bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion Phenomena of the Oxygen and Nitrogen in Niobium by Mechanical Spectroscopy
Authors: Florêncio Odila , Silva Paulo Sergio , Grandini Carlos Roberto
Published: April 2010

The short-range diffusion phenomenon (Snoek Effect) was investigated by mechanical spectroscopy measurements between 300 K and 650 K, in a polycrystalline niobium sample, containing oxygen and nitrogen, using a torsion pendulum. Experimental spectra of anelastic relaxation were obtained under three conditions: as-received sample; annealed sample and subsequently annealed in an oxygen atmosphere for three hours at 1170 K in partial pressure of 5x10-5mbar. The experimental spectra obtained were decomposed in elementary Debye peaks and the anelastic relaxation processes were identified. With anelastic relaxation parameters and the lattice parameters, the interstitial diffusion coefficients of the oxygen and nitrogen in niobium were calculated for each kind of preferential occupation (octahedral and tetrahedral). The results were compared with the literature data, and confirmed that the best adjustment is for the preferential occupation octahedral model for low concentrations of interstitial solutes, but at higher concentration of oxygen were observed deviations of experimental data for the interstitial diffusion coefficients of oxygen in niobium when compared with the literature data, this could be related to the possible occurrence of a double occupation of interstitial sites in the niobium lattice by oxygen interstitials.
A Mathematical Model for the Estimation of the Energetic Potential for Several Renewable Energy Sources: Application on the Design of a Modern Power Plant
Authors: Tsikis I. , Coutelieris Frank A.
Published: April 2010

This work presents a mathematical model to support the electrical energy production in a specific area by using Renewable Energy Sources (RES). More precisely, three RES types (namely, wind, solar and hydropower) are considered while biomass is used to satisfy thermal demands. The actual goal of the model is to generate one or more scenarios for the efficient production of electrical energy for a specific area by selecting the most suitable RES in terms of energy efficiency and cost effectiveness. More specifically the decision criteria are the minimization of installation and operational costs produced for each scenario and the maximization of the electrical energy produced by the specific power plant. Finally, feasibility analyses for selected case studies as well as an evaluation against similar best practices are also carried out for each scenario proposed.
On the Significance of Flow Regime for the Heat Transfer in Solid Oxide Fuel Cells
Authors: Coutelieris Frank A.
Published: April 2010

The steady state heat transfer that takes place in a hydrogen-fed tubular Solid Oxide Fuel Cell is considered here. The heat is produced due to the electrochemical reaction of the hydrogen that feds the cell with oxygen anions. An averaging technique is used to formulate a relatively simple one-dimensional heat transfer problem. The conduction-convection equation describing the heat transfer from the electrolyte’s surface to the moving gas that surrounds the cell’s cathode is solved analytically under the assumption of iso-thermal conditions. Three different cases are considered for the flow of the cathode gas: (a) plug flow, (b) fully developed incompressible laminar flow, and (c) compressible flow. Analytical expressions for the spatial distribution of gas and cell temperature along the cell's length are obtained. For constant mass flow rate, different flow regimes produce almost the similar spatial distributions for the gas temperature and, consequently, the consideration of the flow regime is of low importance in the design of fuel cell stacks.
Diffusion and Reaction in Hierarchical Structured Metal Oxides – A Transient TAP Study
Authors: Galinsky M. , Lutecki M. , Breitkopf Cornelia
Published: April 2010

Transient TAP measurements have been performed for the first time on nanostructured hierarchical sulfated zirconias prepared by a template-assisted route. The newly designed catalytic materials showed different catalytic activities in the n-butane isomerization. The tailored pore systems had a significant influence on the diffusion properties of reactant and product molecules thus influencing the microkinetics.
Natural Convection in Vertical Channels with Porous Media and Adiabatic Extensions
Authors: Andreozzi Assunta , Buonomo Bernardo , Manca Oronzio , Nardini Sergio
Published: April 2010

A numerical investigation on natural convection in air in a vertical heated channel, partially filled with porous medium, with adiabatic extensions downward and collinear the heated plates is accomplished. The fluid flow is assumed two-dimensional, laminar, steady state and incompressible. The porous material is considered as homogeneous and isotropic and the Brinkman-Forchheimer-extended Darcy model is considered. A finite-extension computational domain is employed to simulate the free-stream condition and allows to account for the diffusive effects and the numerical results are obtained using the finite volume method by FLUENT. Results in terms of wall temperature profiles are presented to evaluate the effects of the main thermal and geometrical parameters. The adiabatic extensions determine a wall temperature decrease and wall temperature decreases increasing Darcy number. In full filled heated channels wall temperature presents a significant increase for Darcy number decrease.
Selected Analyses and Observations in Multicomponent Diffusion
Authors: Dayananda Mysore A.
Published: April 2010

Selected isothermal diffusion studies in ternary and quaternary systems are reviewed in order to present analytical and experimental approaches adopted for the determination of interdiffusion fluxes of components, interdiffusion coefficients, diffusional interactions among components, and internal consistency in the experimental data. Several interesting phenomena and observations including uphill diffusion, zero-flux planes and flux reversals, and double serpentine diffusion paths are illustrated with selected single phase Cu-Ni-Zn, Fe-Ni-Al and Cu-Ni-Zn-Mn diffusion couples. The main challenges involved in the experimental determination of interdiffusion data from multicomponent diffusion couples and in the application of such data are also addressed.
Molecular Ion Channels; Electrodiffusion in R3
Authors: Bożek Bogusław , Wierzba Bartek , Danielewski Marek
Published: April 2010

Ion transport across the membrane of the living cell (molecular ion channels) is a critical
process, e.g., the triggering of nerve cells and heart muscle cells is coupled with mechanisms controlled
by ion diffusion (electrodiffusion). Although the process is described by the century old Nernst-
Planck-Poisson system of equations, it is not well understood and a clear understanding of how the
interaction between channel and ions affects the flow is still missing. We present a three-dimensional
model of the molecular channel. An appropriate quantitative description of the ion transport process
allows proper explanation of molecule channel interactions (e.g. the ions flow for a given concentration
gradient should depend on the potential and other parameters describing the interaction, i.e.
asymmetric transport). We show the simulation of the stationary electrodiffusion in the ion channel
showing radial symmetry.
Investigation of a Mathematical Model of High-Temperature Diffusion Controlled Heterogeneous Reaction between Metal and Oxide Melts
Authors: Radune Maya , Radune Alex , Assous F. , Zinigrad Michael
Published: April 2010

A deterministic computational model of high-temperature heterogeneous re-
action between metal and oxide melts has been developed. Transport of reagents and
products of reaction occur simultaneously both by diusion and by laminar natural con-
vection of the melting metal and oxide
uxes. The convection-diusion equations have
been numerically solved by a nite-dierences time-implicit discretization scheme. The
model was implemented by program which had been written in C# language. The com-
putations have been performed for desulfurization reaction between liquid steel and slag
phases.The computed results agree well with the results which were found by experimen-
tal methods.
Comparison of Four Thermo-Mechanical Models for Simulating Reactive Flow in Porous Materials
Authors: de Lemos Marcelo J.S. , Mesquita Maximilian S.
Published: April 2010

The objective of this paper is to present numerical simulations of combustion of an air/methane mixture in porous materials using a model that considers the intra-pore levels of turbulent kinetic energy. Transport equations are written in their time-and-volume-averaged form and a volume-based statistical turbulence model is applied to simulate turbulence generation due to the porous matrix. Four different thermo-mechanical models are compared, namely Laminar, Laminar with Radiation Transport, Turbulent, Turbulent with Radiation Transport. Combustion is modeled via a unique simple closure. Preliminary testing results indicate that a substantially different temperature distribution is obtained depending on the model used. In addition, for high excess air peak gas temperature are reduced.
A Lattice Monte Carlo Analysis of Thermal Transport in Phase Change Materials
Authors: Fiedler Thomas , Belova Irina V. , Öchsner Andreas , Murch Graeme E.
Published: April 2010

Heat sinks enable the storage of energy that would otherwise be lost, thus ensuring significant energy-savings and fewer greenhouse gas emissions. Heat sinks also play the major role in the efficient temperature control of devices such as batteries. In principle, any material can act as a heat sink – traditionally, copper is used for many applications. However, copper is relatively expensive, has a high density and only a limited energy storage capacity. In contrast, a phase-change material (PCM) allows in effect an additional storage of energy through its phase change thus greatly increasing the achievable energy density. The aim of this work is the numerical analysis of the transient heat transfer in composite heat sinks containing phase-change materials. For the first time, a recently formulated Lattice Monte Carlo Method is applied to determine temperature distributions and the amount of energy transferred versus time in phase change materials.
Heat and Mass Transfer for a Constant Heat Boundary in Porous Reactive Medium under Local Non Equilibrium Conditions
Authors: Bousri A. , Bouhadef K. , Beji Hassen , Rahli Omar
Published: April 2010

A two dimensional mathematical model has been developed to simulate the coupled heat and mass transfer in a porous medium undergoing a strong exothermic reaction. The problem has received a lot of interest due to its relevance in a wide variety of engineering applications such heat pipes, nuclear reactors, drying technologies, catalytic reactors and others. The fluid flow is modelled via the Darcy-Brinkman-Forchheimer equation. This model is solved numerically by the finite volume method, and the code is validated by comparing with previously published works. The influence of the exothermic chemical reaction on the heat and mass transfer in the porous medium is discussed. The effects of pertinent parameters such as the Biot number, the Reynolds number and the Frank-Kamenetskii number were analyzed. Quantitative and qualitative results are presented. Comparisons with other works in the literature are performed and excellent agreement between the results is obtained.
Models for the Porosity Growth and Dissolution in Single-Crystal Nickel-Base Superalloys
Authors: Bokstein Boris S. , Esin Vladimir , Rodin Alexey , Svetlov I.L.
Published: April 2010

During the solidification and the homogenization of single-crystal nickel-base superalloys, pores form which lead to the degradation of the mechanical properties, especially the fatigue lifetime. Hot Isostatic Pressing (HIP) is used for the pores dissolution. In this paper, analytical models for the formation of the homogenization pores and their dissolution during the HIP are developed. The results are compared with experimental data.
The Study of Droplet Impact Behavior on Flat Surface with Different Surface Properties
Authors: Ku Shaari Ku Zilati , Turton Richard
Published: April 2010

The impact behavior of a liquid droplet on solid surface is a complex phenomenon and yet is a basic component of various industrial processes particularly in the pharmaceutical industry. In this industry, film coating technique is used in tablet coating, in which coating uniformity is important especially if the coating is for functional purposes. Coating uniformity on a tablet could be affected by several factors, one of which is the impingements of droplets on its surface. In this work, the maximum spreading diameter and the initial impact behavior of a single droplet on pharmaceutical tablet surfaces and metal surfaces having different surface properties are investigated. A Charged-Coupled-Device (CCD) high-speed camera with framing rate of 2,000, attached to a 10X microscope, was used to capture the phenomena. The results show that the initial impact behavior of a droplet is not affected by the porosity of a surface. The results on the pharmaceutical tablets, stainless steel and etched silicon surfaces show that the rougher the surface the lower the spreading factor. The droplets on all surfaces demonstrate that a droplet that produces higher spreading factor gives a lower bouncing factor.
Thermosolutal Convection in a Partly Multi-Layred Porous Annular Cavity
Authors: Benzeghiba Mouhamed , Khenfer K. , Chikh Salahs
Published: April 2010

The present study analyzes numerically the mixed thermosolutal convection in a vertical partly porous annular cavity. The fluid motion in the porous matrix is described by the generalized Darcy-Brinkman-Forchheimer model. The results show that the composite porous layer tends to improve the heat transfer and moderately reduce the transfer of aqueous solution compared to the case of a homogeneous porous partition. This conclusion is valid for all characteristic values (Da, ) or the flow modes set up in the porous matrix.
Defects Removal Using a Triangular-Shape Designed Tool
Authors: Pa Pai Shan
Published: April 2010

A new triangular-shape designed tool as a cathode in microelectromechanical etching process is a precision nanoscale production of a reclamation system of Indium tin oxide (ITO) thin-films defects removal from optoelectronic flat panel displays’ color filter surface is demonstrated in the current study. Through the ultra-precise removal of the thin-film nanostructure, the optoelectronic semiconductor industry can effectively reclaim defective products, reducing production costs. In the current experiment, a large size triangular shape cathode is accompanied by a small gap-width between the cathode and the workpiece takes less time for the same amount of ITO removal. A higher feed rate of displays’ color filter or a small end radius of the cathode combined with enough electric power produces fast machining. Pulsed direct current can improve the effect of dregs discharge and is advantageous in association with a fast workpiece feed rate. However, it raises the current rating. A large flow rate of the electrolyte corresponds to a higher removal rate for the ITO nanostructure. The electrochemical etching just needs a short time to make the ITO remove removal easy and clean.
Enhanced Mechanical Properties of Stainless Steel 316 L via Friction Stir Processing
Authors: Salekrostam R. , Givi M.K. Besharati
Published: April 2010

Friction stir processing (FSP) is a solid state process to modify microstructure and mechanical properties of sheet metals and as-cast materials. In this process stirring action of the tool causes the material to intense plastic deformation that yields a dynamical recrystalyzation. In this study the effect of FSP and process parameters on hardness, and microstructure of stainless steel 316L has been investigated. Also by using of FSP, a composite layer of 316L/SiC has been produced. Results show that FSP leads to a finer and homogenized grain structure, as well as increased hardness, strength, toughness, and elongation at failure of the material. The composites produced by FSP have a uniform distribution of SiC particles between the grains of the base metal.
Influence of Friction Stir Processing Parameters on the Fabrication of SiC/316L Surface Composite
Authors: Salekrostam R. , Givi M.K. Besharati , Asadi P. , Bahemmat P.
Published: April 2010

Compared to the many fusion welding processes that are routinely used for joining stainless steel 316L, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and is being recast. The welding parameters play a major role in deciding the weld quality. In this investigation an attempt has been made to understand the influences of rotational speed and traverse speed of the tool on the microstructure of the friction stir processing zone in stainless steel 316L. Five different tool rotational speeds have been used to fabricate the joints at four different traverse speeds from this investigation which is the optimum for the tool speed and higher or lower amounts of these parameters are not useful for the process.
Effects of Processing Factors on Microstructure and Diffusivity of Diethylbenzene Dehydrogenation Catalyst
Authors: Zeynali Mohammad Ebrahim , Soltani I.
Published: April 2010

In this study, different mechanisms of diffusion such as Knudsen and bulk were investigated for diethylbenzene diffusion into a catalyst and it was concluded that the pore sizes should be in the range that permit transitional diffusion (both Knudsen and bulk diffusion). The catalyst grain size can be controlled and varied by different parameters such as speed and time of mixing, type of alkali, temperature and pH. Particle size distribution experiments were conducted for different types of alkali and speed of mixing to characterize the catalyst. The effects of grain size formed during coprecipitation on pore size distribution of the catalyst pellet which affect the effective diffusivity were discussed. Pore size distribution of the model catalyst was obtained and the effective diffusivities were calculated by numerical integration of Johanson-Stewart equation.
Liquid Diffusion in Polymers by Electrochemical-Impedance Spectroscopy (EIS)
Authors: Chauffaille S. , Devos Olivier , Jumel Julien , Shanahan Martin E.R.
Published: April 2010

Preliminary results on a technique of Electrochemical-Impedance Spectroscopy (EIS) applied to the characterization of diffusion and absorption properties of water in an epoxy resin are reported. Thin films of polymer adhering to aluminum constitute simulated adhesive bonds. Immersion in water and assessment via electro-chemical impedance measurements allowed estimation of diffusion rates and water uptake. In parallel, classic gravimetric experiments were undertaken on thin, free films of the same polymer. Results of the two techniques are acceptably comparable, and thus EIS could be developed as a new tool for in situ assessment of adhesives.
Reactive Diffusion of Uranium in Compacted Clay: Evaluation of Diffusion Coefficients by a Kinetic Approach
Authors: Korichi S. , Bensmaili A. , Keddam Mourad
Published: April 2010

The effect of compaction of bentonite on the diffusion behavior of uranium was studied for the safety assessment of radioactive waste (storage and disposal practices). Since the permeability of the compacted clay is very low, the main mechanism for radionuclide transport is governed by the diffusion phenomenon. The diffusion process of uranium in compacted clay as a porous medium has been modeled by Fick's second law taking into account the effect of sorption and considering the non-steady state. The diffusion coefficients and profiles concentration values were calculated by a computational method using a numerical program based on the Newton-Raphson algorithm. In this simulation, the experimental values were used to determine the uranium concentration profiles versus depth of the clay pellet. It was concluded that the dry density of the compacted clay and the aqueous solution properties (pH and ionic strength of background electrolyte) played an important role in the uranium transport through compacted clays.
Dependence between the Boron Surface Concentration and the Growth Kinetics of Boride Layers in AISI 4140 Steels
Authors: Ortíz-Domínguez M. , Campos-Silva Ivan , Martínez-Trinidad José , Elías-Espinosa Milton , Hernández-Sánchez E. , Bravo-Bárcenas D.
Published: April 2010

The present work estimated the growth kinetics of Fe2B layers formed at the surface of AISI 4140 steels. The thermochemical treatment was applied in order to produce the Fe2B phase, considering temperatures of 1123, 1173, 1223 and 1273 K with five exposure times (2, 4, 5, 6, and 8 h), using a 4 mm thick layer of boron carbide paste over the material surface. The growth of boride layers was described by the mass balance equation between phases in thermodynamic equilibrium, assuming that the growth of boride layers obeys the parabolic growth equation and the boron concentration at the interfaces remains constant. Also, the boron diffusion coefficient at the Fe2B ( ) was established as a function of boriding temperature. Likewise, the parabolic growth constant (k), the instantaneous velocity (v) of the Fe2B/substrate interface and the weight-gain of borided steels were established as a function of the parameters and , which are related to the boride incubation time ( ) and boron surface concentration ( ), respectively.
Effects of Nickel on Interface Morphology during Oxidation of Fe-Cu-Ni Alloys
Authors: Yin Lan , Balaji S. , Seetharaman S.
Published: April 2010

Steel produced in Electric Arc Furnaces (EAF) contain a high amount of copper that causes a detrimental surface cracking phenomenon called hot shortness. Studies have found that nickel can alleviate hot shortness by increasing copper solubility in the Fe phase, decreasing oxidation rate and promoting occlusion [1-3]. Occlusion is a phenomenon whereby the copper-rich phase becomes incorporated into iron oxides. Nickel promotes occlusion by causing an uneven interface and increasing the number of internal oxides. The uneven interface is likely a result of the two concentration fields resulting from ternary diffusion of nickel, copper and iron in the Fe phase. This work is aimed at explaining why nickel causes wavy oxide/liquid-Cu and liquid-Cu/Fe interfaces. Constitutional super-saturation criterion [4] was applied to explain uneven interfaces caused by nickel. A model simulating diffusion behaviors of copper and nickel in Fe was developed by coupling Comsol Multiphysics® and Matlab®. Interface concentrations of copper and nickel and perturbation criterion values were calculated as a function of time. Modeling results show that (i) the nickel interface concentration first increases to a peak value then decreases slowly during oxidation process as a result of the change in oxidation rates, and (ii) the alloys with higher nickel contents have more potential for interface breakdown and this occurs within the initial linear oxidation regime.
The Effects of Homogenization Time and Cooling Environment on Microstructure and Transformation Temperatures of Ni-42.5wt%Ti-7.5wt%Cu Alloy
Authors: Omrani E. , Shokuhfar Ali , Etaati A. , Dorri M. A. , Saatian A.
Published: April 2010

The present paper deals with different effects of homogenization time and cooling environment on Ni-42.5wt%Ti-7.5wt%Cu alloy. The alloy was prepared by vacuum arc melting. Afterwards, three homogenization times (half, one and two hour) and three cooling environments (water, air and furnace) at 1373 K were selected. Optical and Scanning Electron Microscopic methods, EDX, DSC and hardness tests have been used to evaluate the microstructure, transformation temperatures and hardness. Results indicate that specimens that were cooled in air are super-saturated. Also, the microstructure from furnace cooling has many disparities with the other cooling environments’ microstructure and two types of precipitates exhibit in the matrix, but in other cooling environments, only one phase can be seen. Particles of the Ti2(Ni,Cu) phase are distributed in the matrix in all of the microstructures irrespective of cooling rate. Observations show that increasing the time of homogenization results in finer precipitates and uniform distribution in the matrix. In addition, alteration of cooling rate and time of homogenization affect the martensitic transformation temperatures. On the other hand, the hardness varies slightly for different homogenization times but declines extremely with decreasing cooling rate. Moreover homogenization time and the cooling environment affect the transformation temperatures on furnace cooled samples.
Mechanical Performance of the Annealed NiTi Shape Memory Alloy Coating onto 316L Stainless Bio-Steel
Authors: Abubakar Tuty Asma , Rahman M. , Dowling Denis P. , Stokes Joseph , Hashmi M.S.J.
Published: April 2010

This paper presents the mechanical performance of the annealed NiTi Shape Memory Alloy (SMA) coating deposited onto 316L stainless steel substrate. The as-deposited SMA coating, Ni55.9 Ti44.1, showed an amorphous behaviour. The crystalline NiTi (SMA) coating was produced by annealing the as-deposited NiTi with a thickness about 2.0 µm, at above its crystallisation temperature in a vacuum ambient. The annealed NiTi coatings were characterised to determine the effect of the annealing parameters on their mechanical behaviour. The NiTi phases and structures were determined by x-ray diffraction (XRD) and scanning electron microscopy (SEM) whereas the mechanical properties were measured using the Rockwell C adhesion test. Three main phases; NiTi B2 parent phase, Ni3Ti and TiO2 were found in the annealed samples and the intensities of each phase were dependent on the annealing temperature and annealing time. Each phase significantly affected the mechanical behaviour of the coatings. Higher intensities of Ni3Ti and TiO2 phases were believed to contribute to the low adhesion of the annealed NiTi coatings due to their brittle properties. The annealing parameters; 600 °C for durations of 30 min was considered as the optimum parameter, yielding no fine cracks at the Rockwell C indentation interface compared to other samples at high magnification under the SEM. Adding a hard top layer of TiN would potentially provide a hard coating with an interlayer capable of absorbing impact which would be very suitable for ball joints used in hip replacement therapy.
Characterization of the Intermetallic Compounds Formed during Hot Dipping of Electrical Steel in a Hypo-Eutectic Al-Si Bath
Authors: Danzo I. Infante , Verbeken Kim , Houbaert Yvan
Published: April 2010

In order to improve the magnetic properties of electrical steels, it may be desirable to increase the Si and/or Al content of the steel. A possible and alternative route to realize this is through the application of an Al-Si-rich coating on the steel substrate using a hot dipping process, followed by a diffusion annealing treatment. Previously, a series of compositions were used for dipping, namely: pure Al, Al + 10wt% Si (hypo-eutectic composition) and Al + 25wt% Si (hypereutectic composition). After these dipping experiments, and the subsequent evaluation of the coating and its formed intermetallic phases, the use of a hypo-eutectic Al-Si-bath was recommended for further investigation, because of certain advantages: i.e. hypo-eutectic concentrations allow lower dipping temperatures and reduce the formation of ordered Fe-Si-structures that cause brittleness in the coating and substrate.
The present work reports on the results obtained on materials that were hot dipped in a hypo-eutectic Al-Si bath. An Al + 1wt%Si bath was used to coat electrical steel substrates with different silicon contents with dipping times, varying between 0 to 20 seconds, after a preheating of the samples to a temperature of 700°C. A thorough characterization of the formed intermetallics was made by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). Three different compounds were identified as Fe2Al5, FeAl3 and a nearly pure Al phase.
Phase-Field Simulation on Coarsening of the γ'Phase Particles in Ni-Based Superalloys Considering Elastic Inhomogeneity
Authors: Tsukada Yuhki , Murata Yoshinori , Koyama Toshiyuki , Morinaga Masahiko
Published: April 2010

A phase-field simulation is performed to examine the effect of elastic inhomogeneity between the  and ’ phases on coarsening of the ’ phase in Ni-based superalloys. In the calculation of elastic strain energy, the mechanical equilibrium equation in elastically inhomogeneous system is solved by an iterative-perturbation scheme. On the basis of the elastic constants of a practical Ni-based superalloy, a series of simulations is performed in which both elastic anisotropy and shear modulus are varied independently. The variation of elastic anisotropy gives significant effect on both morphology and size distribution function of the ’ particles, whereas the variation of shear modulus gives little effect on them. Furthermore, it is found that the coarsening rate constant of the cubic growth raw changes and increases with increasing the standard deviation of the ’ size distribution.
Effect of Lubricant Volume and Working Gap on the Surface Roughness and Material Removal Rate in Magnetic Abrasive Finishing
Authors: Vahdati Mehrdad , Sadeghinia E. , Shokuhfar Ali
Published: April 2010

Technological requirements urges high technology industries using materials with advanced properties. Although it is compulsory using these materials due to their advantages, some of them should be tolerated because of their weak machining and mechanical properties. Attempts for qualitative machining of complex curves on many work pieces may result in the advent of new finishing techniques. One of the most newly introduced techniques is Magnetic Abrasive Finishing, MAF. In this paper a study on the effects of tool and work piece gap, and lubricant volume, on the roughness and material removal rate have been studied. The results show that setting the working gap to 3 mm and the lubricant volume to 0.7 ml, yields a change in surface roughness (Ra), and the material removal (MR) will gain its best result.
Air Characteristics in Air Turbine Spindle of Ultra Precision Machines
Authors: Vahdati Mehrdad , Azimi E. , Shokuhfar Ali
Published: April 2010

Air Spindles have been used in ultra precision machines for several years due to their advantages such as high speed rotation, low friction, and low vibration, [1]. Air spindles are widely used in these machines for producing precise work pieces. Although, spindles function on a very complicated theoretical basis, [2, 3], their structure is very simple and consists of mainly a rotor and a stator. The rotor/stator could be made of different shapes. A cylindrical shape is the one commonly in use. The spindle designed in this work has a spherical configuration. It has been designed so that it could be moved without application of electric motor and only by a wind turbine system, [4]. The spindle studied in this research uses compressed air for rotor suspension, and has an air turbine for rotating its shaft. A thin air film acts as bearing layer between rotor and stator. In design procedure, operation parameters such as air inlet pressure for turbine, air inlet pressure for bearing, diameter of turbine nuzzles, diameter of bearing nuzzles, clearance between rotor and stator and etc. have been considered, [5]. A prototype spindle has been manufactured using design criteria. The influence of above mentioned parameters have been recognized through experiments.
Fluid Flow in Tree-Shaped Constructal Networks: Porosity, Permeability and Inertial Parameter
Authors: Miguel Antonio Ferreira
Published: April 2010

This paper aims to contribute to the ongoing research on tree-shaped flow structures. First, it briefly traces the progress made on constructal tree-shaped flow networks. Then, the paper focuses on tree pattern of tubes connecting the centre and the rim of a circular area. It shows that the physical description underlying the classical Darcy-Forchheimer-Ergun equation may provide a legitimate correlation for this kind of flow structure. The porosity, hydraulic permeability and the inertial factor of the flow structure are also presented.
Analysis of Component Depth Profiles at the Interface of Ti6242 Alloy and SiC, SiN Coatings after High Temperature Oxidation in Air
Authors: Galdikas A. , Rivière Jean Paul , Moskalioviene T. , Pichon L.
Published: April 2010

We have analyzed the interfacial elemental depth profile evolution after high temperature isothermal oxidation of SixCy and SixNy protective coatings deposited by dynamic ion mixing on a Ti6242 alloy (Ti-6Al-2Sn-4Zr-2Mo). Isothermal oxidation tests have been carried out at 600°C during 100 hours in air. We have observed a non-monotonic depth distribution of zirconium in GDOES and SIMS depth profiles after oxidation of SiC/Ti6242 and SiN/Ti6242 and we propose a kinetic model based on rate equations for analyzing the results. It is shown by modeling that a non-monotonic depth profile of zirconium occurs because zirconium from the Ti6242 alloy forms a zirconium oxide compound. As a result, the atomic concentration of zirconium decreases at the interface which induces a diffusion flux of zirconium from the bulk to the interface. This process leads to the increase of the total amount of zirconium at the film interface and thus formation of a non-monotonic depth profile.
Embrittlement of Cu and Cu-Based Alloys by Bi and Bi2Te3
Authors: Zhevnenko Sergei , Vaganov Danil V. , Gershman Evgeny I.
Published: April 2010

Degradation of the mechanical properties of copper and copper based alloys after the treatment with telluride bismuth (Bi2Te3) at 570oC has been studied in the present work. The experiments were performed in a H2 deoxidizing atmosphere. The kinetics of embrittlement of pure copper has been shown to be parabolic. Bi2Te3 was in the solid state and was not in direct contact with the copper specimens during the experiments, i.e. the plating was performed through the gas phase. The brittle fracture along the GB was observed after 3 point bending test. The surface of fracture was investigated with the use AES. It was shown that intergranular penetrations of liquid bismuth and bismuth from Bi2Te3 have different mechanisms.
The Effect of Matrix Stiffness on the Mechanical Properties of the Composite Reinforced with Multi-Wall Carbon Nanotube
Authors: Her Shiuh Chuan , Yeh Shun Wen
Published: April 2010

Carbon nanotubes have shown the superior mechanical, electrical and thermal properties. These outstanding properties as well as a high aspect ratio and low density make carbon nanotubes an ideal reinforcement to develop superior nanocomposites. Mechanical tests indicated that the reinforcement role of carbon nanotubes is affected by the stiffness matrix. It is well known that the degree of cure of the epoxy has great influence on their mechanical properties. In this investigation, the matrix stiffness is controlled by changing the mixture ratio between the epoxy and hardener. Two different contents (1% wt. and 2% wt.) of the multi-wall carbon nanotubes in the epoxy are proposed in this work. Tensile tests are conducted to determine the mechanical properties of the nanocomposites, including the Young’s modulus, yield stress, tensile strength and fracture strain. Experimental results show that the mechanical properties are increasing with the increase of the addition of multi-wall carbon nanotubes. The reinforcement role of the multi-wall carbon nanotubes is decreasing while increasing the stiffness matrix.
Formation of the Modulated Structure in a Steel by the Addition of a Strong Carbide Forming Element
Authors: Murata Yoshinori , Kita T. , Tsukamoto T. , Tsukada Yuhki , Koyama Toshiyuki , Morinaga Masahiko
Published: April 2010

The modulated structure characterized by periodic concentration fluctuations is caused by the up-hill diffusion of solute atoms due to the spinodal decomposition, when the Gibbs free energy surface of the solid solution has a convex curve. This convex shape in the free energy surface will appear in multi-component systems, even though the energy in each binary system does not show the convex curve, when a binary system exhibits a strong attractive interaction, i.e., the Gibbs free energy shows a deep concave curve. This may be the case that steel containing an element having a strong tendency of carbide forming. The Fe-Ni-V-C system was selected in this study. V is a strong carbide forming element and forms VC carbide based on f.c.c. lattice. A series of experiments was carried out using Fe-25Ni-3V-3C (mol%) alloy after aging at elevated temperatures. A modulated structure was observed in specimens aged at temperature range of 550 °C to 650 °C, and the maximum temperature occurring the spinodal decomposition was estimated to be 715 °C in Fe-25Ni-3V-3C alloy. Furthermore, the coefficient of the gradient energy caused by composition fluctuations was estimated to be 2.8 x 10-15 J.m2/mol.
Diffusion Studies in A3B Compounds with A15 Structure
Authors: Ravi R. , Kumar A.K. , Paul Aloke
Published: April 2010

There is a constant effort to understand the defect structure and diffusion behavior in intermetallic compounds with the A15 structure. Diffusion of elements in intermetallic compounds depends mainly on antisites and vacancies on different sublattices. In this article, we shall discuss the diffusion of elements in A3B compounds with the A15 structure.
Drying of Kaolin Clay Cylinders: Dynamic Neutron Radiography Studies
Authors: Fijał-Kirejczyk Izabela , Milczarek Jacek J. , Banaszak Jacek , Żołądek Joanna , Trzciński Andrzej
Published: April 2010

The results of the dynamic neutron radiography studies on drying of wet kaolin cylinders in the forced warm air flow are presented. The sample shrinkage and loss of water during drying was analyzed in terms of the brightness of registered neutron radiographs, and sample mass and temperature. The water saturation of the sample with water was discussed in comparison to the changes in local neutron effective macroscopic cross section. The neutron radiography results reveal more details of the drying process than gravimetric measurements indicating nonuniform distribution of water within samples. The obscuring effect of the scattered neutrons on the determination of the water content is discussed on the basis of the MC simulations results.
Internal Interface Strains Effects on UO2/U3O7 Oxidation Behaviour
Authors: Creton Nicolas , Optasanu Virgil , Garruchet Sébastien , Raceanu Laura , Montesin Tony , Desgranges Lionel , Dejardin Steeve
Published: April 2010

The growth of a U3O7 oxide layer during the anionic oxidation of UO2 pellets induced very important mechanical stresses due to the crystallographic lattice parameters differences between UO2 and its oxide. These stresses, combined with the chemical processes of oxidation, can lead to the cracking of the system, called chemical fragmentation. We study the crystallographic orientation of the oxide lattice growing at the surface of UO2, pointing to the fact that epitaxy relations at interface govern the coexistence of UO2 and U3O7. In this work, several results are given:
- Determination of the epitaxy relations between the substrate and its oxide thanks to the Bollmann’s method; epitaxy strains are deduced.
- Study of the coexistence of different domains in the U3O7 (crystallographic compatibility conditions at the interface between two phases: Hadamard conditions).
- FEM simulations of a multi-domain U3O7 connected to a UO2 substrate explain the existence of a critical thickness of U3O7 layer.
In Situ Synthesis of B4C / TiB2 Composites from Low Cost Sugar Based Precursor
Authors: Çakır E. , Ergun Celaletdin , Şahin Filiz Çinar , Erden İ.
Published: April 2010

In the present study, a method based on sulfuric acid dehydration of sugar was developed to synthesis a precursor material, which can yield B4C/ TiB2 composites at much lower temperatures compared to traditional carbothermal methods. The precursor material for pure B4C and B4C / TiB2 composites were heat treated at 1650oC under Ar and Ar+H2 atmosphere. Then the samples were characterized by X-ray diffraction (XRD) and crystallized B4C and B4C / TiB2 composites can be obtained at 1650oC
Investigation of Thermal Properties of Thin Semiconductor Layers Deposited on a Glass Substrate by the Photothermal Deflection Technique
Authors: Gaied Imen , Rabeh Mohamed Ben , Rabhi Adel , Kanzari Mounir , Yacoubi Noureddine
Published: April 2010

In this work we describe a method based on the Photothermal Deflection Technique adapted for the determination of thermal properties of thin semiconductor layers deposited on a glass substrate. The sample placed in air is heated thanks a modulated pump uniform beam coming from a halogen lamp. The thermal conductivity and the thermal diffusivity are obtained by comparing the amplitude and phase variations versus square root modulation frequency between the experimental curves and the corresponding theoretical ones. The best coincidence permits to deduce the thermal properties of the sample.
Influences of Dye Doping and Hole Blocking Layer Insertion on OLED Performance
Authors: Tesng C.H. , Liu C.H. , Cheng Chin-Pao
Published: April 2010

This study presents the influences of dye doping and hole blocking layer insertion on the electroluminescent properties of the blue organic light emitting diode. The luminance of the device was significantly improved by BCzVB doping because of the utilization of effective Förster energy transfer and the improvement of carrier injection and trapping; a BCzVB dominant emission was observed. Furthermore, when a BCP layer was inserted between the TBADN:BCzVB and Alq3 layers, a thin BCP layer insertion enhanced the injection of electrons and improved the luminance of the device. In contrast, a thick BCP layer insertion caused a delay in electron transport, resulting in a decrease in current density and a deterioration in luminance.
Efficiency Improvement of Organic Light Emitting Diodes with Co-Deposited Hole Blocking Layer
Authors: Liu C.H. , Tesng C.H. , Cheng Chin-Pao
Published: April 2010

There are several kinds of methods in improving the efficiency of organic light emitting diodes (OLEDs). In this work, we used a co-deposited hole blocking layer to improve the efficiency of OLEDs. The structure of the component is: ITO/ MTDATA(15 nm) /NPB(40 nm) /BCP(10 nm) /BCP: Alq(15 nm) /LiF(0.7 nm)/ Al(180 nm). We changed the mixing rate of the BCP:Alq layer to be capable of hole blocking and electron transporting, and then improved the efficiency of OLEDs. Finally, we prepared white light OLED with doping Rubrene in NPB. When the concentration of the NPB: Rubrene layer was 2.0 wt.%, the device could emit the white light at 100 mA/cm2, and the luminance was above 2300 cd/m2, and the color coordinate was x = 0.36, y = 0.37.
The Kinetics of Gas Nitrided Layer Growth on Austenitic Stainless Steel
Authors: Baranowska Jolanta
Published: April 2010

This paper presents the results of investigations on gas nitrided austenitic stainless steel. The treatment was conducted at various temperatures (400-515°C), gas compositions of atmospheres used (20-100% NH3) and times (0.5-12h). The layers were investigated by X-ray diffraction, Light and Electron Microscopy and Glow Discharge Optical Spectrometry. The kinetics of layer growth has been analysed in terms of the process parameters and compared with the data presented for plasma treated steel. The specific nitrogen profiles of nitrided layers are discussed in the context of the layers’ microstructure and phase composition.
Microstructure and Properties of Nanoclay Reinforced Asphalt Binders
Authors: Zare-Shahabadi A. , Shokuhfar Ali , Ebrahimi-Nejad S.
Published: April 2010

In this paper, sodium bentonite (BT) and organically modified sodium bentonite (OBT) are used to reinforce and modify asphalt binder. The microstructures of the reinforced asphalt binders are investigated using transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD). Two models for the microstructure of the BT and OBT modified asphalts are suggested considering the colloidal structure of the base asphalt binder. The physical properties of the modified asphalt binders were studied.
A Contribution to the Analysis of the Thermo-Hydrodynamic Lubrication of Porous Self-Lubricating Journal Bearings
Authors: Boubendir S. , Larbi Salah , Bennacer Rachid
Published: April 2010

In this work the influence of thermal effects on the performance of a finite porous journal bearing has been investigated using a thermo-hydrodynamic analysis. The Reynolds equation of thin viscous films is modified taking into account the oil leakage into the porous matrix, by applying Darcy’s law to determine the fluid flow in the porous media. The governing equations were solved numerically using the finite difference approach. Obtained result show a reduction in the performance of journal bearings when the thermal effects are accounted for and, this reduction is greater when the load capacity is significant.
Diffusion of Hydrogen in Single Crystals of Monoclinic-ZrO2 and Yttrium Stabilized Cubic Zirconia
Authors: Khatamian D.
Published: April 2010

Transport of hydrogen through oxide layers formed on zirconium alloys has been the focus of studies associated with hydrogen ingress into nuclear reactor core components. The studies have shown that microstructure and microchemistry of the underlying alloy can affect the characteristics of the oxide and in turn the transport of hydrogen through the oxide and into the underlying metal. In certain cases the oxide layer can be a homogeneous medium for hydrogen diffusion, while in most cases it is found to be heterogeneous and comprised of homogeneous, nonporous and fully oxidized, cells surrounded by a network of fast diffusion paths for hydrogen. Since in such heterogeneous systems the derived diffusion parameter and the cell size are interdependent, an absolute diffusion parameter could only be derived if the cell size were known. However, no such information is available from the microstructural studies on the oxides grown on these alloys. Another alternative is to carry out the measurements in a material, which is homogeneous at least within the dimensions of a few μm - the range of the measurements. With this in mind, hydrogen diffusion measurements were carried out in a set of single crystal zirconia specimens with the prospect that the single crystals would provide a non-porous and homogeneous medium to study the diffusivity of hydrogen. These measurements show that the single crystal specimens, contrary to the initial thinking, are not entirely homogeneous and the results do not yield an absolute diffusion coefficient for hydrogen in zirconium oxides. The details and analyses of the results from the single crystal zirconia specimens are discussed in this paper.