Biblioteca Digital

Nesse trabalho estudou-se a influência da adição de 0,5 % at. de zircônio (Zr) e gálio (Ga) nos ímãs permanentes à base de praseodímio (Pr) HD sinterizados obtidos por uma mistura de ligas. As ligas utilizadas foram: Pr12,6Fe68,3Co11,6B6Zr0,5Ga1, Pr16Fe75,5B8Zr0,5 e Pr13Fe80,5B6Zr0,5. A investigação foi realizada a partir das medidas das propriedades magnéticas e da microestrutura. Inicialmente, compararam-se as fases das ligas com as fases obtidas nos ímãs sinterizados. Posteriormente, os ímãs foram submetidos a um ciclo de tratamento térmico (de duas horas a 1000º C com resfriamento rápido até 10 horas, em seguida, de cinco horas nas mesmas condições, até 35 horas). Para o entendimento do papel de cada aditivo na fase magneticamente dura (fase Φ), foram analisadas as mudanças na microestrutura e relacionadas com as mudanças nas propriedades magnéticas. O Ga e Zr atuam como refinadores da fase Φ (matriz). O Ga atua no grão da fase Φ possibilitando a estabilidade da sua forma e melhorias das propriedades magnéticas. Para o ímã Pr14,3Fe71,9Co5,8B7Zr0,5Ga0,5 a evolução das propriedades magnéticas, após 15 h de tratamento térmico, foi: remanência de (1,25±0,02) T para (1,30±0,02) T...

A study of both zirconium and hafnium alpha-hydroxycarboxylates for analytical applications is presented, These compounds are studied by infrared spectroscopy, thermal analysis and X-ray diffractometry. dl-Mandelic, dl-p-bromomandelic and dl-2-naphthylglycolic acids are the more adequate reagents for gravimetric determinations of zirconium and hafnium, the ligands dl-2-hydroxyhexanoic and dl-2-hydroxydodecanoic acids were used for the first time and the results showed that they are also adequate reagents for the same purpose.

Liquid liquid extraction of tetravalent zirconium and hafnium from acidic chloride solutions has been investigated using 3-phenyl-4-acyl-5-isoxazolones in xylene such as 3-phenyl-4-benzoyl-5-isoxazolones (HPBI), 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI). The extraction of zirconium(IV) / hafnium(IV) shows a ion exchange mechanism: MO2+ (aq) + 2 HA (org) « MOA2 (org) + 2 H+(aq), where M = Zr(IV) / Hf(IV) and HA = HPBI or HFBPI or HTPI. The variation of the D ([MOA2] (org) / [MO2+](aq); ratio of the possible extraction equilibrium species) values with an increase of the acid / extractant concentration showed a linear plot with a slope of 2. The effect of the nature of the diluents like carbon tetrachloride, cyclohexane, n-hexane, benzene, nitrobenzene, xylene, toluene and chloroform on the extraction of zirconium(IV) / hafnium(IV) has been studied. The extraction behavior of zirconium(IV) / hafnium(IV) was also compared with that of other metal ions like titanium(IV), aluminium(III) and iron(III), which can be generally associated with the metal ions studied.

99mTc may be produced from 99Mo/99mTc zirconium molybdate gel generators. These gels are part of the generator matrix and their chemical and physical characteristics directly influence the generator performances. In this work zirconium molybdate gels were synthesized under different preparation conditions and characterized by TGA, IR and INAA. Our goal was to investigate and correlate generator performance with the physical-chemical properties of the gel. The two factors studied were the molybdate solution pH and the preparation conditions of the zirconyl salt solutions. Several polymolybdate and zirconium species can be formed in solution which can inhibit or favor the zirconium molybdate gel formation or the insoluble polymolybdate-rich and zirconium oxy-hydroxide phases. The 99Mo/99mTc gel generator performance is directly correlated with gel structures. More regular network gels present lower generator performances compared to gels with more flexible random framework. The physico-chemical properties of the gels as well as their behavior as technetium-99m generators are presented and discussed.

Shadow corrosion of zirconium alloy fuel cladding in BWR environments, the phenomenon in which accelerated corrosion is experienced when the cladding surface is in close proximity to other metals, has become a potentially life-limiting issue for BWR fuel. Recent results from experimentation at MIT, Halden, and Studvik suggest that a galvanic coupling drives the phenomenon between the cladding and the adjacent material. However, the actual processes involved are not understood. One key parameter that would help in the understanding of the phenomenon would be a measurement of the actual corrosion current between fuel cladding and adjacent materials in the actual in-reactor environment. The limitations placed on the bum-up of uranium oxide fuel correlates to the amount of corrosion seen through a directly measurable oxide thickness on the waterside of the zirconium alloy cladding. This oxide corrosion product directly correlates to distance from structural components, leading to the effect commonly referred to as shadow corrosion. In recent experiments, Studvik determined that there are large ECP differences associated with Inconel and zirconium alloys that correlate to increased galvanic current density when the materials are coupled.; (cont.) In this thesis research...

Im Rahmen dieser Arbeit wurden die Synthese und die Stabilitäten von neuen Oxidnitriden im System der Zirconium-Scandium-Oxide untersucht. Schwerpunktsmäßig sollte untersucht werden, ob in diesen Verbindungen Zirconium und Scandium in den Kationengittern und Sauerstoff und Stickstoff in den Anionengittern ausordnen. Auftretende Überstrukturen hervorgerufen durch eine Fehlstellordnung sollten ebenso erfasst werden. Dazu wurden die Proben einmal mittels Neutronenbeugung und zum anderen mit Röntgen-Pulverdiffraktometrie untersucht. Die Stabilität der Verbindungen wurde durch das Erfassen ihres Zersetzungsverhaltens mit in situ Methoden wie der zeit- und temperaturaufgelösten Röntgenbeugung und durch thermogravimetrische Untersuchungen erfasst. Bis zu einer Temperatur von 1200 °C ergibt sich die Bildung von verschieden Produkten mit einer Fehlstellenordnung innerhalb der Fluoritstruktur. Die Bildung solcher Oxidnitride unter NH3 Atmosphäre aus Zr50Sc12O118 beginnt zwischen 760°C und 780°C mit der Nitridierung des kubischen Zr50Sc12O118 . Dabei wird zunächst Zr50Sc12O109N6 und bei höherer Temperatur 780 °C Zr50Sc12O82N24 gebildet. Beide Produkte sind isostrukturell mit den Verbindungen Zr10Sc4O26 (MX1.86) und Zr3Sc4O12 (MX1.71)...

Zirconium alloys have been widely used in the CANDU (CANada Deuterium Uranium) reactor as core structural materials. Alloy such as Zircaloy-2 has been used for calandria tubes; fuel cladding; the pressure tube is manufactured from alloy Zr-2.5Nb. During in-reactor service, these alloys are exposed to a high flux of fast neutron at elevated temperatures. It is important to understand the effect of temperature and irradiation on the deformation mechanism of zirconium alloys. Aiming to provide experimental guidance for future modeling predictions on the properties of zirconium alloys this thesis describes the result of an investigation of the change of slip and twinning modes in Zircaloy-2 and Zr-2.5Nb as a function of temperature and irradiation. The aim is to provide scientific fundamentals and experimental evidences for future industry modeling in processing technique design, and in-reactor property change prediction of zirconium components. In situ neutron diffraction mechanical tests carried out on alloy Zircaloy-2 at three temperatures: 100˚C, 300˚C, and 500˚C, and described in Chapter 3. The evolution of the lattice strain of individual grain families in the loading and Poisson’s directions during deformation, which probes the operation of slip and twinning modes at different stress levels...

Zirconium alloys are susceptible to engineering problems associated with the uptake of hydrogen throughout their design lifetime in nuclear reactors. Understanding of hydrogen embrittlement associated with the precipitation of brittle hydride phases and a sub-critical crack growth mechanism known as Delayed Hydride Cracking (DHC) is required to provide the engineering justifications for safe reactor operation. The nature of bulk zirconium hydrides at low concentrations (< 100 wt. ppm) is subject to several contradictory descriptions in the literature associated with the stability and metastability of γ-phase zirconium hydride. Due to the differing volume expansions (12-17%) and crystallography between γ and δ hydride phases, it is suggested that the matrix yield strength may have an effect on the phase stability. The present work indicated that although yield strength can shift the phase stability, other factors such as microstructure and phase distribution can be as or more important. This suggests that small material differences are the reason for the literature discrepancies. DHC is characterised by the repeated precipitation, growth, fracture of brittle hydride phases and subsequent crack arrest in the ductile metal. DHC growth is associated primarily the ability of hydrogen to diffuse under a stress induced chemical potential towards a stress raiser. Knowledge of the factors controlling DHC are paramount in being able to appropriately describe DHC for engineering purposes. Most studies characterise DHC upon cooling to the test temperature. DHC upon heating has not been extensively studied and the mechanism by which it occurs is somewhat controversial in the literature. This work shows that previous thermo-mechanical processing of hydrided zirconium can have a significant effect on the dissolution behaviour of the bulk hydride upon heating. DHC tests with γ-quenched...

Zirconium alloy pressure tubes are an important component in CANDU nuclear reactors. During operation these tubes can pick up hydrogen as a result of a corrosion reaction, which can eventually lead to the precipitation of a secondary, brittle zirconium hydride phase. Hydrides tend to first form at flaws (stress concentrations), and when they fracture can initiate a time-controlled crack growth mechanism known as delayed hydride cracking (DHC). Since DHC is a known failure mechanism for pressure tubes, and an ongoing concern in the nuclear industry, more fundamental knowledge is required about the behaviour of hydrides precipitated at flaws. Several approaches were employed in this thesis to better characterize the effects and behaviour of hydrides at such stress concentrations. High energy X-ray diffraction, as well as in-situ SEM testing coupled with digital image correlation, were used to map the strains around stress concentrations where hydrides were present. These studies highlighted important differences in the behaviour of the hydride phase and the surrounding zirconium. To gain greater insight into hydride morphology, neutron tomography was used in an attempt to measure the through-thickness hydride distribution at flaws. A finite element model was also developed and verified against the X-ray strain mapping results. This model provided greater insight into details that could not be obtained directly from the experimental approaches...

Zirconium and its alloys are of technical importance, finding application as a structural material in the nuclear industry. Engineering components fabricated from zirconium slowly pick-up hydrogen as a result of in-reactor corrosion, degrading the components mechanical properties as a brittle hydride phase forms. This dissertation applies high energy X-ray diffraction to directly measure the mechanical properties of zirconium hydrides in the bulk and at stress concentrations in zirconium alloys. The current study is presented as a manuscript format dissertation comprised of three manuscript chapters. Chapter 3 reports the in-situ loading of hydrided Zircaloy-2 and discusses hydride/Zircaloy-2 matrix interactions as a function of applied load. Chapter 4 reports the mechanical behavior at a fatigue pre-crack in un-hydrided Zircaloy-2, comparing the results to finite element and polycrystalline plasticity models of the crack tip. Chapter 5 reports the effect of hydrides on the notch tip strain field. The three manuscript chapters are followed by a general discussion in Chapter 6 and conclusions in Chapter 7.; Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-09-27 20:32:01.455

Résumé: Dans le but de préparer des complexes de Zr pour la catalyse homogène de la polymérisation des lactides et de l’hydroamination des olefines, l’elaboration et l’optimisation d’une méthode systématique et efficace de synthèse des ligands dikétimines ayant différents substituants alkyles (R) à la position N,N’ a été realisée. Des dikétimines (nacnacRH) symétriques ont été obtenus avec une pureté de plus de 95 % et un rendement de 65 % lorsque R = Me et des rendements allant de 80 à 95 % lorsque le groupe R = n-Pr, i-Pr, i-Bu, Bu, Cy et (+)-CH(Me)Ph. La synthèse des dikétimines ayant des substituants N-alkyls différents, dite asymétriques, donne toujours un mélange statistique de trois ligands: nacnacR,R’H, nacnacR,RH et nacnacR’,R’H qui n’ont pu être separés. Seuls les dikétimines asymétriques avec un substituant N-alkyl et un autre N-aryl (nacnacR,ArH) ont été obtenus avec des rendements plus élevés que celui du mélange statistique. Par la suite, la complexation de ces ligands bidentés au Zr, la caractérisation de ces complexes et l’investigation de la réactivité ont été étudiés. Les complexes de Zr de type (nacnacR)2ZrCl2 ont été obtenus par deux voies de synthèse principales: la première consiste à traiter le sel de lithium du ligand avec le ZrCl4. La seconde est la réaction du ligand avec les complexes neutres d’alkyl-zirconium(IV) par protonation de l'alkyle coordonné. En solution...

L'étude suivante décrit la synthèse des ligands nacnacxylH, nacnacBnH, nacnacR,RH et nacnacCyH en utilisant une méthode générale qui implique des rendements élevés et des coûts raisonnables, la complexation de ces ligands au Zr, la caractérisation de ces complexes et l’investigation de leurs réactivités. Les complexes de zirconium ont été obtenus en utilisant deux méthodes synthétiques principales : la première consiste en traitement du sel de lithium du ligand avec le ZrCl4. La seconde est la réaction du ligand neutre avec les complexes d’alkyl-zirconium(IV) par protonation de l'alkyle coordonné. Le ligand adopte deux modes de coordination avec le Zr. Une coordination 2 est observée dans les complexes octaèdriques contenant un ou deux ligands nacnac. En présence d'un autre ligand ayant une coordonnation 5, par exemple Cp ou Ind, le ligand nacnac se trouve en coordination x avec le centre métallique de zirconium. En solution, les complexes obtenus de (nacnac)2ZrX2 montrent un comportement dynamique via un « Bailar-twist » et les paramètres d'activation de cette isomérisation ont été obtenus. Le complexe octaèdrique (nacnacBn)2ZrCl2, 2c, n'a pas montré de réactivité dans la carbozirconation et son alkylation n'était pas possible par l’échange des chlorures avec les alkyles. L’analogue dimethylé (nacnacBn)2ZrMe2...

Poly(amic acid)s (PAAs) of pyromellitic dianhydride (PMDA), 4, 4'-oxydianiline (ODA), and mellitic dianhydride (MDA), PAA(PMDA-ODA-MDA), and PAAs of 4,4'- oxydiphthalic anhydride (ODPA), ODA, and MDA, PAA(ODPA-ODA-MDA), were synthesized by solution polycondensation with different anhydrides ratios. Their zirconium containing polyimides, which are atomic oxygen resistant materials with potential applications on the International Space Station, were prepared by introducing a mixed ligand zirconium complex (4-amino-N,N'-disalicylidene-l,2-phenylenediaminato) (N,N,-disalicylidene-l,2-phenylenediaminato)zirconium(IV), Zr(adsp)(dsp), onto the polymer chain as a pendant group. The attachment was accomplished by the nucleophilic substitution between the amino group in the complex and the anhydride carbonyl group in the polymer chain formed by the dehydration of adjacent carboxylic acid groups of MDA components with dicyclohexycarbodiimide (DCC). The attachment reaction was followed by the thermal imidization of the poly(amic acid) precursors. The Zr(adsp)(dsp) was chosen for its atomic oxygen resistance. The synthesized poly(amic acid)s were characterized as follows. Proton Nuclear Magnetic Resonance ( 'H NMR ) revealed the polymer backbone structures and the presence of unremoved NMP solvent. Gel Permeation Chromatography (GPC) indicated that average molecular weights of Zr pendent and nonpendent PAAs were in the range of 60...

The first soluble linear Schiff-base heavy-metal coordination polymer has been synthesized via the condensation of 1,2,4,5-tetraaminobenzene and tetrakis(salicylaldehydato)zirconium(IV) in dry dimethyl sulfoxide. The (N, N',N”,N”’-tetrasalicylidene-1,2,4,5-tetraaminobenzenato)zirconium(IV) polymer has a number-average molecular weight of up to 4.9 X 10^4 based on inherent viscosity, gel permeation chromatography, and elemental analysis. Spectral properties of this polymer indicate a structure analogous to the model compound bis(N,N’-disalicylidene-l,2-phenylenediamino)zirconium(IV). Thermal characterization of the polymer is also discussed.

The goals of this research are to synthesize novel two and four-component pendent polyimides by attaching the zirconium complex to the respective polymer backbones, and then to compare their characteristics, e.g. thermal properties, atomic oxygen resistance, and film properties, with those of previous students of Dr. Illingsworth, Derek Chow and Wei Wang. Our work focuses on increasing the atomic oxygen resistance of polyimides by increasing their pendent group concentrations. This result can best be achieved by increasing the flexibility of the polymer backbone, which also lowers glass transition temperature (Tg), improves polyamic acid solubility, and, thus, improves processibility. The novel four component "parent" polyamic acid (PAA) based on 1,3-aminophenoxybenzene (APB), 3,4'-oxydianiline (3,4'-ODA), 4,4'-oxydiphthalic anhydride (ODPA), and mellitic acid dianhydride (MADA) was synthesized in freshly dried solvent l-methyl-2-pyrrolidone (NMP), and the Zr(adsp)(dsp) pendent groups attached in the presence of dicyclohexylcarbodiimide (DCC). Portions of each solution, i.e. parent and pendent PAA, were treated with nonsolvent or cast into films. After precipitation, the parent polyamic acid and Zr(adsp)(dsp) pendent polyamic acid powders were thermally imidized using three different processing conditions: 1) 100C...

The objective of this thesis is to synthesize functionalized zirconium complex pendent polyamic acids and polyimides, then compare their characteristics, e.g. thermal properties, atomic oxygen resistance, and film properties (adhesion, flexibility, and solvent resistance). Towards this end, five different zirconium complexes were attached to the polyamic acid, which is based on 3,4'-oxydianiline (3,4'-0DA), 4,4'-oxydiphthalic anhydride (ODPA), and mellitic dianhydride (MADA), in the presence of dicyclohexylcarbodiimide (DCC). The resulting zirconium complex pendent polyamic acids and the parent polyamic acid were cast onto glass substrates, then thermally imidized by heating at 100C, 200C, and 300C for one hour each. The synthesized zirconium complex pendent polyamic acids and polyimides were characterized by Thin Layer Chromatography (TLC), Fourier Transform Infrared (FT-IR), Proton Nuclear Magnetic Resonance (H1 NMR), Gel Permeation Chromatography (GPC), Light Scattering test (LS), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Scanning Electronic Microscopy (SEM), Refractive index, and Contact Angle Measurement to investigate their adhesive properties. TLC results indicate that no free zirconium complexes remain in the polymer solutions. Spectroscopic results support the conclusion that the structures obtained are consistent with the proposed ones. Both the GPC results and LS results indicate that a moderate degree of polymerization occurred (average degree of polymerization ca. 1 00)...

The synthesis of bis(quadridentate)-zirconium (IV) complexes was completed of which two new complexes, bis(N,N'-disalicylidene-cis-1,2,diamino-cyclohexane( zirconium (IV) and bis(N,N'disalicylidene-trans-1,2-diaminocyclohexane)zirconium(IV), were deemed suitable for physical and chemical comparisons to bis(N,N'-disalicylidene-1,2-phenylenediamino)-zirconium(IV). Using H-NMR spectroscopy at low temperatures, it was determined that the interconversion of the cyclohexane moiety of bis(N,N'disalicylidene-cis-1,2-diaminocyclohexane) zirconium(IV) begins to slow whereas, the motions associated with the backbones of the other two complexes do not. Furthermore, using H-NMR spectroscopy, it was determined that heating solutions of pairs of the complexes for four days at 155 C causes the complex to exchange ligands to form mixed-ligand complexes.

Zirconium hydroxide [Zr(OH)4] was synthesized by the sol-gel method using zirconium n-butoxide and 1-butanol as synthesis precursors. A part of the synthesized material was impregnated with phosphotungstic acid (H3PW12O40) in order to evaluate the effect of this dopant agent on the thermal, textural and structural properties of zirconium oxide (ZrO2). Pure and modified hydroxides were calcined in an air flow at 400, 500 and 600°C for 3 h and afterwards were characterized by thermal analysis, infrared spectroscopy, X-ray diffraction and nitrogen physisorption. Results showed that the interaction between the heteropolyanion and zirconium oxide surface produces a stabilizing effect of the crystalline structure and delays the drastic sintering of the material caused by the thermal treatment, obtaining high specific surface areas and small crystallite size for the modified zirconium oxides.

More than 30 percent of the global demand for zircon (ZrSiC>4) is supplied by South Africa. A significant amount of the zircon is exported, and beneficiated products are then imported for industrial applications locally. Beneficiating the zircon locally could have a positive impact on the local market, since zircon is only one of many such cases. Ammonium acid fluoride serves as an alternative anhydrous fluorinating agent for zircon in the synthesis of several metal fluoridesi,2. It provides an effective dry fluorinating method and is easier to handle than hydrogen fluoride or fluorine gas. Zircon exposed to extreme plasma temperatures dissociates and becomes more reactive. The reaction of the plasma-dissociated zircon (ZrO2SiO2) with the ammonium acid fluoride (NH4FxHF, where x= 1 to 5) forms two main intermediate compounds (NH4)3ZrF7(s) and (NH4)2SiF6(s), the latter decomposing to form volatile products at relatively low temperatures, providing easy separation of the silicon and zirconium compounds. The ammonium zirconate compound decomposes to form zirconium tetrafluoride (ZrF4), which can be further manufactured into zirconium metal, to name but one product. Data on the kinetics of the reaction of ammonium acid fluoride with zircon and plasma-dissociated zircon...

The Kroll process is the traditional method of producing zirconium metal by reduction of zirconium tetrachloride with magnesium metal. This paper discusses the production of zirconium metal in a plasma reactor. Anhydrous low-hafnium ZrCl4 and Mg metal were fed continuously to a 30 kW non-transfer plasma reactor at a rate of 0.31 kg.h-1. Due to losses in the system the recovery of crude product was 77.5 %. After purification to remove unreacted feed material and MgCl2 by leaching, >98 % pure zirconium metal powder was obtained. The overall recovery of purified Zr was 74 %. The conversion efficiency of the process was 95 %.