Diffusion in the System K ₂ O‐SrO‐SiO ₂ : III, Interdiffusion Coefficients*

Abstract

The matrix of interdiffusion coefficients, [ D ], was determined by measuring spatial composition distribution in couples with compositions (in wt fractions) near 0.21K 2 O‐0.17SrO‐0.62SiO 2 after they were heat‐treated for various times at 630° to 810°C. The results are consistent with the Onsager hypothesis in that [ D ] at a given temperature is independent of diffusion time and the direction (in composition space) of the diffusion couple. The eigenvectors and eigenvalues of the [ D ] matrix were determined; the diffusion paths in composition space are thus easily understood. As is consistent with intuition, the “fast” eigenvector nearly parallels the direction of constant SiO 2 concentration.