The aim of this thesis was to evaluate the feeding and nutrition of tropical farmed fish and shrimp, targeting its applicability to aquaculture farming. The study of the actual panorama of aquafeed quality for tilapia Oreochromis niloticus and shrimp Litopenaeus vannamei farmed in Brazil showed that the proximate compositions between the analyzed feeds were mostly consistent with the declared values from the manufacturers, however, the feed water stability showed the opposite; the in vitro pH-stat species-specific method to determine the protein degree of hydrolysis (DH) showed to be a useful tool to evaluate feed quality; and NIRS technique can be used in many applications throughout the aquafeed industry, being an efficient tool for rapidly assessing feed quality in terms of DH. A second study evaluated the acid-insoluble ash (AIA) and chromic oxide (Cr2O3) as inert markers and feed processing method (industrial extruded vs. laboratory cold pelleted) to determine apparent digestibility coefficient (ADC) of dry matter and crude protein of juvenile L. vannamei. The AIA showed to be an effective natural endogenous marker for digestibility trials with L. vanammei, however, for commercial feeds attention should be paid to feed AIA level; the extruded feed showed better animal performance than the cold pelleted feed, however, ADC of both feeds were not significantly different from each other. Further, two feeding trials were conducted with juvenile cobia Rachycentron canadum: (1) feeding trial conducted within floating net cages to test the nutritional efficacy of different dietary feeding regimes ranging from the use of trashfish, in-house formulated feeds, to dry commercial extruded marine fish feed; and (2) feeding trial conducted within indoor water-recirculated tanks to test the nutritional efficiency of different potential dietary fishmeal replacers within dry in-house prepared diets. Generally, fish performance was superior in the net-cage feeding trial compared with the indoor water-recirculated tank trial; overall, the fish growth and performance of the experimental diets were very similar, showing that the alternative ingredients could be included and replace part (50%) of the fishmeal component; the results from both trials concluded that the cobia requires practices diets with high levels of crude protein and lipid, and the inclusion of alternative plant-based and terrestrial animal protein sources was possible; the quantitative essential amino acid (EAA) requirement values estimated by the protein accretion method was highly correlated to the average of each of the EAA requirement for the species of carnivorous fish reported in the literature, and could be recommended for formulation of commercial feed for cobia R. canadum. Finally, a tentative to quantify the total sulfur amino acid requirement of juvenile Florida Pompano Trachinotus carolinus, was performed using combinations of various soybean protein products in order to develop cost-effective and environmentally-friendly diets. Although there was an apparent tendency in the results, the range of methionine levels employed in this study may not have been broad enough to accurately measure the dietary concentration necessary to estimate the total sulfur amino acid requirement; in addition, high variation results among the three replicates per diet did not provide sufficiency robustness for its estimation; this study within 45 days should not have been enough to show significant differences among the treatments. Long term feeding trials would be recommended from fingerling/juvenile to market size with full nutritional and economic evaluation of results. / O objetivo dessa tese foi avaliar a alimentação e nutrição de peixes e camarões tropicais cultivados, visando a sua aplicação à aquicultura. O estudo do atual panorama da qualidade das rações para tilapia e camarão cultivados no Brasil mostrou que a maioria das composições proximais das rações analisadas foram consistentes com os valores declarados pelos fabricantes, porém, a estabilidade das na água mostrou-se o oposto; o método in vitro pH-stat com enzimas espécie-específica, para determinação do grau de hidrólise da proteína (DH), mostrou ser uma ferramenta útil para avaliar a qualidade das rações; a técnica da espectrofotometria do infravermelho próximo (NIRS) pode ser usada em várias aplicações na indústria de alimentos aquáticos, sendo uma ferramenta eficiente para avaliar rapidamente a qualidade dos alimentos em termos de DH. Um segundo estudo avaliou a cinza insolúvel em ácido (AIA) e óxido de cromo (Cr2O3) como marcadores inertes, além de métodos de processamento de alimentos (extrusado industrial vs. peletizada a frio no laboratório) para determinar o coeficiente de digestibilidade aparente (ADC) da matéria seca e proteína bruta de juvenis de L. vannamei. O AIA mostrou ser um marcador endógeno natural eficaz para ensaios de digestibilidade com L. vanammei, no entanto, atenção especial deve ser dada aos níveis de AIA nas rações comerciais; a ração extrusada teve a melhor performance dos animais, porém, os valores de ADC entre as rações não foram diferentes significantemente. Além disso, dois experimentos de alimentação foram conduzidos com juvenis de beijupirá Rachycentron canadum: (1) experimento realizado em tanques-rede flutuantes para testar a eficácia nutricional de diferentes regimes alimentares, variando entre rejeito de pesca, rações preparadas em laboratório, e ração comercial extrusada; e (2) um experimento realizados em tanques com recirculação de água para testar a eficiência nutricional de diferentes potenciais substitutos de farinha de peixe, com dietas completadas preparadas em laboratório. Em geral, o desempenho dos peixes foi superior no experimento nos tanques-rede, comparado com o experimento nos tanques de recirculação de água; no geral o crescimento e performance dos peixes das dietas experimentais foram bem similares, concluindo que ingredientes alternativos podem ser incluídos e substituírem parte (50%) da farinha de peixe das rações; os resultados de ambos os estudos concluíram que o beijupirá requer dietas práticas com alto teores de proteína bruta e lipídeos, e a inclusão de fontes proteicas de origem vegetal e animal foi possível. Os valores quantitativos das exigências de amino acido essenciais (EAA) estimados pelo método de acreção de proteína na carcaça foram altamente correlacionados com as médias de exigência de cada EAA das as espécies de peixes carnívoros encontrados na literatura, e pode ser recomendado para a formulação de ração comercial para beijupirá R. canadum. Por ultimo, uma tentativa de quantificar as exigências de amino ácidos sulforosos totais para Florida Pompano Trachinotus carolinus, foi realizada utilizando combinações de vários ingredientes proteicos a base de soja, a fim de desenvolver dietas de baixo custo e ecologicamente sustentáveis. Embora houve uma tendência clara nos resultados, os intervalos dos níveis de metionina utilizados nesse estudo podem não ter sido amplos o suficiente para medir com precisão a concentração alimentar necessária para estimar a exigência dos de amino ácidos sulforosos totais; além disso, a alta variação entre as replicas não forneceu uma estimativa robusta; este estudo de 45 dias não deve ter sido suficiente para mostrar diferenças significativas entre os tratamentos.

A técnica de soldagem apresenta vantagem de união de partes metálicas que permite melhora na adaptação e uniformidade na distribuição das forças mastigatórias, minimizando falhas no tratamento reabilitador. O objetivo foi avaliar a resistência flexural entre três métodos de soldagem diferentes: Chama Direta a maçarico, método TIG - Tungstênio gás inerte (Soldadora NTY - Kernit, Brasil) e o método de solda a Laser (Soldadora Desktop - Dentaurum, Alemanha) comparando a um grupo controle (Monobloco). Os espécimes cilíndricos foram obtidos a partir de canais de cera pré-fabricados com 3mm de diâmetro e 30mm de comprimento, fundidos em liga de Ni-Cr e seccionados transversalmente, formando os grupos T1 e L1. Depois da secção, dez espécimes dos grupos L e T receberam chanfros em 45° para preenchimento, formando os grupos (L2 e T2). As extremidades foram unidas com resina acrílica obedecendo a uma distância pré-determinada, de 0,3mm para o grupo chama direta, 0,1mm para o grupo TIG e juntas do tipo topo a topo para o grupo laser. Os corpos foram incluídos e soldados de acordo com a proposição. Após a soldagem os corpos de prova foram torneados e levados ao teste de flexão. Os dados foram submetidos aos testes estatísticos (ANOVA e Student-Newman-Keuls - p <0,05) para comparações múltiplas. De acordo com os resultados (MPa) o grupo M (1796,55) obteve o maior valor, seguindo pelo grupo C(1370,56), ficando o grupo T1(990,84) com o valor menor. Não houve diferença estatística entre os grupos soldados, existindo somente diferença entre os grupos de teste para o grupo controle em monobloco. No entanto podemos afirmar que o preenchimento parece influenciar discretamente os resultados da resistência flexural no grupo TIG. Conclui-se que o método TIG produz resultado semelhante ao laser e a chama direta, o que é clínica e operacionalmente importante. / The welding technique presents advantage of union of metallic parts that improves the adaptation and appropriate distribution of the bite forces, minimizing flaws in the dental prostheses. The objective was to evaluate the flexural strength in different welding methods: Brazing; Laser (Welder Desktop - Dentaurum, Germany) and Tungsten inert gas - TIG (Welder NTY - Kernit, Brazil), comparing to a control group (non-welded). The cylindrical specimens were obtained from prefabricated wax conduits with 3mm of diameter and 30mm of length, melted in Ni-Cr alloys and split up transversally, forming the groups T1 and L1. After of the section the groups L and T received slices in 45° for fulfill, forming the groups (L2 and T2). The extremities were united with acrylic resin obeying a predetermined distance, from 0,3 mm to the brazing group, 0,1 mm to the TIG group, and in the laser group there wasn\' t any space between the extremities of jointing. The specimes were included and welding in agreement with the proposition, turned and conducted to the flexion test. The data were submitted to the statistical test (ANOVA and Student-Newman-Keuls - p<0,05) for multiple comparisons. According to the results (MPa) the control group (1796,55) obtained the largest average value, followed by the brazing group (1370,56), being the group T1(990,84) with the smallest value. In terms of statistics there was no difference between the groups with welding, existing only difference among the tested groups for the control group. However, we can affirm that the completion seems to influence the results of the resistance flexural discreetly in the TIG group. It can be concluded that the TIG method produces similar result to the laser and the brazing, what is clinical and important operationally.

The aim of this thesis was to evaluate the feeding and nutrition of tropical farmed fish and shrimp, targeting its applicability to aquaculture farming. The study of the actual panorama of aquafeed quality for tilapia Oreochromis niloticus and shrimp Litopenaeus vannamei farmed in Brazil showed that the proximate compositions between the analyzed feeds were mostly consistent with the declared values from the manufacturers, however, the feed water stability showed the opposite; the in vitro pH-stat species-specific method to determine the protein degree of hydrolysis (DH) showed to be a useful tool to evaluate feed quality; and NIRS technique can be used in many applications throughout the aquafeed industry, being an efficient tool for rapidly assessing feed quality in terms of DH. A second study evaluated the acid-insoluble ash (AIA) and chromic oxide (Cr2O3) as inert markers and feed processing method (industrial extruded vs. laboratory cold pelleted) to determine apparent digestibility coefficient (ADC) of dry matter and crude protein of juvenile L. vannamei. The AIA showed to be an effective natural endogenous marker for digestibility trials with L. vanammei, however, for commercial feeds attention should be paid to feed AIA level; the extruded feed showed better animal performance than the cold pelleted feed, however, ADC of both feeds were not significantly different from each other. Further, two feeding trials were conducted with juvenile cobia Rachycentron canadum: (1) feeding trial conducted within floating net cages to test the nutritional efficacy of different dietary feeding regimes ranging from the use of trashfish, in-house formulated feeds, to dry commercial extruded marine fish feed; and (2) feeding trial conducted within indoor water-recirculated tanks to test the nutritional efficiency of different potential dietary fishmeal replacers within dry in-house prepared diets. Generally, fish performance was superior in the net-cage feeding trial compared with the indoor water-recirculated tank trial; overall, the fish growth and performance of the experimental diets were very similar, showing that the alternative ingredients could be included and replace part (50%) of the fishmeal component; the results from both trials concluded that the cobia requires practices diets with high levels of crude protein and lipid, and the inclusion of alternative plant-based and terrestrial animal protein sources was possible; the quantitative essential amino acid (EAA) requirement values estimated by the protein accretion method was highly correlated to the average of each of the EAA requirement for the species of carnivorous fish reported in the literature, and could be recommended for formulation of commercial feed for cobia R. canadum. Finally, a tentative to quantify the total sulfur amino acid requirement of juvenile Florida Pompano Trachinotus carolinus, was performed using combinations of various soybean protein products in order to develop cost-effective and environmentally-friendly diets. Although there was an apparent tendency in the results, the range of methionine levels employed in this study may not have been broad enough to accurately measure the dietary concentration necessary to estimate the total sulfur amino acid requirement; in addition, high variation results among the three replicates per diet did not provide sufficiency robustness for its estimation; this study within 45 days should not have been enough to show significant differences among the treatments. Long term feeding trials would be recommended from fingerling/juvenile to market size with full nutritional and economic evaluation of results. / O objetivo dessa tese foi avaliar a alimentação e nutrição de peixes e camarões tropicais cultivados, visando a sua aplicação à aquicultura. O estudo do atual panorama da qualidade das rações para tilapia e camarão cultivados no Brasil mostrou que a maioria das composições proximais das rações analisadas foram consistentes com os valores declarados pelos fabricantes, porém, a estabilidade das na água mostrou-se o oposto; o método in vitro pH-stat com enzimas espécie-específica, para determinação do grau de hidrólise da proteína (DH), mostrou ser uma ferramenta útil para avaliar a qualidade das rações; a técnica da espectrofotometria do infravermelho próximo (NIRS) pode ser usada em várias aplicações na indústria de alimentos aquáticos, sendo uma ferramenta eficiente para avaliar rapidamente a qualidade dos alimentos em termos de DH. Um segundo estudo avaliou a cinza insolúvel em ácido (AIA) e óxido de cromo (Cr2O3) como marcadores inertes, além de métodos de processamento de alimentos (extrusado industrial vs. peletizada a frio no laboratório) para determinar o coeficiente de digestibilidade aparente (ADC) da matéria seca e proteína bruta de juvenis de L. vannamei. O AIA mostrou ser um marcador endógeno natural eficaz para ensaios de digestibilidade com L. vanammei, no entanto, atenção especial deve ser dada aos níveis de AIA nas rações comerciais; a ração extrusada teve a melhor performance dos animais, porém, os valores de ADC entre as rações não foram diferentes significantemente. Além disso, dois experimentos de alimentação foram conduzidos com juvenis de beijupirá Rachycentron canadum: (1) experimento realizado em tanques-rede flutuantes para testar a eficácia nutricional de diferentes regimes alimentares, variando entre rejeito de pesca, rações preparadas em laboratório, e ração comercial extrusada; e (2) um experimento realizados em tanques com recirculação de água para testar a eficiência nutricional de diferentes potenciais substitutos de farinha de peixe, com dietas completadas preparadas em laboratório. Em geral, o desempenho dos peixes foi superior no experimento nos tanques-rede, comparado com o experimento nos tanques de recirculação de água; no geral o crescimento e performance dos peixes das dietas experimentais foram bem similares, concluindo que ingredientes alternativos podem ser incluídos e substituírem parte (50%) da farinha de peixe das rações; os resultados de ambos os estudos concluíram que o beijupirá requer dietas práticas com alto teores de proteína bruta e lipídeos, e a inclusão de fontes proteicas de origem vegetal e animal foi possível. Os valores quantitativos das exigências de amino acido essenciais (EAA) estimados pelo método de acreção de proteína na carcaça foram altamente correlacionados com as médias de exigência de cada EAA das as espécies de peixes carnívoros encontrados na literatura, e pode ser recomendado para a formulação de ração comercial para beijupirá R. canadum. Por ultimo, uma tentativa de quantificar as exigências de amino ácidos sulforosos totais para Florida Pompano Trachinotus carolinus, foi realizada utilizando combinações de vários ingredientes proteicos a base de soja, a fim de desenvolver dietas de baixo custo e ecologicamente sustentáveis. Embora houve uma tendência clara nos resultados, os intervalos dos níveis de metionina utilizados nesse estudo podem não ter sido amplos o suficiente para medir com precisão a concentração alimentar necessária para estimar a exigência dos de amino ácidos sulforosos totais; além disso, a alta variação entre as replicas não forneceu uma estimativa robusta; este estudo de 45 dias não deve ter sido suficiente para mostrar diferenças significativas entre os tratamentos.

Sérios problemas ambientais têm origem em processos de combustão incompletos. Entre os produtos indesejados está a fuligem, considerada como um dos principais fatores da mudança climática observada nos último anos. Desta forma, ferramentas para diagnóstico da emissão de material particulado se fazem necessárias. Com o advento do laser, o desenvolvimento de técnicas óticas não intrusivas teve início. Dentre elas, destaca-se a técnica denominada incandescência induzida por laser (laser induced incandescence – LII), a qual pode gerar resultados resolvidos no espaço para a fração volumétrica de fuligem. Neste contexto, este trabalho apresenta um estudo experimental sobre a produção de fuligem em duas situações: na primeira, foram estudadas chamas laminares pré-misturadas de etileno e ar aplicando-se a técnica LII. Os resultados foram calibrados a partir da fração volumétrica de fuligem média empregando a técnica de extinção de luz, obtendo-se, então, resultados quantitativos espacialmente resolvidos da fração volumétrica de fuligem. A utilização de diferentes gases no escoamento anular também foi avaliada. A segunda situação abordada envolve o estudo de chamas laminares não pré-misturadas utilizando o gás natural como combustível. O impacto da diluição de inertes em diferentes proporções sobre a fração volumétrica de fuligem em diversas alturas da chama foi estudado por meio da técnica LII. Os resultados obtidos foram comparados à outros resultados presentes na literatura e servirão como validação de futuros modelos de formação de fuligem. / Serious environmental problems are assigned to incomplete combustion processes. Among the unwanted products, soot can be related as an important factor of climate changes observed in the last years. Thus, particulate material emissions diagnostic tools are necessary. Due the laser advent, the development of non-intrusive optical techniques was possible. One of the most importante technique is the laser induced incandescence, LII, which can generate spatially and temporally resolved results of soot volume fraction. In this context, an experimental study regarding the soot production was developed in two different situations: in the first one, premixed laminar flames of ethylene and air were investigated by applying the LII technique. The results were calibrated through the average of soot volume fraction results obtained by the light extinction technique. Therefore, it was possible to obtain quantitative results of spatially resolved soot volume fraction. Different gases employment at the annular flow were also evaluated. The second situation studied involves the analysis of natural gas laminar non-premixed flames. The impact of different inert gas dilution ratio on the soot volume fraction at different heights of the flame was evaluated by the LII technique. The results were compared to other authors and will serve as validation for future soot formation models.

La thèse s’inscrit dans le cadre d’un projet de recherche visant à élaborer une anode permettant le dégagement d’oxygène en milieu de cryolithe fondue à 960°C et dont l’utilisation supprimerait les émissions de dioxyde de carbone du procédé de production d’aluminium Hall-Héroult. Le type d’anode envisagée est un composite Cermet (CERamique – METal), généralement constitué d’une phase métallique à base de nickel, cuivre et fer et d’une ou plusieurs phase(s) oxyde(s) conductrice(s) du type NixFe3-xO4 et Ni1-xFexO. Deux types de cermet, biphasé et triphasé, ont été étudiés dans le cadre de ce projet. L’objectif principal a été de comprendre les mécanismes de dégradation de telles anodes durant les électrolyses. Les cermets ont été testés sous une densité de courant de 0,80 A/cm² pour différentes durées, puis analysés par microscopie optique et microscopie électronique à balayage couplée à une analyse dispersive en énergie. Les premières électrolyses, effectuées dans un électrolyte synthétique, sans aluminium métallique et sous atmosphère argon ont révélé à la fois une dégradation chimique et électrochimique. L’étude de la dégradation chimique a été réalisée grâce à des immersions dans l’électrolyte sans polarisation. Les résultats ont mis en évidence une dissolution de la phase spinelle, liée à un phénomène de substitution entre les ions Al3+ de l’électrolyte et Fe3+ du spinelle, entrainant la formation d’un aluminate du type NixFe3-x-yAlyO4. Lorsque x = 0 et y proche de 2, la phase spinelle est dissoute alors que lorsque x est proche de 1, la phase spinelle est stabilisée et sa dissolution ralentie. Les électrolyses menées jusqu’à la fin de vie des matériaux ont révélé l'attaque préférentielle de la phase métallique pour former des composés fluorés et oxydes. Grâce aux caractérisations micrographiques et aux calculs thermodynamiques (logiciel FactSage 7.1), un mécanisme de dégradation global des anodes a été proposé. La compréhension des mécanismes de dégradation chimique et électrochimique des matériaux a permis de proposer des voies d'amélioration concernant à la fois le matériau d'anode et la chimie du bain cryolithique. / The thesis is a part of a research project which develop an anode permitting the release of oxygen in molten cryolite medium at 960°C, in order to eliminate carbon dioxide emissions from the aluminium production process called Hall-Héroult process. The type of anode envisaged is a Cermet composite (CERamic - METal), generally consisting of a metallic phase based on nickel, copper and iron and one or more conductor oxide phase(s) such as NixFe3-xO4 and Ni1-xFexO type. Two types of cermet, two-phase and three-phase, have been studied in this project. The main objective was to understand the degradation mechanisms of such anodes during electrolysis. The cermets were tested at a current density of 0.80 A/cm² for different durations and analyzed by optical microscopy and scanning electron microscopy coupled with dispersive energy analysis. The first electrolyses, carried out in a synthetic electrolyte, without metallic aluminum and under argon atmosphere revealed both chemical and electrochemical degradations. Study of chemical degradation was carried out thanks to immersions in the electrolyte without polarization. The results showed a dissolution of the spinel phase, linked to a substitution phenomenon between the Al3+ ions from the electrolyte and Fe3+ from spinel, resulting in the formation of a NixFe3-x-yAlyO4 aluminate type. When x = 0 and y close to 2, the spinel phase is dissolved whereas when x is close to 1, the spinel phase is stabilized and its dissolution slowed down. Electrolyses conducted to the end of life of the materials revealed the preferential attack of the metal phase to form fluorinated compounds and oxides. Thanks to micrographic characterizations and thermodynamic calculations (FactSage 7.1 software), a global degradation mechanism of the anodes has been proposed. The understanding of the chemical and electrochemical degradation mechanisms of the materials made it possible to propose ways of improvement concerning both the anode material and the cryolithic bath chemistry.

<p>A thorough investigation was performed on the behaviour of Ni, Fe and Cu oxides dissolved in cryolite melts, and the solubility of these species was measured as a function of alumina content, NaF/AlF₃ molar ratio (CR) and temperature. Predominance area diagrams showing the solid phases containing Ni, Fe and Cu, respectively, as a function of the partial oxygen pressure and the alumina activity at 1020 ^oC were constructed. These diagrams were based on present emf and solubility measurements.</p><p>The interpretations of the solubility measurements for the oxides of Ni and Fe gaveconclusive and consistent results. The oxides of Ni and Fe exhibit decreasing solubility with decreasing temperature and with increasing alumina concentration. The Ni(II) concentration decreased from 0.32 wt% in cryolite to 0.003 wt% in alumina-saturated melts, while that of Fe(II) decreased from 4.17 to 0.32 wt% in similar melts. FeO and NiO are stable solid phases at low alumina concentrations, while FeAl₂O₄ and NiAl₂O₄ are stable at high concentrations. The alumina concentrations corresponding to the points of coexistence between FeO and FeAl₂O₄ and between NiO and NiAl₂O₄ were determined to be 5.03 and 3.0 wt% Al₂O₃, respectively, corresponding to the following Gibbs energy of formation from the oxide compounds,∆G⁰_fNiAl2o4 = –28.6 ± 2 kJ/mol and ∆G⁰_{f FeAl2O4} = –17.6 ± 0.5 kJ/mol.</p><p>The solubilities of FeAl₂O₄ and NiAl₂O₄as a function of the CR were investigated in alumina-saturated melts at 1020 ^oC. For both compounds a maximum solubility was found at CR ~5, being 0.008 wt% Ni(II) and 0.62 wt% Fe(II). The results are discussed with respect to the species present in solution. Both Fe(II) and Ni(II) dissolve as fluorides with different numbers of associated “NaF’s”. Ni(II) seems to form Na₃NiF₅ in melts with molar ratios 2 to 12, while Fe(II) is present as NaFeF₃ in acidic (CR 3–10) melts and as Na₃FeF₅and probably some Na₄FeF₆ in basic melts (CR > 3).</p><p>The solubility of both Cu oxidation states Cu(I) and Cu(II) decreases with decreasing temperature. The solubilities of Cu(I) initially decreased with increasing alumina concentration, showing a minimum at a certain alumina concentration followed by an increase. The solubilities were 0.36 wt% Cu(I) and 0.92 wt% Cu(II) in cryolite, and 0.30wt% Cu(I) and 0.45 wt% Cu(II) in alumina-saturated cryolite at 1020 ^oC.</p><p>At 1020 ^oC the solubilities of Cu₂O and CuO were little influenced when changing the CR from 3 to 8 in alumina-saturated melts (~0.30 wt% Cu(I) and ~0.45 wt% Cu(II)), but there was an upward trend for CR < 3. Solubility measurements for CuO in alumina-saturated melts at CR 3.0 to 1.2 clearly showed that the saturation concentration is dependent on both temperature and melt composition.</p><p>Copper ions in solution show a complex behaviour, since they form fluorides and oxycomplexes simultaneously. The extent of co-existence of Cu(I) and Cu(II) in the same melt is also considerable, and it is depending on the alumina activity in the melt. According to thermodynamics the stable copper oxide phases at high alumina activities are the aluminates CuAlO₂ and CuAl₂O₄. However, no clear changes in the solubilities were found for the points of coexistence between Cu₂O and CuAlO₂ and CuO and CuAl₂O₄, respectively, as was the case for Ni(II) and Fe(II). Although there are uncertainties regarding the thermodynamic data available for the formation of copper aluminates, models for the dissolution mechanisms and for the species present in the melt are suggested. Cu(I) seems to form mainly CuF at low alumina contents, while Na₅CuO₃ dominates at higher alumina concentrations. Likewise, Cu(II) seems to form CuF₂, but the concentration of CuF₂ decreases with increasing alumina content. The species that gave the best fit for the cupric oxy-complexes was Na₁₆CuO₉, and the amount increased with increasing alumina content.</p><p>Cermet anodes were prepared with a NiFe₂O₄-based oxide phase mixed with a ~20 wt% copper-rich metal phase. The electrical conductivity for these materials was measured as a function of temperature, showing semiconductor behaviour in the temperature range from room temperature to 1050 ^oC. The highest electrical conductivity measured was ~30 S/cm at 1000 ^oC, which is on the low side for use as an anode material for aluminium production.</p><p>Three cermet anodes were tested by electrolysis for 48 hours. After the experiments the anodes were examined with SEM. There was no metal phase present in the outer 100 µm of the anode, not even pores were observed that could indicate where the metal grains had been. A copper-rich phase was found in one case ~2 mm from the outer surface, and it is believed that copper diffuses out of the anode.</p><p>The cermet anodes dissolved slowly in the electrolyte during electrolysis. The steady state concentrations of Fe and Cu in the electrolyte were below the saturation concentrations, while the concentration of Ni was 3 - 4 times above saturation. The dissolution of the anode does not fit a first order mass-transport model, but it can probably be explained by a controlled dissolution mechanism with some additional disintegration/spalling of the anode material. Further work is needed to draw a firm conclusion. In general, correct solubility data for the anode constituents are needed to make a proper evaluation of various anode materials. Perhaps the first order mass-transport model agrees for some materials, but based on the present results it seems untenable for cermet materials made of NiFe₂O₄ with a copper-rich metal phase.</p><p>The solubilities of the oxides of Ni(II) and Fe(III) are very low for the alumina-saturated melt used during electrolysis, which make them promising candidates for inert anodes. However, if nickel aluminate, which is an insulator, is formed and deposited on the anode surface, it is a cause of concern. Fe(II) aluminate is not expected to form on the anode surface, since Fe(III) is the stable oxidation state in the presence of oxygen gas. However, solid Fe(II) aluminate may be formed in the bulk of the electrolyte where the partial oxygen pressure is lower.</p>

A thorough investigation was performed on the behaviour of Ni, Fe and Cu oxides dissolved in cryolite melts, and the solubility of these species was measured as a function of alumina content, NaF/AlF3 molar ratio (CR) and temperature. Predominance area diagrams showing the solid phases containing Ni, Fe and Cu, respectively, as a function of the partial oxygen pressure and the alumina activity at 1020 oC were constructed. These diagrams were based on present emf and solubility measurements. The interpretations of the solubility measurements for the oxides of Ni and Fe gaveconclusive and consistent results. The oxides of Ni and Fe exhibit decreasing solubility with decreasing temperature and with increasing alumina concentration. The Ni(II) concentration decreased from 0.32 wt% in cryolite to 0.003 wt% in alumina-saturated melts, while that of Fe(II) decreased from 4.17 to 0.32 wt% in similar melts. FeO and NiO are stable solid phases at low alumina concentrations, while FeAl2O4 and NiAl2O4 are stable at high concentrations. The alumina concentrations corresponding to the points of coexistence between FeO and FeAl2O4 and between NiO and NiAl2O4 were determined to be 5.03 and 3.0 wt% Al2O3, respectively, corresponding to the following Gibbs energy of formation from the oxide compounds,∆G0fNiAl2o4 = –28.6 ± 2 kJ/mol and ∆G0f FeAl2O4 = –17.6 ± 0.5 kJ/mol. The solubilities of FeAl2O4 and NiAl2O4 as a function of the CR were investigated in alumina-saturated melts at 1020 oC. For both compounds a maximum solubility was found at CR ~5, being 0.008 wt% Ni(II) and 0.62 wt% Fe(II). The results are discussed with respect to the species present in solution. Both Fe(II) and Ni(II) dissolve as fluorides with different numbers of associated “NaF’s”. Ni(II) seems to form Na3NiF5 in melts with molar ratios 2 to 12, while Fe(II) is present as NaFeF3 in acidic (CR 3–10) melts and as Na3FeF5 and probably some Na4FeF6 in basic melts (CR &gt; 3). The solubility of both Cu oxidation states Cu(I) and Cu(II) decreases with decreasing temperature. The solubilities of Cu(I) initially decreased with increasing alumina concentration, showing a minimum at a certain alumina concentration followed by an increase. The solubilities were 0.36 wt% Cu(I) and 0.92 wt% Cu(II) in cryolite, and 0.30wt% Cu(I) and 0.45 wt% Cu(II) in alumina-saturated cryolite at 1020 oC. At 1020 oC the solubilities of Cu2O and CuO were little influenced when changing the CR from 3 to 8 in alumina-saturated melts (~0.30 wt% Cu(I) and ~0.45 wt% Cu(II)), but there was an upward trend for CR &lt; 3. Solubility measurements for CuO in alumina-saturated melts at CR 3.0 to 1.2 clearly showed that the saturation concentration is dependent on both temperature and melt composition. Copper ions in solution show a complex behaviour, since they form fluorides and oxycomplexes simultaneously. The extent of co-existence of Cu(I) and Cu(II) in the same melt is also considerable, and it is depending on the alumina activity in the melt. According to thermodynamics the stable copper oxide phases at high alumina activities are the aluminates CuAlO2 and CuAl2O4. However, no clear changes in the solubilities were found for the points of coexistence between Cu2O and CuAlO2 and CuO and CuAl2O4, respectively, as was the case for Ni(II) and Fe(II). Although there are uncertainties regarding the thermodynamic data available for the formation of copper aluminates, models for the dissolution mechanisms and for the species present in the melt are suggested. Cu(I) seems to form mainly CuF at low alumina contents, while Na5CuO3 dominates at higher alumina concentrations. Likewise, Cu(II) seems to form CuF2, but the concentration of CuF2 decreases with increasing alumina content. The species that gave the best fit for the cupric oxy-complexes was Na16CuO9, and the amount increased with increasing alumina content. Cermet anodes were prepared with a NiFe2O4-based oxide phase mixed with a ~20 wt% copper-rich metal phase. The electrical conductivity for these materials was measured as a function of temperature, showing semiconductor behaviour in the temperature range from room temperature to 1050 oC. The highest electrical conductivity measured was ~30 S/cm at 1000 oC, which is on the low side for use as an anode material for aluminium production. Three cermet anodes were tested by electrolysis for 48 hours. After the experiments the anodes were examined with SEM. There was no metal phase present in the outer 100 µm of the anode, not even pores were observed that could indicate where the metal grains had been. A copper-rich phase was found in one case ~2 mm from the outer surface, and it is believed that copper diffuses out of the anode. The cermet anodes dissolved slowly in the electrolyte during electrolysis. The steady state concentrations of Fe and Cu in the electrolyte were below the saturation concentrations, while the concentration of Ni was 3 - 4 times above saturation. The dissolution of the anode does not fit a first order mass-transport model, but it can probably be explained by a controlled dissolution mechanism with some additional disintegration/spalling of the anode material. Further work is needed to draw a firm conclusion. In general, correct solubility data for the anode constituents are needed to make a proper evaluation of various anode materials. Perhaps the first order mass-transport model agrees for some materials, but based on the present results it seems untenable for cermet materials made of NiFe2O4 with a copper-rich metal phase. The solubilities of the oxides of Ni(II) and Fe(III) are very low for the alumina-saturated melt used during electrolysis, which make them promising candidates for inert anodes. However, if nickel aluminate, which is an insulator, is formed and deposited on the anode surface, it is a cause of concern. Fe(II) aluminate is not expected to form on the anode surface, since Fe(III) is the stable oxidation state in the presence of oxygen gas. However, solid Fe(II) aluminate may be formed in the bulk of the electrolyte where the partial oxygen pressure is lower.

With respect to nitrides being considered as potential fast reactor fuels, research is conducted on the out-of-pile thermophysical properties, sintering and fabrication processes, gas migration mechanisms, self-diffusion and point defect behaviour of actinide nitrides, their surrogate materials, and the inert matrix material ZrN . The experimental research, carried out in the framework of qualifying fuel for the European Lead Cooled Training Reactor (ELECTRA), shows that sintered ZrN and (Dy,Zr)N pellet densities are influenced by the oxygen concentration in the material. The effect is confirmed in sintered (Pu,Zr)N pellets. Oxygen concentration also plays a role in the thermophysical properties of inert matrix nitride fuels, but does not have an impact on the electrical properties of these materials. With the fuel fabrication methods applied here, clean nitride powders can be synthesized. However, the subsequent fabrication phases, including milling and solid solution formation, increases the impurity levels significantly. Research of equal importance is performed on materials free of fabrication-induced impurities, whose properties are studied by employing first-principles methods. ZrN, UN and (U,Zr)N are studied, whereas the results from ZrN are expected to be applicable for actinide nitrides as a first approximation. The migration of noble gases in ZrN, on the atomic scale, confirms the experimentally observed tendency for noble gases with higher atomic number to be retained in the fuel matrix, while the majority of He is released to the fuel pin. Materials modelling implies that self-diffusion of nitrogen and metal atoms in inert matrix nitride fuels is accelerated under irradiation, since noble gas retention reduces migration barriers which govern self-diffusion. Unlike Kr and Xe, He has the capacity to be released into the fuel matrix, after having been trapped in a vacancy. The results are expected to aid in providing an explanation to the macroscopic diffusion phenomena in nitride fuels, as the diffusion behaviour of noble gases is sparsely studied. In addition, a study on the miscibility of ZrN and UN in a narrow composition range suggests solubility, based on the negative mixing energies. The results obtained from research on inert matrix nitride fuel underline several beneficial properties which are desirable in a fast reactor fuel. The relevance of these results is analyzed and contextualized in the thesis, from the perspective of current research and development in the field. / <p>QC 20130611</p>

abstract INERT SUBGROUPS AND CENTRALIZERS OF INVOLUTIONS IN LOCALLY FINITE SIMPLE GROUPS &uml / Ozyurt, Erdal Ph. D., Department of Mathematics Supervisor: Prof. Dr. Mahmut Kuzucuo&amp / #728 / glu September 2003, 68 pages A subgroup H of a group G is called inert if [H : H Hg] is finite for all g 2 G. A group is called totally inert if every subgroup is inert. Among the basic properties of inert subgroups, we prove the following. Let M be a maximal subgroup of a locally finite group G. If M is inert and abelian, then G is soluble with derived length at most 3. In particular, the given properties impose a strong restriction on the derived length of G. We also prove that, if the centralizer of every involution is inert in an infinite locally finite simple group G, then every finite set of elements of G can not be contained in a finite simple group. In a special case, this generalizes a Theorem of Belyaev&amp / #8211 / Kuzucuo&amp / #728 / glu&amp / #8211 / Se&cedil / ckin, which proves that there exists no infinite locally finite totally inert simple group.

Dual phase magnesia-zirconia ceramics were developed, characterized, and evaluated as a potential matrix material for use in light water reactor inert matrix fuel intended for the disposition of plutonium and minor actinides. Ceramics were fabricated from the oxide mixture using conventional pressing and sintering techniques. Characterization of the final product was performed using optical microscopy, scanning electron microscopy, x-ray diffraction analysis, and energy-dispersive x-ray analysis. The final product was found to consist of two phases: cubic zirconia-based solid solution and cubic magnesia. Evaluation of key feasibility issues was limited to investigation of long-term stability in hydrothermal conditions and assessment of the thermal conductivity. With respect to hydrothermal stability, it was determined that limited degradation of these ceramics at 300^oC occurred due to the hydration of the magnesia phase. Normalized mass loss rate, used as a quantitative indicator of degradation, was found to decrease exponentially with the zirconia content in the ceramics. The normalized mass loss rates measured in static 300^oC de-ionized water for the magnesia-zirconia ceramics containing 40, 50, 60, and 70 weight percent of zirconia are 0.00688, 0.00256, 0.000595, 0.000131 g/cm2/hr respectively. Presence of boron in the water had a dramatic positive effect on the hydration resistance. At 300^oC the normalized mass loss rates for the composition containing 50 weight percent of zirconia was 0.00005667 g/cm2/hr in the 13000 ppm aqueous solution of the boric acid. With respect to thermal conductivity, the final product exhibits values of 5.5-9.5 W/(m deg) at 500^oC, and 4-6 W/(m deg) at 1200^oC depending on the composition. This claim is based on the assessment of thermal conductivity derived from thermal diffusivity measured by laser flash method in the temperature range from 200 to 1200^oC, measured density, and heat capacity calculated using rule of mixtures. Analytical estimates of the anticipated maximum temperature during normal reactor operation in a hypothetical inert matrix fuel rod based on the magnesia-zirconia ceramics yielded the values well below the melting temperature and well below current maximum temperatures authorized in light water reactors.