The dislocation etch pits formed on the cleavage surfaces of lithium fluoride in an aqueous solution containing varying concentrations of ferric ions are investigated by electron microscopy. The results obtained reveal the powerful influence of the inhibitor in the stabilisation of kinks and macroledges. There is some evidence for the nucleation of disso­lution at imperfections other than the dislocations. Dissolution spirals are observed in some cases suggesting the presence of helical dislocations in lithium fluoride. / Thesis / Master of Science (MS)

Dissimilatory iron reduction (DIR) is significant to the biogeochemical cycling of iron, carbon and other elements, and may be applied to bioremediation of organic pollutants, toxic metals, and radionuclides; however, the mechanism(s) of DIR and factors controlling its kinetics are still unclear. To provide insights into these questions, the interaction between a common dissimilatory iron reducing bacterium (DIRB)was studied, Shewanella oneidensis MR-1, and ferric iron (Fe(III)) (oxy)(hydr)oxide mineral surfaces. Firstly, atomic force microscopy was used to study how S. oneidensis MR-1 dissolved Fe(III) (oxy)(hydr)oxides and compared it to two other cases where Fe(III) (oxy)(hydr)oxides were either dissolved by a chemical reductant or by a mutant with an electron shuttling compound. Without the electron shuttling compound, the mutant is unable to respire on Fe(III) (oxy)(hydr)oxides, but with the electron shuttling compound, it can. It was found that the cells of S. oneidensis MR-1 formed microcolonies on mineral surfaces and dissolved the minerals in a non-uniform way which was consistent with the shape of microcolonies, whereas Fe(III) (oxy)(hydr)oxides were uniformly dissolved in both of the other cases. Secondly, confocal microscopy was used to study the adhesion behavior of S. oneidensis MR-1 cells on Fe(III) (oxy)(hydr)oxide surfaces across a broad range of bulk cell densities. While the cells were evenly distributed under low bulk cell densities, microcolonies were observed at high bulk cell densities. This adhesion behavior was modeled by a new, two-step adhesion isotherm which fit better than a simple Langmuir or Freundlich isotherm. The results of these studies suggest that DIR is in-part transport limited and the surface cell density may control DIR.

In order to investigate the formation of different types of pit shapes on the crystalline surfaces, a mathematical model has been considered, which does not take into account surface diffusion and which defines the removal or transformation of different characteristic sites on the surface according to a set of frequencies. The characteristic sites are defined according to Terrace-Ledge-Kink model for the simple cubic crystal. With the help of the geometry of the step systems, specific conditions have been obtained under which the step systems considered could be obtained for a pit of monoatomic thickness. The dissolution of a simple cubic crystal has been simulated according to a set of probabilities. / Thesis / Master of Engineering (ME)