We report diffraction experiments on some representative Fast Ion Conductors. The structures of anhydrous stoichiometric deuterium (DAl₁₁O₁₇) and silver (AgAl ₁₁O₁₇) beta aluminas have each been determined at four temperatures in the range 4 . 2K - 773K using powder neutron diffraction (PND) data. In DAl₁₁O₁₇, a strong D-O(5) hydroxyl linkage is maintained at all four temperatures .For AgAl₁₁O₁₇ at 4.2K,we have observed, for the first time in metal beta aluminas, a completely ordered cation distribution. The material, which was prepared by a new route, is accurately stoichiometric. At 298K,the silver atoms have become somewhat delocalised and by 773K they are organised in a highly diffuse manner. Single crystal neutron diffraction was used to elucidate the proton distributions in ammonium beta alumina, (NH₄) _1.25Al₁₁- 0_17.125, and the two derivatives (NH₄) _0.78H_0.25Al₁₁0₁₇ and 'HA1₁₁- 0₁₇.In the parent compound, the positions and orientations of the two independant (NH⁺₄) species are such that all protons are involved in favourable hydrogen-bonding schemes. In formation of the first derivative, one of these sites becomes completely depopulated. Our results clarify the thermal behaviour of (NH₄) _1.25Al₁₁0_17.125 and we propose schemes by which stoichiometric beta aluminas are formed from this precursor and the related (H₃0)_1+x- Al₁₁0_17.+x/2. The crystal structures of I-Ag₃PO₄(25°C and 375°C) , II-Ag₃PO₄(650°C) ,II-Na₃PO₄ (γ) (400°C) and the solid solutions Na_3(1-x)Al_xPO₄are described. The high-temperature forms are considered in relation to the fluorite structure and mechanisms for the ionic conduction of these phases are proposed. A single crystal X-ray diffraction study of β-Ag₂SO₄ (25°C) reveals that it is isostructural with thenardite, V-Na ₂SO₄.The high-temperature modifications a-Ag₂SO₄ (490°C) and α-K₂SO₄ (620°C) have been characterised using PND data. A PND experiment on silver (I) fluoride confirms that it adopts the rocksalt structure and we find no firm evidence for a significant population of defects.

No description available.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 84-86). Also available via the Internet.

Thesis (MScAgric)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Colorado, 2001. / Includes bibliographical references.

No description available.

We were unable to verify the existence of ion mobility discontinuities in either superfluid helium at 1 K or liquid nitrogen. The velocity-field dependence in helium was described by an increased interaction with the normal fluid, due to an increase in the roton number density close to the ion surface. The mobility results in nitrogen were interpreted as being due to liquid motion, following a theory by Kopylov. The D.C. results showed that the effect of a grid on the transmission of an ion beam could be described by a field dependent grid transmission coefficient, independent of the ion velocity. The vortex ring transmission through a grid was a complex function of vorticity being captured by the grid, the capture and escape probabilities of the bare ions by vorticity, and the onset for vorticity propagating throughout the ion cell.

Superplasticity and superionic conductivity (SIC), both thermally activated processes, have been independently observed in certain materials with a high diffusion coefficient in high temperature ranges. Intuitively, this observation leads one to the idea that both types of behavior may be inter-related with one another. Therefore, it is the purpose of this research to investigate, specifically, the deformation characteristics of two SIC's, Bi₂O₃ and YSZ (yttria-stabilized zirconia), and to attempt a correlation of their behavior. Compressive deformation of these two materials was conducted over a wide range of temperatures and at various strain rates in an effort to characterize the temperature and/or strain-rate dependences of any observed superplasticity. Steady-state flow stress values were utilized to calculate the strain-rate sensitivity, m, of the materials, as well as the activation energies (Q_C) of superplasticity. Next, the obtained values of Q_C. were compared to SIC activation energies from the literature. Bi₂O₃ exhibited structural superplasticity within the range of test conditions utilized. However, published values of SIC activation energy were lower than experimentally derived Q_C by a factor of four. Therefore, one is not able to state whether or not there is any correlation between the two behaviors. Unfortunately, YSZ exhibited brittle behavior over the entire temperature and strain-rate ranges, so the same analysis could not be performed. Furthermore, SEM micrographs showed that YSZ samples, as processed, did not possess the proper microstructure required for superplasticity. Hence, no final conclusions on YSZ can be drawn from this study. / Master of Science

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2007. / Two–thirds of South Africa, including more than 280 towns and settlements are largely dependent on groundwater for their drinking water supply and development. However, groundwater resources in South Africa are limited both in terms of quantity and quality, especially in the semi–arid parts of the country (Sililo et al., 2001, p. i). Therefore, the importance of protecting groundwater resources from pollution has been recognized. The first objective of this research was to investigate the attenuation capacity of a selection of soil horizons and materials representing major types of diagnostic horizons and materials in the South African soil classification in order to validate their chemical attenuation ratings as provisionally specified by Sililo et al. (2001, p. 4.6). The second objective was to assess the pollutant attenuation capacity of South African soil horizons and materials as well as describe the diagnostic value of key chemical properties of soils for conveying information on their contaminant transport/attenuation potential. The third objective was to investigate whether it is possible to apply acid/base priming using H2SO4 and Ca(OH)2 to a bulk quantity of soil in order to reduce the mobility of contaminants.