Papers by Keyword: Reactive Diffusion

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Authors: Soumitra Roy, Soma Prasad, Aloke Paul
Abstract: The growth of phases by reactive diffusion in Mo-Si and W-Si systems are compared. The crystal structures of MSi2 and M5Si3 phases (M = Mo, W) are similar in these two systems. However, the diffusion rates of the components change systematically with a change in the atomic number. Integrated diffusion coefficients in both phases increase with an increasing atomic number of refractory elements i.e. from Mo to W. On the other hand, the ratio of diffusivities of the components decreases. This indicates a relative increase in the diffusion rates of the metal components with increasing atomic number and a difference in defects concentrations in these two systems.
Authors: Alain Portavoce, Khalid Hoummada, Franck Dahlem, Christophe Girardeaux, Boubekeur Lalmi
Abstract: Silicide growth via reaction between a metallic film and a Si substrate has been well documented. In general, atomic transport kinetic during the growth of silicides is considered to be the same as during equilibrium diffusion, despite the reaction and its possible injection of point-defects in the two phases on each side of the interface. To date, the main studies aiming to investigate atomic transport during silicide growth used immobile markers in order to determine which element diffuses the fastest during growth and in which proportion. The quantitative measurements of effective diffusion coefficients during growth was also performed using Deal-and-Groove-type of models, however, these effective coefficients are in general not in agreement with the interdiffusion coefficients calculated using the equilibrium diffusion coefficients measured during diffusion experiments. In general, atomic transport kinetic measurements during growth and without growth are performed using different types of samples for experimental reasons. In this paper, we discuss the possible use of ultrahigh vacuum in situ Auger electron spectroscopy in order to measure the effective diffusion coefficient during growth, as well as the equilibrium self-diffusion coefficients, in the same samples, in the same experimental conditions. The first results on the Pd-Si system show that atomic transport during Pd2Si growth is several orders of magnitude faster than at equilibrium without interfacial reaction.
Authors: Jolanta Gilewicz-Wolter, Zbigniew Żurek, J Dudala, Jerzy Lis, Martah Homa, Marcin Wolter
Abstract: As the result of oxidation of Cr-Mn steels in SO2 the three layer scale is formed. The intermediate layer of this scale is composed mainly of MnCr2O4 spinel whereas FeCr2O4 spinel is present in small amount. MnO dominates in the outer layer. The inner, very thin scale layer contains oxides/sulfides mixture. The aim of this study was to examine self-diffusion processes in both spinels by multitracer method of diffusion measurements to know which of the transport processes during oxidation is the smallest one and deciding on the corrosion rate. In diffusion experiments the radioisotopes 54Mn, 51Cr and 59Fe were used. The serial sectioning method was applied to simultaneous evaluation of diffusion rates of chromium, manganese and iron in both spinels at 1073 K and 1173 K under the pressure of 105 Pa in SO2 containing 10 Pa O2. These spinels were obtained by modified sol-gel method from nitrates. Structures of the spinels were examined by X-ray spectrometry. It was found, that the diffusion rates of metals are higher in MnCr2O4 spinel. Moreover the dominant mechanism of manganese transport (the highest one) in studied samples is the volume diffusion while chromium and iron are transported mainly through the high diffusivity paths.
Authors: E.N. Popova, Vladimir V. Popov, E.P. Romanov, S.V. Sudareva, L.V. Elohina, A.E. Vorobyova, A.K. Shikov, V.I. Pantsyrny, S.V. Sudiev
Abstract: Multifilamentary Nb3Sn-based superconducting composites manufactured by an internal-tin method have been studied by transmission (TEM) and scanning (SEM) electron microscopy. The main goal of this study is to reveal the effect of diffusion annealing regimes as well as the external diameter of the wires on the structure of nanocrystalline Nb3Sn layers (average grain size, grain size distribution, layer thickness, amount of Sn, etc.). It is demonstrated that multistep diffusion annealing results in quite a complete transformation of Nb filaments into Nb3Sn though some amount of the residual Nb remains in the filaments center. With an external diameter decrease the superconducting layers structure has been found to refine and get somewhat more uniform. An additional high-temperature annealing results in marked growth of Nb3Sn grain sizes and their scattering in sizes, which may negatively affect the current-carrying capacity of a wire.
Authors: E.N. Popova, Vladimir V. Popov, E.P. Romanov, S.V. Sudareva, E.A. Dergunova, A.E. Vorobyova, S.M. Balaev, A.K. Shikov
Abstract: Kinetics of formation of superconducting Nb3Sn layers and the structure of bronzeprocessed Nb/Cu-Sn composites with Zr, Zn or Mg-doped matrixes or Ti-doped Nb filaments of different geometry have been studied by the methods of TEM, SEM and electron-probe microanalysis. All the doping elements have been found to accelerate the rate of growth of the diffusion Nb3Sn layers and consequently their thickness. Correlation between the diffusion annealing schedules, the geometry of Nb filaments, the structure of the diffusion Nb3Sn layers and the current-carrying characteristics of multifilamentary Nb/Cu-Sn composites has been established.
Authors: V.V. Fedorov, E.V. Dyomina, T.M. Zasadny, R.I. Koroluk, M.D. Prusakova, N.A. Vinogradova
Authors: Omar Abbes, Feng Xu, Alain Portavoce, Christophe Girardeaux, Khalid Hoummada, Vinh Le Thanh
Abstract: An alternative solution for producing logic devices in microelectronics is spintronics (SPIN TRansport electrONICS). It relies on the fact that in a magnetic layer, the electrical current can be spin polarized. To fabricate such components, a material whose electronic properties depend on its magnetic state is needed. The Mn-Ge system presents a lot of phases with different magnetic properties, which can be used for spintronics. The most interesting phase among the Mn-Ge system is Mn5Ge3 because of its stability at high temperatures, its Curie temperature which is close to room temperature and its ability of injecting spin-polarized electrons into semiconductors. In this paper, we have combined Reflection High-Energy Electron Diffraction (RHEED) and X-ray Diffraction (XRD), to study the sequence of formation of MnxGey phases during reactive diffusion of both a 50 nm and a 210 nm thick Mn films deposited by Molecular-Beam Epitaxy (MBE) on Ge (111).
Authors: E.N. Popova, E.P. Romanov, I.L. Deryagina, S.V. Sudareva, E.A. Dergunova, A.E. Vorobyova, S.M. Balaev
Abstract: Bronze-processed Nb3Sn-based multifilamentary composites with external diameter of 0.8 and 0.5 mm and coupled Nb filaments have been studied by transmission (TEM) and scanning (SEM) electron microscopy. After the two-staged annealing, 575°С, 150 h + 650°С, 200 h, commonly used for ITER conductors, a nanocrystalline layer of superconducting Nb3Sn compound is formed in every Nb filament as a result of solid-state reactive diffusion of Sn from the bronze matrix. It is demonstrated that in the wires of smaller external diameter the Nb filaments transformation into the Nb3Sn compound is more pronounced, that is the amount of the residual Nb is smaller. Besides, the nanocrystalline structure of the Nb3Sn diffusion layers is more perfect in 0.5 mm diameter wires, namely, the Nb3Sn grains are finer (their average size being 60 nm compared to 70 nm in 0.8 mm diameter wires) and are more uniform in sizes (the root mean square deviation of grain size distribution is correspondingly 15 and 17 nm).
Authors: C. Lavoie, C. Cabral, François M. d'Heurle, J.M.E. Harper
Authors: Andriy Gusak, Guido Schmitz, Nadiya Storozhuk
Abstract: The problem of phase competition during reactive diffusion is revisited. Nucleation of an intermediate phase at an interface under external fluxes in the neighboring phases is considered in the frame of kinetic Fokker-Planck approach. Effective nucleation barrier depending on the divergence of external fluxes is introduced. New suppression/growth criteria are obtained.
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