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Texto completo. Acesso restrito. p. 117–124 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-06-26T13:31:02Z No. of bitstreams: 1 222222222222.pdf: 1169758 bytes, checksum: 9a29ff82116535957ee24667b9b5d00c (MD5) Made available in DSpace on 2013-06-26T13:31:02Z (GMT). No. of bitstreams: 1 222222222222.pdf: 1169758 bytes, checksum: 9a29ff82116535957ee24667b9b5d00c (MD5) Previous issue date: 2013 Solid acid–base sensors were prepared by encapsulating alizarin red pH indicator within a silica matrix using the sol–gel method with four different routes: (1) non-hydrolytic, (2) acid catalyzed, (3) basic catalyzed and (4) without catalyst hydrolytic. The silica–indicator interactions in the resulting materials were investigated by cyclic and differential pulse voltammetry. Ultraviolet–visible photoacoustic spectroscopy was also employed in the characterization. The absorption band shift (49 to 72 nm, depending on the route) between neat alizarin and alizarin encapsulated within the silica network was observed. The electrochemical behavior and the pH indicator interactions with the silica network were dependent on the nature of the employed sol–gel route. For the sensors prepared by the acid and hydrolytic (without catalyst) routes, the interactions with the silica network occurred through alizarin red hydroxyl groups. For the basic route, different cathodic and anodic peaks were observed depending on the pH, suggesting different phenomena during preparation or analysis. In the non-hydrolytic route, it is possible that the quinone form of alizarin red was consumed during the process. The voltammetric results were related to the sensor performance, whereby the acid route produced a solid sensor with the shortest response time, probably because alizarin structure was preserved after the synthetic process. Salvador

Texto completo: acesso restrito. p. 256–263 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-02-13T11:49:05Z No. of bitstreams: 1 Zenis Rocha.pdf: 702039 bytes, checksum: 28a2396b4c23f380be2313391561c1dc (MD5) Made available in DSpace on 2014-02-13T11:49:05Z (GMT). No. of bitstreams: 1 Zenis Rocha.pdf: 702039 bytes, checksum: 28a2396b4c23f380be2313391561c1dc (MD5) Previous issue date: 2011 Solid acid–base sensors were prepared by encapsulating two pH indicators (brilliant yellow or acridine) within a silica matrix by the sol–gel method using three different routes: (1) non-hydrolytic, (2) acid catalyzed and (3) base catalyzed. The interactions of the silica-indicator with the resulting materials were then investigated by cyclic and differential pulse voltammetry. Complementary, ultraviolet–visible, photoacoustic spectroscopy was employed for the characterization of the interactions by monitoring the band shifts (bathochromic or hypsochromic, depending on the sol–gel route) between the neat pH indicators and those encapsulated within the silica network. Furthermore, X-ray photoelectron spectroscopy showed that the N 1s binding energy in brilliant yellow was shifted for the material resulting from the acid route. The electrochemical behavior and the pH indicator interactions with the silica network were dependent on the nature of the employed sol–gel route. For the sensors prepared with acridine, the interactions with the silica network took place through the nitrogen group from the pyridinic ring. For the brilliant yellow indicator, different behaviors were observed depending on the route, suggesting different processes during preparation or analysis. For the basic catalyzed and non-hydrolytic routes, it was not possible to assign a specific interaction. Nevertheless, it seemed that interactions might have taken place through the hydroxyl and/or sulphonic groups. Furthermore, for the brilliant yellow sensor prepared through the acid route, it was possible to show that the interaction probably or partially occurred through the azo groups.

This paper evaluates the adsorption capacity of zirconocene-based silica materials in the pre-concentration of antimicrobians (tetracycline, sulfamethoxazole and trimethoprim) in aqueous medium. These materials were prepared by grafting the zirconocene onto silicas pre-treated at different temperatures. The retention capacity of these materials was evaluated by off line SPE and HPLC-UV and the proposed methodology was validated in ultrapure, tap and river water. The recovery for tetracycline was 72% (in the solid phase A) and, for sulfamethoxazole and trimethoprim was 68 and 95% in the commercial C18, respectively. The target antimicrobians were not detected in the Arroio Dilúvio (Porto Alegre - RS).

Trabalho completo: acesso aberto, p.505–512 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-05-09T16:35:05Z No. of bitstreams: 1 (5)1-s2.0-S1385894710000604-main.pdf: 997792 bytes, checksum: 2d0cc710be5193173196d3a550e8f80e (MD5) Made available in DSpace on 2012-05-09T16:35:05Z (GMT). No. of bitstreams: 1 (5)1-s2.0-S1385894710000604-main.pdf: 997792 bytes, checksum: 2d0cc710be5193173196d3a550e8f80e (MD5) Previous issue date: 2010-04-15 The degradation of dyes (methylene blue, direct blue 71, direct yellow 8) by a series of titania-supported catalysts generated in situ via the impregnation of TiCl4 onto a series of zeolite, which was synthesized using rice husks as the silicon source, was individually evaluated. After calcination, the resulting supported catalysts were characterized by X-ray diffraction spectrometry, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy, small angle X-ray scattering and differential pulse voltammetry. The titania generated is present in the anatase phase, without affecting the zeolite framework. Catalyst activity was shown to be comparable to that of the commercial P-25 catalyst after 1 h of UV light exposition. Monitoring the catalyst performance of several batches of material showed that P-25 provided the highest photodecomposition until the third cycle. On the other hand, the activity of the in situ-supported titania catalyst, in spite of showing lower catalytic activity, remained roughly constant up to the fifth cycle. This suggests that the catalyst generated in situ is more suitable for both filtering and reuse. Salvador

Trabalho completo: acesso restrito, p. 114–122 Submitted by Bruna Lessa (lessbruna@gmail.com) on 2012-06-19T13:43:26Z No. of bitstreams: 1 (77)1-s2.0-S0926860X0900667X-main.pdf: 597622 bytes, checksum: 69c78cbd0366af80dd8a0da61536eba3 (MD5) Made available in DSpace on 2012-06-19T13:43:26Z (GMT). No. of bitstreams: 1 (77)1-s2.0-S0926860X0900667X-main.pdf: 597622 bytes, checksum: 69c78cbd0366af80dd8a0da61536eba3 (MD5) Previous issue date: 2009-11-30 The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxide SiO2–WO3 using a non-hydrolytic sol–gel route. The catalyst and oxide matrix were characterized by complementary techniques (Rutherford backscattering spectrometry, ultraviolet–visible diffuse reflectance and infrared transmission spectroscopy, differential pulse voltammetry, adsorption–desorption of N2, and X-ray diffraction). The catalyst performance in terms of catalytic activity and polymer properties was evaluated by ethylene polymerization. Catalyst characterization suggested that the entrapped complex exhibited lower Zr electronic density than the corresponding unsupported metallocene. The polymerization results also revealed that this low Zr electronic density is optimized in terms of complex activation with low MAO concentration (low [Al/Zr] ratio) and reactivity. This fine tuning results in a catalyst system that is active with a low [Al/Zr] ratio and that achieves high catalytic activity. The results demonstrate that the entrapping method allows the generation of a catalyst system in which part of the activation process is attributed to the support. In this sense, the support may partially play MAO functions by stabilizing the active catalytic species.

Acesso restrito: Texto completo. p. 88-101 Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-05-11T12:32:46Z No. of bitstreams: 1 __ac.els-cdn.com_S092686...ba98c6b3a6ff88921a34c06e36241.pdf: 740634 bytes, checksum: d36f2a6df06f6aeb1e674635e8c66570 (MD5) Made available in DSpace on 2012-05-11T12:32:46Z (GMT). No. of bitstreams: 1 __ac.els-cdn.com_S092686...ba98c6b3a6ff88921a34c06e36241.pdf: 740634 bytes, checksum: d36f2a6df06f6aeb1e674635e8c66570 (MD5) Previous issue date: 2009 Bis(cyclopentadienyl)zirconium dichloride was immobilized within binary oxides of SiO2–TiO2 via a non-hydrolytic sol–gel route. Different coordinatively unsaturated Ti species were identified within the oxide structure depending on the TiO2 content, which can interact with the encapsulated metallocene complex and affect its catalystic performance in ethylene polymerization. The catalysts were shown to be active in the polymerization using MAO as the cocatalyst in a low Al/Zr ratio. High molecular weight polymer was obtained, probably due to the suppression of chain termination reactions that occur by belimination. Furthermore, oxide network structures are suggested from analysis of the catalysts (via Rutherford backscattering spectrometry, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, diffuse pulse voltammetry), molecular simulation and polymerization performance.

Texto completo: acesso restrito. p. 125-134 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-10-14T13:25:59Z No. of bitstreams: 1 1-s2.0-S0926860X09000179-main.pdf: 1382827 bytes, checksum: c2fe35fcfd4ec9c8e5adef33d0b42b17 (MD5) Made available in DSpace on 2013-10-14T13:26:01Z (GMT). No. of bitstreams: 1 1-s2.0-S0926860X09000179-main.pdf: 1382827 bytes, checksum: c2fe35fcfd4ec9c8e5adef33d0b42b17 (MD5) Previous issue date: 2009 The degradation of methylene blue dye was evaluated for a series of in situ generated titania resulting from the impregnation of TiCl4 into a series of NaA zeolites, which were synthesized using alternative silicon sources, namely rice husk and chrysotile, and submitted to different treatments. The resulting catalysts were characterized by X-ray diffraction spectrometry, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy and differential pulse voltammetry. The generated titania are present in the form of anatase phase, without alteration of the zeolite framework. Homogeneous distribution of Ti is reached for up to 10 wt.% Ti, where higher contents seem to afford isolated conglomerates. The highest catalyst activity was reached with samples having 10 wt.% Ti. Catalyst activity was shown to be comparable to that exhibited by commercial P-25 after 1 h of UV light exposition. Experiments carried out in natural sunlight reached 92% decomposition of the methylene blue dye.

Texto completo: acesso restrito. p. 129-136 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-01-28T17:04:33Z No. of bitstreams: 1 1-s2.0-S1381116906013859-main.pdf: 792382 bytes, checksum: ea828a8616f7f3346df0f8ed180dda1d (MD5) Made available in DSpace on 2014-01-28T17:04:33Z (GMT). No. of bitstreams: 1 1-s2.0-S1381116906013859-main.pdf: 792382 bytes, checksum: ea828a8616f7f3346df0f8ed180dda1d (MD5) Previous issue date: 2007 The catalyst activity of zirconium and titanium complexes bearing bidentade ligands was evaluated in ethylene polymerization at different experimental conditions with methylaluminoxane (MAO) as the cocatalyst. The best activity was achieved for dichlorobis(3-hydroxy-2-methyl-4-pyrone)zirconium(IV) at Al/Zr = 2500 at 60 °C. Conversely, dichlorobis(3-hydroxy-2-methyl-4-pyrone)titanium(IV) exhibited a higher catalyst activity at lower Al/Ti ratio and temperature. According to 1H NMR analysis, two stereoisomers are present for the zirconium complex. Electrochemical analyses evidenced a higher stability in the reduction of Zr(IV) in comparison to the analogous Ti(IV) complex. The cyclic voltammogram of the Ti complex in the presence of MAO and ethylene shows a potential shift to lower values, suggesting the formation of the Ti cationic species, which might be stabilized by ClMAO−. For the Zr complex in the presence of MAO, stabilization of the active species takes place only in the presence of an ethylene atmosphere.

Texto completo: acesso restrito.p.96–101 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-11-07T11:21:01Z No. of bitstreams: 1 Lílian Simplício.pdf: 316650 bytes, checksum: 5851e02d53e46b1105b105bc9f71bc46 (MD5) Made available in DSpace on 2013-11-07T11:21:02Z (GMT). No. of bitstreams: 1 Lílian Simplício.pdf: 316650 bytes, checksum: 5851e02d53e46b1105b105bc9f71bc46 (MD5) Previous issue date: 2005 The ethylene polymerization using TpMs*TiCl3 (1) (TpMs* = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)−) and TpMsTiCl3 (2) (TpMs = HB(3-mesityl-pyrazolyl)3−) was performed in toluene or hexane at 60 °C in the presence of MAO or TiBA/MAO (1:1) as cocatalysts. Higher activities were found for the polymerization reactions carried out in hexane, and using a combination of TiBA/MAO as cocatalysts. Absorciometric measurements in the UV–vis region and cyclic voltammetric have shown that such complexes when activated by MAO were not stable. Measurements carried out in the presence 1-hexene have demonstrated the necessity to add the cocatalyst in the presence of an olefin, i.e., ethylene or hexene-1 in order to stabilize the active species. Furthermore, these studies have revealed that after the activation process most of Ti remains as TiIV.

Texto completo: acesso restrito.p.96–101 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-11-07T11:21:01Z No. of bitstreams: 1 Lílian Simplício.pdf: 316650 bytes, checksum: 5851e02d53e46b1105b105bc9f71bc46 (MD5) Made available in DSpace on 2013-11-07T11:21:02Z (GMT). No. of bitstreams: 1 Lílian Simplício.pdf: 316650 bytes, checksum: 5851e02d53e46b1105b105bc9f71bc46 (MD5) Previous issue date: 2005 The ethylene polymerization using TpMs*TiCl3 (1) (TpMs* = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)−) and TpMsTiCl3 (2) (TpMs = HB(3-mesityl-pyrazolyl)3−) was performed in toluene or hexane at 60 °C in the presence of MAO or TiBA/MAO (1:1) as cocatalysts. Higher activities were found for the polymerization reactions carried out in hexane, and using a combination of TiBA/MAO as cocatalysts. Absorciometric measurements in the UV–vis region and cyclic voltammetric have shown that such complexes when activated by MAO were not stable. Measurements carried out in the presence 1-hexene have demonstrated the necessity to add the cocatalyst in the presence of an olefin, i.e., ethylene or hexene-1 in order to stabilize the active species. Furthermore, these studies have revealed that after the activation process most of Ti remains as TiIV.

Orientador: Heloise de Oliveira Pastore Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química Resumo: Diversos alquilamônios-AlPO-kanemitas foram preparados e caracterizados de forma a apresentar distâncias interlamelares diversificadas devido à presença de diferentes quantidades de íons n-butilamônio e n-dodecilamônio. Esses materiais lamelares reagiram com diferentes metalocenos e foram caracterizados, confirmando o ancoramento dos organometálicos e a integridade dos suportes. Um segundo teste foi realizado ancorando-se o cocatalisador seguido do metaloceno. Neste caso, o processo causou mudanças químicas nos orgânicos do suporte e desfolhamento de parte do sólido. Este estudo teve como objetivo avaliar, pela primeira vez, o desempenho dessas amostras, pela primeira vez, em polimerização in situ de eteno e propeno e estudar a influência das diferentes distâncias interlamelares dos suportes, concentração do catalisador, temperatura de síntese e pressão do monômero na atividade dos sistemas. Os polímeros obtidos foram caracterizados quanto à variação das propriedades térmicas e morfológicas devido à presença do suporte disperso nos polímeros formados. Os dados mostram que os novos sistemas catalíticos apresentam boas atividades para polimerização das olefinas e são eficazes na produção de nanocompósitos: no caso do metaloceno suportado, pelo processo de polimerização intercalada no alquilamônio-AlPO-kanemita e no caso do cocatalisador-metaloceno suportado, por esses materiais se encontrarem desfolhados no início do processo de polimerização. O aumento do espaço interlamelar favorece altos valores de atividade. O aumento da temperatura de síntese gera aumento na velocidade de conversão de propeno em polypropylene. Já um aumento da pressão, afeta negativamente a atividade. As polimerizações com catalisadores suportados produziu polietileno com maiores e polipropileno com menores massas molares, mas ambos os polímeros apresentaram redução na polidispersidade em comparação com o polímero homogêneo. A presença das lamelas gerou alteração nas propriedades térmicas dos polímeros. Houve diferentes graus de desfolhação das lamelas nas matrizes poliméricas, dependendo da atividade apresentada pelo sistema catalítico correspondente Abstract: Several alkylammonium-AlPO-kanemites were prepared and characterized to display diverse interlayer distances due to the presence of variable amounts of n-butylammonium and n-dodecylammonium ions. These layered materials reacted with different metallocenes and were characterized, confirming the organometallics anchoring and the support integrity. A second essay was performed anchoring the cocatalyst followed by the metallocene. In this case, the process caused chemical changes and delamination of part of the solid. This study aimed at evaluating, for the first time, the performance of these samples on in situ polymerization of ethene and propene and to study the influence of the different support interlayer distances, catalyst concentrations, syntheses temperatures and monomer pressures on the activity of the systems. The obtained polymers were characterized by the variation of thermal and morphological properties due to the presence of disperse support in the formed polymers. The data showed that the new catalytic systems presents good activities for olefin polymerizations and they are effective in producing nanocomposites: in case of the supported metallocene, by the process of intercalated polymerization in alkylammonium-AlPO-kanemites and in the case of the supported cocatalyst-metallocene, due to these materials been found delaminated in the beginning of polymerization process. The increase in the syntheses temperatures acted to increase the conversion velocity of propene in polypropylene. Contrarily, pressures increase adversely affects the activity. The polymerizations with supported catalysts produced polyethylene with higher molar masses and polypropylene with lower molar masses, but both polymers showed reduction of the polydispersities in comparison with the homogeneous polymer. The presence of the layers generated changes in the thermal properties of the polymers. There are different degrees of delamination of the layers in the polymer matrices, depending on the activity displayed by the corresponding catalytic system Doutorado Físico-Química Doutora em Ciências CAPES

The aluminum alloy AA2024-T3, u sed extensively in the aerospace industry, dueto the heterogeneous microstructures intentionally designed to optím ize the m echanical properties, is very susceptible to localízed corros ion. In order to preven! the corros ion several surface treatments have been investigated to replace the chromate treatment and, in thís way, sílica based films can be regarded as a promising alternatíve. The aim ofthis work ís the obtaíníng, development and characterízation offilms vinyltrímethoxysilane (VfMS) combíned wíth tetraethylorthosílícate (TEOS) or y-glycídoxypropyltrímethoxysílane in the presence and absence of ethylenedíamíne tetrametílene phosphoníc a cid (EDTPO) as pretreatments agaínst corros ion of alumínum alloy AA2024-T3 in NaCI 0.05 mol L-1. Furthermore, ít was investígated the effect of addíng clayto sol-gel hybríd matríx and sílica nanoparticles to the matrix of VfMS/GPTMS films containing EDTPO. Different ratios of precursor and silica concentrations of phosphonic acid andel ay were evaluated. The anticorrosíve properties ofthe alloycoated with the modífied sílíca films were studied using electrochemical impedance spectroscopy (El S) after different immersion times. The chemical structure ofthe films and the starting solutíons were characterízed by ínfrared spectroscopy (FT-IR), whíle the morphology and com posítion of the film s were examíned on usíng Scanníng Electron Microscopy (SEM), Energy Dispersive Spectroscopy X-Ray (E O X) and 1 or Photoelectron Spectroscopy X-Ray (XPS). The results obtained were posítive for the corros ion protectíon of AA2024 using the coatings obtaíned by the sol-gel method and modífied with phosphonic a cid. Mer optimization ofthe coatings of silica and silica/phosphonic acid we applied !he bes! systems as anticorrosíve pretreatments and adhesion promoters for one epoxy primer paínt. Accelerated corros ion tests allowed check the beneficia! action ofthe silica layer as anchoring system for the epoxy paint. lt was found that the systems composed by: silica/epoxy paint and silica + phosphonic acid/epoxy paint and silica/ epoxy paint modified with conducting polymer provide effective corros ion protection for the alloy AA2024-T3. The results deríved from the present thesis have been accepted or have been sent for publicatíon in ínternational journals and also reported in sorne international congresses, as we point below: [1] V. Dalmoro, J . H. Z. dos Santos, E. Armelin, C. Alemán, O. S. Azambuja, Phosphonic acid/silica-based films: A potential treatm en! for corros ion protection, Corros. Sci. 60 (2012) 173-180. [2] V. Dalmoro, J. H. Z. dos Santos, E. Armelín, C. Alemán, D. S. Azambuja, A synergistic combination oftetraethylorthosilicate and multiphosphonic acid offers excellent corros ion protectíon to AA1100 aluminum alloy, Appl. Surf. Sci . 273 (2013) 758-768. [3] V. Dalmoro, J . H. Z. dos Santos, l. M. I.M. Baibich, E. Armelin, C. Alemán, O. S. Azambuja Cooperatíve effect between VfMS/TEOS and phosphonic acid for corros ion protection of AA2024, Submitted, 2013. [4] V. Dalmoro, J. H. Z. dos Santos, E. Armelín, C. Alemán, D. S. Azambuja, Organosílane and Montmorílloníte-based hybríd films produced by sol-gel: A potencial treatrnent for corros ion of AA2024, Manuscript on preparation, 2013. [5] V. Dalmoro, J. H. Z. dos Santos, E. Armelin, C. Alemán, D. S. Azambuja, Characterization ofTEOS/phosphoníc acíd films, 63rd Annual Meeting of lnternatíonal Socíety of Electrochem ís try 19-24 August 2012, Prague, Chech Republíc, A liga de alumínio AA2024-T3, extensivamente empregada na indústria aeronáutica, devido as microestruturas heterogêneas intencionalmente desenvolvidas para otimizar as propriedades mecânicas é susceptível a corrosão localizada. Com o intuito de prevenir a corrosão vários tratamentos de superfície têm sido investigados para substituir o tratamento de cromatização, e os filmes a base de sílica podem ser considerados como uma alternativa promissora. O objetivo deste trabalho é a obtenção, desenvolvimento e caracterização de filmes de viniltrimetoxisilano (VTMS) combinado com tetraetilortosilicato (TEOS) ou γ-glicidiloxipropiltrimetoxisilano (GPTMS) na presença e na ausência de ácido 1,2-diaminoetanotetrametileno fosfônico (EDTPO) como pré-tratamentos contra a corrosão da liga de alumínio AA2024-T3 em NaCl 0,05 mol L-1. Além disso, foi investigado o efeito da adição de argila na matriz híbrida sol-gel e de nanopartículas de sílica na matriz VTMS/GPTMS contendo EDTPO. Diferentes razões de precursores de sílica e concentrações de ácido fosfônico e de argila foram avaliadas. As propriedades anticorrosivas da liga com os filmes foram estudadas usando espectroscopia de impedância eletroquímica (EIS) após diferentes tempos de imersão. A estrutura química dos filmes e das soluções de partida foi determinada por espectroscopia de infravermelho (FT-IR), enquanto que a morfologia e composição dos filmes foram examindas através de Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Energia Dispersiva de Raios-X (EDX) e/ou Espectroscopia Fotoeletrônica de Raios-X (XPS). Os resultados alcançados foram satisfatórios para a proteção contra a corrosão da AA2024 utilizando os revestimentos obtidos a partir do processo sol-gel e modificados com ácido fosfônico. Após a otimização dos revestimentos de sílica e de sílica/ácido fosfônicos estes sistemas foram avaliados como pré-tratamentos anticorrosivos e promotores de adesão de pintura epóxi comercial. Ensaios acelerados de corrosão permitiram comprovar a ação benéfica da camada de sílica como sistema de ancoragem da pintura epóxi. Foi verificado que os sistemas constituídos por sílica/pintura epóxi, sílica + ácido fosfônico/pintura epóxi e sílica/pintura epóxi modificada com polímero condutor propiciam uma efetiva proteção contra a corrosão da AA2024-T3., La aleación de aluminio AA2024-T3, que se utiliza ampliamente en la industria aeronáutica, debido a las microestructuras heterogéneas intencionadamente diseñadas para optimizar las propiedades mecánicas, es muy susceptible a la corrosión localizada. Para prevenir la corrosión diversos tratamientos de superficie han sido investigados para reemplazar el tratamiento con cromato, en este sentido las películas a base de sílice constituyen una alternativa prometedora. El objetivo de este trabajo es la obtención, desarrollo y caracterización de películas de viniltrimetoxisilano (VTMS) combinado con tetraetilortosilicato (TEOS) o γ-glicidiloxipropiltrimetoxisilano (GPTMS) en presencia y ausencia de ácido etilendiamina tetrametilenofosfônico (EDTPO) como tratamientos previos contra la corrosión de la aleación de aluminio AA2024-T3 en NaCl 0,05 mol L- 1. Por otro lado, se investigó el efecto de la adición de arcilla en la matriz híbrida y la presencia de nanopartículas de sílice a la matriz sol-gel VTMS/GPTMS que contienen EDTPO. Se evaluaron diferentes proporciones de concentraciones de sílice y precursores de ácido fosfónico y arcilla. Las propiedades anticorrosivas de la aleación recubierta con los filmes de sílice modificados se estudiaron mediante espectroscopia de impedancia electroquímica (EIS) después de diferentes tiempos de inmersión. La estructura química de los filmes y de las soluciones de partida se caracterizaron por espectroscopia de infrarrojo (FT-IR), mientras que la morfología y la composición se examinaron por microscopía electrónica de barrido (SEM), espectroscopia de energía dispersiva de rayos-X (EDX) y/o espectroscopia de fotoelectrones de rayos-X (XPS). Los resultados obtenidos son positivos para la protección contra la corrosión del AA2024-T3 con el uso de los recubrimientos preparados con el método sol-gel y modificado con ácido fosfónico. Después de la optimización de los recubrimientos de sílice y sílice/ácido fosfónico, se aplicó los mejores sistemas como tratamientos anticorrosivos y promotores de la adherencia de una pintura epoxi de imprimación. Los ensayos de corrosión acelerados permitieron comprobar la acción beneficiosa de la capa de sílice como sistema de anclaje de la pintura epoxi. Se encontró que los sistemas compuestos por: la sílica/pintura epoxi, sílica + ácido fosfónico/pintura epoxi y sílica/pintura epoxi modificada con polímero conductor proporcionan una protección eficaz contra la corrosión de la aleación AA2024-T3.

Orientador: Regina Buffon Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica 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 Química Inorgânica Mestre em Química