Effects of Grain Boundary Segregation on Grain Boundary Diffusion and Chemical Kinetics in Olivine Aggregates

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Marshall Sundberg has been granted an NSF Earth Sciences postdoctoral fellowship to develop an integrated program of research and education at the University of Minnesota. This experimental study will quantify the effects of grain boundary chemistry and structure on grain boundary diffusion of Mg2+, O2-, and Si4+. Synthetic, fine-grained forsterite aggregates will be doped with controlled amounts of Ca, Pr, and Ni. Following high-temperature/high-pressure anneals, tracer diffusion profiles of 30Si, 26Mg, and 18O will be measured in order to calculate the bulk diffusivity of these cations in both doped and un-doped samples. One important goal of this research is to evaluate the role that trace elements play in influencing the kinetic behavior of rocks and thus better apply the results of laboratory experiments to the Earth. The kinetic effects of grain boundary segregation will facilitate a better understanding of grain boundary structure and properties, with potential applications as diverse as the fracture toughness of fine-grained materials, fast-ion conductors, the kinetics of solid-state electrolytes, and the high-temperature creep strength of ceramics, metals, and alloys.The education plan will consist of graduate/undergraduate level seminar in solid-earth kinetics, in which the results of these experiments will be included. In addition, Dr. Sundberg will mentor undergraduate students in this investigation through the summer research program (REU) currently run by the Department.