The synthesis and high pressure behavior of nanoquartz
Bertone, Jane Frances
Colvin, Vicki L.
Doctor of Philosophy
This work describes the first chemical method for the preparation of quartz nanocrystals. Microscopic characterization to evaluate phase purity, size distribution and extent of aggregation is performed. In addition, pressure dependent thermodynamic properties are also assessed. Submicron quartz powders are initially produced in hydrothermal reactions where soluble silica precursors reprecipitate as pure crystalline silica. To yield nanocrystalline material these particles can be purified and size selected by dialysis, filtration and centrifugation. Transmission electron microscopy and x-ray diffraction illustrate that the product is phase-pure alpha-quartz, consisting of isolated (i.e. non-aggregated) nanocrystals. Depending on the size selection method, crystallites with average sizes of 10 to 100 nanometers can be recovered. The high-pressure behavior of nanocrystalline alpha-quartz is studied by synchrotron x-ray diffraction up to 8.6 GPa. The unit cell volume change with pressure is fitted with the third order Birch-Murnaghan equation of state giving a bulk modulus, K0, of 40 +/- 1.3 GPa. The reported value of compressibility for nanoquartz is, with reasonable agreement, the same as previously published values for bulk quartz. However, quartz nanoparticles exhibit an increased pressure dependence of the bulk modulus. In addition, a size dependent lattice expansion at ambient as well as elevated pressure is observed.
Geology; Physical chemistry; Engineering; Materials science