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The growth of strontium sulfate precipitate by diffusion in various gels was studied by using optical transmission and confocal microscopies, scanning and transmission electron microscopies, and energy dispersive X ray fluorescence. Pure silica gel, pure agarose gel and the silica/agarose mixed gel at pH 7 - 10 were used throughout the present study. Precipitate morphology is sensitive to pH and to the nature of the growth medium. The morphology was observed as a function of time. The lack of change is presumably because of rapid depletion of the limiting reagent after the very beginning of precipitation. The problem of separating strontium sulfate precipitate from the gel medium is discussed.

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The thermoelectric properties of lanthanum-doped strontium titanate (LSTO) were investigated for high temperature applications. Ceramics with the formulation La(2x/3)Sr(1-x)TiO(3-delta) (x = 0.1, 0.3, 0.5, 0.7, 0.9) were produced using the conventional mixed oxide route. After 18 hours of milling the powders were calcined at 1373 K for 4 hours and sintered at 1733 K (± 180 K/hour) for 4 hours in air. SEM, XRD, and TEM techniques were employed to characterise the microstructure of the ceramics as well as density measurements. Subsequently the electrical conductivity, Seebeck coefficient, and thermal conductivity in order to determine the thermoelectric figure of merit of the ceramics. Key thermal conductivity results were further investigated using a computational approach. This production method resulted in high quality, high density (> 97 %) ceramics that were mostly single phase determined by XRD with a Pm3m space group, with the exception of the x = 0.9 ceramic that had a Cmmm space group. SEM imaging confirmed this finding and revealed a core-shell structure in x = 0.1 and x = 0.3 ceramics whereby the core was La-rich/Sr-deficient. Thermal conductivity of the ceramics decreased with increasing La content. This was investigated further computationally employing the Green-Kubo method. It was established that the decrease in thermal conductivity was due to phonon-scattering from A-site vacancies, and not from the stabilisation of oxygen vacancies as suggested elsewhere. The electrical properties were dramatically improved through sintering the LSTO ceramics in a 5 % H2 95 % Ar atmosphere. This led to a reduction of Ti4+ to Ti3+. The maximum electrical conductivity increased to 789 S.cm-1 resulting in a power factor of 0.0013 W.m-1 K-2 at 477 K for x = 0.3. A zT of 0.27 at 870 K for x = 0.5 was obtained due to a lower thermal conductivity. The ceramic LSTO x50H was subsequently doped with excess lanthanum; A maximum of 3 % excess was able to be fully incorporated into the lattice. This resulted in a further increase of the electrical conductivity to 875 S.cm-1 at 377 K. A decrease in the lattice thermal conductivity of ∼ 1 W.m-1 K-1 was also achieved due to the oxygen vacancies that were introduced as a result of the reducing sintering conditions. Overall a zT 0.27 at 1016 K was obtained for 3 % excess lanthanum. The ceramic LSTO x50H was also doped with niobium and vanadium. Reduction in the lattice parameter from the La substitution inhibited the niobium from fullyincorporating into the matrix. This was not the case for vanadium that resulted in an electrical conductivity of 144 S.cm-1 , Seebeck coefficient of -106 µV.K-1 , and thermal conductivity of 2.08 W.m-1 K-1 at 308 K, resulting in an overall maximum zT of 0.08 at 1070 K.

The aim of this project was to study the in vitro release of cephalothin, vancomycin and strontium from hydroxyapatite particles and its PMMA composite. The hydroxyapatite spheres containing strontium were prepared in the laboratory. The in vitro release study for the hydroxyapatite was carried out in phosphate buffer saline solution (PBS) with differing pH value at 37 °C for five days and the PMMA composites for 21 days. All of the releases showed a burst release within the first 24 hours followed by a slow release. The pH value of the release medium had influence on the release rate to some extent for the antibiotic release and the acidic solution had a more significant impact on the strontium release. All of the composite groups had a much lower strontium release rate than the strontium release from the hydroxyapatite spheres.

The area of advanced gate dielectrics has gained considerable attention recently, and there are significant leakage current and reliability concerns for oxy-nitride in this regime. So it¡¦s an important business to use alternate high-k dielectrics instead of oxy-nitride. Titanium dieoxide shows a high dielectric constant for dielectric applications. Besides, strontium can create additional oxygen vacancies that can enhance dielectric constant. In this study, we prepared SrTiO3 film by liquid phase deposition which is a novel material considered to have high dielectric constant. From several characteristic measurements, we found that SrTiO3 with exhibiting higher dielectric constant and well interface state which is very promising candidates to instead of titanium dieoxide. The physical and chemical properties of SrTiO3 films by means of several measuring instruments, including Fourier transform infrared spectrometer (FTIR), secondary ion spectrometer (SIMS), and X-Ray diffractometer (XRD). An Al / SrTiO3 / Si metal-oxide-semiconductor (MOS) capacitor structure was used for the electrical measurements. To improve the electrical properties, we investigated the characteristics of SrTiO3 films after annealing in oxygen, nitrous oxide, and nitrogen ambient. Including the variations of thickness, structure, dielectric constant, and leakage current were discussed in this work.

published_or_final_version / abstract / toc / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

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