In the field of nuclear medicine, radioisotopes are used for applications such as diagnostic imag- ing, treatment, and equipment sterilization. The most commonly used radioisotope in medicine is technetium-99m (Tc-99m). It is used in 80% of all nuclear medicine procedures. Its parent isotope is molybdenum-99 (Mo-99). NRU, which is now closed, formerly produced 40% of the worlds demand for Mo-99. The production capacity of this reactor has been supplemented by a network of cyclotrons and a modified research reactor. This study aims to provide an alternative means of production for Mo-99, as well as other radioisotopes by modifying the center pin of a standard 37-element bundle of a CANDU reactor. The neutron transport code DRAGON, and the neutron diffusion code DONJON were used to model a CANDU-9 reactor. The lowest, median, and highest power channels were chosen as candi- dates for the modified bundles. It was found that the reactor parameters were altered by a negligible amount when any one channel was used to house the modified bundles. Significant quantities of the radioisotope lutetium-177 as well as the generating isotopes of the alpha-emitting radioisotopes lead- 212/bismuth-212, and radium-223 were produced. However, only minute amounts of molybdenum-99, and the generating isotope of bismuth-213 were produced. / Thesis / Master of Applied Science (MASc)

The aim of this thesis is to develop a tribocatalytically active solid coating that exhibits strong wear resistance, while also inducing the formation of carbon-based tribofilms when used in a hydrocarbon environment. By using tribocatalytic MoN-Cu synthesized through combinatorial DC reactive magnetron co-sputtering, a gradient between MoN and Cu is deposited and used to determine an ideal Cu composition exhibiting high wear resistance and the formation of a carbon-based tribofilm. To determine the properties of the thin film, various characterization methods were used before and after wear tests from an Anton-Paar pin-on-disk tribometer in a decane or ethanol bath. XRD, SEM, and EDS determined the phase structures and compositions. Nanoindentations and optical profilometry found hardness, Young's modulus, and wear rates. Raman analysis saw carbon presence on the surface of the wear tracks, confirming the formation of carbon tribofilms. For the wear rates, it was found that each fuel had different reactions to the changing Cu at%. From the Raman data, carbon presence, wear rates, and Cu at% did not reveal a strong correlation between the three sets of information. Specifically for the ethanol tracks, the was a connection between a high carbon amount and lower wear rate. It was inconclusive if there was one Cu at% that afforded the most ideal conditions. The information found here has developed the knowledge of MoN-Cu as a solid protective coating, and for using combinatorial DC reactive magnetron co-sputtering as an aid for materials development.

Climate change and environmental degradation, in addition to the challenges of limited fossil fuel resources, have driven governments to pursue creative renewable energy sources. Natural gas and biofuels are limitless energy sources produced from both fossil fuels and biomass that is renewable. SOFCs (Solid Oxide Fuel Cells) are a type of renewable energy system that can convert biofuels into power and heat whenever needed. They often operate at high temperatures (> 850 °C), which allows for fuel flexibility; nevertheless, such high temperatures are associated by rapid material deterioration and performance loss, usually before 40,000 hours of operation. As a result, many recent studies and activities have concentrated on lowering the operating temperature of SOFCs. Lowering the temperature causes decreased ionic conductivity, decreased catalytic activity, and increased carbon deposition on the anode side catalysts. This project aimed at developing an innovative cathode-supported SOFC to be fed by biofuels and operating at low-intermediate temperatures. Colloidal processes and co-sintering were selected to fabricate the final SOFC owing to their flexibility in optimizing the final desired properties and saving more manufacturing costs. The first chapter of this thesis provides an introduction to the essential concepts as well as professional specifics and previous work. The cell design and component materials are defined, as are additional requirements for lowering the operating temperature in SOFCs. Commercialization challenges and recommended solutions are also discussed, which involve the development of both new anode materials and production procedures. The project's goal is detailed at the end of Chapter 1, along with the reasons why various approaches were chosen. Molybdenum was chosen as a suitable anodic material to be doped into LSCF, and tape casting was developed further to create the cathode. The cathode support layer should have a consistent thickness, balanced flexibility and mechanical strength, and better shrinkage qualities. The plasticizer is a high molecular weight polyethylene glycol (PEG 4000), which improves these characteristics. Chapter 2 covers the steps involved in creating the button SOFC, starting with powder synthesis and ending with cathode tape casting. SOFC performance and anode catalytic activity are investigated to assess SOFC durability while fed by biogas. In Chapter 3, the findings are presented and explored in various contexts. Meanwhile, the anode material performance and cathode design and structure receive the greatest attention. Molybdenum was doped into LSCF via auto-combustion, yielding a fine and porous powder form. X-ray diffraction patterns demonstrated that increasing the Mo dopant increases anodic stability. In parallel, flat and crack-free green cathodes with 47% solid loading can be obtained by adjusting the PEG 4000 to binder quantity ratio at 1.00 wt% and drying the tapes at 70% relative humidity. The tapes had an excellent mechanical strength to flexibility ratio, which allowed them to be readily handled and rolled. The tapes benefited from a strong balance of flexibility and mechanical strength, allowing them to be easily handled and rolled while also exhibiting very low residual stresses during subsequent lamination and co-sintering procedures. The final manufactured SOFC revealed a porous anode structure and a less porous cathode layer using electron microscopy. Whereas the electrolyte was dense enough to ensure gas tightness. There was no delamination throughout the cell. The cells were then electrochemically measured, and the reactivity of LSCFMo to various fuels and temperatures was investigated. LSCFMo performed best when fed by methanol at 700 °C, leaving no carbon traces after operation. The very low ohmic resistance of the electrodes indicates a very good design and manufacture technique. A conclusion is presented in the final section of this thesis to highlight the most significant achievements of this research.

Zn-Mo coatings are very promising environment friendly anticorrosive coatings as replacement materials for cadmium and chromium (VI) based conversion layers. Electrodeposition has become a favorable technique in fabricating coatings due to its low cost, ease of use, and overall experimental control of coating quality. Very little research so far has been done for the electrodeposition of Zn-Mo coatings under alkaline conditions. In this work, Zn and Zn-Mo coatings were electrochemically deposited on stainless steel from an aqueous alkaline citrate solution. An organic compound, vanillin, was added to the electrolyte as a leveling agent for improving interlayer adherence and corrosion resistance of Zn-Mo coatings. Ni-Mo alloys have been known to possess high tensile strength and excellent corrosion protection of steels, and MoTe2 layers have a potential for the application in anticorrosive coatings due to their hydrophobic properties. In this study, MoTe2-Ni-Mo coatings were deposited on stainless steel using both sputtering and electrodeposition methods. These coatings with high corrosion resistance and other desirable properties are in demand in the oil and gas industry since they can protect and thus extend the lifetime of the underlying materials when exposed to aggressive environments. The Zn-Mo and MoTe2-Ni-Mo coatings were evaluated for chemical composition and corrosion behavior using different types of instrumental and electrochemical techniques. The addition of vanillin to the electrolyte did not change the crystalline structure or composition of the Zn-Mo coating, however, the corrosion resistance of the coating was significantly improved by the leveling effect of vanillin during the electrodeposition. The corrosion resistance of the Ni-Mo coating was also enhanced by applying the hydrophobic MoTe2 monolayer on the top surface.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 170-176).

A probe for measuring the specific heat of superconductors at low temperatures and in high magnetic fields has been built and commissioned. The probe has been tested using the relaxation method on samples of copper and the accuracy of the data is 1.3 % between 5 K and 30 K, data taken using the long range pulse method has a resolution of 10 mK. Specific heat measurements have been performed on members of the series (Pb(_1)-(_x))Cu(_1.8x)Mo(_6)S(_8), (Sn(_1-x))Eu(_x)Mo(_6)S(_8) and (Pb(_1-x)M(_x))Mo(_6)S(_8) where M = Gd and Eu, from 3 K up to 30 K and in magnetic fields up to 15 T. Additional results from resistivity, susceptibility, magnetisation. X-ray diffraction, transmission electron microscopy and electron dispersive-ray measurements are also presented. These data have been compared to results from other authors and are analysed in terms of the BCS and GLAG theories of superconductivity and the magnetic properties of these materials. The mean field model has been used to calculate numerically the magnetic contribution to the specific heat (cm) of both ferromagnetic and antiferromagnetic systems as a function of temperature and applied field both above and below the ordering temperature. In addition an approximate analytic form for the magnetisation has been used to calculate Cm above the ordering temperature. Expressions have been derived for the saturation value of the peak in C(_m): C(^sat)(_m) = 1.1245n(_cell)RJI(J+1) and the temperature dependence of the peak with applied field ȡ(μ(_o)H(_ext))/ȡT(_peak)=6.540/g(_J)(J+1). They allow the simple calculation of the values of J and g(_J)(J + 1) from specific heat data. The magnetic contribution to the specific heat of the samples (Sn(_0.65)Eu(0.35)Mo(_6)S(_8)) and (Sn(0.50)Eu(_0.50)Mo(_6)S(_8)) have been modelled using these calculations and excellent agreement is found by considering the magnetic ions as free ions. The sample is accurately modelled by including an additional minority phase (Gd(_2)S(_3)). The approximate expressions have also been used to analyse data on high temperature superconductors producing values of J and g(_J)}{J + 1) consistent with a doublet ground state. The properties of Chevrel phase materials have been determined as a function of doping level. The critical temperature is degraded by doping but an increase in the critical current density is observed in the series (Pb(_1-x)Cu(_1-8x)Mo(_6)S(_8) for very low levels of doping. Increases of up to 28 % in the upper critical field, that are probably due to the compensation effect and an increase in the normal state resistivity, are also observed in the series (Sn(_1-x)Eu(_x)Mo(_6)S(_8)) at high levels of doping and in the series (Pb(_1-x)Gd(_x)Mo(_6)s(_8) for low levels of doping.

Les molybdoenzymes (MoEs) à bisPGD sont des métalloprotéines dont le site actif est constitué d'un cofacteur à molybdène (Mo) mononucléaire. Elles sont impliquées dans les cycles biogéochimiques de l'azote, du carbone et du soufre et catalysent essentiellement des réactions d'oxydoréduction à 2 e-/2 H+ envers une grande variété de substrats. En dépit de la connaissance de la structure cristallographique de nombreuses MoEs, leur fonctionnement reste encore largement incompris. Ces enzymes présentent un intérêt biotechnologique car certains de leurs substrats sont des composés toxiques notoires, tels que les oxydes de sélénium ou d'arsenic. L'objectif de ma thèse a été d'identifier quels facteurs structuraux gouvernent la réactivité d'une MoE à bisPGD, la nitrate réductase A d'E. coli. Le premier axe de mes travaux de thèse a consisté à étudier l'activité de l'enzyme envers différents substrats et examiner le rôle du ligand protéique du Mo dans sa réactivité, en combinant des approches de mutagenèse dirigée, de biochimie et de spectroscopie RPE. J'ai montré que le ligand protéique du Mo est impliqué dans une étape clé du cycle catalytique. Le second axe a consisté à identifier les relations existantes entre la structure atomique du site actif et ses signatures spectrales. Pour augmenter la résolution et permettre d'identifier les transitions structurales mises en jeu lors de l'interconversion entre les différentes formes spectrales, j'ai utilisé la spectroscopie RPE impulsionnelle, qui permet de détecter les noyaux magnétiques (1H et 14N, …). Mes résultats constituent un pré-requis nécessaire pour l'étude structurale à haute résolution du site actif de la nitrate réductase. / Molybdenum (Mo) is a rare transition metal that is indispensable to most living organisms. In particular, it makes part of the active site of metalloenzymes involved in the biogeochemical cycles of carbon, nitrogen and sulphur. In this context, prokaryotic molybdoenzymes (MoEs) with the bisPGD cofactor at their active site essentially catalyze oxidoreduction reactions with 2 e-/2 H+ towards a wide range of substrates. Given that some MoEs can activate substrates that are well-known pollutants, understanding the mechanism of these enzymes accounts for a major prerequisite for future enzymatic engineering strategies aimed at optimizing enzyme reactivity towards bioremediation processes. To identify the molecular determinants of the reactivity of MoEs, we have explored the importance of the Mo proteic ligand aspartate in the respiratory Nitrate Reductase from E. coli. We have combined biochemistry and EPR spectroscopy to analyze the impact of the Mo-ligand substitution on both the enzymatic and the structural properties of the molybdenum cofactor. Our results show that the nature of the proteic ligand plays a critical role in the reactivity of the active site. A second part of my thesis work consisted in establishing the link between spectroscopic data on the MoV centre and its atomic structure. To get a high level of resolution and to identify which kind of structural modification is responsible for the spectroscopic differences between every Mo(V) signature, pulsed EPR spectroscop is most promising. Our results constitute a pre-requisite for structural studies of every species of the MoV center of the NRA.

Ce travail de thèse porte sur la synthèse de carbures de molybdène sur support afin de tester leurs performances catalytiques dans des réactions d’hydrogénation. Dans ce but, la conversion d'acide succinique en phase aqueuse dans un réacteur discontinu et du dioxyde de carbone en phase gazeuse dans un réacteur à flux continu, ont été effectuées. Les catalyseurs ont été préparés par la méthode de carburation par réduction en température programmée, pendant laquelle des paramètres ont été modifiés conduisant à différents rapports molybdène/carbone. Les différents catalyseurs testés dans cette réaction étaient actifs pour la conversion de l'acide succinique en gamma-butyrolctone et, plus remarquablement, en acide butyrique, ce dernier n'était pas obtenu en quantités significatives avec des catalyseurs à base de métaux précieux. L’augmentation de la conversion d’acide succinique avec une sélectivité plus élevée en acide butyrique a été faite avec les catalyseurs contenant plus de carbone, préparés en augmentant la vitesse spatiale horaire gazeuse. Les intermédiaires ont été ensuite convertis en tétrahydrofurane, butanol, 1,4-butanediol et butane. La désactivation observée lors de recyclage du catalyseur a été principalement attribuée à une diminution de la quantité de molybdène et de carbone carbidique, démontrée par l'analyse XPS. Des essais préliminaires de ces catalyseurs dans l'hydrogénation du dioxyde de carbone ont montré qu'ils fonctionnaient principalement en tant que catalyseurs pour la réaction du gaz à l’eau inverse, et l'excès de carbone entrave l'activité catalytique d'une manière opposée à la réaction en phase aqueuse. Le support semble jouer un rôle dans la réactivité des catalyseurs, la conversion du dioxyde de carbone ainsi que la sélectivité en méthane et méthanol, qui ont augmenté dans l'ordre suivant: carbure de molybdène sur support DT51 TiO2> P25 TiO2 ˜ ZrO2 / This work focuses on the synthesis of supported molybdenum carbides and evaluating their catalytic performance in succinic acid hydrogenation reactions in aqueous phase using batch reactor and carbon dioxide hydrogenation in gas phase using continuous flow reactor. The catalysts were prepared by the temperature programmed reduction carburization method, where the parameters were modified leading to different molybdenum to carbon ratios. The different catalysts tested were active in converting succinic acid to gamma butyrolctone and more remarkably butyric acid which is not reported in significant quantities in this reaction with precious metal based catalysts. The catalysts containing more carbon contents that were prepared by increasing the gas hourly space velocity showed higher activity in converting succinic acid and higher selectivity to butyric acid. The intermediates were then converted to tetrahydrofuran, butanol, 1,4-butanediol and butane gas. The deactivation observed while recycling the catalyst was mainly attributed to a decrease in the amounts of carbidic molybdenum and carbidic carbon, as demonstrated by XPS analysis. Preliminary tests for these catalysts in carbon dioxide hydrogenation showed that they functioned mainly as reverse water gas shift catalysts, and the excess of carbon hinders the catalytic activity in an opposite manner of the reaction in aqueous phase. The support seems playing a role in the reactivity of the catalysts, carbon dioxide conversion as well as methane and methanol selectivity increased in the order: molybdenum carbide supported on DT51 TiO2 > P25 TiO2 ˜ ZrO2

No description available.

O desenvolvimento dos aços inoxidáveis Super-Martensíticos (SM) nasce da necessidade de implementar novas tecnologias, mais econômicas e amigáveis ao meio ambiente. Os aços inoxidáveis SM são uma derivação dos aços inoxidáveis martensíticos convencionais, diferenciando-se basicamente no menor teor de carbono, na adição de Ni e Mo. Foram desenvolvidos como uma alternativa para aços inoxidáveis duplex no uso de dutos para a extração de petróleo offshore em meados dos anos 90. Para que esses aços apresentem as propriedades mecânicas de resistência à tração e tenacidade é necessário que sejam realizados tratamentos de austenitização, seguido de têmpera, e de revenimento, onde, particularmente para este último, há várias opções de tempos e temperaturas. Como os tratamentos térmicos geram as propriedades mecânicas através de transformações de fase (precipitação) podem ocorrer alterações da resistência à corrosão. São conhecidos os efeitos benéficos da adição de Nb em aços inoxidáveis tradicionais. Por isso, o objetivo desta pesquisa foi estudar aços inoxidáveis SM contendo Nb. Foi pesquisada a influência da temperatura de revenimento sobre a resistência à corrosão de três aços inoxidáveis SM, os quais contêm 13% Cr, 5% Ni, 1% a 2% Mo, com e sem adições de Nb. No presente trabalho, foram denominados de SM2MoNb, SM2Mo e SM1MoNb, que representam aços com 2% Mo, 1% Mo e 0,11% Nb. Dado que os principais tipos de corrosão para aços inoxidáveis são a corrosão por pite (por cloreto) e a corrosão intergranular (sensitização), optou-se por determinar os Potenciais de Pite (Ep) e os Graus de Sensitização (GS) em função da temperatura de revenimento. Os aços passaram por recozimento a 1050°C por 48 horas, para eliminação de fase ferrita delta. Em seguida foram tratados a 1050 °C por 30 minutos, com resfriamento ao ar, para uniformização do tamanho de grão. A estrutura martensítica obtida recebeu tratamentos de revenimento em temperaturas de: 550 °C, 575 °C, 600 °C, 625 °C, 650 °C e 700 °C, por 2 horas. O GS foi medido através da técnica de reativação eletroquímica potenciodinâmica na versão ciclo duplo (DL-EPR), utilizando-se eletrólito de 1M H2SO4 + 0,01M KSCN. Para determinar o Ep foram realizados ensaios de polarização potenciodinâmica em 0,6M NaCl. Os resultados obtidos foram discutidos através das variações microestruturais encontradas. Foram empregadas técnicas de microscopia ótica (MO), microscopia eletrônica de varredura (MEV), simulação termodinâmica de fases através do programa Thermo-Calc e determinação de austenita revertida mediante difração de raios X (DRX) e ferritoscópio. A quantificação da austenita por DRX identificou que a partir de 600 °C há formação desta fase, apresentando máximo em 650 °C, e novamente diminuindo para zero a 700 °C. Por sua vez, o método do ferritoscópio detectou austenita nas condições em que a analise de DRX indicou valor nulo, sendo as mais críticas a do material temperado (sem revenimento) e do aço revenido a 700 °C. Propõe-se que tais diferenças entre os dois métodos se deve à morfologia fina da austenia retida, a qual deve estar localizada entre as agulhas de martensita. Os resultados foram discutidos em termos da precipitação de Cr23C6, Mo6C, NbC, fase Chi, austenita e ferrita, bem como das consequências do empobrecimento em Cr e Mo, gerados por tais microconstituintes. São propostos três mecanismos para explicar a sensitização: o primeiro é devido a precipitação de Cr23C6, o segundo a precipitação de fase Chi (rica em Cr e Mo) e o terceiro é devido a formação de ferrita durante o revenimento. O melhor desempenho quanto ao GS foi obtido para os revenimentos a 575 °C e 600°C, por 2 horas. Os resultados de Ep indicaram que o aço SM2MoNb, revenido a 575°C, tem o melhor desempenho quanto à resistência à corrosão por cloreto. Isso associado ao baixo GS coloca este aço, com este tratamento térmico, numa posição de destaque para aplicações onde a resistência à corrosão é um critério de seleção de material, uma vez que, segundo a literatura a temperatura de 575 °C está no intervalo de temperaturas de revenimento onde são obtidas as melhores propriedades mecânicas. / Supermartensitic (SM) stainless steels were developed in response to the need of new technologies that are more economical and environmentally friendly. SM steels are different from classic martensitic stainless steels due to their lower carbon content and the addition of Mo and Ni. SM steels were developed as an alternative for duplex stainless steels in oil extraction pipelines offshore in the mid-1990s. To acquire the desired mechanical properties quenching and tempering treatments can be conducted, with tempering which can be performed in different temperatures and times. Since the previous heat treatments change the mechanical properties by phase transformations (precipitation), changes in the corrosion resistance properties can be expected. The beneficial effects of Nb additions in traditional stainless steels are well known. Therefore, the aim of this investigation was to study the influence of tempering temperature on the corrosion resistance of three SM stainless steels, containing 13% Cr, 5% Ni, 1-2% Mo, with and without Nb. The steels used in this investigation were denominated SM2MoNb, SM2Mo and SM1MoNb, according to their Mo (2% or 1%) and Nb (0.11%) content. Considering that the usual types of corrosion observed in stainless steels are pitting and intergranular corrosion, the pitting potential (Ep) and the degree of sensitization (DOS) were determined in function of tempering temperature. The steels were annealed at 1050° C during 48 hours to eliminate delta ferrite phase. Afterwards, the samples were normalized for 30 minutes at 1050 ºC (air cooling) to standardize the grain size. Finally, the samples were tempered at 550 °C, 575 °C, 600 °C, 625 °C, 650 °C or 700 °C, for two hours. The DOS was measured through double loop electrochemical potentiodynamic reactivation technique (DL-EPR), using as electrolyte a solution containing 1 M H2SO4 + 0.01 M KSCN. To determine the Ep, potentiodynamic polarization tests were carried out in a 0.6 M NaCl solution. The results were discussed based on the observed microstructural changes. Optical microscopy (OM), scanning electron microscopy (SEM), phase diagram simulation using Thermo-Calc software and quantification of reversed/retained austenite were done using the following two methods: X-ray diffraction (XRD) and magnetic measurements with a ferritscope. The quantification analysis by XRD showed the formation of austenite above a temperature of 600 °C, reaching the maximum volume at 650 °C and decreasing again to zero at 700 °C. However, the ferritscope measurements detected the presence of austenite in the whole temperature range. The largest difference between the two methods used was observed for the specimens only quenched and quenched/tempered at 700 °C. It is proposed that the observed differences between XRD and ferritscope methods correspond to the presence of nanometric retained austenite, which is localized among the martensite laths. The results were discussed based on the precipitation of Cr23C6, Mo6C, NbC, Chi-phase, austenite and ferrite, and by the resulting Cr and Mo depletion caused by the precipitation of these microconstituents. Three mechanisms were proposed to explain the degree of sensitization: i) Cr23C6 precipitation, ii) Chi-phase (Cr and Mo enrichment) precipitation and, iii) ferrite formation during the tempering treatment. The best performance in terms of DOS was obtained for the tempering conditions of 575 ºC and 600 ºC. In addition, the Ep results showed that the steel SM2MoNb tempered at 575 °C offers the best pitting corrosion resistance in chloride environment. Therefore, the previous results can be used as criteria for best material and tempering temperature selection. Moreover, according to published literature, 575 °C is within the temperature range that offers the best mechanical properties.