Papers by Author: G.L. Katona

Abstract: In a set of recent papers we have shown that the diffusion asymmetry in diffusion couples (the diffusion coefficient is orders of magnitude larger in one of the parent materials) leads to interesting phenomena: i) sharp interface remains sharp and shifts with non Fickian (anomalous) kinetics [1-5], ii) originally diffuse interface sharpens even in ideal (completely miscible) systems [6,7], iii) an initially existing thin AB phase in A/AB/B diffusion couple can be dissolved [8], iv) there exists a crossover thickness (typically between few nanometers and 1m) above which the interface shift turns back to the Fickian behaviour [9], v) the growth rate of a product of solid state reaction can be linear even if there is no any extra potential barrier present (which is the classical interpretation of the “interface reaction control” for linear kinetics) [10]. These latter results will be summarized and reformulated according to the usual expression for linear-parabolic law containing the interdiffusion coefficient, D, and interface transfer coefficient, K. Relation between the activation energies of D and K will be analyzed and compared with available experimental data.

Abstract: 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.

Abstract: According to classical Nernst-Einstein equation the diffusive flux is proportional to the driving force. However, this linear law is not valid if the driving force is very large. Attempts in the literature for the derivation of an “improved relation” till now were mostly restricted to the cases when the diffusion coefficient was independent of the composition. On the other hand, even if there are no externaldriving forces (other than related to the chemical driving force) present, deviations from the Fick I law are expected (transition from parabolic to linear growth-behaviour) on nanoscale for composition dependent diffusion coefficients. General description for the case when the driving forces and the diffusion asymmetry are large, is treated. The special case of large pressure gradients is discussed in detail and their effects on the deviation form the parabolic growth law on nanoscale will be analyzed. Effect of a pressure gradient on the crossover thickness between parabolic and linear regimes and on the interface transfer coefficient, K, is also treated.