Titel
Sodium-potassium interdiffusion in potassium-rich alkali feldspar I: Full diffusivity tensor at 850 °C
Autor*in
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Abstract
Anisotropic diffusion is described by a tensor of diffusivities, Dαβ, which may be composition dependent leading to nonlinear anisotropic diffusion. In this work the practical problem of reconstructing such a tensor for Na-K interdiffusion in potassium-rich alkali feldspar in the composition range 0.85 ≤ XOr ≤ 1.00 is addressed. Gem quality sanidine with an initial composition of XOr = 0.85 was exchanged with KCl salt melt at 850 °C and ≈1 bar. The diffusivity tensor Dαβ(XOr) and its composition dependence was reconstructed from composition profiles produced by cation exchange in six different crystallographic directions using a generalization of the Boltzmann approach. Na-K interdiffusion in potassium-rich alkali feldspar is considerably anisotropic and composition dependent. The principal axes of the diffusivity tensor representing the directions of highest and lowest diffusivity lie in the a-c plane with highest diffusivity parallel to the [101] direction, lowest diffusivity perpendicular to the (101̄) plane, and the direction with intermediate diffusivity parallel to the crystallographic b-axis. All diffusivities Dαβ(XOr) increase as XOr tends to unity. Our main result is given in the form of numerical values for all components of the Dαβ(XOr) tensor for 0.85 ≤ XOr ≤ 1.
Stichwort
Sodium-potassium interdiffusionalkali feldspar, diffusivity tensor, composition dependence
Objekt-Typ
Sprache
Englisch [eng]
Persistent identifier
Erschienen in
Titel
American Journal of Science
Band
314
Ausgabe
9
Seitenanfang
1284
Seitenende
1299
Publication
American Journal of Science (AJS)
Erscheinungsdatum
2014
Zugänglichkeit
Rechte
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