Papers by Keyword: Uphill Diffusion

Abstract: It has been shown that the plane surface of a stressed solid can become morphologically unstable relative to the perturbations of the electron density. The above instability is referred to as dynamic and evolves under the relaxation mechanism determined by the electron-electron interaction. The development of the dynamic instability is accompanied by the formation of a dynamic pattern differing from that which is formed under elastic-diffusion instability. To describe the dynamic pattern, a method has been proposed which takes into account the dynamic displacements of the atoms caused by a change in the interatomic interaction during the electron density redistribution. The origin of the different types of the pattern earlier observed experimentally on the free surface of the stressed solids has been explained. The dynamic displacements of the atoms have been shown to stimulate the diffusion mass transfer resulting in a change of the value and the sign of the diffusion coefficient.

Abstract: There exist several interesting phenomena and observations reported in literature for isothermal diffusion in multicomponent systems. Such phenomena include uphill diffusion, development of zero-flux planes and flux reversals for individual components, flux reversals at interfaces, and instability at interfaces and multiphase layer development. In addition, uncommon diffusion structures exhibiting unusual diffusion paths can develop in both single phase and multiphase diffusion assemblies. An overview of such phenomena is presented to highlight the role of interactions among diffusing components with the aid of selected diffusion studies carried out in multicomponent alloy systems, aluminides, silicides, and nuclear fuels.

Abstract: 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).

Abstract: Single crystal superalloy TMS82+ and model alloys of Ni-12Al and Ni-6Cr-8Co-12Al were electroplated with 5-6μm of platinum and heat treated at 1000°C for up to 100hrs. In the model alloys the platinum concentration gradient in the interdiffusion region caused uphill diffusion of aluminium. The subsequent surface enrichment led to formation of aluminium-rich γ′ phase. In TMS82+ superalloy inward diffusion of platinum resulted in loss of the γ/γ′ microstructure and formation of new γ and γ′ grains. The initial dissolution of the γ′ cubes was due to the outward diffusion of aluminium. Again, the presence of a platinum gradient in the interdiffusion region resulted in uphill diffusion of aluminium and a net increase in aluminium content at the alloy surface, leading to a near-surface single-phase γ′ layer being formed, however topologically close-packed (TCP) phase formation was not observed.