Defect and Diffusion Forum Vol. 353

Abstract: Abstract. It is shown, by the combination of SNMS, (Secondary Neutral Mass Spectrometry), XRD, XPS and APT (Atom Probe Technique) that the growth of the Cu₃Si crystalline layer at 408 K between the amorphous Si and nanocrystalline Cu thin films follows a linear law and the shifts of the Cu₃Si/Cu and Cu₃Si/a-Si interfaces approximately equally contributed to the growth of this phase. It is also illustrated that the Si atoms diffuse fast into the grain boundaries of the nanocrystalline Cu, leading to Si segregation. Both the SNMS and APT results indicate that even during the deposition of Cu on the amorphous Si an intermixed region is formed at the interface. This region easily transforms into a homogeneous Cu₃Si crystalline reaction layer subsequently which further grows following apparently an interface controlled linear kinetics. Similar experiments performed in Co/a-Si system to study the formation and growth kinetics of the intermetallic phase. However, interestingly, homogenous formation of the new phase at the Co/a-Si interface was not always observed.

Abstract: In this paper, the effects of porous bush elastic deformation on the static characteristics of finite porous journal bearing are investigated using Darcy’s law. The modified Reynolds equation applied to thermo-hydrodynamic problems is modified by considering the viscosity variation along the film thickness. The film pressure distribution and other characteristics such as the load carrying capacity and attitude angle are obtained by solving the governing equations numerically. Obtained results showed that deformation is considerable in the maximum pressure zone, and the elastic deformation will decrease the load carrying capacity. The viscosity variation parameter tends also to decrease the load carrying capacity.

Abstract: We determine the sorption isotherm in the infiltration model of contaminated water into porous media. We assume that the contaminated water infiltrates into the dry porous media, flow through the sample and flows out at the other side of the sample. We suppose that the contaminant dissolved in the water reversibly adsorbs into the porous media. We use the Richards equation with van Genuchten relation between effective saturation and pressure head. Further, we use Fick’s law to model the contaminant transport in the water and arbitrary adsorption isotherm to model the evolution of the adsorption. By running the direct problem simulation, we obtain the “measurements” of the expelled water mass and its concentration. Then we “forget” the adsorption isotherm function. We solve this inverse problem by evaluating the gradient of the distance function (between “measured” and computed bottom contaminant flux) in an iterative way. We construct the gradient (variation) of the distance function by solving the corresponding dual system of partial differential equations.

Abstract: Hydrogen diffusion in metals is still an ongoing topic of research due to its technical relevance (hydrogen embrittlement, hydrogen storage...). In the last decades, significant progress in understanding the time evolution of the hydrogen concentration in solids was completed. This paper presents a modeling of hydrogen diffusion with a general and thermodynamically based diffusion concept coupled with mechanical and chemical aspects. This model was previously used to simulate the oxidation of a metal [1][2]. This concept has been upgraded to offer a thoroughly macroscopic behavior law used to simulate hydrogen diffusion in metal parts under mechanical loadings. The thermodynamic approach of the stress-diffusion coupling was implemented in a finite element code in order to study the hydrogen diffusion mode into a strained metal. Simulations were performed on a cylindrical austenitic steel tank under important internal pressure. The results of this study allow us to understand how hydrogen diffusion and mechanical stresses are mutually induced and modified.

Abstract: In this article we present a different view on the results of experimental investigation of the self - diffusion on Pd (111) published in „Surface Science“ [1]. Our consideration is based on the band model of diffusion. This model is able to explain the Meyer-Neldel rule (MNR) and to clarify “puzzles” mentioned in [1]. The aim of this article is also to familiarize the readers with this model, to the band model of diffusion.

Abstract: We investigate the convergence rate of two iterative procedures that approximate the solutionof fluid flow problems in heterogeneous porous media. Porous media flows at large scales arecomplex problems, which require fine grid solutions to provide accurate results. Pressures and velocitiesassociated to these problems are governed by second order elliptic equations. We discretizesuch equations by a mixed and hybrid finite element method, combined with domain-decompositioniterative procedures. In order to minimize the computational effort involved in the numerical approximation,we have presented an iterative procedure to accelerate the convergence rate in the approximation.In this paper, we perform numerical experiments to compare iterative procedures in order tocheck which one provides the best convergence rate. We believe that steady-state diffusion problemscan be solved efficient and accurately by the most robust procedure.

Abstract: The transport phenomenon of mass transfers between a moving fluid and a reacting sphere buried in a packed bed, with “uniform velocity”, was analysed numerically, for solute transport by both advection and diffusion to obtain the concentration field and, from it, the dimensionless concentration boundary layer thickness, , for , and . The bed of inert particles is taken to have uniform voidage. For this purpose, numerical solutions of the partial differential equations describing mass concentration of the solute were undertaken to obtain the concentration boundary layer thickness as a function of the relevant parameters. Finally, mathematical expressions that relate the dependence with the Peclet number and inert particle diameter are proposed to describe the approximate size of the concentration boundary layer thickness.

Abstract: Rising damp constitutes one of the main causes of monumental heritage and old buildings degradation, especially, its thick walls with heterogeneous composition. The LFC-FEUP has been developed important research in rising damp domain. In recent years, was validated and experimentally characterized the operation principle of a technique called "wall base ventilation system" for the treatment of rising damp in monumental heritage and ancient buildings consisting of circulating air at the base of the buildings walls with high thickness and heterogeneity in its constitution, with a saturation distant relative humidity. The studies previously developed allowed the interest and viability of the proposed system, taking time to develop a methodology for optimizes it. In this paper it is presented the optimization of the wall base ventilation system based on some important physical parameters. To optimize the system, it was developed a 2D evaporation model that describes the moisture transfer between the system and the wall as well as the water vapour transport throughout the system (Evaporation and Transport Model – ETM). It was also used and adapted another 2D model, to describe the rising damp phenomenon in buildings walls, considering the wall base ventilation system (Rising Damp and Evaporation Model – RDEM). Finally, the design model was developed, using both models (ETM and RDEM) and some experimental validation was done, which allowed the comparison between the levels archived by the wet front analytically and experimentally.