Defect and Diffusion Forum Vols. 237-240

Abstract: The "C" factor for the calculation of the relative activation energy for solute impurity diffusion using LeClaire's theory as modified by Burachynsky and Cahoon has been determined for the diffusion of several solutes in FCC Cu , FCC Fe and BCC Fe. Inclusion of the "C" factor results in good agreement between the calculated and experimental values of relative activation energy for impurity diffusion inn the solvents considered. For positive values of relative valence, Z, the value of C is given by C » 20 Z. For negative values of Z, C » 0.

Abstract: The application of the effective interdiffusion coefficients for describing the interdiffusion process in ternary systems is discussed. It is shown that the relative values of effective interdiffusion coefficients, which are directly related to the diffusion path developed in a given diffusion couple, are responsible for deviation of the diffusion paths from linearity. The relationship between effective interdiffusion coefficients and partial (intrinsic) coefficients in ternary systems is analysed. It is shown that Boltzmann’s solution for diffusion equation with variable diffusion coefficient by means of relatively easy calculation procedure gives reliable results for the calculation concentration distributions in a ternary diffusion couple.

Abstract: In this paper we propose a couple of experimental lines in order to probe specific features of oxygen and silicon diffusion in -quartz and SiO2 in general. We start from the results of atomistic first principles calculations and from their predictions concerning point defects formation free enthalpies; we suggest that measurements with variable oxygen partial pressure could confirm that, in well defined regimes, oxygen diffusion is controlled by doubly negative oxygen interstitials. Along similar lines, for silicon diffusion, one should check the real equilibrium conditions of samples, with gaseous oxygen or bulk silicon, or closed conditions. We discuss our predictions for silicon diffusion, that could clarify some discrepancies between experimental results. Another possible probe would be to perform measurements under hydrostatic pressure, in order to measure the formation volume of the migrating species and to compare it to the theoretical values.

Abstract: In this paper we give a brief presentation of the approaches we have recently developed on the oxidation of metals. Firstly, we present an analytical model based on non-equilibrium thermodynamics to describe the reaction kinetics present during the oxidation of a metal. Secondly, we present the molecular dynamics results obtained with a code specially tailored to study the oxidation and growth of an oxide film of aluminium. Our simulations present an excellent agreement with experimental results.

Abstract: In the presence of strong external fields and steep gradients the flux formulae are not linear. The relation between the flux and the diffusion coefficient must be modified. The different flux-limited theories are presented. The flux formulae for solid systems far from equilibrium are derived and different forms of phenomenological flux limiters are discussed. It is shown that in order to accurately compute diffusion flow that is generated by strong force fields and/or discontinuities, the flux-limited diffusion must be considered. The flux limiters improve the spatial accuracy and allow to avoid baseless oscillations in the solutions.