Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography : leaves 58-59. / M.S.

Thesis. 1976. B.S.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / B.S.

Orientador: Daniela Micheline dos Santos / Coorientadora: Elidiane Cipriano Rangel / Banca: Marcelo Coelho Goiato / Banca: Aldiéris Alves Pesqueira / Banca: Valentim Adelino Ricardo Barão / Banca: Dodolfo Bruniera Anchieta / Resumo: Devido ao alto conteúdo cristalino na composição da zircônia, o condicionamento com ácido hidrofluorídrico não é capaz de promover as alterações topográficas necessárias na superfície da zircônia para promover adequadamente retenção micromecânica com os cimentos resinosos. Esse fato faz com que adesão da zircônia com tais cimentos seja pequena e problemática. Atualmente, não existe um protocolo bem estabelecido para a cimentação da zircônia (Y-TZP) com cimentos resinosos. Os plasmas de baixa temperatura (PBT) podem ser uma alternativa para os problemas clínicos relacionados à adesão. O objetivo do presente estudo foi caracterizar a superfície da Y-TZP exposta ao tratamento com plasmas de metano (CH4) ou submetida à aplicação de primer para ligas metálicas e ainda a associação de ambos os métodos, além de avaliar o efeito do tratamento com PBT na força de adesão da Y-TZP com dois cimentos resinosos. Um total de 235 discos de Y-TZP (8 × 2 mm) foram divididos em 5 grupos: Co (controle, sem tratamento de superfície), Pr (primer), PBT (plasma de metano), Pr + PBT e PBT + Pr. O efeito do tipo de tratamento na energia de superfície, morfologia, topografia e composição química da Y-TZP foi investigado. Os discos foram cimentados com substratos de resina composta utilizando Panavia F2.0 e Rely X U200. A análise de força de união (n = 10) foi realizada em uma máquina de ensaio universal com velocidade de 1mm/min, antes e depois da termociclagem (5-55°C, 2.000 ciclos) nos espécimes cime... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The desirable morphologic modifications for a proper adhesive retention with resin cements is not obtained through the etching promoted by hydrofluoridic acid gel because of the high crystalline content present in the composition of zirconia material. This fact leads to a problematic and deficient adhesion between such ceramic material and resin cements. There is no established protocol for b onding zirconia (Y - TZP) with resin cements. Non - thermal plasma (NTP) may be an alternative for the clinical problems related to adhesion. The aim of the present study was to characterize the surface of Y - TZP exposed to methane (CH 4 ) NTP or coated with a layer of primer for metal alloys and the association between the two methods and to evaluate the effect of NTP treatment on bond strength between Y - TZP and two resin cements. A total of 235 Y - TZP discs (8 × 2 mm) were distributed int o five groups: Co (no surface treatment), Pr (primer), NTP (methane plasma), Pr + NTP and NTP + Pr. The effect of the treatment type on the surface free energy, morphology, topography and chemical composition of the Y - TZP discs was investigated. The discs were cemented to composite resin substrates using Panavia F2.0 or RelyX U200. Shear bond strength (n=10) analyses were performed on a universal testing machine at a cross - head speed of 1 mm/min, before and after thermocycling (5 - 55°C, 2 000 cycles) on the bonded specimens. The data were analyzed with one and three - way ANOVAs and Bonferroni tests ( α = .05). NTP affected surface energy and roughness of the Y - TZP discs. SEM - EDS and XPS analyses showed the presence of the organic thin film, which significantly improved the bond strength results when Rely X U200 was used, whereas the primer treatment was more effective with Panavia F2.0. Thermocycling significantly reduced the bond strength results...(Complete abstract electronic access below) / Doutor

No description available.

Graduation date: 2005

In order to understand better the defect structure and dynamics associated with lower valent dopants complexed with native defects in group IV oxides, In/Cd perturbed angular correlation spectroscopy was performed in ceria and zirconia. Examining the orientation symmetry axis of defects in ceria single crystals at low temperature has allowed the identification of a cadmium with a bound near-neighbor oxygen-vacancy complex as well as a complex involving a cadmium with two opposing, near-neighbor oxygen vacancies. The orientation of the symmetry axis of a third complex is reported; however, this information is not sufficient to identify it. Complementing these low temperature studies, the dynamics of the cadmium/oxygen-vacancy interaction in zirconia at high temperatures was studied. The motion of the oxygen vacancy at high temperatures results in a damping of the PAC signal. This damping is not well characterized by the heuristic Marshall-Meares PAC fitting function, and a model is proposed to fit the data in terms of three physical parameters associated with the vacancy's motion. These parameters are the rate at which a bound oxygen vacancy hops among equivalent sites about the probe, the rate at which a bound vacancy detraps, and the rate at which a vacancy is trapped by cadmium. Fits of individual spectra using this model give respective activation energies of 0.3-0.6 eV, 0.9-1.6 eV, and 0.4-0.6 eV. The uncertainty in these energies can most likely be reduced by fitting spectra from multiple temperatures simultaneously. Despite the large uncertainty in the fitted energies, the values are physically reasonable and indicate that the model adequately describes the motion of the oxygen vacancy about cadmium. / Graduation date: 1997

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references. Also available in electronic version.

The generation of electricity in light water nuclear power plants uses zirconium alloys as the primary containment and cladding of the nuclear fuel. The environmental impacts of the production of zirconium alloys have been analyzed form a lifecycle perspective. From the mining of the zirconium-bearing mineral zircon to the finished zirconium alloy tube. A qualitative study indentifying the production processes and their potential environmental impacts have been performed. A quantitative study to perform a lifecycle analysis of the zircon mining and mineral separation was carried out. The life cycle analysis for the zircon mining was compared to the current lifecycle analysis (LCA) in Vattenfall's Forsmark nuclear power plant environmental product declaration (EPD). The results showed that the additional impact on Forsmark's EPD, when including the mining of zircon, is below 0.1% of the current levels for all parameters analyzed. A lifecycle analysis for the production of zirconium metal and zirconium alloy tube could not be performed due to lack of data from the zirconium metal industry. The major direct emissions from the zircon mining industry are related to the use of fossile fuels in machinery. The major direct emissions from the zirconium metal manufactoring industry are related to the use of acids.

The experiments performed for this thesis were designed to define the primary process variables of time, temperature, and atmosphere for an engineering system that will produce metal powder from recycled nuclear fuel cladding. The proposed system will hydride and mill Zircaloy cladding tubes to produce fine hydride powder and then dehydride the powder to produce metal; this thesis is focused on the hydride formation reaction. These experiments were performed by hydriding nuclear grade Zircaloy-4 tubes under flowing argon-5% hydrogen for various times and temperatures. The result of these experiments is a correlation which relates the rate of zirconium hydride formation to the process temperature. This correlation may now be used to design a method to efficiently produce zirconium hydride powder. It was observed that it is much more effective to hydride the Zircaloy-4 tubes at temperatures below the a-B-d eutectoid temperature of 540°C. These samples tended to readily disassemble during the hydride formation reaction and were easily ground to powder. Hydrogen pickup was faster above this temperature but the samples were generally tougher and it was difficult to pulverize them into powder.

A series of bi- and tri-dentate amido phosphine ligands H[Ph-PNP] (bis(2-diphenylphosphinophenyl)amine), H[iPr-PNP] (bis(2-diisopropylphosphino- phenyl)amine), H[Cy-PNP] (bis(2-dicyclohexylphosphinophenyl)amine), H[iPr-NP] (N-(2-diphenylphosphinophenyl)-2,6-diisopropylaniline), and H[Me-NP] (N-(2-diphenylphosphinophenyl)-2,6-dimethylaniline) have been synthesized in high yield. Lithiation of these compounds with n-BuLi in ethereal solutions afforded the corresponding lithium complexes. The metathetical reactions of MCl4(THF)2 (M = Zr, Hf) with [iPr-NP]Li(THF)2 or [Me-NP]Li(THF)2 in toluene produced the corresponding [iPr-NP]MCl3(THF) and [Me-NP]2MCl2, respectively, in high yield. In contrast, attempts to prepare [Me-NP]MCl3(THF) and [iPr-NP]2MCl2 led to the concomitant formation of mono- and bis-ligated complexes, from which purification proved rather ineffective. The solution and solid-state structures of [iPr-NP]MCl3(THF) and [Me-NP]2MCl2 were studied by multinuclear NMR spectroscopy and X-ray crystallography. Treatment of PdCl2(PhCN)2 with [iPr-NP]Li(THF)2 in THF afforded dimeric {[iPr- NP]PdCl}2, which was reacted with tricyclohexylphosphine to produce [iPr-NP]PdCl(PCy3). The two phosphorus donors in [iPr-NP]PdCl(PCy3) are mutually cis as indicated by the solution NMR and X-ray crystallographic studies. Both {[iPr-NP]PdCl}2 and [iPr-NP]PdCl(PCy3) are highly active catalyst precursors for Suzuki coupling reactions of a wide array of aryl halides, including those featuring electronically deactivated and sterically hindered characteristics. The metathetical reaction of NiCl2(DME) (DME = dimethoxyethane) with [iPr-PNP]Li(THF) and [Cy-PNP]Li(THF), respectively, produced the diamagnetic nickel complexes [iPr-PNP]NiCl and [Cy-PNP]NiCl. These nickel chloride complexes were reacted with Grignard reagents to afford thermally stable nickel alkyl and aryl complexes [iPr-PNP]NiR and [Cy-PNP]NiR (R = Me, Et, n-Bu, Ph). A series of divalent nickel alkoxo, amido, thiolate complexes [iPr-PNP]NiX and [Cy-PNP]NiX (X = OPh, NHPh, SPh) were also easily prepared. Reaction of H[Ph-PNP] with Ni(COD)2 (COD = cycloocta-1,5-diene) produced the transient [Ph-PNP]NiH, which underwent COD insertion to give [Ph-PNP]Ni(£b1- cyclooctenyl). Instead, reactions of Ni(COD)2 with H[iPr-PNP] and H[Cy-PNP], respectively, afforded isolable diamagnetic complexes [iPr-PNP]NiH and [Cy-PNP]NiH without alkene insertion. The reactivity of these nickel hydride complexes was investigated.