bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Studies of Diffusion by the Dissociative Mechanism in the Case of a Foreign Atom Source
Authors: Benmakhlouf A.
Published: March 2009

The analytical treatment of dissociative diffusion by using the matched perturbation method given in the literature deals with a virtually infinite foreign-atom source producing a constant^concentration at the boundary. In this paper, a new mathematical model is developed for analysing the dissociative diffusion of the solute atoms in the case of finite-source conditions. The mathematical model combines the reaction-diffusion equations which govern solute atom diffusion by the dissociative mechanism and the boundary condition expressing the fact that the rate at which solute leaves the source is always equal to that at which it enters the sheet over the surface x=0. Solutions obtained by applying the matched perturbation method and their comparison with those of the numerical study are also presented in this paper.
Breaking Atomic Bonds through Vibrational Mode Localization
Authors: Dmitriev Sergey V. , Li Ju , Yoshikawa Nobuhiro , Tanaka Yoshihisa , Kagawa Yutaka , Kitamura Takayuki , Yip Sidney
Published: March 2009

We apply the lattice instability analysis to homogeneously strained single crystal with a flat or defected surface to demonstrate that, in the process of emission of dislocation by an unstable surface, prior to the breaking of atomic bonds, a vibrational mode localizes, foretelling the location and the manner of the impending microscopic catastrophic event.
Phase Transformations in ε-/γ'-Iron Nitride Compound Layers in the Temperature Range of 613 K - 693 K
Authors: Liapina Tatiana , Leineweber Andreas , Mittemeijer Eric Jan
Published: March 2009

ε/γ'-iron nitride (ε-Fe3N1+x, γ'-Fe4N) compound layers with thicknesses of about 10 µm were grown on pure α-Fe by gas nitriding at 823 K followed by quenching and were annealed at different temperatures in the range of 613 K – 693 K for different periods of time. These heat treatments led to a redistribution of nitrogen within the compound layer as well as between the compound layer and the adjacent ferrite, inducing thickness changes of the ε- and γ'-layers. The changes were analysed by light microscopy, electron probe microanalysis and X-ray diffraction. Models to describe and interpret the phase transformations in the ε/γ'-iron nitride compound layers as a function of time and temperature are discussed.
Diffusion of Confined Polymer Chains
Authors: Sikorski Andrzej
Published: March 2009

Simple lattice model of polymer systems was developed and studied using the Monte Carlo method. The model chains were star-branched with f = 3 arms and rings. The number of polymer segments in a chain was varied up to 800. The chains were built on a simple cubic lattice with the excluded volume interactions only (the athermal system). The polymers were confined between two parallel impenetrable walls with a set of irregular obstacles what can be treated as porous media. A Metropolis-like sampling algorithm employing local changes of chain conformation was used. The dynamic properties of the model system were studied. The differences in the mobility of chains with different internal architectures were shown and discussed. The possible mechanisms of motions were presented.
Grain Boundary Defects in ZnO Ceramic Doped with Mo
Authors: El-Hofy M.
Published: March 2009

Four Zinc Molybdenum ceramic samples (S1-S4), have been prepared according to the chemical formula (1-x) ZnO - x (MoO3), where (x = 0.1, 0.2, 0.6, 0.8) mol %. The samples were studied through X-ray Diffraction analysis, SEM, EDAX, I-V characteristics at different temperature up to 200 οC and C-V measurements. X-ray results decleared that Mo contributes to the structure mainly substitution in place of Zn. Entrance of Mo into the structure increases the intensity and shifts the X-ray peaks to higher θ values. At lower additions, Mo is segregated along the grain boundaries in the form of short bars, while at higher additions, circular batches of Mo rich phase are appeared on the surface of the large ZnO grains. The formulation of Schottky barrier is indicated, in case of (x < 0.1) the barrier is attributed to the trapping of electrons by the defects at the grain boundaries, while at higher additions the barrier was attributed to the concentration gradient of Zn vacancies in the grain boundary region. The calculated barrier height and non-linearity coefficient α are (1.15, 1.12, 1.15 and 1.48) eV and (59.4, 22.5, 35 and 87) for the samples S1- S4 respectively. Going from S1 to S4, donor density Nd and density of the interface states Ns decrease from 3.81x 1018 to 0.46x1018 cm-3 and from 6.41x1012 to 2.52x1012 cm-2 respectively, while the width W(cm) of the potential barrier increases from the value 1.68x10-6 cm for S1 to the value 5.5x10-6 cm for S4 . The current processed via electron tunneling through the barrier.
High Oxide Ion Conductivity of (Ba1-x-ySrxLay)InO2.5+y/2 Members Derived from the Ba2In2O5 System
Authors: Kakinuma Katsuyoshi , Yamamura Hiroshi , Atake Tooru
Published: March 2009

We have discovered a high oxide ion conductor within the perovskite-type (Ba1-x-ySrxLay)InO2.5+y/2 solid-solution system. The system was derived from brownmillerite-type Ba2In2O5, which possessed a ordered oxide ion vacancies. When we doped La3+ into the Ba site, the vacancy changed to a disordered state. The oxide ion conductivity increased with the amount of doped La3+, reaching a maximum value of 0.12 (S/cm) at 800 oC in (Ba0.3Sr0.2La0.5)InO2.75, a level exceeding that of yttria-stabilized zirconia. The oxide ion conductivity of this system was strongly dependent on the unit cell free volume, which appears to be the key parameter governing oxide ion mobility.
Oxygen Diffusion in La2-xSrxCuO4-δ: Molecular Dynamics Study
Authors: Savvin S.N. , Mazo G.N. , Ivanov-Schitz A.K.
Published: March 2009

The oxygen mobility in La2-xSrxCuO4-δ (x=0.15; 0.6; 1) was studied by the Molecular Dynamics (MD) technique. The parent layered La2CuO4 crystal structure has been shown to give rise to a strong anisotropy of oxygen diffusion coefficient in the lattice. Equatorial oxygen sites in(CuO2) layers were found to provide the paths of the fast oxygen transport in the structure, while the axial ones in (La2O2) blocks were substantially less mobile. The influence of the dopant concentration on structural properties and energetic characteristics of the oxygen migration are discussed. Analysis of the ion trajectories obtained during the simulation allowed explaining the observed dependence of the oxygen diffusion activation energies on the strontium content and provided further insight into the mechanism of oxygen diffusion in the oxides.
Transport and Electrochemical Properties of LiyNixMn2-xO4 (0.1 ≤ x ≤ 0.5) Cathode Materials
Authors: Molenda J. , Ziemnicki M. , Świerczek K. , Marzec J.
Published: March 2009

In this paper structural, electrical, electrochemical and thermal (DSC) characterization of series of manganese spinel samples with manganese substituted to different degree (x = 0 – 0.5) with nickel are presented. The conductivity and thermoelectric power measurements were performed in wide temperature range also versus oxygen partial pressure and for deintercalated samples. Electrochemical studies of these cathode materials were conducted in Li / Li+ / LiyNixMn2−xO4 type cells. Substitution of manganese with nickel causes disappearance of the phase transition characteristic of LiMn2O4 spinel. Studies of electrical properties reveal that Ni ions do not participate in charge transport at low temperatures. In the charge curves of Li / Li+/ LiyNixMn2−xO4 cells there are two visible plateaux, separated with distinct potential jump (~0.5V), which position on Li content perfectly matches the Mn3+ content in the doped cathode material. The lower plateau is related to the Mn3+ → Mn4+ oxidation, while the next of higher voltage, of the dopant Ni2+ → Ni4+ oxidation. The schematic diagrams of relative Mn – Ni electronic levels alignment are proposed.
Collective Correlation Factors in Random Non-Stoichiometric Inermetallic Compounds
Authors: Sandhu I.S. , Chaturvedi D.K. , Belova Irina V. , Murch Graeme E.
Published: March 2009

In this paper Manning random alloy model has been extended to the binary nonstoichiometric intermetallic compound of the B2 structure. Two sub-lattices, that are dynamically independent in six-jump cycle (6JC) mechanism, are coupled together by taking into consideration the vacancy motion as a sequence of nearest neighbour jumps in random directions. The linear response expressions for the phenomenological transport coefficients are evaluated making use of the kinetic equation approach. The expressions for collective correlation factors are derived in terms of the equilibrium partial atomic concentrations and jump frequencies. Results are compared with Monte Carlo simulation results using the four-frequency model.
Tracer Diffusion by Six-Jump-Cycles in Nonstoichiometric B2 Intermetallic Compounds
Authors: Gosain K.L. , Chaturvedi D.K. , Belova Irina V. , Murch Graeme E.
Published: March 2009

Tracer diffusion in non-stoichiometric B2 intermetallic compounds having antistructural disorder is investigated using the six-jump-cycle (6JC) as a fundamental diffusion unit. For non-stoichiometric compositions, the antistructural atoms are assumed to be isolated and located at one of the six [110]-type and [100]-type sites (as only these sites are involved in the 6JC or 2JC). The jump frequencies for the 6JC involving a perfectly ordered configuration are calculated in terms of a four-frequency-model, using the meanfirst- passage concept of Arita et al. The jump frequency of an antistructural atom at [110] or [100]-type sites is taken to be the harmonic mean of frequencies of two successive nearestneighbour jumps of the same kind of atoms. The expressions for the tracer diffusion coefficients are derived for both atomic components at deviations from stoichiometry, assuming that the 6JC mechanism is valid. The results are compared with Monte Carlo simulations based on single vacancy jumps and found to be in fair agreement for compositions close to stoichiometry.
Mathematical Modeling of Solid-State Diffusion during Mechanical Alloying
Authors: Khina Boris B. , Formanek Boleslaw
Published: March 2009

It is known experimentally that solid-state interdiffusion is substantially enhanced during plastic deformation. This is especially noticeable in Mechanical Alloying (MA) which is used for producing a wide range of metastable materials (supersaturated solid solutions, amorphous phases, nanostructures) with unique properties. However, a physical mechanism of enhanced diffusion
during MA is not clearly understood yet, and a comprehensive model of this complex phenomenon has not been developed so far. Moreover, the role of the diffusion process in MA is hotly debated in literature. In this work a new, self-consistent mathematical model of solid-state interdiffusion in a binary substitutional system A-B during periodic plastic deformation is developed. The model includes basic physical factors that affect diffusion, such as generation of non-equilibrium point
defects by gliding screw dislocations during deformation and their relaxation in periods between impacts. The cross-link terms are considered, and interaction of point defects with edge dislocations and incoherent phase boundary A/B is taken into account. Computer simulation is performed using realistic data (e.g., quasi-equilibrium self-diffusion coefficients known in literature) and the process
parameters typical of MA in a vibratory mill. A repeated “deformation-rest” cycle is considered. The results of modeling reveal the physical mechanism of the enhancement of solid-state diffusion by periodic plastic deformation during MA and demonstrate that within the frame of this approach supersaturated solid solutions can form within a reasonably short processing time.
Characteristics of Hydrogen Sorption, Solubility and Diffusivity in Graphites and Carbon Nanomaterials: Relevance to the On-Board Storage Problem
Authors: Nechaev Yuriy S. , Filippov G.A.
Published: March 2009

Results of experimental and theoretical investigations on hydrogen sorption by various carbon nanostructures, including fullerenes, single-walled and multi-walled nanotubes, nanofibers and nanographite-based composites are surveyed. Results of a thermodynamic analysis of the most significant experimental data are presented. The emphasis is placed on the studies reporting the extremum sorption parameters. The thermodynamic and kinetic (diffusion) parameters and equations describing the sorption processes are refined. The prospects of the applications of novel carbon nanomaterials for hydrogen storage in automotive industry are discussed.
Retardation Effect of Grain Boundary Segregation on Grain Boundary Diffusion
Authors: Bokstein Boris S. , Rodin Alexey , Smirnov A.N.
Published: March 2009

The effect of grain boundary segregation (GBS) on grain boundary diffusion (GBD) is analyzed in frame of the new model. This model supposes the formation of the specific “nuclei” in a grain boundary (GB) solid solution. Their composition is close to that of the nearest phase in grain in equilibrium with solid solution in grain. These GB “nuclei” form after the same solubility as in the bulk is reached. The size of these “nuclei” is close to an atomic size and consequently the new interfaces inside the two-dimensional GB are not formed. As the solute concentration in the bulk increases the solute concentration in GB increases as well, but only due to the increase of the “nuclei” fraction. At the same time the solute concentration in a disordered part of GB solid solution remains constant. The fraction of this part decreases. The retardation effect of GBS on GBD is connected with the ordering transition, the “nuclei” formation. A diffusion coefficient (D) in an ordered part of solid solution is close to the diffusion coefficient in a bulk phase. As a rule, it is less than a diffusion coefficient in a disordered part. The growth of an ordered part of GB solid solution (the fraction of the “nuclei”) leads also to the dependence of D on the solute concentration and to the additional curvature of the diffusion profiles.
Some Remarks on the Magnitude of the Chemical Diffusivities at Moving Grain Boundaries
Authors: Zięba Paweł
Published: March 2009

The paper provides a short state of art in the field of diffusion processes at moving grain boundaries (reaction front) at the example of discontinuous solid state reactions. Main emphasis is put on the stop- and go behaviour and its consequences, the role of local characterisation of the discontinuous reactions and the concept of dynamic segregation in the explanation of existing divergences concerning the rate of diffusion at the stationary and moving boundary. Finally, some unsolved problems and perspective for the future research are presented.
Simulation of the Diffusion Features of Point Defects in bcc Metals
Authors: Chirkov Andrey S. , Nazarov Andrei V.
Published: March 2009

This work is devoted to simulation of the diffusion features of point defects in bcc
metals. The properties of point defects have been investigated with the usage of many-body interatomic potentials. This approach, based on the density-functional theory, permitted us to derive more adequate diffusion features of solids. This investigation is carried out within the framework of the Finnis-Sinclair formalism, developed for an assembly of N atoms and represents the secondmoment
approximation of the tight-binding theory. We used a new model, based on the molecular static method for simulating the atomic structure near the defect and vacancy migration in pure metals. This approach gives the opportunity to simulate the formation and the migration volumes of the point defects, taking into consideration the influence of pressure on structure and consequently
on energy. The diffusion characteristics of bcc α-Fe and anomalous β-Zr have been investigated.
The Synthesis and Characterization of ZrW2O7(OH1-X,ClX)2·2H20 (X=0.016, 0.025)
Authors: Cao Yi Long , Deng Xue Bin , Ma Hui , Wang Shui Feng , Zhao Xin Hua
Published: March 2009

ZrW2O7(OH1-x,Clx)2·2H2O (x = 0.016, 0.025) is prepared by using the acid steam
hydrothermal (ASH) method. The chlorine contents of the crystals are measured by means of
potentiometric titration and ICP, respectively. The as-prepared powders are characterized by X-ray
diffraction, and their structures are refined by using the Rietveld method contained in the GSAS
program. The results indicate that the chloride ion occupies the hydroxyl group crystal site
statistically.
Vacancy-Wind Factors and Collective Correlation Factors in Nonstoichiometric B2 Intermetallic Compounds
Authors: Gosain K.L. , Chaturvedi D.K. , Belova Irina V. , Murch Graeme E.
Published: March 2009

The six-jump-cycle (6JC) diffusion mechanism is used to analyze the behavior of vacancy-wind factors and collective correlation factors in partially ordered B2 intermetallic compounds at stoichiometric and near- stoichiometric compositions. Expressions for the vacancywind factors are obtained in the framework of the four-frequency model where the two sublattices exist a priori. The phenomenological coefficients on the two sublattices that remain hitherto independent in 6JC mechanism are connected through a microscopic detailed balance condition. The present results for collective correlation factors when compared with our earlier calculation based on taking the harmonic mean of the sublattice correlation factors show much better agreement with Monte Carlo simulation results. The collective correlation factors and tracer correlation factors are used to calculate the vacancy-wind factors. Our results for vacancy-wind factors agree qualitatively with the simulation data when the frequency ratio ( α ) of structural and antistructural atoms jumps decreases up to the order of unity.
Surface Microstructural Evolution up to Creep Rupture under the Power-Law Regime in Cu-8.5at%Al Alloy at Intermediate Temperatures
Authors: Abo-Elsoud M.
Published: March 2009

Micro-structural change caused by the corresponding change in creep properties of Cu-8.5at.%Al alloy was studied. It was found that a micro-structural observations reveal the formation of different types of defect features during creep of the investigated alloy at intermediate temperatures between 0.46-0.72Tm, where Tm is the absolute melting point. SEM was used to characterize the studied alloy by quantitative micro-analysis. It allowed the observer to defect the micro-structural features such as dislocation that were generated from deformation and could move interagranularly by glide and climb. Clearly, the development of this microstructure could be attributed to the grain refining effect of the Al indicating the role of the applied stress at this alloy. The results show that the creep rupture strength of Cu-8.5at.%Al alloy in the power law creep damage mechanism. This due to the constraint introduced on the matrix creep flow by the Al phase rather than the devolvement of high threshold stress values. While the increase in the length of Al filaments and reduction in interfilament spacing with increasing draw ratio increase the constraint on the creep flow of the matrix, they also enhance the creep damage caused by the diffusion mechanisms because of the easy diffusion paths along the Al filaments and the reduction in the matrix grain size.
Numerical Simulation of Carburization and Decarburization Profiles in Steels
Authors: Stasiek M. , Öchsner Andreas
Published: March 2009

Due to economic significance, industry demands on mathematical models, which
allow for the prediction of realistic carburization and decarburization depth profiles. Analytical
solutions of Fick’s law, however, are of limited aptitude, as the concentration dependence of
the diffusion coefficient of carbon in steel cannot be considered. Thus, the present paper
presents a numerical simulation tool based on the finite element method (FEM). A widespread
commercially available program system was used to ensure industrial applicability and to make
a contribution to the standardizing of operation control.
Effect of Perovskite Coating on Oxide Scale Growth on Fe-22Cr
Authors: Persson Åase , Hendriksen Peter V. , Mikkelsen Lars , Somers Marcel A.J.
Published: March 2009

A coating consisting of La0.85Sr0.15MnO3 (LSM) was deposited onto two Fe 22 wt % Cr
alloys Crofer 22APU and Sandvik 1C44Mo20. The evolution of the oxide layers developing
underneath the coatings during oxidation was investigated. The effect of the LSM coating on
oxidation rate and microstructure of the oxide scale was investigated, and possible effects on the
overall oxidation mechanism are discussed. It was found that the growth rate for coated Crofer
22APU was decreased by a factor of 3 in comparison with the uncoated samples, and the thickness
of the chromia layer in the scales decreased in favor for a (Mn,Cr)-spinel layer.
Interdiffusion Between Ni-Based Superalloy and MCrAlY Coating
Authors: Dahl K.V. , Hald J. , Horsewell A.
Published: March 2009

Interdiffusion at the interface between a Co-36.5Ni-17.5Cr-8Al-0.5Y, MCrAlY coating and the underlying IN738 superalloy was studied in a large matrix of specimens isothermally heat treated for up to 12,000 hours at temperatures 875°C, 925°C or 950°C. Modelled results using the finite difference software DICTRA was compared with experimental average composition profiles measured across the interface using a new experimental approach.
Local Vibrational Modes of Zn-H-P in GaP, InP and ZnTe
Authors: Torres Vitor J.B. , Coutinho J. , Briddon Patrick R.
Published: March 2009

We have investigated the hydrogenation of the zinc acceptor in GaP and InP, and of the phosphorus acceptor in ZnTe, by computer modeling. We used a density-functional supercell code and pseudopotentials to deal with the core electrons. However zinc 3d electrons were explicitly taken to be valence electrons. We have determined the relaxed atomic geometry for seven hydrogen sites. We have found that, in the lowest total energy configuration, hydrogen sits in a bond centered position between zinc and arsenic atoms in all GaP, InP and ZnTe semiconductors and is bonded to the phosphorus atom. We found metastable states, by 0.4, 0.4 and 0.5 eV, for structures where H is antibonding to the phosphorus atom for GaP, InP and ZnTe, respectively. The calculated local vibrational modes (LVM) for the bond-centered configuration agree, within 1%, with the experimental values of 2379.0 cm-1 for GaP:Zn-H, 2287.7 cm-1 for InP:Zn-H and 2193 cm-1 for ZnTe:P-H. The isotopic shift due to the replacement of deuterium by hydrogen is reproduced by less than 2.5% using experimental data. The decrease in the LVM when going from GaP to ZnTe, as the perfect bond length increases, is also well-reproduced. A wag mode at 496 cm-1 and lower LVM, a doublet at 329 cm-1 and a singlet at 242 cm-1, are predicted for P-H in ZnTe.
Modeling of Diffusion Saturation of Titanium by Interstitial Elements under Rarefied Atmospheres
Authors: Matychak Ya. , Fedirko V. , Prytula A. , Pohreljuk I.
Published: March 2009

This paper deals with the development of a theoretical model for reactive diffusion during new-phase
formation when its volume fraction is negligible. A mathematical analysis of this physical model is carried
out and an equation for mass balance at the interface is derived. The latter includes a correlation between the
transport flux of nitrogen to the surface (J1) followed by both diffusion dissolution (Jdiff) and segregation at
the defects due to chemical interaction with metal atoms (JR.). The analytical-experimental procedure for the
determination of the coefficient of mass transfer which controls the density of the outer flux (J1) is proposed.
The effect of temperature and time upon the kinetics of nitriding is estimated. The additive dependences of
both the nitrogen concentration in a distant band and the depth of the diffusion zone upon time, temperature
and pressure during isothermal exposure are shown. Peculiarities of the nitrogen concentration distribution at
the interface, as a function of temperature of isothermal exposure, are found. It is established that, for a given
duration of exposure, an increase in temperature does not always tend to increase the concentration of the
impurity at the interface. This is caused by a more intense diffusion flow into the matrix. In accordance with
the concept of time-independence of the surface concentration during saturation, the diffusion fluxes Jdiff →
∞ with decreasing time (τ→ 0). This artefact is eliminated by an equation, derived here, for a diffusion flux
defined using new boundary conditions. The equations for calculating mass increase include the effect of
segregation to the surface, which causes a deviation from a parabolic dependence of the mass change.
Peculiarities of Discontinuous Precipitation in the Pb-Sn Alloy
Authors: Lyashenko Yu.A. , Zaitzeva N.V. , Shmatko O.A.
Published: March 2009

A model of discontinuous precipitation in binary polycrystalline alloys at low temperatures is presented. The proposed approach allows independent determination of the main parameters, including the interlamellar distance, the maximum velocity of the phase transformation front, and the concentration step at this boundary. This is achieved by using a set of equations for: 1) the mass transfer in the moving interphase boundary; 2) the balance of the entropy fluxes at the phase transformation front, and 3) the maximum rate of the free energy release under constraint of entropy balance. Concepts of mobility and linear interrelation between the driving force and velocity are not used explicitly. Comparison of the model calculation with the experimental results for the Pb-Sn system at different supersaturations is provided.
Diffusional Growth Kinetics of Boride Layers at the 13% Cr Steel Interface with Amorphous Boron
Authors: Dybkov Vasil I.
Published: March 2009

Two borides FeB and Fe2B were found to form as separate layers at the interface between
a 13% Cr steel and boron at 850-950 oC and reaction times up to 12 h. The chromium distribution
within the boride layers is rather irregular. Its average content is 8 at. % in the FeB layer and 9 at. %
in the Fe2B layer. Both layers are characterized by a pronounced texture. The strongest reflections
are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe2B phase.
Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described
by a system of two non-linear differential equations, producing a good fit to the experimental data.
Study of Kirkendall Effect in Ni/Ni3Al Welded Joint after the High Temperature Annealing
Authors: Losertová Monika , Čech Barabaszová Karla , Drápala Jaromír , Kursa Miroslav
Published: March 2009

The study of composition and microstructure of welded joints was performed before and
after the diffusion annealing at elevated temperatures for different annealing time. The Kirkendall
effect in the Ni/Ni3Al diffusion couples was observed by means of different methods, e.g. using
light, scanning electron and atomic force microscopies. The study suitably completes and specifies
the morphology features of Kirkendall voids at different evolution stages, i.e. at nucleation, growing
and coalescence. Kirkendall voids occurred in the region between the Matano and γ/γ´interface
planes. The location of the γ/γ´ interface that moved in the direction of Ni3Al phase during the
annealing resulted from the Al concentration profile measured by EDAX. The Matano plane
location was determined by means of Boltzmann-Matano’s method using concentration profile data.
It was observed that the void size was increasing in the direction from the Matano plane to the γ/γ´
interface. The obtained results were completed by surface topography of Kirkendall voids of
slightly etched specimens by atomic force microscopy (AFM).
On the Role of Stress, Strain and Diffusion in Dissolution – Condensation Mechanism of Liquid Metal Embrittlement
Authors: Glickman Evgeny E.
Published: March 2009

The models of liquid –metal embrittlement (LME) which explore the concept of fast stress/strain
induced liquid phase diffusion as the major factor responsible for acceleration of subcritical cracks are
overviewed and refined. The models are used for further analysis of several focus issues in the LME
kinetics.
Redistribution of Implanted Species in Polycrystalline Silicon Films on Silicon Substrate
Authors: Salman F. , Arnold J. , Zhang Peng , Chai Guan Gyu , Stevie Fred A. , Chow Lee
Published: March 2009

Redistributions of implanted species after thermal annealing in polycrystalline silicon (poly-silicon) were studied by secondary ion mass spectrometry. Ten different elements were implanted into poly-silicon films grown on Si substrates. The implanted energies were chosen such that the expected ion range is within the poly-silicon film. Thermal anneals were carried out at temperatures between 300°C and 1000°C in flowing high purity Ar gas. Three different diffusion behaviors have been observed for these elements. For Be, Na, Ga, and Cr, most of the implanted ions diffused out to the surface of the poly-silicon film after anneal at 1000°C. For K, Ca, Ti, and Ge, the impurity ions diffused deeper into the bulk after anneal at 1000°C. For Cl and Mn ions, the concentration distributions became narrower when annealed at high temperatures.
Diffusion in Bulk Glass Forming Alloys– from the Glass to the Equilibrium Melt
Authors: Rätzke Klaus , Zöllmer V. , Bartsch A. , Meyer Andreas , Faupel Franz
Published: March 2009

Since the discovery of bulk metallic glasses there has been considerable research effort on these systems, in particular with respect to mass transport. Now the undercooled melt between the melting temperature and the caloric glass transition temperature, which has not been accessible before due to the rapid onset of crystallization, can be investigated and theories can be tested. Here we report on radiotracer diffusion measurements in metallic bulk-glass-forming Pd-Cu-Ni-P alloys. Serial sectioning was performed by grinding and ion-beam sputtering. The time, temperature as well as the mass dependence, expressed in terms of the isotope effect E, of Co-diffusion were investigated. The Co isotope effect measurements, which have never been carried out near Tc in any material, show atomic transport up to the equilibrium melt to be far away from the hydrodynamic regime of uncorrelated binary collisions. In the glassy state as well as in the deeply supercooled state below the critical temperature Tc, where the mode coupling theory predicts a freezing-in of liquid-like motion, the experimentally determined very small isotope effects indicate a highly collective hopping mechanism involving some ten atoms. Below Tc the temperature dependence shows Arrhenius-type behavior with an effective activation enthalpy of 3.2 eV. Above Tc the onset of liquid-like motion is evidenced by a gradual drop of the effective activation energy and by the validity of the Stokes-Einstein equation, which is found to break down below Tc. Although having strong covalent bonding tendencies, Phosphorous diffusion is only slightly slower than Co diffusion, indicating that it does not determine the overall viscosity below Tc. The Stokes-Einstein equation is presently tested for other constituents of the alloy.
Assessment of Ternary Multicomponent Diffusion in Alloy 22 (Ni-Cr-Mo)
Authors: Jaques A.V. , LaCombe J.C.
Published: March 2009

Diffusivity [D] matrices are reported for the ternary Ni-Cr-Mo alloy in the approximate
single-phase compositional range of Hastelloy C-22 (Alloy 22), surrounding Ni-63 wt.%, Cr-22.3
wt.%, and Mo-14.7 wt.%. These data will contribute to our understanding of the long-term phase
stability of Alloy 22, and its potential use as a corrosion barrier in nuclear waste packages.
Experimental diffusion couple data were obtained at selected temperatures from a series of diffusion
couples, and evaluated, assuming constant diffusivity. Our approach treats the process as an
optimization problem that simultaneously considers concentration profile data from numerous
diffusion couples surrounding a single end-point composition. We make use of the mathematical
characteristics of the analytical solution to this problem, reducing the number of parameters to be
fitted. The parameter fitting is accomplished using a combination of heuristic and deterministic
methods. Discussion of the sources and magnitudes of uncertainty in the diffusivity values is
included.
First-Principles Computation of Transition-Metal Diffusion Mobility
Authors: Chan Kwai S. , Pan Yi Ming , Lee Yi Der
Published: March 2009

First–principle computational methods have been utilized to compute the diffusion mobility of Mo, Cr, Fe, and W. A local density-based full-potential linearized augmented plane wave (FLAPW) code, named WIEN2K, was utilized to compute the electronic structure and total energy of an n-atom supercell with atom positions designed to simulate the desired diffusion processes. The computational procedure involves the calculations of the energy for vacancy formation and the energy barrier for solute migration in the host metal. First-principles computational results of the energy of vacancy formation, solute migration energy, activation energy for self-diffusion, as well as diffusion of Mo, Cr, Fe, and W solutes in Ni and vice versa are presented and compared against experimental data from the literature.
Investigations of the Defect Structures and EPR Parameters for the Tetragonal and Cubic Ni2+ Centers in AgX (X=Cl, Br)
Authors: Zhang Zhi Hong , Wu Shao Yi , Wei Li Hua , Hu Yue Xia
Published: March 2009

The defect structures and the electron paramagnetic resonance (EPR) parameters zero-field
splitting and the g factors for the tetragonal and cubic Ni2+ centers in AgX (X=Cl, Br) are theoretically
studied from the perturbation formulas of these parameters for a 3d8 ion in tetragonal and cubic
octahedra. In these formulas, the ligand s-orbital contributions, which were usually neglected in the
previous studies, are taken into account based on the cluster approach. The ligand X− intervening in
the Ni2+ and the next nearest neighbour Ag+ vacancy VAg is suggested to suffer a small inward
displacement (≈ 0.11 or 0.15Å for AgCl or AgBr, respectively) towards Ni2+ along the [100] (or C4)
axis. The calculated EPR parameters based on the above defect structures show reasonable agreement
with the experimental data.
Solid-State Reaction in Al-Fe Binary System Induced by Mechanical Alloying
Authors: Kaytbay S.H. , Moustafa S.F. , Daoush W.M.
Published: March 2009

Mechanical alloying (MA) is a solid-state powder processing method which has the ability to
synthesize a variety of new alloy phases including supersaturated solid solutions, nanocrystalline
structures, amorphous phases and intermetallic compounds.
In this investigation, the interaction between aluminum and iron caused by MA of Fe-xAl
(where X ranged from 30 to 90%) was studied as a function of milling time and post heat-treating
temperatures. The sequences of structural and/or phase transformation and the behavior of
mechanically alloyed powders have been assessed using XRD, hardness and magnetometer.
It was found that during mechanical milling of elemental powder Al and Fe, five milling
stages were categorized, namely, particle flattening, welding predominance, equiaxed formation,
random welding orientation and steady state composite particles. All milled powders showed
nano-sized powder mixtures after milling for 20hrs. When Fe-30%Al powder was milled for 150hrs,
a partially ordered AlFe phase was obtained. However, when these saturated solid solutions were heat
treated at 500 °C, the AlFe intermetallic was precipitated fully ordered. When the Al content was
increased up to 40% and milled for 50hr, the XRD pattern showed a broad halo spectrum which
showed the formation of an amorphous phase. When a Fe-60%Al powder mixture was mechanically
milled for 50hr, the Al5Fe2 intermetallic formed that was associated with an amorphous phase, which
transformed into the Al3Fe intermetallic by heat treating at 500°C. In the case of Fe-75% and
Fe-90%Al milled for 150hrs only Al peaks appeared and were shifted to higher angles, suggesting
that Fe atoms diffused into Al, leading to the formation of a solid solution.
Thermal Behaviour of Xenon in a Refractory Metal for Gas Fast Reactor Fuel Elements
Authors: Viaud C. , Carlot G. , Garcia P. , Martin P. , Millard-Pinard N. , Moncoffre N. , Peaucelle C. , Sauvage Thierry , Toulhoat N.
Published: March 2009

Helium cooled Gas Fast Reactors (GFR) are designed for producing energy more efficiently and
improving safety features such as a total retention of fission products (Xe, I, Cs). This study deals
with the diffusion of xenon in refractory liners dedicated to the retention of fission products
produced in GFR fuels. The material (W, Mo, W-Re, Mo-Re) will be located in the heart of the
nuclear fuel element, where the operating temperature is in the 1000°C- 1600°C range. For the
investigation of thermally activated rare gas behaviour, a γ-spectrometry analysis experiment has
been performed on the 133Xenon implanted refractory liner. Preliminary results on the 133Xenon
release at 1600°C from a tungsten single crystal is presented. In spite of the low concentration of
implanted gas (~ppm) and simple microstructure, the prevailing mechanism appears to be complex.
One and two dimensional diffusion models are used to characterize or discriminate the highlighted
phenomena: burst release, diffusion and trapping of rare gas atoms.
Molecular Dynamics Simulation of Brittle Fracture in Bcc Iron
Authors: Xie Hong Xian , Wang Chong Yu , Yu Tao
Published: March 2009

Crack propagation in bcc iron at different strains under low temperature (30K) has been studied using
the atomistic simulation. We show that cracks display a brittle character of extension at low strains,
and at relative higher strains cracks extend with a periodic series of twins(or SF) bursts. These bursts
decrease the crack speed and produce velocity oscillations with an increase in energy dissipation that
increases the toughness. Here we also develop a new form of dynamic fracture energy. Using our
form of dynamic fracture energy, the results therefore are in quantitative agreement with the
theoretical single-crack equation of motion.
Diffusion in the AlMo3 Ordered Intermetallic
Authors: Pascuet M.I. , Fernández Julián R. , Monti A.M.
Published: March 2009

An EAM interatomic potential for the ordered AlMo3 intermetallic is developed and
applied to the study of point defects in the AlMo3. The equilibrium concentrations of vacancies and
antisites are calculated using statistical thermodynamics. Results show that antisites are the most
abundant type of defect in a range of temperatures and compositions close to stoichiometry. Finally,
the diffusion by vacancy mechanism in the same structure is studied through the kinetic Monte
Carlo technique. Possible atomic mechanisms of diffusion are suggested and analyzed in some
detail.
Mathematical Modeling of Interface Movement during Diffusional Bonding of Surfaces
Authors: Ray Rabindranath
Published: March 2009

The concentration profile of Cu is modelled using semi-infinite geometry for diffusion couples of α
and β phases in Cu-Al system. The dimensionless interface movement parameter γ is calculated, for
various combinations of time and temperature, by root bracketing, bisection and inverse quadratic
interpolation. A computational procedure is presented to calculate the concentration profile where
the interface velocity (dε/dt) is high and/or with steep concentration gradient of the specie in the
shrinking phase. In all cases the interface compositions are set at the equilibrium values given in the
phase diagram with fixed composition of end members. The calculated profile match well with the
experimental concentration profile as reported by Romig [3].
Reaction of Iron with Amorphous Silicon and Crystal Silicon for the Fabrication of Iron Silicides
Authors: Gong Dao Ren , Li Dong Sheng , Yuan Zhi Zhong , Yang De Ren
Published: March 2009

Iron silicide films with two different structures were fabricated by electron beam
evaporation (EBE) technique. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and
scanning electron microscope (SEM) were carried out to describe the characteristics and structures of
the films. It was found that after annealing at 800oC for 5 h, the β-FeSi2 film formed in the sample
with the structure of Si/Fe film on silicon substrate, while only FeSi film generated in the sample with
the structure of Si/Fe/Si films on silicon substrate. It is considered that the different iron silicides may
be due to the different reaction of iron with crystal silicon or amorphous silicon, which is related to
diffusion of iron or silicon atoms.
Experimental and Numerical Study on Vapor Condensation of Wet Flue Gas in Chimney
Authors: Delalić Nijaz , Džaferović Ejub , Ganić Ejub
Published: March 2009

Increase of the emission of CO2, which is mostly the result of the combusted fossil
fuels into the atmosphere, exponentially increases. Through increased energy efficiency there is
lower CO2 emission. There is a tendency to reduce exhaust gases temperatures down from their
original value referred to as “acid dew point”, 115-160°C. A result is vapor condensation of wet
flue in chimney. Condensation occurs when the surface temperature is below the dew point of the
vapor-gas mixture. Therefore, Vapor-Liquid Equilibrium models are required in order to determine
the dew point of the mixture. Wet flue gas is simulated with vapor-air mixture. A numerical model
was presented to calculate the velocity and thermal field of turbulent vapor-air mixture flow trough
a chimney. The momentum and temperature field were calculated via a finite-volume CFD code,
using the k – e turbulence model. The validation of this calculation was conducted employing an
experimental set for heat and mass transfer in vertical upward vapor-air mixture. Measurements
were done using a stainless steel tube of 13.2 mm I.D. (internal diameter) and 70 I.D. lengths. Flow
rates of steam and air were varied as the experimental parameters.
The experiment involves two-phase, two-component, heat and mass transfer. Comparisons of wall
temperature and condensate rate were made and the model was shown to give an acceptable results.
Effect of Temperature and Volume Changes on Effective Diffusivities of Sucrose and NaCl during Osmotic Dehydration of Vegetable Tissue
Authors: Mayor Luis , Delgado João M.P.Q. , Vázquez da Silva M. , Sereno Alberto M. , Gonçalves Maria P.
Published: March 2009

Osmotic dehydration of pumpkin (Cucurbita pepo, L.) fruits was carried out with binary
solutions of sucrose and NaCl at different temperatures and solute concentrations. Water loss and
solids gain kinetics were experimentally determined and fitted using a diffusional model. Pumpkins
samples were considered as finite cylinders and the analytical solution of the unsteady diffusion
equation was used considering the external resistance to the mass transfer negligible. The influence
of shrinkage and temperature on the effective diffusion coefficients was also assessed in this work.
Numerical Study of Propane-Air Mixture Combustion in a Burner Element
Authors: Pinho C.E.L. , Delgado João M.P.Q. , Pilão R. , Conde J. , Pinho C.
Published: March 2009

This study considers numerical simulations of the combustion of propane with air, in a
burner element due to high temperature and velocity gradients in the combustion chamber. The
effects of equivalence ratio (φ) and oxygen percentage (γ) in the combustion air are investigated for
different values of φ between 0.5 and 1.0 and γ between 10 and 30%. In each case, combustion is
simulated for the fuel mass flow rate resulting in the same heat transfer rate (Q) to the combustion
chamber.
Numerical calculations are performed individually for all cases with the use of the Fluent CFD
code. The results shown that the increase of equivalence ratio corresponds to a significantly
decrease in the maximum reaction rates and the maximum temperature increase with the increases
of oxygen percentage. Mixing hydrogen with propane causes considerable reduction in temperature
levels and a consequent reduction of CO emissions.
An Investigation on the Mechanism of TiC+Al2O3 Formation in the Combustion Synthesis of the Mechanically Activated TiO2-Al-C System
Authors: Nayeri Sayed Hamid Reza Fatemi , Khaki Jalil Vahdati , Aboutalebi Mohammad Reza
Published: March 2009

A mechanism for the combustion synthesis of TiC+Al2O3 was proposed in a
mechanically activated TiO2-Al-C system. As-milled powder mixture was analyzed using XRD and
TEM techniques where no chemical reaction and/or inter-particle diffusion were identified. The
results obtained from DTA tests on unmilled powder revealed that the combustion synthesis
occurred in a single step at 962 °C while the synthesis of mechanically activated powder mixture
occurred in three different stages. The XRD analysis on the synthesized samples of 8 hour premilled
powder at different temperatures showed that the three stages were as follows: First the
reaction between Al and TiO2 takes place forming Al3Ti, Ti2O3, and Al2O3 at 700 °C. In the second
step, Ti-rich titanium aluminides (AlTi, AlTi2, and AlTi3) and TiO, are formed at 923 °C, and
finally the formation of TiC+Al2O3 is completed at 1329 °C.
Calculations of the Effective Thermal Conductivity in a Model of Syntactic Metallic Hollow Sphere Structures Using a Lattice Monte Carlo Method
Authors: Fiedler Thomas , Öchsner Andreas , Belova Irina V. , Murch Graeme E.
Published: March 2009

In this paper, a Lattice Monte Carlo method is used to determine the effective thermal
conductivity in two dimensional models of adhesively bonded metallic hollow sphere structures
(MHSS). In contrast to earlier approaches, more realistic distributions of spheres without the
simplification of cubic symmetric arrangements are considered in this study. For the Monte Carlo
analyses, two-dimensional periodic lattices representing different cutting planes through MHSS are
generated. Therefore, an algorithm is used which sequentially fills the lattice by adding cut
spherical shells and inclusions in the matrix. Another focus of this work is the analysis of the
influence of different geometric circle distributions on the effective thermal conductivity. The
findings of the random arrangements are also compared to a regular primitive cubic arrangement
and with a Maxwell-type approach.
Mechanical Damping of the Snoek Peak in Tantalum – Oxygen System
Authors: Florêncio Odila , Silva Paulo Sergio , Barbosa Geovani F. , Melo Fábio X. , Grandini Carlos Roberto , Ishikawa Tomaz Toshimi
Published: March 2009

Interstitial solutes in body-centered cubic metals, such as oxygen in tantalum, produce
ideally Snoek effects when they are in solutions enough diluted. However, for higher concentration
of these solutes, more complex relaxation process can occur, as interaction between interstitial
solutes and dislocations. Anelastic relaxation measurements were carried out in polycrystalline
tantalum samples, using torsion pendulum inverted, operating between 300 K and 680 K and
oscillation frequencies in the hertz bandwidth, for three different experimental sample conditions: as
received sample, annealed and annealed followed by a treatment in an oxygen atmosphere. These
measurements have revealed the following behavior: the intensity of the internal friction peak
associated to matrix-interstitial interaction Ta-O decreased between the first run and the next runs,
and this phenomenon did not occur for the others conditions. The variation of relaxation strength of
Ta-O peak, with number of runs is due to a decrease of an amount of oxygen in solid solution,
which can be associated with the precipitation of new phases in Ta sample and with the trapping of
oxygen atoms by dislocations.