Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 304-323). Also available in print.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 72-75).

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaves 216-222).

Thesis (M.S.)--Rutgers University, 2007. / "Graduate Program in Physics and Astronomy." Includes bibliographical references (p. 56-57).

Techn. University, Diss., 2003--Darmstadt.

Tungsten is considered the prime candidate material for plasma facing components within fusion reactors. However, exposure of tungsten to neutron flux brings about transmutation of tungsten into by-products: Re, Os and Ta. Under increasing levels of radiation damage, irradiation induced clustering/precipitation takes place that embrittles and thus reduces lifetime of such tungsten components. This thesis was undertaken to explore this subject on a deeper level. There are three components to this study. The first part considers the effect of Re content on irradiation induced clustering. Lab-made plate W-xRe (x: 2, 5, 10 and 25at.%) alloys were exposed to 1.2, 3.9 and 33dpa, self-ion irradiated at 773K. Analysis of cluster number density and volume fraction found they increase with damage level and bulk Re content. Based on these trends and existing literature data, a hypothesis was proposed suggesting clusters originate from vacancy clusters. Also, at 33dpa, rod shaped clusters form in W-25Re alloys while spherical clusters are present in other alloys. The clusters show close correspondence with irradiation induced precipitates and appear to be precursor phase. In the second part of this thesis, the effect of Os and Ta on cluster formation and alloy mechanical properties is examined. Lab-made plate W-1Re-1Os and W-2Re-1Ta alloys were irradiated at 33dpa at 573 and 773K and compared against control W-2Re alloy. At 33dpa and 573K, the Os and Ta presence suppresses cluster formation. Both ternary alloys contain smaller cluster diameter, composition, number density and volume fraction than the W-2Re alloy. However, at 33dpa and 773K, Os and Ta have opposing effects on cluster behaviour. Os increases the cluster nucleation rate and raises irradiation hardening (compared to W-2Re). Meanwhile, Ta presence decreased cluster number density and reduced the irradiation hardening (compared to W-2Re alloy). As well, Ta showed no evidence of clustering, only Re clusters form in the W-2Re-1Ta alloy. The final aspect of the thesis analyzes the effect of material microstructure and external variables on cluster formation in W-Re alloys. Commercial wire form W-25Re alloy was irradiated at 1.2dpa at 573 and 773K as atom probe needles and bulk sample. The larger free surface on atom probe needle samples appears to act as a sink for self-interstitials and vacancies at both temperatures. The effect of grain size and dislocation density was examined by irradiating commercial W-5Re wire (0.5-1μm diameter) and plate (1-3mm diameter) samples (annealed and unannealed) to 33dpa and 573K. It was found grain boundaries and dislocations act as defect sinks at 573K. Additionally, radiation enhanced Re grain boundary enrichment was observed for first time. The effect of grain size on cluster behaviour at 773K was also analysed. Commercial wire and lab-made plate W-3Re, W-5Re and W-25Re alloys were irradiated to 33dpa at 773K. The larger grain boundary area in wire samples is suspected of acting as a sink for self-interstitials leaving more vacancies for promoting cluster formation compared to lab-made samples. The discoveries made in this thesis broaden our current understanding of irradiation induced phase formation in tungsten. Their implications on plasma facing component design are discussed as well as recommendations for improvements. Further, areas requiring further research in this field are also highlighted.

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Orientador: Regina Buffon / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T22:19:34Z (GMT). No. of bitstreams: 1 Cavalcante_JoseAriMilton_M.pdf: 906597 bytes, checksum: 1b73e383b495e63cd6c110e0cb354848 (MD5) Previous issue date: 2007 / Resumo: Os catalisadores heterogêneos à base de rênio constituem-se importantes sistemas na metátese de ésteres insaturados provenientes dos óleos vegetais. No entanto, os sistemas heterogêneos à base de rênio são ativos na metátese de olefinas funcionalizadas somente se forem combinados com um promotor do tipo SnR4 ou PbR4. Acredita-se que o promotor tem a função de formar a espécie metal-alquilideno (no caso, rênio-alquilideno) que desencadeia o ciclo catalítico. Entretanto, ainda não é compreendido o mecanismo de formação dos promotores na superfície dos sistemas de óxidos. O objetivo principal desse trabalho consistiu em tentar identificar, através da RMN-C no estado sólido, a possível formação da espécie rênio-alquilideno sobre a superfície do sistema de óxidos (2%)Re2O7/(7,5%)B2O3/SiO2-Al2O3(75%) após a interação deste com o organometálico enriquecido com C, Sn( CH3)4. Buscou-se também caracterizar as interações entre os organometálicos (SnBu4, Bu3SnH e Bu2SnH2) com o mesmo sistema de óxidos através das técnicas de RMN-C no estado sólido e de espectroscopia no infravermelho. E finalmente, procurou-se identificar a estrutura do mesmo sistema de óxidos através das técnicas de RMN Al e Si no estado sólido, espectroscopia no infravermelho e difração de raios X / Abstract: Heterogeneous rhenium catalysts are importants systems for the metathesis of unsaturated esters obtained from vegetables oils. Nevertheless, the heterogeneous rhenium systems are actives for the metathesis functionalized olefins when combined with a promoter like SnR4 or PbR4. It is believed that it leads to the formation of the alkylidene species that will start the catalytic cycle. However, the role of the promoters on oxide system surface is not well understood. The main goal of this work was to identify, via CP-MAS C NMR, a possible rhenium-alkylidene species formed by the reaction between Sn(CH3)4 and (2%)Re2O7/(7,5%)B2O3/SiO2-Al2O3(75%). The reactions of SnBu4, Bu3SnH e Bu2SnH2 with (2%)Re2O7/(7,5%)B2O3/SiO2-Al2O3(75%) were also investigated by CP-MAS C NMR and in situ FT-IR experiments. Finally, the structure of the (2%)Re2O7/(7,5%)B2O3/SiO2-Al2O3(75%) material was studied by Al and Si MAS NMR, FT-IR and X ray diffraction / Mestrado / Quimica Inorganica / Mestre em Química

In 1896, Becquerel discovered the natural radioactivity in potassium uranyl sulphate. Since then, Pierre and Marie Curie, E. Rutherford and F. Soddy all made tremendous contributions to the discovery of many other radioactive elements. The work of all these scientists has shown that all elements found in nature with an atomic number greater than 83 (bismuth) are radioactive. Artificial radioactivity was first reported by I. Curie and F. Joliot in 1934. These scientists irradiated boron and aluminium targets with a particles from polonium and observed positrons emitted from the target even after removal of the a particle source. This discovery of induced or artificial radioactivity opened up a brand new field of tremendous importance. Around the same time, the discovery of the cyclotron, deuteron and neutron by various scientists facilitated the discovery of many more artificial radioactivities. At present time more than 2700 radionuclides have been produced artificially in the cyclotron, the nuclear reactor, the neutron generator and linear accelerator. Radiopharmaceuticals are drugs that contain a radionuclide and are used for imaging if the radionuclide is a photon emitter (gamma-g or positron-b+) or for therapy if the radionuclide is a particle emitter (alpha-a or beta-b- or Auger/conversion e-). / Prof. A. Roodt