School of Chemistry - Theses
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ItemOleic acid adsorption at the goethite-water interface( 1976)The adsorption of oleate at the goethite-water interface has been studied. In addition, the interactions of oleate at other mineral-water interfaces were considered. Mainly by means of a literature review, a bulk equilibrium solubility diagram for oleic acid in water was constructed, as a function of total oleate concentration and pH. The competing bulk precipitation equilibria for oleic acid mineral phases such as iron (III) oxides, barite, calcite and fluorite and the relevant metal oleates, were considered graphically. Literature, adsorption, flotation recovery, electrokinetic and infrared work was examined in the light of this bulk precipitation data. It was found that many of these studies have been carried out in pH-concentration regions where bulk equilibrium phase changes were occurring, such as precipitation of oleic acid or of metal oleates. Adsorption behaviour in these systems was obscured by the bulk precipitation effects. Adsorption experiments were carried out with oleate in the presence of goethite, choosing pH and concentration such that bulk precipitation effects were not important. Electrostatic and hydrophobic interactions as well as chemisorption, appeared to be of importance in the adsorption process. A new approach for surfactant adsorption, a multiple equilibrium model, was suggested to describe quantitatively, the adsorption of oleate at the goethite-water interface. This approach considers oleic acid solution equilibria. The adsorption process is represented by the reaction of neutral goethite surface sites with oleate and protons in the manner of solution equilibria. A good fit was obtained to the experimental data. The model predicts that the acid-soap species HOI2 is the most important adsorbed species.
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ItemThe adsorption of polydisperse nonionic surfactants at the solid/aqueous interface( 1987)A high resolution capillary gas chromatography technique has been adapted to the analysis of polydisperse non-ionic surfactants. This technique has enabled the complete characterization of the oligomer distributions of very small samples of surfactants (typically 0.1 µg to 0.5 µg). It has made possible the determination of changes in the oligomer distribution on adsorption of surfactant at the solid/aqueous interface. Isotherms have been measured for the adsorption of a series of polyoxyethylene nonylphenol surfactants from aqueous solution on to various solids. These isotherms indicate that the surfactant – surface interaction increases with an increase in the hydrophobicity of the adsorbent. They also show a dependence upon the average length of the ethylene oxide chain and the ratio of the surface area/solution volume. These latter factors affect both the total partition of surfactant between the surface and the solution, and also the selectivity of the solid surface. A detailed study of the adsorption of N8 (a commercial non-ionic surfactant) by a precipitated silica at various surface area/solution ratios, has been undertaken, where the equilibrium surfactant oligomer distributions in the adsorbed and solution phases have been determined. At surfactant concentrations above the critical micelle concentration, the phase separation approach has been used to estimate the surfactant oligomer distributions in free monomer solution and in micelles. This information has been combined with a surface phase model to interpret the results of the adsorption distribution studies.
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ItemThe structure of the oxide/aqueous electrolyte interface( 1975)The structure of the oxide/aqueous electrolyte interface has been studied. The surface porosity of several oxides to ions is evaluated and the contribution of such porosity to the double layer properties determined by surface charge measurements. The oxides studied are B.D.H. precipitated silica, before and after heat treatment, rutile, goethite, hematite and amorphous ferric oxide. The surface porosity was evaluated using nitrogen adsorption for physical porosity, tritium exchange for surface hydration and dissolution for surface crystallinity. It is found that the surfaces of metal oxides may be divided into two categories; those that are porous to ions and those that are non-porous. Of those studied only the precipitated silica and the amorphous ferric oxide are porous. The porosity is probably due to an easily permeated layer of hydrolysed oxidic material. It does lead to exceptionally high surface charges. However the non-porous oxides also exhibit high surface charges so that while surface porosity may, in some cases, contribute to oxide double layer properties, it cannot be a general explanation of the high differential capacities observed. A site-binding model for non-porous oxide/aqueous electrolyte interfaces is introduced, in which it is proposed that the adsorbed counter ions form interfacial ion pairs with discrete charged surface groups. This model is used to calculate theoretical surface charge densities and potentials at the Outer Helmholtz Plane. The calculated values are consistent with experimental data for oxides provided a high value of the inner zone capacity is accepted. An explanation is provided for the difference between silica and most other oxides in terms of the dissociation constants of the surface groups.
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ItemInterfacial effects on aqueous sonochemistry and sonoluminescence( 1999-06)The dissolution of quantum sized CdS and MnO2 particles in water was conducted using 20 kHz ultrasound. CdS particles were found to dissolve chemically via an oxidation process while MnO2 particles dissolved via a reductive process. It was found that the dissolution of the colloids could be controlled via the addition of surface active chemicals to solution and by varying the saturation gas type. In the presence of Na2S or propan-2-ol and argon gas, the dissolution of CdS was inhibited, whereas the addition of alcohols (methanol, ethanol, propan-2-ol, butan-1-ol and pentan-1-ol) to the MnO2 system led to an increase in the amount of dissolution for a given time of sonication. This increase in dissolution was found to be dependent on the ability of the surface active radical scavenger to accumulate around the bubble interface during the cavitation process. Eventually, at higher alcohol concentration there was a plateau or a limiting value reached for the efficiency of colloid dissolution which was common for each alcohol. (For complete abstract open document)
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ItemIodine speciation in the Yarra River estuary( 1992)An oxygen-deficient (12.8 microM dissolved oxygen and oxygen saturation 5.0-7.4% in the water of the deep hole) isolated water system in the deep hole of the Yarra River estuary was investigated to discover the relationship between iodate and iodide. The iodate concentration in the water of the deep hole was very low (0.039 to 0.062 microM at bottom water, salinity from 26.8-30.0 Practical Salinity Scale, 1978), because iodate reduced to iodide in the water by reducing agents (S2-, Fe2+ and Mn2+) diffused from the sediment of the deep hole. The concentrations of iodine species in the sediment pore water and suspended material in the water of the deep hole were determined to investigate iodine cycling in the deep hole. The iodine flux from sediment into overlying water in the deep hole was 15.6 micromol/m^2.day. The concentration of total inorganic iodine (iodate+iodide) in the dry suspended material from the water of the deep hole was 0.117 micro mol/g. The water residence time in the deep hole was studied. In winter especially, the seawater of high density may intrude into the deep hole with the highest tides. The seawater remains trapped in the deep hole below the halocline, which allows the development of oxygen-deficient conditions. It was found that in the deep hole the iodide concentration increase resulted from sediment diffusion (36%), iodate reduction (27%) and release from suspended material (37%) during the water residence time in the water of the deep hole. The iodine cycling in the deep hole was: iodate in the water reduced to iodide by reducing agents diffused from sediment; suspended material containing soluble or particular iodine may release iodide and also trap iodate and iodide from water during precipitation; iodate in the sediment reduced to iodide and iodide diffused from sediment into overlying water. Iodine is accumulated in the isolated water in the deep hole and might be moved out at the next water exchange.
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ItemThe environmental degradation of pyrotechnic magnesium powder( 2002)Magnesium powder is one of the most common and important metal fuels used in military pyrotechnic systems. However, the major problem with magnesium based pyrotechnic systems is the susceptibility of the magnesium powder to react with moisture in the environment, particularly at elevated temperatures and relative humidities, typical of military storage conditions found in Northern Australia. This study of the bulk and surface chemical and physical changes associated with the environmental degradation of commercial pyrotechnic magnesium powder at elevated temperature and elevated relative humidity results in the formation of magnesium hydroxide (Mg(OH)2, magnesite or hydrated magnesium carbonate (MgCO3.xH2O), magnesium oxide (MgO) and hydromagnesite or basic magnesium carbonate (Mg5(C03)4(OH)2.4H2O). This was confirmed by auger and x-ray photoelectron and infrared spectroscopy and x-ray diffraction. All of these products form as a result of the reaction of the magnesium with moisture and air but they each form in different amounts and at different rates depending on the grade (particle size/surface area) and the type (particle shape) of the magnesium powder. For all the powders, the major degradation product is magnesium hydroxide, which was confirmed by all the analysis techniques. The temporal ageing of magnesium and the subsequent formation of bulk magnesium hydroxide follow a three stage sigmoidal relationship. The first stage represents surface nucleation; the second or main stage represents the progression of the reaction from the surface to the particle interior and exhibits extensive surface and sub-surface cracking; and the third stage represents the exhaustion of the available magnesium. The equation for the second (main) stage of the reaction for the formation of Mg(OH)2 is given by the pseudo first order rate equation where the rate of the reaction is independent of relative humidity and shows Arrhenius dependence. The formation of Mg(OH)2 proceeds from the outside of the particle inwards but is not diffusion controlled; the reaction is controlled by the rate at which the magnesium/reaction products interface moves into the particle. The surface morphology of the particles shows the formation of hexagonal and trigonal plates and trigonal pyramids and prisms. Crystallite formation is also observed in the interior of the particles. The formation of Mg(OH)2 is a complex heterogeneous process involving many separate steps which follows a Rideal type mechanism; the water diffuses to the particle surface, is chemisorbed and then reacts directly with the metal surface to form Mg(OH)2.
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ItemOptical properties of silica-coated metal particles( 1999)The significance of silica coating technology for stabilising metal semiconductor nanoparticles was demonstrated. The physicochemical properties of silica coated colloidal silver (Ag@Si02) and the optical properties of films containing uncoated and silica coated colloidal gold (Au@Si02) were investigated. The factors governing the deposition of silica onto silane-primed silver particles were examined and the deposition conditions (pH and reagent concentrations) optimised. Thin silica shells deposited from aqueous/ethanolic sodium silicate solutions were porous and non-rigid. The shells remained insensitive to boiling in an aqueous-ethanolic solution but were substantially dissolved when boiled in pure water. The silver cores participated in a variety of chemical reactions with charged and neutral molecules to form new structures such as hollow silica nonobubbles, semiconductor cores and silica coated alloys of silver and gold. The rate of the reactions of the core with solution phase substrates decreased with increasing silica shell thickness. The silver cores of Ag@Si02 still remained catalytically active and colloidally stable during the reduction of water. Homogeneous films containing uncoated and silica coated gold particles were prepared using a self-assembly technique. The optical properties of the films were investigated as a function of film thickness and the separation between core particles. For interparticle separations below a silica shell thickness of ≈ 6.3 nm, the absorption band red-shifted and narrowed with increasing film thickness. Moreover, with increasing interparticle separation, the band blue-shifted, and both the transmittance and reflectance spectra increasingly began to resemble those of the same isolated particles in solution, in agreement with the Maxwell-Garnett model. In contrast, above a shell thickness of ≈ 6.3 nm, the absorption peak position remained insensitive to film thickness and interparticle separation, suggesting that the gold cores were no longer electromagnetically coupled. For silica shell thicknesses above 12.2 nm, the dependence of the reflectance spectra o interparticle separation and film thickness still needs to be quantified. Possible scientific and industrial applications associated with the Ag@Si02 particles and Au@Si02 particle films are suggested.
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ItemHeavy metal ion activation of zinc sulphide( 1978)This thesis deals with the activation of zinc sulphide by the heavy metal ions Cu ll, Cd 11 and Pb II over a wide range of pH, metal ion concentration, zinc sulphide concentration and incident light conditions. At acid to neutral pH values the uptake of a heavy metal ion has been observed to take place in two stages: a fast, initial step followed by a second, slower step. Kinetic data have shown that heavy metal ion uptake generally follows a logarithmic dependence on time. At alkaline pH values heavy metal ion uptake is complicated by hydrolysis effects. A sensitive mass spectrometric technique has been developed and is capable of quantitatively detecting down to 1% of a nominal monolayer of elemental sulphur on a mineral of surface area 0.7 m2 g-1. Elemental sulphur was detected on sphalerite surfaces activated by Cu11 and Pb II up to pH 6.6, both in the dark and under UV irradiation. Elemental sulphur was only detected on Cd II activated and unactivated zinc sulphide surfaces under UV irradiation. A mechanism for the activation of zinc sulphide is advanced at acid, neutral and alkaline pH values. At acid to neutral pH values, metal ion uptake occurs by an exchange reaction This is coupled with a surface redox process, which is linked with the semiconductor properties of zinc sulphide. As a result of this surface redox process, elemental sulphur may form on the zinc sulphide surface, depending on the type of metal ion involved and on the incident light conditions. It is proposed that the rate determining step in the exchange reaction is the transfer of an adsorbed metal ion from a surface, adsorbed site to a lattice site. This leads to a logarithmic dependence of metal ion uptake on time, as observed experimentally. At alkaline pH values, the mechanism at acid to neutral pH values is complicated by metal ion hydrolysis, adsorption and precipitation effects. An overall mechanism is proposed which accounts for the observed behaviour.
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ItemOrientated water under insoluble monolayers( 1970)The fact that oil could calm a rough sea was recorded by Pliny the Elder and by Plutarch. More quantitative information was provided by Benjamin Franklin in 1774 when he reported to the Royal Society that a teaspoonful of oil made a half-acre surface of pond ".... as smooth as a looking glass" (24). Subsequent experimentation showed that a similar effect could be observed when small amounts of insoluble soaps or "fatty" organic compounds were spread on water surfaces. Willard Gibbs published his thermodynamic treatment of surface tension and adsorption in 1878, providing the necessary theoretical background for explaining experimental results (66). In 1891 Fraulein Pockels developed the technique of manipulating these insoluble films between "barriers" extending across the entire width of a trough of water, filled so that it almost overflowed. This permitted quantitative information about surface tension and surface area to be obtained and led Rayleigh to propose, in 1899, that surface films were only one molecule thick. The basis for contemporary understanding of the behaviour of molecules in insoluble monolayers was provided in 1817 by Irving Langmuir (97), who devised the surface balance which still bears his name and whose results verified the theories of molecular orientation at surfaces. (From introduction)
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ItemTheoretical and spectroscopic studies of anticonvulsant drugs( 1969)Once upon a time, people who suffered from grand mal were fed mustard, and weasels' blood, and some had their skulls perforated. Grand mal, the falling sickness, had been known since the time of Hippocrates, but even the empirical Greeks resorted to mystical explanations for the thunderclap onset of a grand mal fit, and the churchmen and surgeons of the Middle Ages were of the opinion that a glass of human urine, preferably provided by the first witness to the seizure, would hasten the departure of the offending demon. Although logically reasonable, this and other treatments! failed to alleviate grand mal or any of the related cerebral conditions which are now known collectively as epilepsy, and it was not until 1857 that the first useful anticonvulsant drug, potassium bromide, was introduced. (From introduction)