bluuebunny/crossref_metadata_2025 huggingface dataset:
Verification of a Commercial CALPHAD Database for Re and Ru Containing Nickel-Base Superalloys
Authors: Rettig Ralf , Heckl Astrid , Neumeier Steffen , Pyczak Florian , Göken Matthias , Singer Robert F.
Published: September 2009

The addition of rhenium and ruthenium to single crystal nickel-base superalloys improves the high-temperature properties of the alloys. In this work the applicability of the database TTNi7 (ThermoTech Ltd, UK) for developing 4th generation single crystal superalloys containing rhenium (Re) and ruthenium (Ru) was investigated. We systematically compared experimentally determined alloy properties to the predictions of ThermoCalc with the database TTNi7. The investigated properties were liquidus, solidus and ´ solvus temperature as well as incipient melting point and segregation. Calculations were based on thermodynamic principles with the assumption of either equilibrium or Scheil-Gulliver conditions, i.e. no diffusion in the solid and complete diffusion in the liquid. Furthermore the composition of the  and the  phase of a Re- and Ru-containing superalloy was measured and compared to calculations. Our results show that the database is capable of simulating general trends of 4th generation superalloys up to 6 weight percent (wt.-%) Re and 6 wt.-% Ru. The present work shows that Scheil-Gulliver calculations can only be used as a first approximation for nickel-base superalloys.
Diffusion of 65Zn in AZ91 and QE22 Alloys with Saffil Reinforcement-Influence of Interfaces Matrix/Saffil
Authors: Stloukal Ivo , Čermák Jiří
Published: September 2009

Diffusion of 65Zn in two commercial Mg-based alloys AZ91 and QE22 with short Saffil fibers was studied. Experiments were carried out in the temperature interval 648 – 728 K by serial sectioning method. The effective diffusion coefficients Deff were compared with 65Zn diffusion coefficients Dv obtained with the same alloys without Saffil fibers. The evaluation of the influence of the interface between the matrix and the fibers upon Deff was done and the zinc diffusion coefficient Di in the interface boundary matrix/Saffil was estimated. Unlike the Arrhenius-like behavior of volume diffusion in both alloys, it was observed that the temperature dependence of both Deff and Di was significantly concave in the measured temperature interval. This behavior was attributed to relaxation of thermo-elastic stresses in the composite induced by a large difference between coefficients of thermal expansion (CTE) of Saffil fibers and metal matrix. The maximum values of Deff and Di, respectively, lie close to 693 K, where CTE has a minimum.
Diffusion in Metallic Elements and Intermetallics
Authors: Mehrer Helmut , Divinski Sergiy V.
Published: September 2009

Starting from some fundamentals of solid-state diffusion, we remind the reader to the major techniques for lattice diffusion measurements. Self-diffusion is the most basic diffusion phenomenon in any solid. The paper covers main features of self-diffusion in pure fcc and bcc metals and some important facts about diffusion of substitutional solutes in metals. Binary intermetallics are compounds of two metals or of a metal and a semimetal. Their structures are different from those of the constituents. Some intermetallics are interesting functional materials others have attracted attention as high-temperature structural materials. The paper reviews some results mainly from our laboratory on diffusion in binary intermetallics from the systems Cu-Zn, Ni-Al, Fe-Al, Ni-Ge, Ni-Ga, Fe-Si, Ti-Al, Ni-Mn, Mo-Si and Co-Nb, which have been published in detail elsewhere. Some results for the ternary system Ni-Fe-Al are also mentioned.
Synthesis and Characterization of a Porous Silicon Filter with Si3N4 Whiskers
Authors: Wong-Sifuentes Milagros , Nanko Makoto , Lira-Olivares Joaquín
Published: September 2009

Removal of fine particles from some gas-product effluents from motors and industries, using filters, is an important subject in the field of public health and environment. In the present work, a porous silicon filter was produced, which is able to capture most of the particles undesirable for the environment (transported by gases), larger than the pore diameter (micrometer) of the filter and even smaller size particles. The development of whiskers inside of the pores of the silicon filter, improve its ability to catch smaller particles than the filter’s size pores. Those whiskers are made of Silicon Nitride, produced by a Nitridation process. A different time-temperature schedule for the formation of -silicon nitride (-Si3N4) whiskers by direct Nitridation of the porous silicon filter was studied, in order to optimize the amount of whiskers and improve the filter quality. Four different temperatures (1000, 1100, 1200 and 1300 °C) were selected, each with two different holding times (15 min and 1 hour) for complete Nitridation with N2 and N2+H2 gases. The as-formed whiskers were characterized by SEM, XRD techniques and the process conditions were studied. The filter with the Si3N4 whiskers was characterized evaluating mechanical properties of the porous silicon filter (Micro Hardness and Young Modulus). The permeability measurements were made before and after the Nitridation process. Analysis indicates that the higher Si3N4 whiskers formation temperature was 1300 °C for the gas (N2+H2) phase reaction results from the lower PSiO2/Psio ratio in the Si-N system. Titanium (99% pure) was used with the purpose of reduction of the oxygen partial pressure and the increase of the amount of -silicon nitride whiskers. The porous silicon filter improved its conditions with the silicon nitride whiskers, even though decreases also the fluid permeability measurement. However, it has a smaller flow decrement than filters with smaller porosity. The mechanical properties did not have variation at all, the porosity size increased because of the diffusion of Si to form whiskers in the Nitridation process.
Hydrogen Embrittlement of High Strength Steels
Authors: Sanchez Javier , Fullea Jose , Andrade Carmen , de Andres Pedro
Published: September 2009

Hydrogen embrittlement is believed to be one of the main reasons for cracking of structures under stress. High strength steels in these structures often include a ferritic core made of alpha-iron (body centered cubic lattice).
We compute the interaction of atomic hydrogen with iron using first principles. The interstitial hydrogen can be placed in two high symmetry positions: octahedral and tetrahedral sites. Our calculations provide diffusion barriers between these sites. These barriers have been analyzed to understand the propagation of hydrogen through the iron lattice. We analyze how these barriers can be modified by the hydrogen concentration.
The results show the main site for high and low hydrogen density and they show the diffusion coefficient variation by the hydrogen density.
Grain Boundary Diffusion of Fe in High-Purity Copper
Authors: Ribbe Jens , Schmitz Guido , Divinski Sergiy V.
Published: September 2009

Grain boundary (GB) diffusion of 59Fe in high purity polycrystalline copper was measured using the radiotracer technique and precision parallel sectioning in an extended temperature interval. The results of diffusion measurements below 900 K are consistent with Harrison's C kinetics and yield the GB diffusion coefficient of Fe in Cu with the pre-exponential factor of 5.610-6 m2/s and the activation enthalpy of 121 kJ/mol. Unexpectedly strong GB segregation of Fe in Cu hindered reliable determination of the Fe diffusivity in the B kinetics. Additionally, unconventional penetration profiles were measured for GB diffusion of 59Fe in Cu at high temperatures. Molecular dynamics simulation with the literature Finnis-Sinclair type interatomic potentials was performed to shed light into the observed features. A strong effect of the Fe coverage on GB structure and kinetics in pure Cu is predicted at increased temperatures above 900 K.
Diffusion Enhanced Rumpling Associated with Martensitic Transformation upon Cycling of Aluminide Bond-Coats
Authors: Bouchaud B. , Balmain J. , Pedraza-Diaz Fernando
Published: September 2009

In this work, β-NiAl aluminide coatings (cubic B2 structure) deposited on a DS substrate have been isothermally as well as cyclically oxidised at 1100°C for up to 240 h to study the diffusion mechanisms associated with the growth of the oxide scales. A 24 h cycle has been shown to promote enhanced Al depletion, thus requiring a sufficient Al flux to maintain a protective oxide scale. Glancing incidence X-ray diffraction (GI-XRD) combined to electron microscopy (FEG-ESEM / EDS) has been carried out to characterize the evolution of the phases induced by the progressive Al depletion into the coating. The results show that upon cycling, specimens undergo significant oxide scale spallation and increased roughness that can be ascribed to both the growth stresses and the phase transformation contribution whereas the coating has barely evolved after 240 h of isothermal exposure. In particular, the martensitic transformation (tetragonal L10 structure) that accompanies thermal cycling was found to be much more significant than the evolution of the γ’-Ni3Al (cubic L12 structure) phase over the same thermal cycle and therefore the B2 to martensite transformation could originate the progressive roughening of the surface. Conversely, upon isothermal exposure, the coating exhibited a typical alumina scale with almost no spallation and the appearance of rumples.
Diffusion of a Corroding Electrolyte through Defective Electroplated Ceria Based Coatings
Authors: Poupard S. , Pedraza-Diaz Fernando , Creus J.
Published: September 2009

Among the new environmentally friendly alternatives to improve the corrosion resistance of metallic substrates, cerium oxide based electrodeposited layers have raised particular attention. In this work, various electrodeposited layers on zinc substrate have been elaborated at different conditions to produce tailored compositions, microstructures and different degrees of porosity.
The use of electrochemical techniques (polarisation resistance measurements, electrochemical impedance spectroscopy) has allowed to ascertain the porosity, which coupled to Scanning Electron Microscopy (FEG-SEM) and Energy Dispersive Spectrometry (EDS) studies along the cross sections have revealed the inward and/or outward diffusion of the different elements through the film till the metallic surface. The resulting corrosion mechanisms of these coatings immersed in 3% NaCl are finally discussed.
Long Term Diffusion Studies in Fe Aluminide Coatings Deposited by Slurry Application on Ferritic Steel
Authors: Agüero Alina , González Vanessa , Gutiérrez Marcos
Published: September 2009

Diffusion iron aluminide coatings have shown excellent resistance to high temperature oxidation in air, corrosive atmospheres and steam. A study of the diffusion behaviour of slurry applied diffusion aluminide coatings deposited on ferritic steel have been carried out under a 100% flowing steam atmosphere for up to 50,000 h at 650 °C. The results have shown that initially, the coating forms by outward growth possibly including the dissolution of the steel in molten aluminium. At later stages, during exposure to steam at 650 °C, aluminium diffuses inward and moreover, Fe also diffuses outward resulting in the progressive development of Kirkendall porosity. Results have also indicated that in order to form a pure protective Al2O3 scale the Al wt.% has to be > 4. Below this content Al-Fe mixed oxides develop exhibiting a less protective behaviour.
Scanning Kelvin Probe Study on the Stability of the Steel/Coating Interfaces Contaminated by Soluble Salts
Authors: de la Fuente D. , Rohwerder M. , Chico B. , Morcillo M.
Published: September 2009

The presence of hydrosoluble species, mainly chlorides and sulphates, at the metal/paint interface promotes osmotic blistering of the coating and underfilm metallic corrosion when the concentration of the soluble salts exceeds a critical level due to the accelerated entrance of water to the interface. Loss of adhesion and cathodic disbondment can be also consequences of the presence of soluble salts. These processes can lead to the deterioration of the paint system in a very short period of time. However, since the interface is not easily accessible by experiment, not much is known about interfacial structure, reactions and the processes causing degradation. Scanning Kelvin Probe (SKP) is an ideal tool for the in situ monitoring of the degradation processes at the buried interface. On the other hand, for an in-depth understanding it is important that the superposition of the effects of all different parameters involved can be disentangled. Hence, it is important to design experiments focussing on individual aspects of the complex system.
A study of the fundamental aspects of the stability of the contaminated buried steel/coating interfaces, specially focused on the initial stages of blistering and underfilm corrosion, has been carried out. Results of the characterization study performed with a height-regulated SKP (HR-SKP) on surfaces contaminated at the interface by different salt concentrations with well defined crystal size and distribution are shown.
Diffusion Aluminide Coatings Using Spherical Micro-Sized Aluminium Particles
Authors: Juez-Lorenzo Maria , Kolarik Vladislav , Fietzek H. , Anchústegui M.
Published: September 2009

Previous work on the oxidation of nano- and micro-sized Al particles revealed a particle size window, where no meta-stable alumina phases were observed. Depositing such particles on an austenitic substrate, diffusion layers with reduced Al contents were obtained. These findings opened new perspectives for investigating the potential impact of the Al particle size and shape on the formation of diffusion aluminide coatings. Spherical Al particles sized in the range of 2 to 5 µm were deposited with a binder by brushing on the austenitic steel X6 CrNi 18-10 (Alloy 304H). For the curing process, the samples were annealed in air at 400°C for 1h. The diffusion effect of Al into the base material was studied in isothermal experiments at 700°C and 900°C with exposure times up to 2000 h in air.
The sample surfaces and the diffusion aluminide coatings in cross-section were analysed by field emission scanning electron microscopy (FE-SEM). The results show in the initial state the formation of a diffusion layer consisting of a less aluminium-rich Fe(Cr)-Al phase containing a Fe(Cr)-Al phase with higher content of Al in the region beneath the surface. On further exposure a double-layered structure is found with Kirkendall-pores between the two layers, which may lead to a complete separation of the outer layer. A thin adherent alumina scale is observed on the remaining diffusion layer after 1000 h and 2000 h at both temperatures, however overgrown by Cr2O3 at 900°C. The structure of the diffusion zone beneath agglomerates of Al particles reveals the influence of the particle size on the Al supply for the formation of the aluminide diffusion zone.
Post-Discharge Nitriding: Mathematical Modeling and Numerical Simulation of the Layer Growth
Authors: Castillo F. , Oseguera-Peña J. , Fraguela A. , Gómez J.A.
Published: September 2009

Nitriding by microwave post-discharge process involves molecular nitrogen dissociation. It has been observed that nitrogen flux from surface to solid during the early stage does not follow a parabolic regime and that the growth rate of concomitant nitride layers is sensitive to atomic nitrogen concentration on the surface. In this work a mathematical model has been developed in order to describe the kinetics of the compound layer formation during a post-discharge nitriding process. The model is related to a moving boundary value problem and considers different stages: diffusion process, formation of the layers, layer growth and quasi-stabilization of the layer growth. Natural conditions on the nitrogen concentration consistent with the mass transfer mechanism are assumed. An analytical approximate solution of Goodman’s type is sought and numerical simulation is conducted to study the nitride layer growth.
Study of the Role of Small Additions of Zr in the CVD- FBR Aluminization Process
Authors: Sánchez L. , Bolívar F.J. , Hierro M.P. , Pérez F.J.
Published: September 2009

In this work, iron aluminide coatings were developed by Chemical Vapor Deposition in Fluidized Bed Reactor (CVD-FBR) on ferritic-martensitic steels. Small additions of zirconium powder were introduced in the fluidized bed; as a consequence, the obtained coatings are thicker than that without zirconium additions. When Zr powders are added in the fluidized bed, the deposition atmosphere drastically changes, leading to increase the deposition rate. Thermodynamic calculations were carried out to simulate the modifications in the CVD atmosphere in the Al/Zr deposition system in comparison to the single aluminization. In order to optimize the conditions of the deposition, parameters such as temperature and concentration of zirconium introduced into the bed were evaluated and compared with the results obtained for the single aluminum deposition.
Magnetic Coupling in La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 Trilayers
Authors: Nemes N.M. , Visani C. , Garcia-Barriocanal J. , Bruno F.Y. , Sefrioui Z. , Arias D. , Leon C. , Garcia-Hernandez Mar , Te Velthuis S.G.E. , Hoffmann A. , Santamaría J.
Published: September 2009

We report on the interplay between ferromagnetism and superconductivity in trilayers La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 made of half metallic manganite and high temperature superconductor cuprate. Samples with a fully oxygenated cuprate show a magnetic field interval where the magnetizations of the manganite are aligned antiparallel. A considerable magnetoresistance accompanies the switching between magnetization configurations (parallel vs. antiparallel) of the manganite moments. Suppression of the free carrier density of the cuprate which occurs upon oxygen depletion, results in deep modifications in the shape of the normal state hysteresis loops indicating that there may be a magnetic coupling mediated by free carrier density of the cuprate. This result outlines the importance of quasiparticle transmission in the interplay between ferromagnetism and superconductivity in this kind of samples.
Sedimentation of Impurity Atoms in InSb Semiconductor under a Strong Gravitational Field
Authors: Iguchi Yusuke , Ono Masao , Okayasu Satoru , Mashimo Tsutomu
Published: September 2009

An atomic-scale graded structure has been formed by sedimentation of substitutional atoms under an ultra-strong gravitational field of 1 million G level in alloys and compounds. In this study, we investigate the sedimentation of impurity atoms in semiconductor materials under a strong gravitational field. High-temperature ultracentrifuge experiments (0.59×106 G, 400°C, 60 hours) have been performed on an InSb single crystal wafer which surface was coated with Ge by means of Physical Vapor Deposition (PVD). It was observed that the penetration depth of diffused Ge atoms under the gravitational field was several times larger than under terrestrial field at the same temperatures.
Atom Redistribution during co-Doped Amorphous Silicon Crystallization
Authors: Portavoce Alain , Mangelinck Dominique , Simola Roberto , Daineche Rachid , Bernardini Jean
Published: September 2009

Atom redistribution during crystallization of a B and P co-doped amorphous Si layer produced by Si and P chemical vapor co-deposition and B implantation has been investigated. The crystallization of the entire layer is quasi-instantaneous for annealing temperature greater than 650 °C. The crystallization rate is well reproduced by the Avrami-Johnson-Mehl-Kolmogorov model of transformation. The Avrami n is found equal to 4, which is corresponding to 3D bulk crystallization. Crystallization promotes a non-Fickian redistribution of B atoms, allowing for an abrupt interface between B-doped and B-undoped regions. After crystallization, B diffuses in the polycrystalline Si layer for concentrations lower than 1.5  1020 at cm3 via the type B kinetic regime. Crystallization has no significant (or detectable) influence on the P profile. For temperatures higher than 750 °C, P diffuses in the poly-Si layer towards the region of highest B concentration via the type B kinetic regime, leading to P uphill diffusion. This phenomenon can be simulated considering chemical interactions between B and P atoms in both grains and grain boundaries.
Formation of Amorphous Graded Structure in Bi3Pb7 Intermetallic Compounds under Strong Gravitational Field
Authors: Mashimo Tsutomu , Iguchi Yusuke , Bagum Rabaya , Sano Tomokazu , Takeda S. , Kimura S. , Sakata Osamu , Ono Masao , Okayasu Satoru , Tsurui T. , Hiraga K.
Published: September 2009

A visible four-layers structure with anomalous nano-sturucture was formed from a homogeneous -phase Bi3Pb7 intermetallic compound under a strong gravitational field (1.02x106 G, 130°C, 100 hours). In the 4th layer (lowest-gravity region), pure Bi particles precipitate. In the 2nd 3rd layers, composition graded structures, where Pb content increased along the gravity direction, were formed. It was found that the very broad XRD peak appeared in the 2nd layer, which indicated that an amorphous structure was contained.
Characterization of Intermetallic Layer with Nanoresolution Using X-Ray Standing Wave Technique
Authors: Cserháti Csaba , Erdélyi Z. , Balogh Z. , Daróczi Lajos , Csik A. , Langer G.A. , Varga M. , Zizak I. , Erko A. , Beke Dezső L.
Published: September 2009

X-ray standing wave technique has been used to measure the kinetics of CoSi intermetallic phase growth in a-Si/Co/a-Si sandwich structure. The a-Si/Co/a-Si arrangement were placed into a waveguide structure formed by two Ta films. X-ray fluorescence and extended X-ray absorption fine structure analysis has been used in a combination with X-ray standing wave technique for depth profiling with sub-nanometer resolution of specimens annealed at 493K for different annealing time. The position and the thickness of the growing CoSi intermetallic phase have been monitored.
Growth Mechanism vs Matter Transport in Thermally Growing Oxides on High Temperature Materials: A Brief Survey Based on the Case Study of Alumina Formers
Authors: Jedlinski Jerzy
Published: September 2009

This paper reviews briefly the relationship between the growth mechanism and matter transport using as an example the best currently applied metallic materials being alumina formers. The attention is paid to the experimental approach as well as to the interpretation procedure of experimental results. The scale structure, microstructure, morphology and phase composition are indicated as factors strongly affecting its growth mechanism. The attempt is made to elucidate the possible relationships between the obtained experimental results and actual scale growth mechanisms operating during oxidation exposures.
Diffusion of Oxygen in Thermally Grown Oxide Scales
Authors: Chevalier Sébastien
Published: September 2009

High temperature reactivity of materials under oxidizing atmospheres is based on the formation of protective oxide scales. The protectiveness is obtained when the thermally grown oxide scales are dense, continuous and adherent to the metallic substrates (even during thermal shocks); as a matter of fact, the growth of the scale has to be governed by diffusion of species across the growing scale. The diffusing species are coming from the substrate (metallic ions) and/or from the oxidizing atmosphere (oxygen ions).
The understanding of growth mechanisms can be reached by making two stage oxidation experiments, using oxygen isotopes. The experiment consists in oxidizing first the metallic substrate in 16O2, evacuating the oxygen after the desired time, and replacing it by 18O2. The distribution of oxygen isotopes given by secondary ion mass spectrometry (SIMS) across the oxide scale informs about the growth mechanisms: anionic transport, cations diffusion or mixed diffusion processes.
The use of marker experiment is able to determine the oxygen diffusion coefficients within the growing scales. In this case, a thick scale is grown under 16O2, followed by a shorter diffusion experiment in 18O2. The distribution of 18O isotope across the scale by plotting ln (18O intensity) versus x (depth in oxide) allows determining the oxygen effective diffusion coefficient in the scale, according to the classical Fick’s law solution. A more accurate analysis of these profiles can provide information about bulk and grain boundary diffusion of oxygen. The results can be related to kinetics according to Wagner’s theory. The proposed work consists firstly in making a state of the art review about oxygen diffusion in thermally grown oxide scales, and secondly in connecting the so-obtained outcome (effective, bulk and grain boundary diffusion) to kinetics results. The proposed oxides are chromia, alumina and zirconia.
Evaluation of Si Coating on Ferritic Steels by CVD-FBR Technology in Steam Oxidation
Authors: Bolívar F.J. , Sánchez L. , Hierro M.P. , Pérez F.J.
Published: September 2009

The development of new power generation plants firing fossil fuel is aiming at achieving higher thermal efficiencies of the energy conversion process. The major factors affecting the efficiency of the conventional steam power plants are the temperature and, to a lesser extent, the pressure of the steam entering the turbine. The increased operating temperature and pressure require new materials that have major oxidation resistance. Due to this problem, in the last years numerous studies have been conducted in order to develop new coatings to enhance the resistance of steels with chromium contents between 9 and 12% wt against steam oxidation in order to allow operation of steam turbines at 650 0C. In this study, Si protective coatings were deposited by CVD-FBR on ferritic steel P-91. These type of coatings have shown to be protective at 650 0C under steam for at least 3000 hours of laboratory steam exposure under atmospheric pressure. Morphology and composition of coatings were characterized by different techniques, such as scanning electron microscopy (SEM), electron probe microanalysis, and X-ray diffraction (XRD). The results show a substantial increase of steam oxidation protection afforded by Si coating by CVD-FBR process.
Graded Nitrogen Ingress in FCC Metallic Structures and the Related Microstructures and High Temperature Oxidation Behaviour
Authors: Pedraza-Diaz Fernando , Grosseau-Poussard Jean Luc , Dinhut J.F. , Balmain J. , Bonnet G.
Published: September 2009

Nitriding by low energy high flux processing has been carried out at about 400°C in fcc metal substrates (pure Ni, Ni-20Cr model alloy and a conventional AISI 304L stainless steel). The gradual ingress of this element into the structures will be shown to depend markedly on the chemical composition of the substrate. The associated expansion of the fcc lattices and surface roughness will be discussed in this work with the support of X-ray diffraction, atomic force, scanning and transmission electron microscopy techniques. In light of the resulting composition, microstructures and thickness of nitrided layers, some preliminary results of their behaviour under isothermal oxidation conditions at high temperatures will be discussed. The high temperatures will provoke decomposition of the expanded austenite into a conventional gamma phase and some chromium nitrides. Trapping of chromium therefore shall explain a reduction of the high temperature oxidation resistance against the untreated substrates.
On the Mechanism of Cu2O Oxidation at High Temperatures
Authors: Grzesik Zbigniew , Migdalska Monika
Published: September 2009

Oxidation mechanism of nonstoichiometric cuprous oxide (Cu2 yO) has been studied as a function of temperature (973-1273 K) and oxygen pressure (1-105 Pa), using microthermogravimetric, marker and two-stage oxidation techniques. The last method consisted in using heavy oxygen isotope 18O in order to confirm the results, obtained with marker technique. It has been found that in early stages of reaction not exceeding 30 hours, CuO formation on the surface Cu2 yO follows approximately cubic rate law. In later stages, during long-term oxidation, lasting hundreds of hours, oxidation process follows strictly parabolic kinetics with the rate, being independent of Cu2 yO pre-treatment. Marker and two-stage oxidation experiments have shown that the growth process of CuO layer proceeds by the outward diffusion of cations, clearly indicating that cation sublattice of CuO is predominantly defected.
Behaviour of Aluminide Diffusion Coatings on HCM12-A Steel by Al/Ce and Al/La CVD-FBR in Oxidation.
Authors: Sánchez L. , Bolívar F.J. , Hierro M.P. , Pérez F.J.
Published: September 2009

The steam oxidation behaviour at 800°C of aluminized HCM12A ferritic-martensitic steel has been studied. The aluminization process used was CVD in fluidized bed reactor (CVD-FBR), using a reactive bed modified with Ce or La particles. The obtained coatings were mainly composed of (Fe,Cr)2Al5 intermetallic phase. Long term oxidation (1000h) behaviour of the coated HCM12A was studied in 100%H2O atmosphere. By the application of the protective coating, the ferritic-martensitic steel oxidation rate is reduced considerably because of the alternately formation of Al2O3 and Cr2O3 + (Fe,Mn)3O4 protective scales on the substrate surface due to the diffusion processes that take place during the exposure at high temperatures in combination with the aggressive environment.
The Influence of CVD-FBR Coatings on HCM12 Corrosion Behaviour under Molten Salt Conditions
Authors: Nieto J. , Hierro M.P. , Bolívar F.J. , Pérez F.J.
Published: September 2009

The influence of Al and Al-Si coatings on the corrosion behaviour of HCM12 in molten KCl-ZnCl2 mixture at 650°C in air has been characterized by electrochemical impedance spectroscopy (EIS). Al and Al/Si protective coatings were developed by chemical vapour deposition in fluidized bed reactor (CVD-FBR) at moderate temperature to respect to mechanical properties of substrate. Scanning electron microscopy (SEM) was used to analyse the damage on the HCM12 electrode surface. Al-Si coating was found to be more resistant to the molten chlorides attack than Al coating; and both coatings increased the corrosion resistance of HCM12 in these conditions. The surface composition has been determined by X-ray diffraction (XRD).
Influence of the Processing Parameters on the Nature of Oxides Formed on Sintered Stainless Steels during High-Temperature Exposures
Authors: Bautista Asuncion , Moral Cristina , Velasco Francisco
Published: September 2009

Powder metallurgical (PM) stainless steels can be used for high-temperature applications. However, their characteristic porosity dramatically affects the resistance of the stainless steels to the oxidative attack and modifies the oxidation mechanisms. In this work, it is discussed how the processing parameters of PM stainless steels can modify the diffusion process when the material is exposed at high-temperature in oxidative environments. Processing parameters affect not only the amount but also the nature of the formed oxides. For powders of a given composition, the pressing method, the sintering atmosphere (vacuum, 100% H2 or 75%H2/25%N2) and the sintering temperature can modify the amount of porosity and its shape, often promoting the formation of less-protective oxides, instead of chromia. The different oxygen partial pressures in the inner pores and on the outer surface of the material also tend to make oxides formed inside the stainless steel pores more protective than those formed on their surface. X-ray diffraction, SEM and EDS studies of surface and cross-sectional views of the oxidized materials are used to prove these differences.
Establishment of Thermally Grown Oxides upon the Early Oxidation Stages of Ni20Cr and Ni30Cr
Authors: Bouchaud B. , Douminge Ludovic , Pedraza-Diaz Fernando
Published: September 2009

The performance of Ni-based alloys at high temperature strongly depends on the formation of a protective chromia scale which prevents from fast growth NiO scale. The evolution of the oxide scales will be shown to be strongly dependent on the chromium content especially for the shortest oxidation times. Indeed, transient stages will be reported to condition the subsequent oxidation behavior at longer times until the oxidation rate constant becomes invariant. To this end, a comparative study on the outward and inward diffusion of species upon oxidation at 800°C for short times (0.5 / 1 / 2 / 4 / 8 h) has been evaluated on commercial available Ni20Cr and Ni30Cr alloys through in-situ Raman spectroscopy and supported by post-mortem X-ray diffraction (XRD) as well as scanning electron microscopy coupled to energy dispersive spectrometry (FEG-ESEM / EDS) investigations.
An Insight on the Influence of Ion Implantation on the Pitting Corrosion Resistance of AISI 430 Stainless Steel
Authors: Abreu C.M. , Cristóbal M.J. , Merino P. , Pena G. , Pérez M.C.
Published: September 2009

Research on the effect of ion implantation on the corrosion behaviour of metals has been carried out for years, but some difficulties arise in the comparison of the obtained results due to variations in experimental conditions (alloys, surface preparation, doses, experimental techniques...). This work tries to overcome those differences, presenting the effect of several elements (Ce+, N+, Cr+ and Cr+ N+) implanted in similar conditions on the pitting corrosion resistance of AISI 430 stainless steel. Potentiodynamic measurements in 1M NaCl demonstrate the beneficial effect of all the implanted elements, showing that Ce+ is the less efficient ion, while Cr+ N+ co-implantation gives the best results in terms of localized attack resistance. Pitting morphology is explained in terms of the XPS and GIXRD data that allow chemical and structural characterization of the implanted layer. Those results help to enlighten the protection mechanisms involved in the considered implantations.
Strong-Gravity Effect on Twinned Y1Ba2Cu3O7-x Single Crystal
Authors: Bagum Rabaya , Okayasu Satoru , Iguchi Yusuke , Ono Masao , Mashimo Tsutomu
Published: September 2009

Ultracentrifuge experiments were performed on the twinned Y1Ba2Cu3O7-x (Y123) single crystal at much lower temperatures than the melting point. Two layers structure with slightly different compositions was observed in the sample ultracentrifuged at 250°C(380,000 G), which might be due to the sedimentation of atoms. In the strong gravity layer, it was found that the Y123 phase disappeared, and unknown XRD peaks appeared. Decomposition occurred in the sample ultracentrifuged at 400°C.
Determination of Diffusion Coefficients of Oxygen Vacancies in La0.58Sr0.4Co0.2Fe0.8O3-δ Perovskite Type Oxides
Authors: Schlehuber D. , Wessel Egbert , Singheiser Lorenz , Markus T.
Published: September 2009

One possibility to run a zero CO2-emission power plant is the oxyfuel combustion process. An efficient technology to separate oxygen from air are processes with oxygen transport membranes. It is important that these membranes have a high permeability additional to high chemical stability under power plant conditions. La0.58Sr0.4Co0.2Fe0.8O3- (LSCF) is a mixed ionic electronic conducting material (MIEC) which is considered to have good permeation properties and a high stability. In this work LSCF based membranes are investigated. Data from a TGA (Thermo-Gravimetric Analyser) have been used to determine the diffusion coefficient of oxygen vacancies in LSCF perovskite type oxides for different temperatures.
Li Conductivity of Nanocrystalline Li4Ti5O12 Prepared by a Sol-Gel Method and High-Energy Ball Milling
Authors: Iwaniak W. , Fritzsche J. , Zukalová M. , Winter R. , Wilkening Martin , Heitjans Paul
Published: September 2009

Spinel-type structured Li4+xTi5O12 (0 6 x 6 3 ) is actually one of the most promising
anode materials for Li ion batteries. In its nanostructured form it is already used in some commercially
available Li ion batteries. As was recently shown by our group (Wilkening et al., Phys. Chem.
Chem. Phys. 9 (2007) 1239), Li diffusivity in microcrystalline Li4+xTi5O12 with x = 0 is rather slow.
In the present contribution the Li conductivity in nanocrystalline samples of the electronic insulator
Li4Ti5O12 prepared by different routes is investigated using impedance spectroscopy. The mean
crystallite size of the samples is about 20 nm. The ionic conductivity of nanocrystalline Li4Ti5O12
obtained by mechanical treatment is higher by about two orders of magnitude compared to that found
for a material which was prepared following a sol-gel method. The latter resembles the behaviour of
the microcrystalline sample with an average particle size in the μm range rather than that of a nanocrystalline
ball milled one with a mean crystallite size of about than 20 nm. The larger conductivity
of the ball milled sample is ascribed to a much higher defect density generated when the particle size
is reduced mechanically.
Thin Film Dissolution into Semi-Infinite Substrates: Surprising Interface Kinetics and Dissolution Modes
Authors: Erdélyi Z. , Girardeaux Christophe , Beke Dezső L. , Bernardini Jean , Portavoce Alain , Katona G.L. , Balogh Z. , Rolland Andree
Published: September 2009

Depending on the thermodynamic, structural and diffusion properties of the system, a thin deposit dissolves into a substrate by different mechanisms. In this communication these different behaviours, investigated by surface analytical techniques (AES, XPS, STM, UPS, etc) [ - ], are reviewed. The experiments were also supported by computer simulations. The obtained results are compared and it is summarized how different parameters influence the dissolution of a thin film in a substrate. Furthermore, it is show that i) the volume dissolution kinetics is different on the atomic-/nano-scale than on the microscopic scale due to the diffusion asymmetry ii) the volume and GB diffusion in one measurement can be separated and iii) pure (C-kinetic) GB diffusivities can be determined from thin film kinetics measurements performed under adequate conditions.
On the Formation of Unusual Diffusion Profiles in CdxZn1-xTe Crystals after Implantation of Different Elements
Authors: Wolf Herbert , Wagner F. , Kronenberg J. , Wichert Th.
Published: September 2009

It is known that the diffusion of Ag and Cu in Cd1 xZnxTe crystals exhibits unusual concentration profiles depending strongly on the external vapor pressure of Cd during diffusion. Recent experiments show that the dopant Na forms qualitatively the same diffusion profiles including the phenomenon of uphill diffusion. Also the transition elements Ni and Co show a strong dependence of the diffusion behavior on the external Cd pressure, but the shapes of the concentration profiles differ significantly from those known for Ag and Cu. The different behavior of Ag, Cu, and Na, on the one hand, and Ni and Co, on the other hand, are proposed to be connected to the respective charge states of the dopants at interstitial positions in Cd1 xZnxTe. For the dopants K and Au, unusual diffusion properties have not been observed. The respective diffusion coefficients are DK = 1.2(2)•10 10 cm2/s (750 K) and DAu = 8(2)•10 8 cm2/s (800 K).
Evolution of Concentration Profiles and Diffusion Paths in Single-Phase Multicomponent Multilayered Assemblies
Authors: Kulkarni Kaustubh N. , Dayananda Mysore A.
Published: September 2009

An analysis of multilayered assemblies set up with multicomponent alloys selected in a single phase field has been recently developed on the basis of a matrix of constant interdiffusion coefficients. This analysis employs a transfer matrix method and is applicable to a study of evolution of concentration profiles and diffusion paths as a function of time for multilayered diffusion assemblies (MDAs) where any number of finite layers is sandwiched between two bulk terminal alloys. The analysis is utilized in this study to simulate concentration profiles and diffusion paths for MDAs assembled with (fcc) Cu-Ni-Zn alloys with two terminal alloys, A and B, sandwiching an alloy layer C in the middle. For short diffusion times the diffusion path of the ternary MDA, A/C/B, corresponds to two segments corresponding to the diffusion paths of the infinite diffusion couples, A/C and C/B. At longer times the diffusion zones of the two individual couples overlap and the diffusion path of the MDA varies continuously with time. The evolution of the concentration profiles and diffusion paths is presented and each intermediate path configuration is associated with a unique ratio of the middle layer thickness to the square root of diffusion time.
The simulated concentration profiles clearly show the development of uphill diffusion and zero-flux planes (ZFP) for the individual components due to diffusional interactions among the components. At very long times, the diffusion path of the MDA approaches that of the infinite couple A/B between the two terminal alloys.
Unusual Behaviour of the Dissolutions Kinetics of one Monolayer of Si in Cu(001)
Authors: Lalmi Boubekeur , Girardeaux Christophe , Portavoce Alain , Bernardini Jean , Aufray Bernard
Published: September 2009

We present an experimental study by Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) of the dissolution of about one monolayer of silicon previously deposited at room temperature on Cu (001). The isochronal dissolution has been recorded in the temperature range [50-320°C] (annealing rate 1.5°C/min). The plateau observed in the kinetics dissolution for temperatures between 95°C and 240°C, reveals the formation of an intermetallic two dimensional superficial phase thermally stable in this range of temperature. On the plateau, LEED patterns show the formation of a (5x3) superstructure. Above 255°C, we observe a very fast dissolution of the surface alloy characteristic of a first-order surface transition. Isothermal dissolutions kinetics have been recorded above and under the surface transition temperature (250°C and 270°C). From these measurements, we have evaluated bulk diffusion coefficients of Si in Cu assuming a local equilibrium. The diffusion coefficients measured within this hypothesis at 250°C and 270°C are respectively higher and lower than those extrapolated from high temperature measurements for Ge in Cu.
Alkaline-Earth Diffusion in Mixed Cation Glasses
Authors: Grofmeier M. , Natrup F.V. , Bracht Hartmut
Published: September 2009

Diffusion of alkaline-earth ions in mixed cation glasses of the composition xA2O•(3-x)MO•4SiO2 (x = 0.0, 0.1, 0.3, 0.4 and 1.0; A = Na, K; M = Ca, Ba) was investigated by means of the radiotracer diffusion technique below the respective glass transition temperatures. The mobility of alkaline-earth ions increases with the alkali content in all analyzed glass systems with no decrease in the diffusion activation energy, but a raise in the pre-exponential factor. A distinct dependency of the activation energy of the alkaline-earth ions on the type and content of the alkali ions in the glass is observed. Additional experiments with thin glass films derived by the sol-gel technique reveal an analogous diffusion behaviour. This demonstrates that the dynamic of alkaline-earth ions in mixed cation glasses does not depend on the way of glass preparation.
Diffusion in Nanostructured Materials
Authors: Divinski Sergiy V.
Published: September 2009

Recent results on diffusion in nanostructured materials are reviewed. The analysis highlights the importance of the proper account for a hierarchic microstructure which is often formed in nanostructured materials. The diffusion kinetics is such a material requires a special consideration in dependence on the temperature, diffusion time and the segregation level of the solute. Pressure-less sintering results in clustering of nanograins with significantly enhanced diffusivity of the inter-agglomerate boundaries. Severe plastic deformation produces a broad spectrum of high-angle grain boundaries (GBs) with different kinetic properties. The majority of the high-angle GBs reveals diffusivities very similar to those of general high-angle GBs in their well-annealed coarse-grained counterparts. Nevertheless, considerably faster short-circuit diffusion paths are detected, too. The origin, geometric arrangement, structural and kinetic properties of these high-diffusivity paths are comprehensively investigated and discussed.
Isotope Fractionation due to Sedimentation of Atoms in Centrifuged Indium-Lead Alloy
Authors: Ono Masao , Iguchi Yusuke , Okayasu Satoru , Esaka Fumitaka , Kobayashi Katsura , Hao Ting , Bagum Rabaya , Osawa Takahito , Fujii Kimio , Nakamura Eizo , Mashimo Tsutomu
Published: September 2009

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 x 106 g for 100 hours at 150 °C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). 206Pb/208Pb and 207Pb/208Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy 208Pb isotope abundance increased and the light 206Pb isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of 206Pb/208Pb versus 207Pb/208Pb proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.
Emission Mössbauer Spectroscopy of Grain Boundaries in Poly- and Nanocrystalline Metals
Authors: Popov Vladimir V.
Published: September 2009

Capabilities of the emission nuclear gamma resonance (NGR) spectroscopy in studying grain boundaries in metals are considered. It is demonstrated that this method enables to evaluate grain-boundary segregation factors, to determine grain-boundary diffusion mechanisms, to estimate an effective diffusion coefficient in near-boundary areas, etc. Besides, this method permits to evaluate quantitatively differences in the properties of grain boundaries of polycrystalline and nanostructured materials.
Formation of a Nano-Hole via Oxidation of Metal Nanoparticles
Authors: Nakamura Ryusuke , Nakajima Hideo , Mori Hirotaro
Published: September 2009

The formation of hollow metal oxide nanoparticles through oxidation process has been studied by transmission electron microscopy for Cu, Zn, Al, Pb and Ni in order to clarify the detailed formation mechanism of hollow oxide nanoparticles and their governing factors. For Cu, Zn, Al and Ni nanoparticles, hollow oxide nanoparticles are obtained as a result of vacancy aggregation in the oxidation processes. These results arise from faster outward diffusion of metal ions through the oxide layer in the oxidation processes. On the other hand, Pb nanoparticles turn to solid PbO, because the diffusivity difference DPb < DO in PbO leads to no formation of vacancy clusters.