Orientador: Miguel Angel Ramírez Gil / Coorientadora: Maria Olívia Berengue / Banca: José Vitor Candido de Souza / Banca: Miguel Adolfo Ponce / Resumo: Este trabalho apresenta e discute o uso do óxido de cério na fabricação de filmes espessos por "screen printing" para aplicações em sensores de gás. Nesse estudo o CeO2 puro foi obtido pelo método dos precursores poliméricos utilizando como resina precursora o citrato de céria. O "puff" - espuma resultante da primeira fase do tratamento térmico da resina- foi calcinado a 550, 600, 700 e 750°C. O pó foi caracterizado por termogravimetria (TG) e as propriedades estruturais, morfológicas foram avaliadas por difratometria de raios X (DRX), espectroscopia Raman, área de superfície por isotermas Brunauer, Emmett e Taller (BET) e microscopia eletrônica de varredura (MEV). A resposta sensora foi estudada em uma câmara de teste construída no Laboratório de Catálise e Superfícies do Instituto de Ciência de Tecnologia de Materiais (INTEMA) da Universidade de Mar del Plata. A TG mostrou a formação de óxido de cério a 550°C, temperatura relativamente baixa quando comparada com outros métodos. Mediante DRX todas as amostras mostraram picos correspondentes à fase pura de CeO2 o qual cristaliza em uma estrutura cúbica do tipo fluorita, entretanto, maiores temperaturas de calcinação mostraram aumento da cristalinidade e tamanho do cristalito. No espectro Raman, um forte pico em torno do 461 cm-1 foi detectado, atribuído às vibrações simétricas do Ce-O. A área de superfície BET dos pós foi de 301, 77 m2/g o que evidencia a formação de partículas muito pequenas e altamente reativas. As microgra... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This paper presents and discusses the use of cerium oxide in the production of thick films for "screen printing" for applications in gas sensors. In this study the pure CeO2 was obtained by the polymeric precursor method using as a precursor resin citrate ceria. The "puff" - resulting foam from the first stage of thermal treatment of the resin-calcined at 550, 600, 700 and 750 °C. The powder was characterized by thermogravimetry (TG) and structural, morphological were evaluated by X-ray diffraction (XRD), Raman spectroscopy, isothermal Brunauer surface area, Emmett and Taller (BET) and scanning electron microscopy (SEM) . The sensor response was studied in a test chamber built in the Laboratory of Catalysis and Surface Materials Technology Institute of Science (INTEMA), University of Mar del Plata. The thermogravimetry showed the formation of cerium oxide at 550° C, relatively low temperature compared with other methods. Upon XRD all samples showed peaks corresponding to pure CeO2 phase which crystallizes in a cubic fluorite type structure, however, higher calcination temperatures showed increased crystallinity and crystallite size. In the Raman spectrum, a strong peak around 461 cm-1 was detected, assigned to symmetric vibrations of the Ce-O. The BET surface area of the powders was 301, 77 m2 /g which shows the formation of very small and highly reactive particles. The SEM micrographs show the presence of different sizes in the form of agglomerates. The characterization of the sensor response showed that the sensors manufactured from pure CeO2 powder has a good response time, achieving better performance at 400 °C working temperature in both reducing and oxidizing atmospheres. The main feature observed was that the results are dependent on previous cycles, the system reproducibility is guaranteed when it deletes the "memory" of the system, exposing it to vacuum / Mestre

Made available in DSpace on 2014-10-09T12:49:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:36Z (GMT). No. of bitstreams: 1 09984.pdf: 10774307 bytes, checksum: a193fefe92c978f1963dcaad657ea1e2 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:00/08908-1

Made available in DSpace on 2014-10-09T12:40:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:30Z (GMT). No. of bitstreams: 1 02944.pdf: 4594113 bytes, checksum: a3a3f6866bfb45e2b9c9b02b0a6f7796 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:25:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:20Z (GMT). No. of bitstreams: 1 11266.pdf: 1081304 bytes, checksum: 3622ccd730ee40331cf2e5422faa8189 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Neste trabalho, o complexo de cério (Ce(hdacac)6·xH2O, x0-2) foi sintetizado a fim de se produzir um aditivo redutor de fuligem emitida pela queima de diesel, biodiesel e suas misturas em motores a compressão. Os complexos foram feitos a partir de um novo ligante, a 3-hexadecilpentano-2,4-diona (hdacac), que possui uma longa cadeia alquílica e o dois grupos carbonílicos em posições , permitindo a complexação de cério e sua dissolução em ambientes hidrofóbicos. Com o objetivo de se avaliar as propriedades estruturais do Ce(hdacac)6·xH2O, bem como o seu comportamento em solução, complexos com o íon Eu3+ (que apresenta propriedades luminescentes particulares) foram sintetizados. O ligante e seus complexos foram caracterizados por espectroscopia de ressonância magnética nuclear, titulação complexométrica, análise termogravimétrica, análise elementar, espectroscopia vibracional na região do infravermelho e espectroscopia de luminescência. A miscibilidade dos complexos sintetizados e a influência do Ce(hdacac)6·xH2O sobre a queima da fuligem foram estudadas. Seqüencialmente, o Ce(hdacac)6·xH2O foi adicionado aos novos combustíveis e sua capacidade redutora de fuligem comprovada em um grupo gerador, por comparação da refletância difusa de filtros expostos aos efluentes emitidos. Além disso, filmes de Langmuir-Blodgett com o Eu(hdacac)n .xH2O foram produzidos e, conhecendo-se a eficiência da hdacac na homogeneização do Eu3+ sobre a superfície investigada, comprovou-se a possibilidade de estudos futuros na produção de substratos inorgânicos com sítios de CeO2. / In the work, the complex Ce(hdacac)6·xH2O (x0-2) was synthesized in order to produce an additive capable of reducing soot, that is emitted from the combustion of diesel, biodiesel and its mixtures in compression engines. The complexes were produced from a new ligand, 3-hexadecylpentane-2,4-dione (hdacac), that has a long alkyl chain and two carbonyl groups in the position, thus allowing the complexation of cerium and its dissolution in hydrophobic environments. With the aim to evaluate the structural properties of Ce(hdacac)6·xH2O, as well as its behavior in solution, complexes with the Eu3+ ion (that has particular luminescent properties) were synthesized. The ligand and its complexes were characterized by nuclear magnetic resonance spectroscopy, complexometric titration, thermogravimetry, elementary analysis, and infrared and luminescence spectroscopies. The miscibility of the complexes and the influence of Ce(hdacac)6·xH2O on soot combustion were studied. Subsequently, Ce(hdacac)6·xH2O was added to the new fuels and its soot reducing capacity attested in a generating group by comparison of the diffuse reflectance of filters exposed to the emitted effluents. Moreover, LB films with Eu(hdacac)n .xH2O were produced and, by knowing the efficiency of hdacac in the homogenization of Eu3+ over the investigated surface, one can predict the possibility of future studies on the production of inorganic substrates having CeO2 sites.

Superhydrophobic coatings attract significant attention regarding a variety of applications, such as in friction drag reduction, anti-contamination surfaces, and recently metals corrosion protection. Superhydrophobic surfaces are known to protect metals and their alloys from natural degradation by limiting water access and its surface interaction. Non-wetting properties of superhydrophobic surfaces are attributed to their low-surface energy, in combination with their surface microtexture. Several approaches based on tailoring a microtextured surface followed by surface modification with a low-surface-energy material have been employed for developing non-wetting metallic surfaces. However, developing a durable superhydrophobic coating, in terms of mechanical abrasion, thermal and chemical stability, which could serve in harsh environments, is still an outstanding challenge. In this research work two different approaches have been employed to create durable superhydrophobic aluminium alloy surfaces. In the first approach a practical and cost-effective method, which is based on direct surface acid/base etching is used to promote desired rough microstructure on aluminium alloy. Then, a facile surface modification with chlorosilanes as a low-surface-energy compound is utilized to generate surface superhydrophobicity. The superhydrophobic aluminium alloy has a water contact angle of about 165 ± 2˚ and rolling angle of less than 3 ± 0.2˚. The developed superhydrophobic aluminium alloy surfaces shows remarkable thermal stability up to 375 ˚C for 20 min. In the second approach, a controlled hydrothermal deposition process is utilized to develop cerium oxide based coatings with well-defined microtextured surface on aluminium alloy substrates. The superhydrophobicity of the cerium oxide coatings is acquired by further treatment with trichloro(octyl)silane surface. The impacts of various hydrothermal processing conditions on surface microstructure of coatings, wettability, and ultimate corrosion protection have been also investigated. The fabricated cerium oxide based coating exhibit high level of water repellency with a water contact angle of about 170 ± 2˚ and rolling angle of about 2.4 ± 0.2˚. The superhydrophobic coatings show outstanding wear-resistance by maintaining their non-wetting properties after abrasion by #800 abrasive paper for 1.0 m under applied pressures up to 4 kPa pressure. The coatings also show remarkable chemical stability under acidic and alkaline condition and during immersion in corrosive 3.5 wt % NaCl solution for more than 2 days. They also provide excellent corrosion protection for T6-6061 aluminium alloy substrate by decreasing its corrosion rate for about three orders of magnitude. / Graduate

No description available.

No description available.

Studies various nanostructured materials have gained considerable interest within the past several decades. This novel class of materials has opened up a new realm of possibilities, both for the fundamental comprehension of matter, but also for innovative applications. The size-dependent effect observed for these systems often lies in their interaction with the surrounding environment and understanding such interactions is the pivotal point for the investigations undertaken in this thesis. Three families of nanoparticles are analyzed: semiconductor quantum dots, metallic silver nanoparticles and rare-earth oxide nanomaterials. The radical scavenging ability of cerium oxide nanoparticles (CeO2) is quite controversial since they have been labeled as both oxidizing and antioxidant species for biological systems. Here, both aqueous and organic stabilized nanoparticles are examined in straightforward systems containing only one reactive oxygen species to ensure a controlled release. The apparent absence of their direct radical scavenging ability is demonstrated despite the ease at which CeO2 nanoparticles generate stable surface Ce3+ clusters, which is used to explain the redox activity of these nanomaterials. On the contrary, CeO2 nanoparticles are shown to have an indirect scavenging effect in Fenton reactions by annihilating the reactivity of Fe2+ salts. Cadmium selenide quantum dots (CdSe QD) constitute another highly appealing family of nanocolloids in part due to their tunable, size-dependent luminescence across the visible spectrum. The effect of elemental sulfur treatment is investigated to overcome one of the main drawbacks of CdSe QD: low fluorescence quantum yield. Herein, we report a constant and reproducible quantum yield of 15%. The effect of sulfur surface treatment is also assessed following the growth of a silica shell, as well as the response towards a solution quencher (4-amino-TEMPO). The sulfur treated QD is also tested for interaction with pyronin Y, a xanthene dye that offers potential energy and electron transfer applications with the QD. Interaction with the dye molecule is compared to results obtained with untreated quantum dots, as well as CdSe/ZnS core shell examples. In another chapter of this thesis, the catalytic potential of silver nanoparticles is addressed for the grafting of polyhydrosiloxane polymer chains with various alkoxy groups. A simple one-pot synthesis is presented with silver salts and the polymer. the latter serves as a mild reducing agent and a stabilizing ligand, once silver nanoparticles are formed in-situ. We evaluate the conversion of silane into silyl ethers groups with the addition of several alcohols, whether primary, secondary or tertiary, and report the yields of grafting under the mildest conditions: room temperature, under air and atmospheric pressure.

Orientador: Italo Odone Mazali / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T22:22:44Z (GMT). No. of bitstreams: 1 Silva_IsaiasdeCastro_M.pdf: 4959698 bytes, checksum: 34689bf94c26337d3043ec67881ba30e (MD5) Previous issue date: 2015 / Resumo: Dado que o óxido de cério(IV) é um composto não-estequiométrico e que apresenta uma banda Raman sensível a mudanças na rede cristalina, utilizou-se a estratégia de oxidação e redução in situ empregando gases como agentes redutores e oxidantes para investigar as mudanças ocorridas no perfil da banda Raman do óxido de cério(IV), sintetizado em várias morfologias nanométricas com exposição específica de faces, em condições de controle da concentração de vacâncias de oxigênio não-estequiométricas. Foi observado um deslocamento para menores números de onda da freqüência do máximo da banda Raman quando a amostra se encontrava sob atmosfera redutora, e esse comportamento se mostrou reversível, de modo que a freqüência do máximo da banda deslocou-se para maiores números de onda quando em atmosfera oxidante. Esse deslocamento foi mais pronunciado na morfologia de nanobastões cominuídos, na qual predominam faces de índice {110}, que são favoráveis à formação de vacâncias de oxigênio não-estequiométricas. Ao correlacionar os resultados da espectroscopia Raman com outras técnicas sensíveis ao grau de não-estequiometria do composto, se observou aumento no parâmetro de rede na difratometria de raios X e perda de massa na determinação da capacidade de estoque de oxigênio, medida por termogravimetria, sob atmosfera redutora. As observações mostram que as responsáveis pelo deslocamento da frequência da banda Raman do óxido de cério(IV) são as vacâncias de oxigênio não-estequiométricas. Como certos espectros Raman apresentaram bandas assimétricas, a razão para tal poderia ser a ressonância de Fano, o que foi investigado variando-se a energia da radiação incidente. A razão para a assimetria não foi atribuída à ressonância de Fano, mas sim há outra banda relacionada a modos vibracionais de superfície. Por fim se comparou as atividades catalíticas dos cristais de diferentes morfologias de óxido de cério(IV) frente à oxidação de monóxido de carbono, sendo que a morfologia de nanobastões cominuídos apresentou melhor desempenho. Como o mecanismo de oxidação depende das vacâncias de oxigênio não-estequiométricas, a formação dessas é facilitada na morfologia de nanobastões cominuídos, e por isso o deslocamento da banda Raman é mais pronunciado nessa morfologia / Abstract: One remarking property of cerium(IV) oxide (CeO2) is its oxygen storage capacity (OSC). This property is related to the presence of oxygen vacancies, as CeO2 is a non-stoichiometric oxide. Once CeO2 presents only one Raman active mode, which is sensitive to changes in CeO2 lattice like the oxygen vacancies, it has been investigated the influence of oxygen vacancies over CeO2 Raman band. The crystals were synthesized in different nanometric morphologies, with exposure of specific facets. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, OSC measurements by thermogravimetric equipment and Raman spectroscopy. Besides the microscopy, all other characterizations were performed with in situ control of temperature and atmosphere. The morphology with dominant {110} facets, favorable for oxygen vacancies generation, presents lattice parameter expansion, loss of mass and Raman band maximum red-shift after reduction with hydrogen-containing atmosphere, and sequent lattice parameter contraction, gain of mass and Raman band maximum blue-shift after oxidation with oxygen-containing atmosphere. These observations present reversible behavior as the atmospheres are alternated, consequence of generation or extinction of oxygen vacancies. Thereby, the correct morphology choice for a CeO2 crystal favors oxygen vacancies generation, and once generated they result in CeO2 Raman band maximum red-shift / Mestrado / Quimica Inorganica / Mestre em Química