The presence of deposits leading to corrosion of the steam generator (SG) systems is a major contributor to operation and maintenance cost of pressurized water reactor (PWR) plants. Formation and transport of corrosion products formed due to the presence of impurities, metallic oxides and cations in the secondary side of the SG units result in formation of deposits. This research deals with the characterization of deposit samples collected from the two SG units (unit 1 and unit 2) at Comanche Peak Steam Electric Station (CPSES). X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques have been used for studying the compositional and structural properties of iron oxides formed in the secondary side of unit 1 and unit 2. Magnetite (Fe3O4) was found to be predominant in samples from unit 1 and maghemite (g-Fe2O3) was found to be the dominant phase in case of unit 2. An attempt has been made to customize FTIR technique for analyzing different iron oxide phases present in the deposits of PWR-SG systems.

Flow accelerated corrosion (FAC) is a major concern in the power industry as it causes thinning of the pipes by the dissolution of the passive oxide layer formed on the pipe surface. Present research deals with comparing the protection offered by the magnetite (Fe3O4) versus maghemite (γ-Fe2O3) phases thickness loss measurements. Fourier transform infrared spectroscopy (FTIR) is used in distinguishing these two elusive phases of iron oxides. Representative pipes are collected from high pressure steam extraction line of the secondary cycle of unit 2 of Comanche Peak Steam Electric Station (CPSES). Environmental scanning electron microscopy (ESEM) is used for morphological analysis. FTIR and X-ray diffraction (XRD) are used for phase analysis. Morphological analysis showed the presence of porous oxide surfaces with octahedral crystals, scallops and "chimney" like vents. FTIR revealed the predominance of maghemite at the most of the pipe sections. Results of thickness measurements indicate severe thickness loss at the bend areas (extrados) of the pipes.

Single atom catalysts are prospective class of materials, which holds promises to reach the ultimate limit of improvement in catalyst performance, selectivity, lifetime and cost reduction. The ability to efficiently capture the adsorbates at the active sites is the key prerequisite for catalytic transformation to the products. In this respect, our experimental study aims to describe the interaction of gas molecules (H2O, CO, O2 and NO) with single metal atoms (Rh, Ir, Cu) on the magnetite surface employing scanning tunneling microscopy.

In der vorliegenden Arbeit soll das weit gefächerte Thema der chemischen Nanotechnologie um neue Resultate bereichert werden. Im Einzelnen handelt es sich um neue Synthesemethoden für magnetische Nanorods (Nanoteilchen mit länglicher Form) und Nanoshells (oxidische Nanokristalle mit einer Hülle aus Edelmetall), ein Verfahren zur Modifizierung diverser Oberflächen mit heterogenen Polymerbürsten durch kontrollierte binäre radikalische Polymerisation, neuartige Copolymere zur Stabilisierung und Funktionalisierung von Nanopartikeln und Herstellung von amphiphilen Nanopartikeln durch Oberflächenbehandlung mit Niotensiden. Es sollen ferner die möglichen Anwendungen diskutiert werden. Die Abb. 1 illustriert die Zusammenhänge der bearbeiteten Thematik.

M. Tech. (Chemistry Department, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Benzene, toluene and xylene (BTX) are water pollutants that appear very often in chemical and petrochemical wastewaters due to gasoline leakage from storage tanks and pipelines. These BTX compounds can cause adverse health effects on humans even at very low concentrations. Amongst the available pollutant removal methods from wastewater, adsorption has been used due to its ease of operation, simplicity and cost-effectiveness. Different adsorbents have been used for BTX removal, however the use of Magnetite-organic acid composites as an adsorbent seems to offer a much cheaper alternative. This work seeks to develop a one-step microwave synthesis and optimization of magnetite-oleic (MNP-OA) and magnetite-palmitic (MNP-PA) acid) composites. Response surface methodology was used to optimize the magnetite-organic acid composites. The optimum conditions estimated for MNP-OA acid composite were 78.3 % Fe content, 1561.9 S/cm conductivity, 82.2, 84.1, 85.3 mg/g for BTX adsorption capacity. The MNP-PA composite were 75.6 % Fe content, 1325.66 S/cm conductivity, 60.55, 64.47, 63.06 mg/g for BTX adsorption capacity. The materials were characterized, and the adsorption process was optimized for BTX removal from aqueous solution. X-ray analysis confirmed the formation of magnetite by the presence of both ferric and ferrous ion states on the surface. It was noted that after modification, the magnetite-organic acids characteristics peaks became broad and the height of the peaks decreased indicating that surface modification with organic acid controls the crystallinity of the material. The average cystalline size of MNP, MNP-OA, and MNP-PA composites were 19.7, 17.1 and 17.9 nm. FTIR analysis confirmed the target materials were produced and also to determine if the organic acids were imobilised on the surface of the magnetite. TEM images presented that the MNP, MNP-OA, and MNP-PA composites were spherical in shape with particle average sizes of 18.4 ± 0.5, 15.6 ± 0.5 and 16.5 ± 0.5 nm. The magnetite-organic acids show the particles with better isolated as compared to that of the MNP. The BET isotherms of the materials were described by a type IV characteristic related to uniform mesoporous materials. The magnetic saturation value for MNP, MNP-OA, and MNP-PA composites were 62.9, 59.0 and 51.0 emu/g. The decrease in magnetization was explained by the presence of the non-magnetic layer on magnetite surface. The pHpzc of MNP, MNP-OA, and MNP-PA composites were 6.9, 6.4 and 6.1. The decrease in pHpzc aftern modification was due to the charging acid-base interaction mechanism of metal oxide nanoparticles. The optimum pH for the adsorption of BTX onto MNP, MNP-OA, and MNP-PA composites was determined to be pH 7 for benzene, pH 8 for toluene and xylene. Among the three pollutants, xylene had the highest adsorption capacity followed by toluene and benzene. The optimum adsorbent dose for the adsorbents for the adsorption process was 0.1 g/dm3. The effect of time on the uptake of BTX onto MNP, MNP-OA, and MNP-PA composites show that initial adsorption of BTX occured between 0 and 3 min of contact time. The effect of initial concentration results shows the initial concentration of BTX increases from 100 to 350 mg/dm3 with an increase in adsorption capacity. The results suggest that the adsorption process is controlled by concentration driving force. The experimental data was fitted to the pseudo-first and pseudo-second-order kinetic models for all adsorbents and all pollutants. The pseudo-second-order models showed good correlation as compared to the first-pseudo model. Desorption studies for benzene, toluene and xylene using the pure magnetite, magnetite-palmitic and magnetite oleic acid composites indicate adsorption mrchanism can be explained in relation to acid–base chemistry. Electron donation from the phenyl ring of each benzene, toluene and xylene compound to surface iron atoms of magnetite has been suggested. The CH3OH and H2O desorbing agents were used and regeneration using five cycles show that the percentage desorption decreses from Benzene < Toluene < Xylene. The reduction in adsorption capacity after the cycles are attributed to decomposition of the adsorbents active sites and mass loss of the sample.

No description available.

No description available.

Die vorliegende Arbeit befasst sich mit synthetischen Ansätzen zur Verbesserung der Handhabung von Pd-Nanopartikeln in der heterogenen Umwelt- und Elektrokatalyse. Nanopartikuläres Pd an Magnetit sowie an Silica-Sphären mit Magnetit-Kern erreichten eine hohe Aktivität bei der Dechlorierung von Hexachlorbenzol. Im Gegensatz zu ungeträgerten Nanopartikeln gelang die Abtrennung jener mit einem Magnet aus der Reaktionslösung. Weitere Untersuchungen ergaben, dass die Shewanella oneidensis eine heterogene Keimbildung im mikrobiellen Herstellungsverfahren von Pd-Nanomaterialien vermittelte. Die Mikroorganismen waren vermutlich nicht aktiv am Elektronenübergang beteiligt. Die partiell aggregierten Produkte des mikrobiellen Verfahrens ließen sich zur Herstellung von Aerogelen durch Selbstassemblierung verwenden. Elektrodenfilme aus mikrobiell als auch chemisch synthetisiertem nanopartikulären Pd zeigten ähnliche Eigenschaften bei der elektrochemischen Oxidation von Methanol. Darüber hinaus ermöglichte die Anwendung der fraktalen Dimension strukturelle Veränderungen abhängig von Verfahrensparametern bei der Selbstassemblierung festzustellen.:Inhaltsverzeichnis i Abbildungsverzeichnis iii Tabellenverzeichnis v Einleitung 1 1. Grundlagen 5 1.1. Eigenbewegung von Nanopartikeln in Suspension 6 1.2. Die DLVO-Theorie der Stabilität von lyophoben Kolloiden 7 1.3. Aggregation und die fraktale Dimension 11 1.4. Lichtstreuung an Kolloiden 15 1.5. Transmissionselektronenmikroskopie 19 1.6. Röntgenpulverdiffraktometrie 24 2. Edelmetall-Nanopartikel 27 2.1. Synthese von Palladium-Nanopartikeln 30 2.1.1. Reduktion mit Natriumborhydrid 30 2.1.2. Reduktion mit Citrat und Dicarboxyaceton 31 2.1.3. Keimvermitteltes Wachstum 33 2.2. pH- und Temperatur-Stabilität der Suspensionen 35 2.3. Integration in Polymerbeschichtungen 37 2.4. Resümee 41 3. Mikrobiell hergestellte Pd-Nanostrukturen 43 3.1. Dissimilatorische Metall-Reduktion 44 3.2. Eigenschaften von mikrobiellem Pd 49 3.2.1. Herstellung und Präparation 49 3.2.2. Strukturelle Eigenschaften 51 3.2.3. Umsatz und chemische Zusammensetzung 56 3.2.4. Untersuchung der organischen Bestandteile 60 3.2.5. Eigenschaften der Suspensionen 64 3.3. Kontrollversuche zur mikrobiellen Herstellung 66 3.4. Dechlorierung von Hexachlorbenzol 69 3.5. Resümee 71 4. Palladium-Magnetit-Nanokatalysatoren 75 4.1. Synthese von Magnetit-Nanopartikeln 78 4.2. Kombination von Magnetit- und Pd-Nanopartikeln 81 4.3. Abscheidung von Pd an Magnetit 84 4.4. Zwischenfazit 85 4.5. Oberflächen-modifizierte Pd-Magnetit-Komposite 86 4.6. Dechlorierung von Hexachlorbenzol 89 4.7. Resümee 91 5. Selbstassemblierung von Edelmetallnanopartikeln 93 5.1. Verfahren zur Herstellung von Pd-Hydrogelen 96 5.1.1. Variation der Verfahrensparameter 97 5.1.2. Einfluss von Temperatur und Anreicherungsfaktor 99 5.2. Aerogel-Monolithe 103 5.3. Netzwerkstrukuren aus mikrobiellem Pd 105 5.4. Elektrochemische Oxidation von Methanol 106 5.5. Resümee 111 Zusammenfassung und Ausblick 113 A. Terminologie zu Kolloiden, Aggregaten, Gelen & Co. 115 B. Experimentelle Methoden 117 B.1. Synthesevorschriften 118 B.2. Charakterisierungsmethoden 128 B.3. Elektrochemische Untersuchungen an Aerogel-Elektroden 132 Literaturverzeichnis 135 / The present work deals with synthetic approaches for the implementation of Pd-based materials in environmental and electrocatalysis. Nanoparticles of Pd either coupled to magnetite or to silica-spheres with a magnetic core showed a high activity in the dechlorination of hexachlorbenzene similar to unsupported nanoparticles. However, in contrast to unsupported nanoparticles they could be separated from the reaction solution by a magnet. Structural and chemical properties of Pd nanomaterials from a microbial synthesis were comparatively investigated. The results lead to the conclusion that the Shewanella oneidensis were not actively involved into the electron transfer and the microorganisms acted more as a substrate for heterogeneous seeding. Partially nanostructured Pd-aggregates from the microbial synthesis were further subjected to self-assembly to form noble metal aerogels. Electrode films made of both microbially and synthetically produced Pd aerogels showed similar structural and electrochemical properties in the electrooxidation of methanol. Finally, the fractal dimension was implemented as a parameter allowing to monitor the evolution of both aerogel structure and its density during the process of selfassembly.:Inhaltsverzeichnis i Abbildungsverzeichnis iii Tabellenverzeichnis v Einleitung 1 1. Grundlagen 5 1.1. Eigenbewegung von Nanopartikeln in Suspension 6 1.2. Die DLVO-Theorie der Stabilität von lyophoben Kolloiden 7 1.3. Aggregation und die fraktale Dimension 11 1.4. Lichtstreuung an Kolloiden 15 1.5. Transmissionselektronenmikroskopie 19 1.6. Röntgenpulverdiffraktometrie 24 2. Edelmetall-Nanopartikel 27 2.1. Synthese von Palladium-Nanopartikeln 30 2.1.1. Reduktion mit Natriumborhydrid 30 2.1.2. Reduktion mit Citrat und Dicarboxyaceton 31 2.1.3. Keimvermitteltes Wachstum 33 2.2. pH- und Temperatur-Stabilität der Suspensionen 35 2.3. Integration in Polymerbeschichtungen 37 2.4. Resümee 41 3. Mikrobiell hergestellte Pd-Nanostrukturen 43 3.1. Dissimilatorische Metall-Reduktion 44 3.2. Eigenschaften von mikrobiellem Pd 49 3.2.1. Herstellung und Präparation 49 3.2.2. Strukturelle Eigenschaften 51 3.2.3. Umsatz und chemische Zusammensetzung 56 3.2.4. Untersuchung der organischen Bestandteile 60 3.2.5. Eigenschaften der Suspensionen 64 3.3. Kontrollversuche zur mikrobiellen Herstellung 66 3.4. Dechlorierung von Hexachlorbenzol 69 3.5. Resümee 71 4. Palladium-Magnetit-Nanokatalysatoren 75 4.1. Synthese von Magnetit-Nanopartikeln 78 4.2. Kombination von Magnetit- und Pd-Nanopartikeln 81 4.3. Abscheidung von Pd an Magnetit 84 4.4. Zwischenfazit 85 4.5. Oberflächen-modifizierte Pd-Magnetit-Komposite 86 4.6. Dechlorierung von Hexachlorbenzol 89 4.7. Resümee 91 5. Selbstassemblierung von Edelmetallnanopartikeln 93 5.1. Verfahren zur Herstellung von Pd-Hydrogelen 96 5.1.1. Variation der Verfahrensparameter 97 5.1.2. Einfluss von Temperatur und Anreicherungsfaktor 99 5.2. Aerogel-Monolithe 103 5.3. Netzwerkstrukuren aus mikrobiellem Pd 105 5.4. Elektrochemische Oxidation von Methanol 106 5.5. Resümee 111 Zusammenfassung und Ausblick 113 A. Terminologie zu Kolloiden, Aggregaten, Gelen & Co. 115 B. Experimentelle Methoden 117 B.1. Synthesevorschriften 118 B.2. Charakterisierungsmethoden 128 B.3. Elektrochemische Untersuchungen an Aerogel-Elektroden 132 Literaturverzeichnis 135

<p> The "B" horizon at Tilt Cove occurs in subaqueous mafic volcanics near the base of the Silurian Cape St. John Group. It is 3 metres below a well-banded oxide iron formation ("A" horizon). </p> <p> Mineralization in the "B" horizon is analogous to that of the East Mine in that it is volcanogenic and has resulted in extensive chloritization of the footwall rocks, and in the deposition of banded sulphides or the replacement of the existing mafic volcanics by sulphides. There are differences in the geochemistry mineral textures and mineral types. The East Mine host volcanics are alkali depleted basaltic komatiites to magnesium theleiites. The horizon host volcanics are spillitized magnesium tholeiites. Samples of ore from the East Mine show well-developed colloform and framboidal textures. Pyrite, magnetite, hematite and chalcopyrite are the dominant minerals with minor sphalerite and accessory covellite. Samples from the horizon show relict colloform textures and framboids with less internal structure due to overgrowths. Atoll textures indicating extensive replacement are common. Pyrite is the dominant sulphide followed by sphalerite, chalcopyrite, accessory covellite and gold. The chalcopyrite occurs both as replacement of pyrite and exsolution in sphalerite. The most significant difference between samples from the East Mine and "B" horizon is the greater abundance of gold in the "B" horizon and its correlation with sphalerite. </p> / Thesis / Bachelor of Science (BSc)

There is a need for multifunctional polymer-particle complexes for use in biomedical applications such as for drug delivery or as MRI contrast agents where composition and stability are essential for the complexes to function. This work outlines a general methodology for rationally designing complexes stabilized with polymer brush layers using adapted star polymer models for brush extension and pair potential. Block copolymer micelles were first utilized for experimental validation by using the brush extension model to predict the size and the interaction model to predict the second virial coefficient, A2. Subsequently, the models were used to predict the size and colloidal stability of magnetite-polymer complexes using the modified Deryaguin-Verwey-Landau-Overbeek theory. Novel hydrophilic triblock copolymers comprised of poly(ethylene oxide) tailblocks and a carboxylic acid containing polyurethane center block were examined by static and dynamic light scattering (SLS and DLS), small angle neutron scattering (SANS), and densiometry. Under conditions when the charge is suppressed such as at low pH and/or high ionic strength, the polymer chains self-assemble into micelles, whereas unimers alone are present under conditions where charge effects are important, such as high pH and low ionic strength. A model for effective interaction between star polymers was used to obtain an expression for the second virial coefficient (A2) for micelles in solution. The values of A2 obtained using this method were compared with experimentally determined values for star polymers and micelles. In doing so, not only was a new means of calculating A2 a priori introduced, but the applicability of star polymer expressions to micellar systems was established. Through the analogy of micelles to sterically stabilized nanoparticles, this model was applied to water-soluble block copolymers adsorbed on magnetite nanoparticles for the purpose of tailoring a steric stabilizing brush layer. The sizes of the magnetite-polymer complexes were predicted using the star polymer model employed for the micelle study with an added layer to account for the anchor block. Colloidal stability was predicted from extended DLVO theory using the pair interaction. This work will lead to a better understanding of how to design ion-containing block copolymers for steric stabilization of metal oxide nanoparticles. / Ph. D.