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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

A method for studying electrochemical intermediates in flowing streams

Henes, James Robert, January 1969 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.
42

Synthesis and electrocatalytic properties of polymerizable metallophthalocyanines

Obirai, Joseph Chinye January 2005 (has links)
The syntheses, spectral and electrochemical characterization of new family electropolymerizable pyrrole, thiophene and mercaptopyrimidin substituted metallophthalocyanine (MPc) complexes are described. Tetraamino substituted chromium and manganese phthalocyanine complexes were also synthesized and characterized. The spectral and electrochemical results are comparable to literature reports. The complexes formed stable films when deposited on electrode surfaces. The MPc films were formed by electropolymerization, drop-dry method and self-assembling. Nickel hydroxide-like electrodes were formed by electrotransformation of nickel-tetra-4- (pyrrol-1-yl)phenoxy phthalocyanine polymer films to the corresponding PcNi-O-NiPc modified electrodes in alkaline solution. The thiophene, mercaptopyrimidine functionalized MPcs and amino group containing complexes formed good self-assembled monolayers (SAMs) on gold electrode. The electrode modification processes were reproducible. The conductivities of the electrode were dependent on the surface concentrations of the complexes as a function of electropolymerization scan numbers. The electrodes showed good catalytic responses toward L-cysteine, nitrite, nitric oxide (NO), glycine, phenol and its derivative and oxygen. The results also suggest that the presence of thio groups on the ring substituents lowers the oxidation potential of Lcysteine more compared to literature values. The stability of the amperometric responses toward the various analytes is used to diagnose the applicability of the materials for electroanalytical purposes. The limits of detection for L-cysteine, nitrite, NO and glycine were in the range of ~10⁻⁷ to 10⁻⁵ mol dm⁻³.
43

Detection of neurotransmitters using metallophthalocyanines as electrocatalysts

Oni, Joshua Idowu January 2002 (has links)
Some metallophthalocyanine complexes were synthesized and their catalytic activities towards the detection and quantification of the neurotransmitters dopamine, serotonin and histamine were investigated. The study of the possible interaction between these transmitter substances and the metallophthalocyanine complexes was undertaken. Dopamine, serotonin and histamine formed complexes with Iron (II) tetrasulfophthalocyanine. The rate and equilibrium constants obtained for the coordination are in the range of values reported in the literature for ligand coordination to iron phthalocyanine complexes. Carbon paste electrodes of millimetric diameters modified with Iron (II) tetrasulfophthalocyanine exhibited good electro catalytic activity towards the detection and analysis of dopamine and serotonin while at the same time eliminated the problem of interference posed by ascorbic acid in the electrochemical analysis of neurotransmitters. A detection limit of the order of 10-6 mol dm-3 was obtained for both dopamine and serotonin at the modified electrodes. Carbon paste ultra micro electrodes modified with iron (II) tetrasulfophthalocyanine were also used for the detection of dopamine and serotonin as well as the simultaneous determination of dopamine and ascorbic acid in a mixture. The detection limit obtained for dopamine at the ultra microelectrode was 4.2xlO-7 mol dm-3 The electrode kinetics of vitamin BI as well as the stability of the electrode towards its determination was improved upon by modifying carbon paste electrodes with manganese phthalocyanine. The modified electrodes were used for the analysis of vitamin BI in tablets.
44

Electrochemical control of friction and wear

Ogano, Satoshi January 1998 (has links)
No description available.
45

Magnetoelectrocatalysis: enhanced heterogeneous electron transfer reactions at modified electrodes, Grätzel cells, and manganese dioxide electrodes

Lee, Garett Gordon Walter 01 May 2012 (has links)
Magnetoelectrocatalysis is a physical, catalytic process. When magnetic microparticles are incorporated at an electrode surface, increases in current and system efficiency are observed. These enhancements have been observed in both homogeneous and heterogeneous systems. Here, the effects of magnetic fields on three separate, yet related, systems are analyzed: fundamental heterogeneous rate constants at modified electrodes, dye sensitized solar cells (DSSC), and manganese dioxide electrodes for supercapacitor applications. Previous studies of magnetic field effects on homogeneous systems utilized the cation exchange polymer Nafion and transition metal redox probes, such as tris(bipyridine)ruthenium(II) chloride. At electrodes modified with Nafion films, redox probes experience current enhancement in the presence of a magnetic field. This effect is attributed to increased self exchange, known as Dahms Ruff conduction or hopping between redox species. Here, the impacts of magnetic fields on heterogeneous electron transfer, the electron transfer between the redox probe and solid-state electrode, are demonstrated. A derivative of Nafion, TMODA Nafion is used to study the effect. For transition metal complex redox probes, peak splitting in cyclic voltammagrams are lower for magnetically modified electrodes as compared to analogous nonmagnetic films. The effects of magnetic modification of DSSCs are analyzed. DSSCs are photoelectrochemical cells (PECs) that convert incident light (photons) to electrical power (electrons). DSSCs, or Grätzel cells, are heterogeneous, excitonic devices which undergo multiple electron transfer reactions to complete this process. For studies here, magnetic modification of the electrodes occurs in the semiconductor layer. Enhancements in current density, fill factor, and power output are observed in variety of systems, both n-type and p-type, on glass and PET substrates, utilizing different magnetic microparticles. Lastly, the effects of magnetic fields on the electrochemistry of electrolytic manganese dioxide (EMD) electrodes are examined. Manganese dioxide is an abundant, naturally occurring oxide of manganese that is used ubiquitously in alkaline batteries. manganese dioxide; is a complex material, existing, as many transition metal oxides do, in several polymorphs, each with unique properties. For the studies here, the use of manganese dioxide as a capacitor material in mild aqueous systems is considered. In comparison to traditional electrochemical capacitors, manganese dioxide undergoes both non-faradaic and faradaic charge storage. Magnetic field effects look to exploit this faradaic, pseudocapacitant behavior as a mechanism for increasing this power source's energy and power density.
46

Steady state analysis of a porous flow-through electrode /

Kovach, Ronald Michael January 1968 (has links)
No description available.
47

Investigating the effectiveness of the Sci-Bono outreach programme in the teaching of electrochemistry at grade 11

Nkomo, Trust 11 1900 (has links)
A research project submitted to the University of the Witwatersrand, Faculty of Humanities, Wits School of Education, in partial fulfilment of the requirements for the degree of Master of Science in Science Education. November 2014 / This study was on the investigation of the effectiveness of the Sci-Bono outreach programme in the teaching of electrochemistry at grade11. Two aspects were used to measure effectiveness. The first aspect was a change in learners’ ability to answer questions before and after intervention. The second aspect was the programme’s ability to eliminate common misconceptions in electrochemistry. A sample of five schools was used in the study. At each school a pre-test was given to learners before intervention and a similarly structured and equally difficult task was given after intervention as a post-test. The marks for each learner were compared and the results for each school were analysed using a Wilcoxon signed rank test and a paired data test. Results from both methods of analysis reflected significant improvement in learners’ ability to answer questions after intervention at all five schools that made the sample of the research. A question by question analysis was also done to check a change learners’ ability to answer specific questions. Improvement in answering particular questions differed significantly, pointing out that certain concepts had been grasped better than others. Interviews were held with both learners and their teachers. These interviews were held to try and determine the extent to which misconceptions had been identified and eliminated. Pre-tests and post-test analysis reflected that one common misconception, where learners define oxidation and reduction in terms of addition and removal of oxygen was completely eliminated. Learner interviews however reflected a 75% success rate in the elimination of the misconception. Analysis of pre-tests and post-test results also showed a 75% success rate in the elimination of a misconception of the second misconception, where learners take an oxidising agent as a substance that has been oxidised and a reducing agent as a substance that has been reduced, compared to 76% from analysis of the learners’ interview results. Teacher interview results also reflected that the Sci-Bono outreach programme is to a high degree able to eliminate common misconceptions electrochemistry. From lesson observation and teacher interviews another misconception came to light. The misconception held by some learners is that ‘the oxidation number is the number of oxygen atoms in the molecule of a compound.’ This misconception was also tackled. During teachers’ interviews it emerged that all host teachers perceive the Sci-Bono Subject Matter Experts as effective in eliminating the identified common misconceptions in electrochemistry. The researcher is convinced that the Sci-Bono outreach programme improves the learners’ ability to answer questions in electrochemistry and that they address misconceptions in their teaching. The intervention however does not completely eliminate common misconceptions in electrochemistry. The Sci-Bono outreach programme is thus only effective to a certain extent in the teaching of electrochemistry at grade 11. The study also revealed that the teachers at schools expect the Sci-Bono Subject Matter Experts to have better pedagogical skills and they also expect them to bring scarce resources when they visit schools. They expect them to be able to tackle all formal and informal experiments covered in the grade11 curriculum. They believe that, in addition to enabling the elimination of misconceptions, the practicals carried out by the Sci-Bono SMEs also enhance understanding and provide practical skills to learners.
48

Studies of electrochemical action in the oral cavity

Nilner, Krister. January 1981 (has links)
Thesis (doctoral)--Lunds universitet, Malmö, 1981. / Includes the author's five published papers. Extra t.p. with thesis statement inserted.
49

Electrochemical behaviour of boron-doped diamond electrodes

Naidoo, Kaveshini 21 November 2005 (has links)
Conducting diamond electrodes provide unique advantages for electrochemistry such as a wide potential window, low baseline current, chemical inertness and resistance to fouling. De Beers boron-doped diamond electrodes, manufactured by chemical vapour deposition and containing varying amounts of boron, were therefore investigated in order to determine their suitability for future electrochemical applications. These electrodes were initially characterised using techniques such as SEM, LA-ICP-MS, Raman spectroscopy and XPS. The electrochemical behaviour of these electrodes was investigated in two redox systems (potassium iron (III) cyanide and cerium (III) sulphate) and two biological systems (dopamine and ascorbic acid). These results were compared against that of the conventional glassy carbon electrode. Porous boron-doped diamond, a novel electrode material, was used for the electrochemical detection of thyroid hormones (L-T3 and L-T4). These hormones have never previously been investigated using a boron-doped diamond electrode. The De Beers boron-doped diamond electrode was found to outperform the conventional glassy carbon electrode, which fouled very easily, in the detection of dopamine. Peak separation between dopamine and the interfering ascorbic acid was attained at a pretreated boron-doped diamond electrode. The feasibility of detecting thyroid hormones using a porous boron-doped diamond electrode was demonstrated, and the electrode material was patented. / Dissertation (MSc (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted
50

Processing and properties of nanostructured thin film energy storage devices

Jiang, Meng January 2013 (has links)
A spray deposition manufacturing route has been developed for the fabrication of carbon nano-structured and micro-structured energy storage devices in a thin film format, with controlled film thickness, homogeneous film surface morphology and high electrochemical performance for both supercapacitors and lithium ion battery anodes. Three types of low cost commercially available carbon materials (graphite, activated carbon and carbon black) have been investigated, and electrodes characterised in terms of surface morphology, surface chemistry, microstructure and electrochemical properties. By using ball milling, CO<sub>2</sub> activation and adding suitable carbon conductive additives, nano-graphite-based film electrodes (one meter long and ~ 3 µm thickness) have been fabricated, with excellent ion transport and low electrical resistance (< 1.8 Ω). Specific capacitance of 110 F/g at a scan rate of 100 mV/s in 1 M H<sub>2</sub>SO<sub>4</sub> was achieved. The high rate performance of activated carbon-based electrodes ( ~2 µm thickness) has been enhanced by reducing the contact resistance of electrode/current collector interface and building a well-interconnected and hierachical meso/macro-porous structure. A specific capacitance of over 120 F/g at a scan rate of 600 mV/s or 20 A/g current density in 1 M H<sub>2</sub>SO<sub>4</sub> was achieved. The performance of carbon black-based electrodes (~4 µm thickness) in different electrolytes has been studied in both two- and three-electrode cells. High specific capacitances of 260 F/g at 1 A/g was achieved in 6 M KOH, together with energy and power densities of 21 kW/kg and 18 Wh/kg in 1 M Na<sub>2</sub>SO<sub>4</sub>. Finally, graphite-based electrodes for rechargeable lithium-ion batteries have also been fabricated with controlled film thickness from ~ 900 nm to ~ 40 µm and 98% capacity retention of 371 mA/g after 20 cycles. Spray deposition has been demonstrated to have the potential for scalability in the manufacture of carbon-based thin film electrodes with competitive properties.

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