Ulrich Faul

Associate Professor

Rock Physics Group

Department of Earth Sciences - Boston University - ufaul@bu.edu

Sol Gel Olivine

The starting material for a range of experiments is synthetic olivine of Fo90 composition, made from metal (Mg, Fe) nitrates dissolved in ethanol on a warm hot-plate. After the nitrates are completetely dissolved and well stirred (magnetic stirrer) tetra-ethyl orthosilicate is added to the mix and again well stirred. Gelation is initiated by adding a few drops of nitric acid. The gel is slowly dried, first on a hot-plate, then in a Pt crucible over a bunsen burner in a fume-hood. If drying occurs too fast, percipitation of metal oxides on crucible walls may occur, producing excess silica (opx) in the final product. The gel is reacted at 875°C at controlled oxygen fugacity. The powder is reground and refired twice (see chart) before hot-pressing.

FESEM orientation contrast image of sol-gel sample hot-pressed at 1300°C showing near-ideal "foam" texture of hexagonal grains.

Flow chart for Sol-Gel based deformation experiments.