Orientador: Fenelon Martinho Lima Pontes / Banca: Adenilson José Chiquito / Banca: Alejandra Hortencia Miranda González / Resumo: As estruturas hierárquicas do WO3-Ag tridimensional (3D) auto-montadas foram sintetizadas através da rota hidrotérmica utilizando como soluções precursoras o ácido túngstico (H2WO4) e peróxido de hidrogênio (H2O2), adicionando diferentes quantidades de Ag. As amostras foram analisadas por difração de raios X (DRX), Microscopia Eletrônica de Varredura de Campo (MEV-FEG), análise termogravimétrica (TGA), espectroscopia micro Raman, espectroscopia no infravermelho por transformada de Fourier (FTIR), espectroscopia no ultravioleta visível UV-VIS e espectroscopia de fotoelétrons excitados por raios X (XPS). Os estudos de DRX e micro Raman mostraram que à medida que a quantidade de Ag variou de 0 a 10% em peso na solução de crescimento hidrotérmico, a fase do cristal mudou gradualmente de WO3•0,33H2O ortorrômbica para WO3 hexagonal. Os estudos de FTIR e TGA revelaram diferentes níveis de hidratação, apoiando os resultados de DRX e micro Raman. Ao controlar a quantidade de Ag na solução precursora, foram obtidos blocos de construção semelhantes a plaquetas e blocos de construção hexagonais, destacando o papel da prata no crescimento hidrotérmico dos microcristais 3D WO3•0.33H2O e WO3. Além disso, as imagens de MEV-FEG de alta magnificação mostraram que as nanopartículas de Ag estão ancoradas na superfície das estruturas hierárquicas WO3-Ag 3D. Medidas no UV-vis demonstraram que as estruturas hierárquicas 3D absorveram gradualmente mais luz quando a quantidade de Ag foi aumentada. Al... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The self-assembled three-dimensional (3D) WO3-Ag hierarchical structures were synthesized through the hydrothermal route using tungstic acid (H2WO4) and hydrogen peroxide (H2O2) as precursor solutions, adding different amounts of Ag. The samples were analyzed by diffraction X-ray diffraction (XRD), field scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), micro Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), visible ultraviolet UVVIS spectroscopy and spectroscopy Photoelectrons (XPS). XRD and micro Raman studies showed that as the amount of Ag ranged from 0 to 10% by weight in the hydrothermal growth solution, the crystal phase gradually changed from orthorhombic WO3•0.33H2O to hexagonal WO3. The FTIR and TGA studies revealed different levels of hydration, supporting the XRD and micro Raman results. By controlling the amount of Ag in the precursor solution, platelet-like building blocks and hexagonal building blocks were obtained, highlighting the role of Ag in the hydrothermal growth of the 3D microcrystals WO3•0.33H2O and WO3. In addition, high magnification FESEM images showed that Ag nanoparticles are anchored on the surface of the WO3-Ag 3D hierarchical structures. UV-vis measurements demonstrated that the 3D hierarchical structures gradually absorbed more light when the amount of Ag was increased. In addition, the energy of the band gap was decreased when the amount of Ag increased from 0% by weight (Eg = 2.65 eV) to 10% by weight... (Complete abstract click electronic access below) / Mestre454

Made available in DSpace on 2014-10-09T12:37:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:05Z (GMT). No. of bitstreams: 1 02041.pdf: 7973448 bytes, checksum: 293424e15491e6c324cc1d3a2cc034c5 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis Submitted in Fulfilment of the Requirements for the Degree Master of Technology: Chemical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / Iron oxide nanoparticles have recently become attractive for use in gas sensing, as catalysts and have also shown promise in other fields, such as biomedicine, for targeted drug delivery and cancer treatment. Despite these growing applications, the ability to produce iron oxide and one dimensional (1D) iron oxide nanoparticles on an industrial scale has proven to be a challenge. The continuous hydrothermal synthesis, (CHS), method has been proposed as the most promising method, yet the effect of the operating parameters on particle characteristics are still widely contested in the literature. One such parameter, temperature, is still widely contested on its effect on APS. To address this issue, a CHS pilot plant was constructed and commissioned. The inability to isolate certain parameters in CHS is a common shortcoming. Parameters such as temperature and flow rate are prime examples, as changing the temperature has several effects on the system resulting in a change in reaction rate, a change in density and a change in the reactor residence time while the flow rate is closely linked to the residence time and mixing conditions. A 3-level Box-Behnken factorial design method was used to statistically analyze the correlations and interactions between operating parameters (temperature, concentration and flow rate) in CHS and evaluate their resulting effect on particle characteristics, with focus on morphology. All particles were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Reactions in the presence of solvents or surfactants proved incapable of modifying particle morphology, although significant particle size reduction revealed that they were actively involved in particle growth and may be used as a further tool for controlling particle characteristics. The concentration was found to have the greatest effect on particle characteristics including a slight alteration of particle shape and a massive influence on the average particle size. The interactions between operating parameters were significant, especially in the case of temperature and concentration. The temperature and concentration were found to interact revealing three different trends on APS, offering a solution to conflicting reports in the literature. The temperature was also observed to interact favourably with the flow rate, presenting a method of increasing the PY and RC, with little change in APS and PSD. This knowledge will prove invaluable for the design of future experiments in CHS.

Made available in DSpace on 2014-10-09T12:37:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:05Z (GMT). No. of bitstreams: 1 02041.pdf: 7973448 bytes, checksum: 293424e15491e6c324cc1d3a2cc034c5 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

No description available.

Plastic strains during investment casting of single crystal Ni-based superalloys arise from differences in thermal contraction between the metal and ceramic mould-and-core. If deformation is above a critical limit, subsequent solution heat treatment of the alloy causes recrystallisation. Crack nucleation and propagation is preferred at the recrystallisation grain boundaries, and this significantly reduces the creep and fatigue properties of the alloy. The as-cast microstructure (Chapter 3) is characteristic of high temperature deformation (~1050�(), where dislocations primarily form loops and networks at the y/y' interface. This validates the process modelling performed by our collaborators. The dislocation density was found to be higher in the interdendritic areas and the dendrite cores were virtually dislocation-free, indicating that deformation occurs at temperatures close to they' solvus, which is 1250-1310�C for CMSX 4, where dislocations accumulate in the interdendritic areas that are the first to precipitate they'. Critical strains for recrystallisation were determined as a function of temperature (Chapter 3). Recrystallisation was found to be sensitive to the surface finish, where alloys with the cast surface were more prone to recrystallisation, tolerating plastic strains of 1-2% at temperatures ~1000�C. On examining the cast surface of CMSX 4, two sources of nucleation for recrystallisation were identified (Chapter 4). Firstly, micro-grains of y', 2-30 ?m deep, forming high angle boundaries with the bulk single crystal were found within the surface eutectic; these grow larger during the heat treatment and maintain high angle misorientations with the matrix. Secondly, in regions where surface eutectic is absent, the metal adheres to the mould and forms intense local deformation, 5- 20 ?m deep, during subsequent detachment. During the heat treatment local surface recrystallisation occurs, where small grains develop in orientations similar to the deformed matrix and subsequently twin to form high angle boundaries. Experimental trials show that in the presence of deformation in the bulk the nuclei in the casting surface can cause recrystallisation. By removing the cast surface with etching, recrystallisation can be completely mitigated . Recrystallisation studies on alloys varying systematically in composition (Chapter 5) show that high . Co alloys (with up to 8 wt%) are more prone to recrystallisation. Co lowers they' solvus temperature and the stacking fault energy of y. Ru, Mo and W appear to have no direct effect on recrystallisation. The nucleating grains for recrystallisation form in orientations similar to the deformed matrix, and subsequently twin to form high angle boundaries and proliferate within the deformed microstructure. They' phase and topologically close packed phases hinder grain boundary migration.

The penetration of thin aluminum oxide films by liquid bismuth was studied between 350 and 500°C. A correlation was sought between the type and thickness of the oxide film, and the time and nature of the attack. Mechanical and electropolished, and anodized films of different thicknesses were exposed to liquid bismuth either by immersing a plate in the liquid and measuring the contact angle or by melting a drop of bismuth on a specific area of a plate. Electropolished surfaces had no resistance to attack by the bismuth. Pitting and edge attack occurred with all other surface preparations. The anodized films often separated from the aluminum under thermal stresses and allowed the bismuth to spread under the film, sometimes removing it entirely. Attempts were made to control the number and nature of defects in the oxide film, but the difficulty of this is shown by the scatter in the results. No attack on aluminum oxide itself is likely and no diffusion of bismuth through the oxide was found at the temperatures used. The conclusion was reached that the bismuth penetrated the oxide film only at points where there was a high concentration in the film of some impurity oxide (such as nickel or copper oxides) that reacts with bismuth. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

An investigation into the effect of oxygen on the three ultraviolet optical absorption bands in magnesium oxide was carried out. These peaks were located at 5.75, 5.0 and 4.40 eV within the range 212 to 350 mu. The single crystal platelets were heated in air or oxygen for increasing times at various temperatures. It was found that the increase in peak height with time followed a diffusion relation. A mechanism of formation of the centers causing the 5.75 and 4.40 eV peaks was proposed. The mechanism was based on the oxidation of iron and manganese impurities and the diffusion of magnesium to the crystal surface. The absorbing center was defined as (Fe⁺³∙VMg⁺²). From this it was shown that the diffusion process governing both the 5.75 and the 4.40 eV peaks followed the same Arrhenius relation: D=1.7 X 10⁵ e -77,000/RT cm²/sec. over the temperature range of 800 to 1100° C. No similar conclusions could be drawn concerning the 5.0 eV peak. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Efficient preparative routes to several new rhodium complexes and some iridium compounds containing sulfoxide ligands are described. Chiral sulfoxide complexes of rhodium were tested as possible catalysts for the homogeneous asymmetric hydrogenation of prochiral olefins. Also tested were chiral sulfoxide-iridium complexes as potential catalysts for H2 transfer from isopropanol to prochiral olefins and ketones. The sulfoxides used include: the monodentate ligands dimethyl (DMSO), tetramethylene (TMSO), di-n-propyl (NPSO), methyl phenyl (MPSO), and diphenyl sulfoxide (DPSO); the monodentate chiral ligands (+)-(R)-methyl-p-tolyl sulfoxide (MPTSO), (+)-(R)-t-butyl-p-tolyl sulfoxide (TBPTSO), (-)-(S)-o-tolyl-p-tolyl sulfoxide (OTPTSO), and (+)-(S)-2-methylbutyl-(S,R)-methyl sulfoxide (MBMSO); and the potentially chelating ligands meso-l,2-bis(methyl sulfinyl)ethane (MSE), (R,R)-1,2-bis(p-tolyl sulfinyl)ethane (PTSE), and (-)-(2R,3R)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulfinyl)butane (DIOS). Displacement of the labile acetone ligand from [Rh(diene)(PPh₃) (acetone)]A (diene=l,5-cyclooctadiene (COD), norbornadiene (NBD); A=PF₆ ⁻, SbF₆ ⁻ ) allows facile coordination of dialkyl or diaryl sulfoxides, and [Rh(diene)(PPh₃)L]⁺ complexes (L=DMSO,TMSO,NPSO,MBMSO,MPSO,MPTSO, and TBPTSO) have been synthesized; compounds with L=AsPh₃, py and (CO)₂ also form. Diaryl sulfoxides and DIOS coordinate, but no solids were isolated. The upfield shifts of the sulfoxide resonances (¹H nmr), reflecting shielding by the adjacent phenyl groups of PPh₃, and the decrease in v(SO) on coordination, are indicative of O-bonding in all cases. NMR data on the olefinic diene protons suggest the occurrence of some disproportionation of the mixed ligand complexes to [Rh(diene) (PPh₃)₂]⁺ and [Rh(diene)(L)2]⁺ depending on L, and the presence of 3-coordinate, and 5-coordinate (for diene=NBD only) intermediates. The hydrogenation of itaconic acid using catalysts with L=R-MPTSO or DIOS resulted in no asymmetric induction in the a-methyl succinic acid product because of disproportionation and catalysis via the bis(triphenylphosphine) system. Efficient hydroformylation of 1-alkenes is effected using [Rh(diene) (PPh₃)(CO)₂j⁺ as catalyst precursors. Aqueous isopropanol solutions of RhCl₃-3H₂O on treatment with sulfoxides provide an efficient route to RhCl₃L₃ complexes (L=DMSO, R-MPTSO,MPSO,TMSO) that contain in solution, at least for the first three systems, two S-bonded sulfoxides trans to a chloride, and an 0-bonded ligand. The 0-bonded sulfoxide is displaced by amides, amine oxides, and phosphine oxides to give mer- RhCl₃ (DMSO)₂(OL) complexes. The DMSO cis to OL in RhCl₃DMSO)₂(OL) or RhCl₃ (DMSO)₃(OL) can be identified in the nmr by using the ring current shielding effects of OPPh₂Me. RhCl₃L₃ react with H₂ (1:1) in base promoted reactions to yield Rh(I) presumably via undetected Rh(III)-H species. RhCl₃.3H₂O reacts with DPSO in isopropanol to give Rh(I) as the chloride-bridged species [RhCl(DPSO)₂]₂. The reaction with NPSO gives a Rh(I) dimer (indirect evidence) and a Rh(III) product, isolated as [H(NPSO)₂][RhCl₄(NPSO)₂] containing a symmetrical hydrogen-bridged cation. A crystal structure of trans-[H(DMSO)₂] [RhCl₄(DMSO)₂] reveals the short oxygen-oxygen distance (~2.45Å) in the cation expected for strong H-bonds. Such cations display intense v[sub a] (OHO) bands at 1700- 1100 and 900-600 cm⁻¹. The air-sensitive complexes [RhCl(C₈H₁₄)(DPSO)]₂, [RhCl(DMS0)₂]₂, [RhCl(DIOS)₂]₂ and [RhCl(MPSO)(PPh₃)]₂, isolated from [RhCl(cyclooctene)₂]₂/ ligand solutions, contain very labile Rh-S bonds that do not appear to involve Rh(dπ)+S (d-π) backbonding. Attempts at generating hydride complexes by oxidative addition of H₂ or HCl to Rh(I) resulted normally in either metal formation or sulfoxide reduction; even in the presence of prochiral olefins these complications occurred rather than catalytic asymmetric hydrogenation. The compound [Rh(MSE) ₂]PF₆ was isolated from the reaction of H₂ with [Rh(NBD) ₂]PF₆, and 2 MSE in alcohol solutions. The compounds mer-IrCl₂(H)(DMS0)₃ with trans chlorides, and mer-IrCl(H)₂(DMSO)₃ with cis hydrides, were obtained from oxidative addition reactions involving HCl and H₂, respectively, with [IrCl(C₈H₁₄)₂]₂ in DMSO. The former catalyzes the efficient selective reduction of α,β-unsaturated aldehydes to the unsaturated alcohols. Attempts at asymmetric synthesis using as catalysts IrCl₃H₂0/chiral sulfoxide mixtures failed. A simple bent M<-O=L vibrational model is used to estimate from v(M0) and v(S0) the force constants F[sub MO] and F[sub OL] using data for seventy 0-bonded DMSO, DMSO-D₆, and TMSO complexes of several metals. The correlation F[sub OL]=-(1.24±0.12)F[sub MO].+(8.78±0.12) mdyne/Å appears to hold for all metal complexes excepting those of group IVA and VA elements. / Science, Faculty of / Chemistry, Department of / Graduate

Orientadores: Richard Landers, Abner de Siervo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T07:30:46Z (GMT). No. of bitstreams: 1 Carazzolle_MarceloFalsarella_D.pdf: 4221752 bytes, checksum: 6156780985399992bdd317898895589e (MD5) Previous issue date: 2014 / Resumo: O descobrimento de novos materiais com alta constante dielétrica e compatível com o atual processo de fabricação de dispositivos CMOS (complementary metal-oxide-semiconductor) tem sido uma grande barreira tecnológica que está impedindo as indústrias de semicondutores a manter o contínuo aumento de desempenho desses dispositivos. O principal limitante da atual tecnologia está sendo os efeitos indesejáveis de corrente de fuga através do dielétrico que ocorrem devido à contínua miniaturização dos transistores. Além de esse novo material possuir uma alta constante dielétrica também é fundamental que ele tenha uma estabilidade térmica sobre a superfície de Si ou Ge, uma vez que o processo de fabricação desses CMOS requererem tratamentos térmicos necessários para ativação dos dopantes que chegam a temperaturas da ordem de 900 oC para Si e 400 oC. O HfO2 é um excelente candidato devido a sua alta constante dielétrica mas tem apresentado problemas de estabilidade térmica sobre as superfícies de Si e Ge pois forma uma liga metálica de siliceto de háfnio em contato com o Si ou óxido de germânio em contato com o Ge. Essa tese descreve e discute os resultados de estudos sistemáticos de estabilidade térmica de filmes ultrafinos de HfO2 crescidos sobre as superfícies de Si3N4/Si nas direções cristalográficas (100) e (111) e variando as espessuras do filme de nitreto de silicio, o uso de nitreto de silício foi proposto para formar uma barreira física separando HfO2 do Si. Também foram realizados estudos de estabilidade térmica de filmes ultrafinos de HfO2 crescidos sobre as superfícies de Ge/Si(100) and Ge/Si(111), sendo que nesse caso o Ge foi crescido camada sobre camada usando o Sb como surfactante. As técnicas experimentais de XPS, ARPXS e LEED foram amplamente utilizadas e essenciais para a execução desse trabalho, especialmente em combinação com a fonte de radiação síncrotron do LNLS que permitiu a geração de espectros de alta resolução energética. Com os resultados desses trabalhos foi possível identificar uma espessura mínima do filme de Si3N4 de forma a possibilitar o seu uso como uma camada intermediária mantendo o sistema termicamente estável até 950 oC. As análises dos resultados de Ge também identificaram uma configuração termicamente estável, em especial o sistema HfO2/Ge/Si(111) não apresentou a formação da liga GeO2 durante o tratamento térmico, resultados estes atribuídos ao aumento na energia de formação do GeO2 causado pela diferença de empacotamento na direção (111) em relação a (100) / Abstract: The development of alternative high-k gate dielectrics for future complementary metal-oxide-semiconductor (CMOS) devices is indispensable in achieving both low leakage current and small equivalent oxide thickness. The thermal stability of these dielectrics on Si or Ge is a crucial issue to integrate them into CMOS, because standard device fabrication requires high temperature annealing, i.e. a dopant activation process (> 900 oC for Si and > 400 oC for Ge). HfO2 is one of the best candidates because of its high dielectric constant and high conduction band offset. On the other hand the formation of metallic Hf-silicide or GeO2 during the annealing process for activation is one of the most serious problems for Si-CMOS or Ge-CMOS, respectively. This thesis reports the results of a systematic study on the thermal stability of the HfO2 ultrathin films grown on Si3N4/Si, (100) and (111) surfaces, for different silicon nitride film thickness deposited by low energy nitrogen ion implantation technique. Also the thermal stability of HfO2 ultrathin films grown on Ge/Si(100) and Ge/Si(111) surfaces were studied as a function of annealing temperature. From these studies it was possible (1) to determine the minimum thickness of Si3N4 buffer layer to stabilize the HfO2 film up to 950 oC on top of the silicon surfaces and (2) to avoid the formation of GeO2 interlayer in the HfO2/Ge/Si(111) system probably because the crystallographic orientation of Si surface / Doutorado / Física / Doutor em Ciências