Approximately 96,000 tonnes of the UK Higher Activity Waste (HAW) inventory consists of irradiated nuclear graphite. The current Nuclear Decommissioning Authority (NDA) baseline strategy for irradiated graphite in England and Wales is isolation in a future Geological Disposal Facility, with Scottish policy endorsing an alternative decision of near surface long-term storage. Irradiated graphite disposal routes in the UK remain under review, however, as there are concerns surrounding timing and whether deep geological disposal is the most appropriate course of action for graphite. An alternative waste management solution is treatment prior to disposal to separate mobile radioactive isotopes such as 3H and 14C from the bulk material, allowing for HAW volume reduction and concentration. Optimisation of an existing thermal treatment process at the Nuclear Graphite Research Group (NGRG) of the University of Manchester has been effected and a detailed review of the uncertainties associated with quantitative determination of radioisotope releases during thermal treatment of irradiated graphite samples has been conducted. Thermal treatment experiments in both an inert atmosphere and 1% oxygen in argon atmosphere have been conducted for temperatures ranging from 600°C to 800°C, and durations from 4 to 120 hours, to determine the effects of oxidation time and temperature, and the consequent oxidation characteristics on the release rate of prominent radioisotopes, with a focus on the release of 14C. Lower temperature treatments in an oxidising atmosphere have shown that a preferential release of 14C-enriched graphite can be achieved from the bulk material of Oldbury Magnox reactor irradiated graphite, with evidence demonstrating that this liberated 14C-enriched region is located at the graphite surfaces throughout the porous structure. A large proportion of radiocarbon found in this irradiated graphite, however, is uniformly distributed throughout the bulk material and cannot be selectively oxidised. It is found that prominent metallic radioisotopes such as 60Co are not mobile at these temperatures and remain in the bulk graphite material, inclusive of radioactive caesium which the literature suggests will volatilise. The preliminary results were undertaken as part of the EU FP7 EURATOM Project: CARBOWASTE.

Magister Scientiae - MSc (Chemistry) / Electrochemical platforms were developed based on pencil graphite electrodes (PGEs) modified electrochemically with reduced graphene oxide metal nanoparticles (ERGO-metalNPs) composite and used for the high-sensitivity determination of Bisphenol A (BPA) in water samples. Synergistic effects of both reduced Graphene Oxide sheets and metal nanoparticles on the performance of the pencil graphite electrode (PGE) were demonstrated in the oxidation of BPA by differential pulse voltammetry (DPV). A solution of graphene oxide (GO) 1 mg mL-1 and 15 ppm of metal stock solutions (1,000 mg L-1, atomic absorption standard solution) (Antimony or Gold) was prepared and after sonication deposited onto pencil graphite electrodes by cyclic voltammetry reduction. Different characterization techniques such as FT-IR, HR-SEM, XRD and Raman spectroscopy were used to characterize the GO and ERGO-metalNPs. Parameters that influence the electroanalytical response of the ERGO-SbNPs and ERGO-AuNPs such as, pH, deposition time, deposition potential, purging time were investigated and optimized. Well-defined, reproducible peaks with detection limits of 0.0125 ?M and 0.062 ?M were obtained for BPA using ERGO-SbNPs and ERGO-AuNPs respectively. The rGO-metalNPs-PGE was used for the quantification of BPA in tap water sample and proved to be suitable for the detection of BPA below USEPA prescribed drinking water standards of 0.087 ?M. / 2021-12-31

Magister Scientiae - MSc (Chemistry) / Electrochemical platforms were developed based on pencil graphite electrodes (PGEs) modified electrochemically with reduced graphene oxide metal nanoparticles (ERGO–metalNPs) composite and used for the high-sensitivity determination of Bisphenol A (BPA) in water samples. Synergistic effects of both reduced Graphene Oxide sheets and metal nanoparticles on the performance of the pencil graphite electrode (PGE) were demonstrated in the oxidation of BPA by differential pulse voltammetry (DPV). A solution of graphene oxide (GO) 1 mg mL-1 and 15 ppm of metal stock solutions (1,000 mg L-1, atomic absorption standard solution) (Antimony or Gold) was prepared and after sonication deposited onto pencil graphite electrodes by cyclic voltammetry reduction. Different characterization techniques such as FT-IR, HR-SEM, XRD and Raman spectroscopy were used to characterize the GO and ERGO–metalNPs. Parameters that influence the electroanalytical response of the ERGO–SbNPs and ERGO–AuNPs such as, pH, deposition time, deposition potential, purging time were investigated and optimized. Well-defined, reproducible peaks with detection limits of 0.0125 μM and 0.062 μM were obtained for BPA using ERGO–SbNPs and ERGO–AuNPs respectively. The rGO-metalNPs–PGE was used for the quantification of BPA in tap water sample and proved to be suitable for the detection of BPA below USEPA prescribed drinking water standards of 0.087 μM.

Molecular Dynamics (MD) simulation methods were used to perform simulations of the adsorption of multilayer films of three fluoromethane compounds -- nonpolar CF4 and its polar relatives, CF3Cl and CF3Br -- onto two chemically and structurally different substrates: graphite and hydroxylated α-quartz (a form of silica). The purpose of the simulations was to determine how differences in polarity and substrate type affect the structure of film layers at the adsorption surface, as well as to compare how these factors affect the mobility of molecules near the surface as they move along or away from the surface, to see how each of these factors affects the substrate affinity for the adsorbed compound. Simulations were performed for pure fluoromethane films as well as films created from binary mixtures of the above fluoromethanes adsorbed on each substrate over a range of temperatures from 80 K to 280 K. Analysis suggests a strong influence of substrate characteristics on both the structure and mobility of molecules in adsorbed layers, an effect that is partially temperature dependent but only weakly suggestive of effects due to the differences in polarity of the adsorbed molecules.

Eletrodos compósitos à base de grafite/poliuretana foram preparados contendo diferentes quantidades de hexacianoferratos de cobre(II), cobalto(II) e ferro(III). Os complexos foram preparados de acordo como procedimentos descritos na literatura e caracterizados por análise elementar, análise térmica e espectrometria na região do infra-vermelho. A análise térmica mostrou que há 10 moléculas de água de hidratação no hexacianoferrato de cobre(II), 11 no hexacianoferrato de cobalto(II) e 16 no hexacianoferrato de ferro(III). Após desidratação ocorre decomposição exotérmica violenta dos complexos. No caso do cobre a decomposição se dá com formação de CuO seguida da degradação do Fe(CN)3 com formação de Fe2O3. Para o hexacianoferrato de cobalto(II) e o hexacianoferrato de ferro(III) a mistura de Co3O4/Fe2O3 e o Fe2O3, respectivamente, se formaram após uma única etapa de decomposição. Apenas os eletrodos preparados com os complexos de cobalto e cobre apresentaram sinais voltamétricos, enquanto que o complexo de ferro não respondeu, provavelmente devido à sua baixa solubilidade em água. As condições de preparação dos eletrodos, tais como composição, ordem de adição de reagentes, pH, eletrólito suporte e intervalo de potenciais foram otimizadas. Um mecanismo para explicar a não estabilização do sinal voltamétrico, mesmo após ciclagem de potencial foi proposto com base na baixa solubilidade dos sais em água e a sua imobilização no eletrodo sólido a qual dificulta a formação do filme de hexacianoferrato na superfície. Finalmente um método analítico para a determinação de piridoxina, usando o eletrodo de grafite/poliuretana modificado com hexacianoferrato de cobre(II) foi proposto, com base na redução de sinal do complexo, na presença do analito. Neste caso foi observada uma resposta linear entre 1,08 x 10-6 a 1,07 x 10-5 mol L-1, com limite de detecção de 8,78 x 10-7 mol L-1 (3 x S/N) e o método foi aplicado na determinação de piridoxina em duas formulações comerciais. Coeficientes de recuperação entre 98-120% foram observados sem interferência dos componentes das formulações e sem necessidade de renovação da superfície do eletrodo. / Graphite-poliurethane solid composite electrodes were prepared containing different amounts of copper(II), cobalt(II) and iron(III) hexacianoferrates. The complexes were synthesized according to procedures previously described and characterized using elemental analysis, infrared spectrometry and the thermal analytical techniques: thermogravimetry/derivative thermogravimetry and differential thermal analysis. The thermal analysis revealed that there are 10 hydration water molecules in the copper(II) hexacianoferrate, 11 in the cobalt(II) and 16 in the iron(III) complexes. After dehydration, a strong exothermal degradation occurred in all cases. The copper complex decomposed in two steps with generation of CuO, followed by degradation of the Fe(CN)3 and formation of Fe2O3. The cobalt(II) and iron(III) hexacianoferrates decomposed in a single step with generation of Co3O4/Fe2O3 mixture and Fe2O3 as residues respectively. Only the electrodes prepared with copper and cobalt complexes presented voltammetric signals, while the iron complexes did not responded, probably due to its very low solubility in water. The conditions for the electrode preparation such as composition, order of addition of the components supporting electrolyte, pH and useful potential window were optimized. A mechanism to explain the non-stabilization of the voltammetric signal even after 200 cycles has been proposed on the basis of the complexes solubility in water as well as the immobilization of the complex in the solid electrode that turns difficult the formation of the hexacianoferrate film on the electrode surface. Finally, a graphite polyurethane electrode modified with the Cu(II) hexacianoferrate has been used in the voltammetric determination of pyridoxine, based on the diminution of the voltammetric signal of the modifier in the presence of the analyte. In this case a linear dynamic range of 1.08 x 10-6 to 1.07 x 10-5 mol L-1, with a detection limit of 8.78 x 10-7 mol L-1 (3 x S/N). The proposed electrode was used in the determination of pyridoxine in two solid pharmaceutical formulations with recoveries of 98 - 120% without interference of the other substances present in the formulation and no adsorption on the electrode surface.

Made available in DSpace on 2014-10-09T12:24:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:10Z (GMT). No. of bitstreams: 1 00032.pdf: 1355141 bytes, checksum: 01f9cb92c30eca4c85591156ed8c22d5 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-12-17T14:57:47Z (GMT). No. of bitstreams: 1 AldoNB.pdf: 3131669 bytes, checksum: a469d65770b09c49837e4f01097e9f91 (MD5) Previous issue date: 2007-06-02 / The electric can be converted into thermal, luminous, electromagnetic, and also in mechanical energy. In this context the electric engines plays a fundamental role, specially that they work very below of its nominal capacity, with consequent decrease load density. In industrial environment, these characteristics of work of DC engines had also generated an extreme consumption of coal brushs and attack in the commutator reducing the useful life of the engine and increasing maintenance demand and cost. The general objective of the present work is to study the influence of the granulometry of the coal brush used in DC engines with the resistance to the consumption of the same ones, as well as in the performance presented by the commutator of the engine. Additionally, determining the measurable and not measurable profits when the brush used is adjusted to the application. The brushes had been produced by an industry of the sector and tested in industrial environment to evaluate their performance and consumption. Preliminary results evidence a substantial improvement in the performance of these brushes in function of its microstructure and the application in which it is used / A energia el?trica pode ser reconvertida em energia t?rmica, luminosa, eletromagn?tica, e tamb?m em energia mec?nica. Neste contexto os motores el?tricos desempenham papel fundamental, em espec?fico os motores el?tricos de corrente continua que trabalham muito abaixo da sua capacidade nominal, com conseq?ente baixa densidade de carga. Em ambiente industrial, estas caracter?sticas de trabalho dos motores CC geraram um consumo excessivo de escovas de carv?o e tamb?m ataque no comutador, reduzindo a vida ?til do motor, aumentando as horas de manuten??o e o custo. O objetivo geral do presente trabalho ? caracterizar os diferentes tipos de escovas de grafite utilizados em motores de corrente cont?nua e avaliar seu desempenho em fun??o do processamento a que foi submetido durante sua fabrica??o, assim como determinar os ganhos mensur?veis e n?o mensur?veis quando a escova utilizada ? a mais adequada ? aplica??o. As escovas foram produzidas por ind?strias do setor e testadas em ambiente industrial, quanto ao seu desempenho e desgaste. Resultados preliminares evidenciam uma substancial altera??o no desempenho destas escovas e no seu desgaste em fun??o da sua microestrutura e da aplica??o na qual ? utilizada

Les fontes de fer sont des matériaux largement utilisés dans de nombreux domaines allant de l’industrie automobile au secteur de l’énergie en passant par la fabrication des tuyaux d’adduction d’eau. Du fait de la teneur en carbone élevée de ces alliages, du graphite et/ou des carbures de fer précipitent pendant la solidification. Les propriétés finales des pièces dépendent alors de la nature de la matrice, de la présence ou non de carbures et surtout de la forme du graphite. Celui-ci peut cristalliser sous la forme de lamelles, de sphères ou de particules de formes intermédiaires. Les éléments présents à l’état de traces dans le bain de fonte liquide influencent de manière considérable la croissance du graphite et conditionnent sa forme finale. Leur moyen d’action ainsi que le mécanisme de croissance du graphite sphéroïdal sont encore un sujet de débat et cette thèse a pour objectif de contribuer à la compréhension des phénomènes mis en jeu. Les échantillons utilisés ont été élaborés selon le procédé de coulée par centrifugation, son influence sur les mécanismes étudiés est d’ailleurs au cœur de ce projet. Les différents essais et analyses réalisés prouvent que la structure des nodules observés dans les échantillons centrifugés est la même que dans le cas des pièces moulées en sable. De plus, les éléments traces montrent une action similaire lors de la solidification et pendant la croissance en phase solide durant le traitement thermique destiné à éliminer les carbures. Ces résultats suggèrent que le mécanisme de croissance du graphite sphéroïdal est le même lors de la croissance à partir du liquide ou en phase solide par décomposition des carbures. Une proposition est d’ailleurs faite pour expliquer le développement des nodules par une germination continue du graphite sur les plans de base conjuguée à une croissance selon les directions prismatiques. Un modèle mathématique associé à ce mécanisme est présenté et son application au procédé de centrifugation donne des résultats en accord avec les observations expérimentales.

A crescente necessidade de fabricação de moldes com prazos e custos cada vez menores exige das ferramentarias a personalização e melhoria de seus processos de fabricação. Uma das maneiras de atingir isso é através da melhoria na usinagem dos eletrodos, já que esse processo afetará diretamente a precisão dimensional e tempo de produção de um molde. O uso de grafite como matéria-prima para esses eletrodos é altamente satisfatório, pois esse material apresenta a vantagem de ser usinado mais rapidamente e permitir uma grande variedade de formas geométricas, contudo, sua principal desvantagem é o alto poder abrasivo o que ocasiona desgastes elevados nas ferramentas. Os processos de tratamentos de gume são aplicados a fim de reduzir o efeito deste problema, aumentando a durabilidade das ferramentas. Com isso em vista, este trabalho realizou o estudo sobre o efeito de tratamentos de gume no desgaste de ferramentas com revestimento de diamante policristalino (PCD), no fresamento de eletrodos em grafite. Foram realizados ensaios experimentais com fresas sem tratamento, com tratamentos pelo método de polimento com cerdas abrasivas e por acabamento por arraste. Os testes consistiram em usinar eletrodos com parâmetros definidos e verificar o desgaste gerado nas fresas a cada 200 metros de comprimento usinado. Foram realizados também, análises de rugosidade e caracterização das fresas após os tratamentos, caracterização da mídia e da esponja utilizadas nos polimentos e caracterização do grafite usinado. Os resultados apontam que os tratamentos de gume resultam em alterações na superfície do revestimento, reduzindo o valor da rugosidade em média de 23%, e, no caso do processo de acabamento por arraste, uma redução na variação dos valores, já que este processo é considerado mais confiável e reprodutível. A caracterização da mídia e da esponja utilizadas indicou a presença de Silício como material abrasivo, o que provavelmente pode caracterizar um material de carbeto de silício. Com relação ao desgaste das ferramentas, pela curva de vida das mesmas, foi evidente ganhos como redução do desgaste de flanco e um aumento no comprimento usinado de até 63% em comparação com as ferramentas originais. Todas as ferramentas passaram pelos Estágios I e II da curva de desgaste e não chegaram ao Estágio III, conhecido como Desgaste Catastrófico. O mecanismo de desgaste, aparentemente, mais presente no processo foi a abrasão, apresentando como características os desgastes de flanco, cratera e entalhe. De forma geral, os dois processos de polimento apresentaram ganhos e demonstraram seus potenciais para serem aplicados em ferramentas de produção. / The rising need for manufacturing molds with increasingly smaller deadlines and costs is demanding from the toolmakers to customize and enhance their fabrication processes. One of the ways to achieve that is by improving their electrode machining, since this process will affect directly in the result of the dimensional precision and production time of the mold. The usage of graphite as raw material for electrodes is known to be highly satisfactory since the graphite has the advantage of machining faster and allowing a great variety of geometrical forms, however, its main disadvantage is that the graphite also has a high level of wearing during the machining process. The cutting edge preparations are used in order to reduce the effects of this problem, increasing the durability of the tools. In that interest, this paper has researched the effect of edge preparations on the wear of tools with polycrystalline diamond coating (PCD), in the milling of graphite electrodes. Therefore, experimental tests were performed with untreated tools, tools polished with abrasive brushes and tools treated by the polishing method with drag finishing. The tests consisted in machining electrodes with defined parameters and checking the wear generated on the cutters every 200 meters of machined length. Analysis of roughness, characterization of the tools after the treatments, characterization of the media and the brush used in the polishes and characterization of the machined graphite were also performed. The findings indicate that the edge preparation results in modifications on the coating surface, reducing the roughness value by a mean of 23%, and in the case of drag finishing process, a variation of the values reduction, since this process is more reliable and reproducible. The media and brush characterization indicated the silicon presence as an abrasive material, which may characterize a silicon carbide material. With regard to the tools wear, due to their life curve, gains such as reduction of flank wear and a length-machined increase of up to 63% were noticed, in comparison to the original tools. All tools passed through Stages I and II of Wear Curve, and did not reach Stage III, known as Catastrophic Wear. Abrasion was, apparently, the most present wear mechanism in the process, presenting as characteristics the flank wear, crater wear and notch wear. In conclusion, the two polishing processes showed gains and demonstrated their potential to be applied in tools production.

Made available in DSpace on 2014-10-09T12:24:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:10Z (GMT). No. of bitstreams: 1 00032.pdf: 1355141 bytes, checksum: 01f9cb92c30eca4c85591156ed8c22d5 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP