A comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 mM K₂PtCl₆ solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and methanol electro-oxidation reactions (MOR) were investigated by potentiodynamic and potentiostatic methods in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions at various concentrations of ethanol and methanol. The kinetics of ethanol and methanol on a Pt/ceria composite electrode were measured in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions using a rotating disk electrode (RDE). Cyclic voltammetry was employed in temperatures ranging from 15 to 55°C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. The temperature dependence of the electro-catalytic activities afforded the determination of apparent activation energies for ethanol and methanol oxidation.

Cerium oxide nanoparticles are established scavengers of reactive oxygen and nitrogen species. They have many potential biomedical applications that depend on their physicochemical properties and mode of preparation. Recent studies have found these nanoparticles possess phosphatase mimetic activity. Studying such catalytic activities will qualify their biomedical applications and render information on their bioavailability and potential toxicity. Two oxidation states of cerium exist in these nanoparticles (3+ or 4+). It is hypothesized that the oxidation state of cerium in the nanoparticles determines the amount of adsorbed water on the crystal lattices. This in turn governs their activity as phosphatases. Nanoparticles with higher levels of cerium in the 4+ state exhibit phosphatase activity while those with higher levels of cerium in the 3+ state do not. This phosphatase activity may be controlled with the addition of inhibitory anions. It is hypothesized that anions with structures similar to phosphate can inhibit phosphatase activity by leading to the production of complexes on the surface of cerium oxide nanoparticles. Substrates that were used to test this activity include para-nitrophenyl phosphate (pNPP), 4-methylumbelliferyl phosphate (MUP) and adenosine triphosphate (ATP). To highlight the role of adsorbed water, we also performed experiments on pNPP with methanol as a solvent. The activity was measured by absorbance (pNPP and ATP) or fluorescence (MUP) and reported as nmol of phosphate/min. In some cases this rate was calculated through coupled reactions or by measuring the rate of formation of other colored products formed along with the release of phosphate such as pNP (para-nitrophenol). The phosphatase activity increased as the amount of adsorbed water increased implying that the abundance of adsorbed water makes the surface of 4+ ceria nanoparticles more active. Phosphatase activity for all the substrates exhibited Michaelis-Menten kinetics. Although the phosphatase activity of these nanoparticles is slow (turnover rate) as compared to real biological phosphatases, it can be used as a model catalytic activity to follow other catalytic activities that are associated with nanoparticles that have an abundance of cerium in the 4+ state, such as catalase activity. These results also provide information on the nature of the active sites involved in the catalytic activities associated with these nanoparticles. We identified three inhibitors, tungstate, molybdate and arsenate, which decreased the phosphatase activity of these nanoparticles in a dose dependent manner. Vmax, Km and Ki values were determined by varying substrate concentrations in the presence and absence of inhibitors. A partial mixed inhibition model was fit for each of these inhibitors. Summary: Phosphatase activity of cerium oxide nanoparticles with higher levels of cerium in the 4+ oxidation state was used as a model catalytic activity to study the nature of the active sites involved in catalysis. The study of inhibitors can reveal more information as to the surface binding of substrates in catalysis.

<p> An experimental evaluation of three desulphurisers for pig iron has been conducted. Sodium vapor, blast furnace slag enriched with cerium oxide and a rare earth alloy named misch metal have been used. </p> / Thesis / Master of Engineering (MEngr)

Desulfovibrio alaskensis G20 and other sulfate-reducing bacteria cause significant damage to metal pipelines and other infrastructure through a metabolic pathway that releases toxic hydrogen sulfide into their surroundings. The biocorrosion that results from the release of hydrogen sulfide creates significant economic burden, and can pose health risks for those exposed to this chemical. They are commonly present in the form of biofilms, an extracellular matrix composed of bacterial cells, polysaccharides, proteins, nucleic acids, and other materials. These biofilms are difficult to remove, and they provide protection to the bacteria within from anti-bacterial treatments. Desulfovibrio alaskensis G20 is a strain derived from a wild-type bacterium collected from an oil well corrosion site and is a model organism for understanding biofilm formation of sulfate-reducing bacteria and how these biofilms can be prevented or inhibited by techniques such as cerium oxide nanoparticle coating. To this end, samples of Desulfovibrio alaskensis G20 were grown anaerobically in 24-well and 96-well plates, and the resultant biofilm growth was measured through spectrophotometry. Several different environmental parameters were tested, including temperature, electron donor molecules, basal and enriched growth media, and oxidative stress, revealing several affinities for production of biofilm growth.

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In the Gamma-Alpha phase transition in Cerium, the magnetic properties change from a temperature-dependent Curie-Weiss susceptibility in the high temperature gamma phase to a temperature-independent paramagnetic susceptibility in the low temperature alpha phase. Taking into account the crystal-field split Hamiltonian, the energy eigenvalues and eigenfunctions are calculated for the doublet and the quartet ground states which are then used to determine the Kondo temperature for different crystal field splittings. The susceptibility and B-T phase diagrams are obtained for both the ground states and it is concluded that the doublet ground state is in better agreement with the experimental results. The P-T phase diagram is obtained using the Anderson model and the Non-Crossing Approximation. This numerical method determines the free energy for a given hybridization and subsequently the susceptibility, specific heat and the Fermi-liquid temperature. Using these, the P-V phase diagram is first obtained and then the P-T phase diagram derived from it using Maxwell's equal area construction. CePdSb is one of the few ternary compounds which exhibit Kondo lattice behavior along with a ferromagnetic ground state. The competitions between the RKKY interaction and the Kondo interactions are consistent with expectations based on the Doniach phase diagram. The susceptibility in the high temperature regime calculated using the linear response theory concurs well with the experimental results. At low temperatures, the exchange interaction dominates the magnetic behavior of the system. Taking into consideration the single-ion anisotropy and the Heisenberg interaction, the spin-wave dispersion spectrum is obtained using the Holstein-Primakoff transformation and renormalized Stevens coefficients. The spin-spin correlation function is obtained and found to agree very well with the inelastic neutron scattering data. / Physics

Additive friction stir deposition (AFSD) is a solid-state additive manufacturing (AM) technique that breaks down large constituent particles into more refined and uniformly disturbed microstructure. AFSD was used to print Al-Ce alloys. Current commercial Al-alloys upon elevated temperatures go through dissolution and coarsening of strengthening precipitates causing mechanical degradation of these alloys. Al-Ce alloys do not have this issue as cerium's low solubility restricts dissolution into the aluminum matrix at elevated temperatures, thus giving great thermal stability to the microstructure. Al-Ce alloys lack solid solubility that affects the solid solution strengthening and precipitation strengthening. Al-Ce alloys have limitation at room temperature as they can only reach a maximum of ~65 MPa yield strength. Elements like magnesium have been added to alloy to enable solid solution strengthening, and scandium to enable precipitation strengthening to improve strength before going through the AFSD process. By adding new elements to the Al-Ce alloys, an increase in the yield strength from ~60 MPa to ~200 MPa was achieved before AFSD. The casted alloys form coarse particles that reach 300 µm in size; resulting in stress concentration that causes material fracture before necking, giving >10% ductility. AFSD breaks down these coarse particles to increase strength and ductility increases. The particles were broken down to >20 µm which increased the ductility to 10%. The results of this research shows that Al-Ce alloys are able to reach commercial aluminum alloy mechanical standards of 400 MPa ultimate tensile strength and 10% ductility at room temperature for aerospace applications.

Ceria is a lanthanide series element that can exist as Ce3+ or Ce4+. Cerium oxide nanostructures are being developed for use in industry as catalysts. Nanostructures often behave differently from their corresponding macrostructures and these new behaviors can result in novel and important biological and chemical properties. The free radical theory of aging suggests that free radicals many of which are reactive oxygen species, damage cellular macromolecules. This damage can contribute to degenerative diseases, cancer and aging. Recent research has shown that ceria oxide nanoparticles protected cells from UV and radiation damage as well as decrease intracellular reactive oxygen species in primary cell cultures. The enzyme superoxide dismutase (SOD) protects the cell from free radicals by reacting with superoxide, a reactive oxygen species. Chemicals that catalyze the same reaction as SOD are referred to as SOD mimetics. Another biologically significant free radical is nitric oxide, a reactive nitrogen species. Nitric oxide is an important signaling molecule in both the cardiovascular and nervous system; however it can also cause damage to proteins through nitrosylation. When superoxide and nitric oxide react with each other they form the highly potent free radical, peroxynitrite. This reaction naturally occurs in the phagolysosome of the macrophage and is utilized by the immune system to kill pathogens. Nanoceria was tested for activity against superoxide, nitric oxide and peroxynitrite. The results presented in this work show that ceria oxide nanoparticles exhibit SOD mimetic activity and reduce protein nitrosylation in vitro.