Diffusion-diffusive phase transformations in alkali feldspar
Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
Final Report Abstract
Alkali feldspar is one of the most abundant minerals in the Earth’s crust. By cooling, alkali feldspar undergoes a series of phase transformations leading to grain-internal microstructures that contain information about the cooling history. The collaborative project was devoted to basic investigations of cooling-induced exsolution of alkali feldspar, in particular, it aimed to refine the thermodynamic description of the sub-solidus equilibrium phase relations and calibration of the underlying intracrystalline diffusion and phase separation for potential geo-speedometry applications. These goals were distributed between one German and two Austrian teams as a combined research (i) on the exsolution experiments and thermodynamic description (Prof. R. Abart, University of Vienna), (ii) on MD simulation of the diffusion phenomena (Prof. C. Dellago, University of Vienna) and (iii) on the radiotracer diffusion measurements (apl.-Prof. S. Divinski, University of Münster). The present report is focused on the experimental measurements of Na diffusion in crystalline feldspars, part (iii), i.e. the work performed by the German team in a close collaboration with the project partners. Following this main task, tracer diffusion of Na in numerous natural alkali feldspars, in particular sanidine, adularia and orthoclase with different Na:K ratios, was measured using the radiotracer technique and applying the 22Na radioisotope. In alularia feldspar, the tracer diffusion measurements were performed along different crystallographic directions revealing a distinct anisotropy of Na diffusion with the faster diffusion rates perpendicular to (001). In orthoclase, the anisotropy of Na diffusion was addressed in more details and the full diffusion tensor was determined. The impact of temperature and composition on diffusion in natural alkali feldspars was analyzed with respect to the composition, i.e. the Na:K ratio, alkaline impurities and intrinsic defects. For the first time, the state of Al/Si ordering was shown to have a significant influence on the Na diffusion rates in alkali feldspars. A phenomenological model of tracer diffusion was proposed to account for the Al/Si ordering. The outputs of the project contribute to better understanding of diffusion dynamics in a broad spectrum of alkali feldspars that together with an improved thermodynamic description and exsolution experiments provide reliable data on diffusion chronometry of geological scale times.
Publications
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Atomistic modeling of bulk and grain boundary diffusion in solid electrolyte Li₆PS₅Cl using machine-learning interatomic potentials. Physical Review Materials, 8(11).
Ou, Yongliang; Ikeda, Yuji; Scholz, Lena; Divinski, Sergiy; Fritzen, Felix & Grabowski, Blazej
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Combined measurements of composition-dependent tracer-, impurity- and intrinsic diffusion coefficients and atomic correlation factors from a binary diffusion couple. Acta Materialia, 293, 121088.
Esakkiraja, Neelamegan; Berndt, Jasper; Klemme, Stephan; Wilde, Gerhard; Paul, Aloke & Divinski, Sergiy V.
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Sodium diffusion in alkali feldspars: towards the impact of Al/Si ordering. Philosophical Magazine, 105(23), 1606-1621.
Tas, Bengü; Gorfer, Alexander; Petrishcheva, Elena; Wilde, Gerhard; Abart, Rainer & Divinski, Sergiy
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The impact of non-equilibrium vacancies on mobilities and Kirkendall porosity formation in diffusion couples: Experiments and theory for the Cu–Fe–Ni system as a case study. Acta Materialia, 292, 121035.
Mohan Muralikrishna, G.; Esakkiraja, Neelamegan; Kundin, Julia; Hisker, Frank; Berndt, Jasper; Klemme, Stephan; Belova, Irina V.; Murch, Graeme E.; Paul, Aloke & Divinski, Sergiy V.
