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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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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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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ItemAdsorption of polyphosphate dispersants onto oxide surfaces( 1993)The production of high-performance advanced material products based on controlled colloidal dispersions has received increased attention in recent times. In many cases, the mechanical strength of the final product relies on a homogenous microstructure resulting from a well-dispersed slurry. This may be achieved by the addition of dispersing agents to the colloidal dispersion. Inorganic dispersions offer greater durability than many of the organic compounds currently available. Polyphosphate dispersants are thought to act through electrostatic stablization, however the exact method of their action is unclear. The adsorption of polyphosphates onto colloidal zirconia (ZrO2) and titania (TiO2) particles has been studied as a function of chain length and pH. Adsorption isotherms and electroacoustic measurements have been used to study the adsorption process. Isotherms showed "high-affinity" type behavior. The extent of adsorption increased in each case as the pH decreased. Adsorption onto both oxide surfaces increased in the order P1 < P2 < P-5, where the subscript refers to the number of phosphate units in the chain. The shape of the adsorption isotherms indicated that the polyphosphates were adsorbed in a flat configuration in the plane of the surface. Electroacoustic results showed on a molar basis that the longer chain polyphosphates are more efficient at shifting the isoelectric point of the oxides. This was attributed to the greater specific adsorption of these molecules. The results of this study were consistent with an adsorption mechanism that is electrostatic in nature.