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Zirconium and its alloys are used extensively in the nuclear industry. In the Canadian Deuterium Uranium reactor, the primary containment in the primary coolant system is composed of Zr-2.5wt%Nb in the form of a pressure tube. The permissible chemical composition of Zr-2.5wt%Nb for use in the pressure tube in nuclear reactors is dictated by ASTMB353. Oxygen and iron are the highest content controlled elements in the standard alloy, after zirconium and niobium. Oxygen is an alpha-stabilizer, and diffuses preferentially to the alpha phase, leading to a well established increase in the yield strength of the alpha phase. Iron is a beta-stabilizer, and is concentrated in the beta phase, as well as near alpha-beta grain boundaries. While the mechanical properties of standard Zr-2.5wt%Nb alloy are well understood, there is a dearth of knowledge on the individual effect of these alloying additions, especially at non-standard concentrations. Additionally, the experimental evidence that does exist does not directly take into account the two-phase nature of the alloy, or the effect of impurities on specific deformation modes. Notably absent is experimental evidence on the effect of interstitial impurities on twinning in the hexagonal close-packed alpha phase. This work seeks to complement the present understanding of these phenomena. Mechanical tests have been performed on three specially prepared Zr-2.5wt%Nb alloys to clarify the contributions of oxygen and iron to Zr-2.5wt%Nb deformation properties. Traditional mechanical measurements were complemented by in situ and ex situ diffraction measurements. Tests were performed at a range of temperatures (77K - 673K) and strain rates (quasi-static to 10^-2/s). Increasing oxygen content from 1176wppm to 3300wppm increases the macroscopic yield stress at room temperature, and results in a transition in work hardening behaviour at low strain rates. Increasing iron content from 547wppm to 1080wppm has no effect on the macroscopic yield stress, but increases the work hardening rate at room temperature. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-10-11 20:06:57.655

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As medidas de atrito interno tem sido muito usadas para o estudo de relaxações anelásticas devido à intersticiais em metais ou ligas metálicas. Estudou-se o comportamento de ligas de Nb-Zr dopadas com Oxigênio e ligas de Nb-Ti dopadas com Oxigênio e Nitrogênio, através de medidas simultâneas de atrito interno (energia dissipada por oscilação do Pêndulo de Torção) e da dispersão dos valores reativos da constante elástica apropriada. No sistema Nb-Zr-O, o multi espectro de relaxação em função da temperatura foi analisado e foram encontrados processos de relaxação devido à reorientação induzida por tensão de um, dois e três átomos de Oxigênio em torno de um átomo de Nióbio e um átomo de Oxigênio em torno de um átomo de Zircônio. No sistema NB-Ti-O-N, foram encontrados processos de relaxação devido à reorientação induzida por tensão de um e dois átomos de Oxigênio em torno de um átomo de Nióbio e um átomo de Titânio, respectivamente; um átomo de Nitrogênio em torno de um átomo de Nióbio e um átomo de Titânio, respectivamente. Com a ajuda das relações desenvolvidas por Kramers-Krönig, foi possível prever e checar com precisão cada intensidade de relaxação através das medidas da variação relativa da constante elástica apropriada (dispersão). / Internal friction measurements have been very often used for anelastic relaxation investigation in order to detect the existence of the interstitials in metal or metal alloys. The behavior of the Nb-Zr alloys doped with oxygen and the Nb-Ti alloys doped with oxygen and nitrogen have been studied using internal friction and relative elastic constants measurements obtained simultaneously. For Nb-Zr-O system, the multi-relaxation spectrum has been analyzed and relaxation processes due to the stress-induced ordenaring of one, two or three oxygen atoms around one niobium atom and also one oxygen atom around one zirconium atom went found. For Nb-Ti-O-N system, the multi-relaxation spectrum has been analyzed and relaxation processes due to the stress-induced ordenaring of one and two oxygen atoms around one niobium and titanium atoms respectively and one nitrogem atom around one niobium and titanium atoms respectively. With aid of Kramers-Krönig relations, it was possible to preview and check with good accuracy each of relaxation measurements.

This thesis focuses on understanding the influence of defect sites in titanium dioxide that drive many types of thermal and photochemical reactions. Two of the most common defects in vacuum are titanium interstitials and oxygen vacancies. Molecular oxygen fills oxygen vacancies and creates oxygen adatoms. We broadly investigate reduction and oxidation reactions of oxygenates driven by titanium interstitials and oxygen adatoms. First, we focus on the thermal chemistry of oxygen adatoms with butyrophenone and find that it reacts with the adatoms to form a strongly bound complex. The large difference in mobility between complexed and uncomplexed butyrophenone, and the corrugated nature of the \(TiO_2(110)\) surface plane, allows a confined one-dimensional gas to persist, which is characterized by scanning tunneling microscopy (STM). Next, we focus on the reductive coupling of benzaldehyde to stilbene that is driven by titanium interstitials. The diolate intermediate of the reaction is identified by STM and the thermodynamic preference of molecular oxygen to interact with titanium interstitials is exploited to selectively reverse the benzaldehyde diolate intermediates. Additionally, we investigate the photo-oxidative coupling of methanol to methyl formate, the photo-oxidation of butyrophenone and the photo-stability of benzoate. Finally, we identify a water splitting mechanism on reduced titania that creates oxygen adatoms. We demonstrate that the photo-generated oxygen adatoms thermally react with titanium interstitials to make TiOx islands and drive the photo-oxidation of formaldehyde and butyrophenone. Methods used include temperature programmed reaction spectroscopy, STM, and density functional theory. / Chemistry and Chemical Biology

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