On the determination of diffusion coefficients in two-component alloys and doped semiconductors. Several implications concerning the International Space Station

Abstract

The accurate determination of interdiffusion coefficients is a technologically relevant problem that has implications on the correctness of the predictions when using the existing models of solidification. It is also important in the validation of different theories of atomic diffusion. The experimental determination of these coefficients when there is a liquid phase is difficult due to the unavoidable presence of buoyancy driven convection currents that enhance mass transport and disturb diffusion measurements. To minimize as much as possible these problems, long capillaries are used in order to confine the fluid and reduce the intensity of the convective motions. More recently, these measurements have been done in reduced gravity environments, but the residual gravity is still able to induce buoyancy driven convection motions. The aim of our work is to numerically analyze the impact of low and moderate Rayleigh number environments on the accuracy of the interdiffusion coefficient measurements using long capillaries. In the present study we deal with two liquid systems; photovoltaic silicon and Al-based liquid binary alloys at high temperature. We have numerically simulated in 3D two different experimental techniques used to determine the diffusion coefficients, this extends previous reported 2D calculations. We also consider the effect of rotating the cylindrical cell along their axis as a general stabilization mechanism of the convective motions. Finally, we use typical accelerometric signals from the International Space Station (ISS) in the quasi-steady range of frequencies. The signals concentrate on typical station reboosts because of the accelerometric level of the rest of disturbances -dockings, undockings and Extra Vehicular Activities, EVAs-is considerably lower. Keywords: Diffusion coefficients, Numerical simulation, Microgravity conditions, Melted semiconductors, Liquid metals, Shear Cell, Long Capillaries

On the accuracy of the interdiffusion coefficient measurements of high-temperature binary mixtures under ISS conditions

“…Notice firstly that all values are lower than the corresponding ones obtained in the 2D part of the present study. As usual, the presence of a third dimension enables us to numerically relax the quantitative bidimensional results [24,25]. In addition and also in 3D, all six values are also lower than the 1% threshold clearly indicating that, under the present conditions, there is no appreciable impact of the environment in the accuracy of the interdiffusion measurements.…”

“…In the 3D case, an unstructured mesh arrangement of 610 000 cells has been used only to make calculations in the interdiffusion-couple configuration. For the sake of brevity, mesh details can be consulted in the literature [22][23][24][25].…”

Time-dependent patterns in quasivertical cylindrical binary convection

“…On one hand, we obtain that the frequency of the SHC state, ω SHC , which determines the velocity of the traveling structures, increases with α: ω SHC (α = 0.018) = 1. 35, ω SHC (α = 0.024) = 1.53 and ω SHC (α = 0.030) = 1.69. However, we do not observe stable SHC patterns for α > 0.034, a fact coincident with experimental observations [34].…”

“…In the equations Ra x = Ra sin α and Ra z = Ra cos α. More details about the obtention of these equations can be found in some previous works in related configurations [35,36]. We consider impermeable and nonslip boundary conditions, with fixed temperature at the lids and insulating boundaries on the lateral wall:…”

Analyzing Slightly Inclined Cylindrical Binary Fluid Convection via Higher Order Dynamic Mode Decomposition

“…To integrate the equations in time, we use the second order time-splitting method proposed in [35] combined with a pseudospectral method for the spatial discretization, Galerkin-Fourier in the azimuthal coordinate ϕ, and Chebyshev collocation in r and z. More details about the derivation of the equations and the numerical method can be found in some previous works in the same or related configurations [14,36,37].…”