fume whose dispersion is tracked all over the surrounding domain. Such a configuration may be found in chimney stacks, ships’ chimneys, etc. We propose to evaluate in the present paper the impact of the jets’ height on the resulting dispersion process. To reach this goal, a numerical simulation of a double jet model of variable height is carried out by means of the finite volume method together with a non uniform grid system. The model, validated by previous experimental data, allowed the tracking of the emitted fume by studying the evolution of a single particle contained within this fume, the Carbone dioxide (CO2) mass fraction. This is possible thanks to the assumption of handling a non reactive fume, which is adopted only to simplify the calculations. The CO2 mass fraction was mainly tracked between the emitting nozzles, in a try to find out the changes brought by the extension of the emitting jet nozzles on the flow trapped between them.

Abstract: The world has been witnessing a growing interest in heavy oil fields as a result of a reduction in conventional oil reserves. In this sense, this work aims to study numerically the process of heavy oil recovering in oil reservoir via water injection. Transient three-dimensional numerical simulations, considering isothermal and non-isothermal processes, were performed using the ANSYS CFX 11 commercial code, and its effects upon the oil recovery factor evaluated. The numerical results indicated an increase of 29% (non-isothermal case) and 18% (isothermal case) in the recovery factor when water was injected on the reservoir surface as compared to the water internal injection in the reservoir.