Papers by Keyword: Multicomponent Diffusion

Abstract: Natural silicate melts (i.e., magmatic liquids) contain 5 to 10 major oxide components. Hence, diffusion in natural melts is always multi-component diffusion with manifestations such as uphill diffusion. However, complexities in rigorous treatment of multicomponent diffusion made geochemists shy away from treating such diffusion in the past. My group has been working on multicomponent diffusion in seven-and eight-component silicate melts for about 10 years. We started with multicomponent diffusion in a seven-component system (SiO₂-TiO₂-Al₂O₃-MgO-CaO-Na₂O-K₂O) and obtained the 66 diffusion matrix [1]. Then we focused on a synthetic mid-ocean ridge basalt with eight components (SiO₂-TiO₂-Al₂O₃-FeO-MgO-CaO-Na₂O-K₂O) [2,3] because basalt is the most abundant volcanic melt in the Earth. From experimental data, we obtained 77 diffusion matrix at three temperatures, and found that the eigenvector matrix is roughly invariant with temperature and each of the seven eigenvalues depends on temperature following the Arrhenius relation. This provides a formulation to calculate the diffusion matrix at any temperature within the experimental temperature range. Furthermore, we hypothesize that the diffusion eigenvectors are independent of melt compositions [4,5]. Therefore, we can examine diffusion in silicate melts in eigen-component space, and each eigenvalue is the diffusion coefficient for its corresponding eigen-component. Our preliminary examination of literature data shows that most data are consistent with the hypothesis. We are beginning to develop an online tool to model multicomponent diffusion in natural silicate melt using the eigen-component approach [5]. Here, I report these developments for the broader diffusion community and present future perspectives.

Abstract: The paper is focused on selecting the optimal modes of Zr/Ti/Fe and Cu/Ni film-support systems treatment with LPHCEBs based on the numerical studies of diffusion mass transfer in a multilayered medium. The mode of alternate application of layers with exposure to an electron beam gives a more uniform profile of the concentration distribution in depth, since they experience a bigger amount of instances of electron exposure. The most preferable conditions are those that do not allow melting of film layers, while maintaining the film temperature high enough, close to melting temperature. The density of incident energy is 1.8-3 J/cm².

Abstract: An analysis of multilayered assemblies set up with multicomponent alloys selected in a single phase field has been recently developed on the basis of a matrix of constant interdiffusion coefficients. This analysis employs a transfer matrix method and is applicable to a study of evolution of concentration profiles and diffusion paths as a function of time for multilayered diffusion assemblies (MDAs) where any number of finite layers is sandwiched between two bulk terminal alloys. The analysis is utilized in this study to simulate concentration profiles and diffusion paths for MDAs assembled with (fcc) Cu-Ni-Zn alloys with two terminal alloys, A and B, sandwiching an alloy layer C in the middle. For short diffusion times the diffusion path of the ternary MDA, A/C/B, corresponds to two segments corresponding to the diffusion paths of the infinite diffusion couples, A/C and C/B. At longer times the diffusion zones of the two individual couples overlap and the diffusion path of the MDA varies continuously with time. The evolution of the concentration profiles and diffusion paths is presented and each intermediate path configuration is associated with a unique ratio of the middle layer thickness to the square root of diffusion time. The simulated concentration profiles clearly show the development of uphill diffusion and zero-flux planes (ZFP) for the individual components due to diffusional interactions among the components. At very long times, the diffusion path of the MDA approaches that of the infinite couple A/B between the two terminal alloys.

Abstract: Interdiffusion in Fe-Ni-Cr (fcc γ phase) alloys with small additions of Si and Ge at 900°C was studied using solid-to-solid diffusion couples. Alloy rods of Fe-24 at.%Ni, Fe-24 at.%Ni- 22at.%Cr, Fe-24 at.%Ni-22at.%Cr-4at.%Si and Fe-24 at.%Ni-22at.%Cr-1.7at.%Ge were cast using arc-melt, and homogenized at 900°C for 168 hours. Sectioned alloy disks from the rods were polished, and diffusion couples were assembled with in Invar steel jig, encapsulated in Argon after several hydrogen flushes, and annealed atz 900°C for 168 hours. Polished cross-sections of the diffusion couples were characterized to determine experimental concentration profiles using electron probe microanalysis with pure elemental standards. Interdiffusion fluxes of individual components were calculated directly from the experimental concentration profiles, and the moments of interdiffusion flux profiles were examined to determine the average ternary and quaternary interdiffusion coefficients. Effects of alloying additions on the interdiffusional behavior of Fe-Ni- Cr-X alloys at 900°C are presented with due consideration for the formation of protective Cr2O3 scale.

Abstract: Selected diffusion couples investigated in the Cu-based and Fe-based multicomponent systems are examined for diffusion path development, zero-flux planes, uphill diffusion, and internal constraints for diffusion paths. The couples are analyzed for interdiffusion fluxes and interdiffusion coefficients with the aid of the “MultiDiFlux” program. Eigenvalues and eigenvectors are also determined from the interdiffusion coefficients determined over various ranges of composition in the diffusion zone. Slopes of diffusion paths at selected sections, including the path ends, are related to interdiffusion coefficients, interdiffusion fluxes and/or eigenvectors. These relations are explored with selected single phase diffusion couples in the Cu-Ni-Zn and Fe-Ni-Al systems and the calculated path slopes are compared with those directly determined from the concentration profiles. Relations between the gradient of interdiffusion flux and the concentration gradient are examined for each component in a two-phase Cu-Ni-Zn diffusion couple. The research is supported by the National Science Foundation.

Abstract: The use of atomic diffusion processes to understand the origin and evolution of the Earth and other Planetary systems are briefly reviewed in this paper. I outline some situations to illustrate how diffusion modeling may find varied applications in the Earth and Planetary Sciences. Some possible areas of research are described where advances in Geosciences may benefit researchers interested in diffusion processes in other fields. These include measurement of diffusion rates under high pressures, studies in multicomponent diffusion and modelling of diffusion and point defect related processes in multiphase and multicomponent non-metallic systems. Finally, I outline some areas where input from specialists in other areas may advance knowledge in the Geosciences.