No description available.

Thesis (M.Sc. (Physics)) --University of Limpopo, 2005 / Self-consistent electronic structure calculations have been performed on ordered cubic-based magnesium-lithium (Mgx-Li1−x) alloys spanning the concentration range 0 ≤ x ≤ 1, using an ab initio plane wave pseudopotential (PWP) method. The first principle pseudopotential planewave approach is used within the local density approximation (LDA) and generalized-gradient approximation (GGA)of the density functional theory (DFT) framework. We have calculated the binding energy curves and the systematic trends in various cohesive and elastic properties at zero temperature, as a function of Li concentration. The calculated equilibrium lattice parameters show a large deviation from Vegard’s rule in the Li-rich region whilst the bulk moduli decrease monotonically with increase in Li concentration. The heats of formation for different ground state superstructures predict that the DO3, B2 and DO22 structures would be the most stable at absolute zero amongst various phases having the Mg3Li, MgLi and MgLi3 compositions, respectively. This stability is reflected in the electronic density of states (DOS). Because of the special significance of the isotropic bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio for technological and engineering applications, we have also calculated these quantities from the elastic constants. The elastic constants indicate the softness of the material as more Li is added with the bcc-based phases becoming mechanically less stable for Li concentration less than 50%. Our results show good agreement within the estimated uncertainty with both experimental and previous theoretical results. / The National Research Foundation (NRF), South Africa-Royal Society (RS), Great Britain collaboration and Council for the Scientific and Industrial Research (CSIR)

Aluminum-lithium alloys have been under development for lightweight - high strength aerospace structures but implementation has been slowed significantly because of poor short transverse fracture toughness and brittle intergranular delamination cracking. The alloy AF/C458 (now designated AA 2099) has been designed to exhibit decreased mechanical anisotropy and improved fracture toughness while maintaining ductility and strength levels. This thesis examines the application of Friction Stir Processing (FSP) of AF/C458 as an approach to refine and homogenize the grain structure and enhance mechanical properties. FSP of peak-aged material results in refined, equiaxed grains but with reduced hardness due to the heat input of the process. The effect of post-FSP heat treatment has been established and the influence of FSP on tensile and fatigue properties has been determined.

Thesis (M. Phil.)--University of Hong Kong, 1987.

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / TM in title is superscripted on title page. Typescript. Vita. Includes bibliographical references (leaves 100-103). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / TM in title is superscripted on title page. Typescript. Vita. Includes bibliographical references (leaves 100-103). Also available on the Internet.

<p> LiYO2 is a lithium ion conductor stable to pure lithium metal. The goal of the present work was to design and construct an electrochemical cell and demonstrate the use of LiYO2 as an electrolyte since this has never been previously done. The electrolyte was fabricated by slip casting in powder molds. A Y2O3-MgO composition was identified and used to fabricate a lid for the cell. Impervious cells were obtained by liquid phase joining and sintering techniques. Heating rate was found to be a key parameter in the success of this procedure. The cell was evaluated in terms of stability as a sensor and chemical pump by measuring EMF for two different Li-Zn alloys between 250 and 600°C. The configuration was as follows: (RE) (-) Ta Li,Sn | LiYO2 | Li,Zn Ta (+) (WE)</p> <p> The cell showed no significant attack after 40 days working with pure lithium. Stability and reproducibility of EMF values was obtained for the concentrations of Li studied. Solidus and liquidus temperatures were determined for the 5 and 10 mol% Li compositions in good agreement with published phase diagrams. Variations of EMF with respect to temperature or concentration followed the expected thermodynamic relationships. Results indicate that the LiYO2 electrolyte cell could be useful in assessment of the thermodynamics of lithium alloys.</p> / Thesis / Master of Engineering (MEngr)