Element distribution in grain boundaries of geomaterials with respect to their geometry

• Applicant: Dr. Katharina Marquardt
• Subject Area: Mineralogy, Petrology and Geochemistry ; Mechanical Properties of Metallic Materials and their Microstructural Origins ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274616592

Diffusional mass transport in a synthetic or natural rock matrix may occur via volume or grain boundary diffusion, or a combination of both. A huge amount of experimental data on volume diffusion exists for many elements within the respective mineral structures; data on grain boundary diffusion are absent. This is particularly true for mass transport within single grain boundaries with well-characterised grain boundary structures. These experimental data are not only needed to correctly interpret geological observations; they also provide the fundament for understanding grain boundary diffusion at all. Single grain boundaries with constant characteristics at the µm-scale are a prerequisite for such studies, these we generate using bicrystal synthesis.Differently oriented garnet and olivine bicrystals are produced and coated using pulsed-laser deposition with various components and subsequently heated at different temperatures and durations. The resulting element distributions and concentration profiles along/across the specific grain boundaries will be measured by Analytical Transmission Electron Microscopy (ATEM) and Synchrotron X-Ray Fluosrescence (SXRF) methods and compared with volume diffusion profiles from the same experiment. Applying continuum models for diffusional transport, and estimating grain boundary widths from High Resolution TEM (HRTEM) observations, grain boundary diffusion coefficients are derived and directly compared with volume diffusion coefficients. Furthermore, we can learn how the grain boundary transport properties are influenced from varying ionic radii and how this influences the effective grain boundary width for diffusion. Furthermore, we gain diffusion information from different elements at various temperatures, yielding the needed data for calculations of geologically relevant parameters, such as rock age and reaction or process durations. This is especially important with respect to short duration processes such as impacts.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Ralf Dohmen