No description available.

Zinc oxide is a II-VI semiconductor with considerable potential for optoelectronic and power-electronic applications in the UV spectrum, due to its wide direct band gap (3.35 eV at 300 K), high exciton binding energy (60 meV), high melting point, and excellent radiation hardness. A key requirement for many device applications is the consistent production of high performance Schottky contacts. Schottky contact formation to n-type ZnO was investigated via systematic studies into the relative performance of different metal and metal oxide Schottky contacts to hydrothermal and melt grown, bulk ZnO. The results of these studies can be explained by the dominating influence of two key mechanisms in the formation of high quality contacts: the removal of the natural hydroxide termination of ZnO and the associated surface accumulation layer, and the minimisation of process induced oxygen vacancies which tend to pin the barrier height of ZnO Schottky contacts in the 0.6 - 0.8 eV range. These investigations also led to the discovery of a new technique for the consistent production of high quality ZnO Schottky contacts, using the deposition of metal oxide films in reactive oxygen ambients. Specifically, silver oxide, iridium oxide, and platinum oxide films were used to consistently produce highly rectifying, very low ideality factor Schottky contacts to bulk ZnO, with figures of merit significantly better than those published in the literature. In addition, a number of previously unreported, surface polarity related effects were discovered in the electrical and optical properties of ZnO, which increase in magnitude with decreasing carrier concentration of the ZnO material. For example, metal oxide Schottky contacts fabricated on the Zn-polar surface of hydrothermal ZnO have significantly higher barrier heights than those on the O-polar surface, and low temperature (4 K) photoluminescence emission, from free excitons and excitons bound to ionised donors, is also significantly stronger from the Zn-polar face of the same material. These effects are thought to be related to the large spontaneous polarisation (-0.057 Cm-2) of ZnO, and indicate that surface polarity is an important variable when comparing experiment results with theoretical models, and in the future design of ZnO based devices.

Dietary zinc deficiency was induced in four healthy male volunteers. The diet used was high in phytate (phytate:zinc molar ratio 381) and the depletion period was preceded by a 3 day starvation period. In the depletion period, there was a significant decrease in plasma zinc and urinary zinc excretion. The subjects also adapted to the low zinc intake by decreasing the faecal excretion of zinc. One subject (No.2) developed clinical signs of zinc deficiency and also had the lowest plasma zinc concentration at the end of the depletion stage. Whole body protein turnover was assessed by an 8hr primed constant infusion of Li-[1-¹³C]leucine. Zinc deficiency had an effect on whole body protein turnover in only one subject (No. 2). In this subject, there was a decrease in leucine oxidation (71%), protein synthesis (31%) and degradation (39%). In this group as a whole, zinc depletion was associated with a significant decrease in urinary excretion of 3-methylhistidine. Zinc deficiency appeared to have no effect on substrate utilization. With regard to zinc kinetics, zinc deficiency was associated with a significant decrease in the size of the plasma zinc pool and a liver pool. There was also a decrease in the flux between these two zinc pools, and an increase in the fractional decay of zinc from the plasma pool to the liver pool. Two further studies were carried out. In 4 volunteers the effect of a 3 day starvation period on whole body protein turnover and zinc kinetics was investigated. There was a significant increase in leucine oxidation and in the size of a liver zinc pool. In 6 volunteers, the effect of phytate on zinc kinetics was investigated. The addition of phytate to the test meal, (phytate:zinc molar ratio 88) was associated with a decrease in the size of a liver zinc pool.

No abstract available. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1975.

Zinc air batteries have great promise as a new age energy storage device due to their environmental benignity, high energy density in terms of both mass and volume, and low cost Zinc air batteries get their high energy density by using oxygen from the air as the active material. This means that all the mass and volume that are normally required for active material in a battery are replaced by a thin gas diffusion electrode which allows for oxygen from the air to diffuse into the cell. Although this seems ideal, there are many technical challenges associated with the cell being open to the atmosphere. Some of these issues include electrolyte and electrode drying out, poor reaction kinetics involving sluggish reaction, the need for bifunctional catalysts to charge and discharge, and durability of the gas diffusion electrode itself. The bifuntional catalysts used in these systems are often platinum or other precious metals since these are commonly known to have the highest performance, however the inherent cost of these materials limits the feasibility of zinc air systems. Thus, there is a need to limit or remove the necessity for platinum carbon catalysts. There are many types of non precious metal catalysts which can be used in place of platinum, however their performance is often not as high, and the durability of these catalysts is also weak. Similar limitations on feasibility are invoked by the poor durability of the gas diffusion electrodes. Carbon corrosion occurs at the harsh caustic conditions present at the gas diffusion electrodes, and this corrosion causes catalyst dissolution. Moreover, many issues with zinc electrode fabrication limit durability and usable anode surface area within these systems. There is a need for a stable, porous, high surface area anode with good structural integrity. These issues are addressed in this work by three studies which each focuses on solving some of the issues pertaining to a crucial component of zinc air batteries, those being the gas diffusion electrode, the zinc electrode, and the bifunctional catalyst necessary for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The first study addresses the need for improvements to the zinc anode electrode. A new process is proposed for the production of porous zinc electrodes in which the porosity can be easily controlled. This process involves the mixing of atomized zinc powder with a filler compound such as ammonium chloride. The mixture is then pressed into a pellet and heat treated to a temperature which simultaneously sublimes/decomposes the filler compound, and anneals the zinc structure to improve structural integrity. The resultant porous anode showed significantly charge and discharge potentials over the solid plate anode, while allowing for increased control of porosity over other porous electrodes due to the ability to adjust pore size based on the filler compound particle size. The discharge potentials observed from these porous anodes were 20% greater than zinc plate anodes at 100mA, but up to 200% greater at elevated currents of 200mA. Similarly the charging potentials were 53.8% lower at 100mA, and 55.5% lower at 200mA., suggesting greatly improved performance by the porous anode. The second study addresses the need for more durable gas diffusion electrodes. In this study, the bifunctional catalyst was bound directly to a stainless steel current collector via polymer binding in an attempt to remove the possibility of carbon corrosion and catalyst dissolution. The new gas diffusion electrode was successful in eliminating carbon corrosion, wherein, the durability of cells which incorporate this type of electrode was significantly increased. The durability of cell was increased to a point where little to no degradation occurred over 1000 cycles of full cell testing, showing great promise for future use and commercial viability. The final study addresses the need for durable and high performance non precious metal catalysts. The effects of catalyst morphology were studied wherein various morphologies of spinel type cobalt oxide were synthesized and compared. Cobalt oxide nanosheets were successfully synthesized and compared to nanoparticles of comparable size. The cobalt oxide nanosheets showed better charge and discharge potentials as well as durability of the nanoparticles. Impedance analyses showed reduced charge transfer and cell component resistances associated with the nanosheet morphology. Cobalt oxide nanosheets were further compared against platinum carbon. Cobalt oxide nanosheets showed significantly better durability as well as lower charging potentials and higher discharge potentials over 75 cycles. After 75 cycles the platinum carbon had lost 55.7% of its discharge potential wherein cobalt oxide nanosheets lost none of its discharge potential. Three issues pertaining to three major cell components a zinc air were addressed with promising solutions proposed for each. This work provides a basis for advanced zinc electrode fabrication in which further improvements can be incorporated to address other issues pertaining to zinc electrode use. This work set up a basis for electrode design which focuses on non carbon supported catalysts, eliminating the issue of carbon corrosion and associated catalyst dissolution. Finally, the results from the morphology study elucidate the benefits of controlled morphology for bifunctional catalysts, showing how morphology can be adjusted to improve performance by improving cell and charge transfer resistances.

Selective ligand coordination of zinc over other metals such as copper (II) and iron (III) is desirable and has potential commercial uses in hydrometallurgy. With this in mind ligands have been synthesised that impart a tetrahedral donor array. Binding to zinc which prefers a tetrahedral binding geometry may achieve selectivity over other non-tetrahedrally coordinating metals. Di-N-alkylated bisbenzimidazole-4,4'-dicarboxylic acids have been synthesised and shown by proton NMR, ESMS and IR analysis to bind zinc as an [L(_2)Zn(_2)] species with selectivity over copper, nickel, lead and cadmium. Hence a reversal of the Irving- Williams sequence is observed. Aqueous extraction tests using a lipophilic N-alkylated derivative indicated that the observed selectivity over copper and iron (III) was not reproduced under these experimental conditions. The ligand began to extract in the pH 2.3-3.8 region.2,9-Diphosphinoxymethyl phenanthroline derivatives were synthesised and shown to bind nickel, copper and zinc with similar stability constants, with only marginal enhancement over that of the parent phenanthroline. The 1:1 complexes were produced at acidities below pH 2. Increasing the length of the pendent arm donor groups by using phenylacetic acid moieties did not enhance zinc selectivity. The donor group was not ideal and [ML(_2)] species were generated (i.e. an N(_4) donor set)Two phenol substituted 12N(_3) ligands were synthesised (N-linked and β-C- linked). Complex stability order followed die Irving-Williams sequence Cu > Zn > Ni. The N-linked derivative formed a six membered chelate on binding and had larger metal-ligand stability constants than for the C-linked derivative which formed an eight membered chelate. The N-linked derivative bound the copper (II) cation in a near tetrahedral arrangement and imparted some copper (I) character to the metal

No description available.

A liquid-extraction procedure for the concentration of zinc in sea water was developed. The metal ion in sea water was chelated with sodium diethyldithiocarbamate and extracted into an organic solvent, methylisobutylketone, at the normal pH of sea water. A back-extraction into HCl followed, providing a concentration of 30X for the entire procedure. Filtration was introduced into the procedure to insure that only dissolved forms were extracted and that no influence from particulate matter would be detected. Problems of loss of zinc and/or contamination arose. These were overcome to a great extent by washing all glassware, including the sinterred-glass filter holder, in nitric acid and by following the filtration through the glass holder with an acid rinse. Purification of reagents was found necessary. With replicate analyses on a given sea water source, the recovery was 97 ± 2%. Upon making varying standard additions to subsamples of sea water, the calculated recovery was 97 ± 5.4%. The contamination figure for the extraction process ranged from zero to 0.8 ppb in the original sea water sample. With filtration, an overall median contamination of 1.4 ± 1 ppb was determined. / Graduation date: 1967

Bibliography:leaf 147. / x,178 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Describes the development of Zn(II) selective ligands for use as fluorescent probes to monitor exchangeable Zn2+ in biological systems. Ligands were synthesized based on the phenyl substituted thiazoline substructure which is the chromophose of pyochelin. The stability and fluorescence of the Zn complexes were determined. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry,1995

Bibliography:leaf 147. / x,178 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Describes the development of Zn(II) selective ligands for use as fluorescent probes to monitor exchangeable Zn2+ in biological systems. Ligands were synthesized based on the phenyl substituted thiazoline substructure which is the chromophose of pyochelin. The stability and fluorescence of the Zn complexes were determined. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry,1995