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Three different B-site additives, Mg1/3Nb2/3, Zr4+, and Cu1/2W1/2, were added to BNT ceramics in varying concentrations. These were abbreviated as BNMN, BNZ, and BNCW, respectively. The compositions were calcined to form a perovskite structure, ground to a fine powder, pressed into tablets and sintered to form dense ceramics. XRD analysis confirmed the formation of the perovskite phase. The electro-mechanical properties of the ceramics were evaluated. There were improvements in the low-field room temperature dielectric constant of 30% with 25% BNMN, 13% with 10% BNZ, and 16% with 2% BNCW. Higher concentrations of the additives degraded the dielectric performance. The conductivity of the BNT ceramics was reduced with very small concentrations (0.25 to 0.5%) of each of the additives. This reduction was maintained at the higher concentrations of the additives, which allowed for higher electric fields to be applied during both the poling process and the strain measurements. Improvements of approximately 30% in the d33 values were found at concentrations of 0.5% of each of the additives, but higher concentrations of the additives degraded the d33 values. The coercive field was affected by the additions to BNT. Increasing concentrations of BNMN reduced the coercive field in bipolar strain measurements. This was accompanied by a reduction in the remanent strain. Small additions (0.5 to 1.5%) of BNZ resulted in an increase in the coercive field by about 12%, followed by a 25% decrease at 5% BNZ. The remanent strain followed the same pattern. All concentrations of BNCW studied reduced the coercive field by about 12%. The remanent strain increased by 25% at 0.5% BNCW, and decreased by 42% at 2.5% BNCW. The electro-mechanical results for the BNMN and BNZ additives were compared to the behaviours of their lead-based counterparts, PMN and PZ. There was no consistent trend in the response of the electromechanical properties to the additions between the current lead-free and the lead-based systems. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-10-03 15:13:24.791

The candidate's investigation of Hilda Ditchburn (nee Rose) (1917 - 1986) attempts to historically place the subject as a teacher and pioneer of stoneware ceramics within the context of studio ceramics in South Africa in the second half of the 20th Century. Through an analysis, discussion and documentation of Ditchburn's life and works on a personal, technical and professional level, her discoveries and advances in studio ceramics in South Africa in the 1950's and 60's will be determined. In the light of Ditchburn's ceramic background, I shall discuss the ceramic pieces she made from the 1940's to late 1970's, focusing on selected stoneware pieces, and including examples of her earthenware and porcelain pieces. I shall discuss her experiments and discoveries with glaze chemistry and clay bodies as well as their different firing methods. I shall highlight her achievement in being the first studio potter in South Africa to design and build an oil fired kiln for high fired stoneware. This kiln was successfully fired in 1954, a time when stoneware was not being made in South Africa, thus predating any stoneware kiln made by a studio potter in the country and pioneering the growth of stoneware ceramics in South Africa. This dissertation is divided into four chapters, each with sub-headings pertaining to the information contained. The first and second chapters give background and foundational information for placing Hilda in context. The third and fourth chapters map out Hilda's personal, academic and professional information. This includes archival material and Hilda's works of art. / Thesis (M.A.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

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