Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-03-17T10:45:40Z No. of bitstreams: 0 / Made available in DSpace on 2015-03-17T10:45:40Z (GMT). No. of bitstreams: 0 / Desenvolveu-se neste trabalho um procedimento para incorporação de nanotubos de carbono (NTC) em uma resina fenol / epóxi a ser utilizado como matriz de um compósito de fibra de carbono. Realizando para tal, a oxidação dos NTC com o uso de micro-ondas e sua funcionalização com 3-amino-propil-tri-etoxi-silano, usado com agente de acoplamento entre a resina e o NTC. Após o processamento, como resultado da adição dos NTC na resina, obteve-se um aumento na sua temperatura de transição vítrea e uma melhora no limite de resistência à flexão e impacto. No material compósito fibra de carbono, obtido por laminação manual, onde a resina fenol / epóxi mais NTC foi usada como matriz, obteve-se o aumento do limite de resistência à tração e ao impacto, confirmado por uma análise de variância com 95% de confiança, mostrando a eficácia no tratamento dos NTC. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-06-11T17:54:41Z No. of bitstreams: 0 / Made available in DSpace on 2015-06-11T17:54:41Z (GMT). No. of bitstreams: 0 / A texturização por microusinagem a laser é uma importante alternativa para que se consiga melhorar a ligação de aderência entre materiais compósitos e o titânio, aplicados em componentes estruturais na indústria aeronáutica. A execução de texturização em chapas de titânio deve-se ao fato de que a técnica de junção preferida para muitos materiais compósitos é a ligação adesiva. Neste trabalho foram realizadas texturizações em chapas de titânio utilizando laser com pulsos ultracurtos de largura temporal da ordem de femtossegundos. Tal processo resultou em mínima transferência de calor para o material, evitando assim deformação superficial da chapa de titânio bem como a formação de material ressolidificado na região ablacionada. Estes inconvenientes ocorreram na utilização do laser chaveado com pulsos de nanossegundos. Foram executadas três tipos de texturizações utilizando laser com pulsos de femtossegundos, com variações nas distâncias entre as linhas usinadas. Pela análise das superfícies obtidas, detectou-se que a molhabilidade aumenta quando há o aumento da distância entre as linhas da texturização. Avançando nas análises, pela perfilometria óptica das superfícies texturizadas observou-se que há sensível aumento do volume disponível para penetração do adesivo estrutural quando são diminuídas as distâncias entre as linhas texturizadas. Nos ensaios de tração realizados observou-se que há o aumento da resistência ao cisalhamento da junta adesiva com a diminuição da distância entre as linhas texturizadas. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Para a bioeletrocatálise de oxidação de etanol, a alteração da superfície eletródica e a otimização do processo de imobilização enzimática se fazem necessárias. Neste cenário, as fibras flexíveis de carbono (FFC) merecem destaque, pois além de sua superfície ser facilmente modificada devido à presença de carbono sp2, as mesmas possuem alta resistência mecânica e elasticidade, combinadas com a alta condutividade elétrica e térmica. Nesta tese de doutorado, apresenta-se como obter bioeletrodos de FFC modificadas com a enzima álcool desidrogenase (ADH) NAD-dependente, visando também aprimorar a oxidação da coenzima NADH (dinucleotídeo de nicotinamida e adenina). Os resultados mostram que quando as FCF são previamente submetidas a um tratamento oxidativo em meio ácido (KMnO4/H2SO4), obtém-se bioeletrodos estáveis, robustos e com alta área superficial. Além disso, observou-se que esses eletrodos possuem grupos funcionais contendo oxigênio que auxiliam na bioeletrocatálise de oxidação do etanol. Presume-se que presença de grupos quinonas seja responsável por facilitar a regeneração da coenzima, ou seja, estes grupos atuam decisivamente na oxidação do NADH. A alta qualidade dos bioeletrodos possibilitou manter a atividade catalítica da ADH por longo prazo, propriedade essa crucial para o estudo da oxidação do etanol acoplada à espectrometria de massas (DEMS). Devido a este estudo, foi possível observar concomitantemente a regeneração da coenzima (NADH -> NAD+) e a geração de acetaldeído como produto de bioeletroxidação do etanol, ambos em estado estacionário. Em suma, o estudo aqui apresentado introduz uma abordagem que combina não só o desenvolvimento de fibras de carbono tratadas quimicamente para aplicação em bioeletrocatálise, mas também um foco inédito no acoplamento entre a espectrometria de massas e a bioeletroquímica para a resolução de mecanismos enzimáticos. / Regarding the bioelectrocatalysis of the ethanol oxidation, the electrodic surface modification and the optimization of enzymatic immobilization are necessary. In this scenario, the flexible carbon fibers (FCF) are noteworthy, because besides their surface can be modified in an easy way due the presence of carbon sp2, they have high mechanical resistance and elasticity, combined with high electrical and thermal conductivity. In this doctoral thesis, it is presented how to obtain bioelectrodes of FFC modified with the enzyme alcohol dehydrogenase (ADH) NAD-dependent, as well as to improve the oxidation of the coenzyme NADH (nicotinamide adenine dinucleotide). The results show that when FCF is previously submitted to an oxidative treatment in acidic medium (KMnO4/H2SO4), stable, robust and high surface area bioelectrodes are obtained. In addition, it was observed that these electrodes have oxygen-containing functional groups that improve the bioelectrocatalysis of ethanol oxidation. There is proposed that the presence of quinone groups is responsible for facilitating the regeneration of the coenzyme, i. e., these groups act decisively in the oxidation of NADH. The high quality of the bioelectrodes allowed it to maintain the catalytic activity of the ADH for long term, property crucial for the study of the oxidation of ethanol coupled to mass spectrometry (DEMS). By using DEMS, there were possible to observe coenzyme regeneration and the generation of acetaldehyde as a bioelectrooxidation product of ethanol, both at steady state, which were simultaneously observed. In summary, the present study introduces an to an approach that combines not only the development of chemically treated carbon fibers for application in bioelectrocatalysis, but also an unprecedented focus on the coupling between mass spectrometry and bioelectrochemistry for the resolution of enzymatic mechanisms.

Orientadores: Gustavo Paim Valença, Ricardo Vieira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-21T00:05:40Z (GMT). No. of bitstreams: 1 Oliveira_NataliaMairaBraga_M.pdf: 2188373 bytes, checksum: 7d467de1163b278869ab8a52ee898f4f (MD5) Previous issue date: 2012 / Resumo: A reação de deslocamento de gás d'água, também conhecida como water gas shift reaction (WGSR), é muito utilizada na produção de hidrogênio, por meio da conversão do monóxido de carbono em CO2 e da água em H2. No presente trabalho, catalisadores de cobre e níquel suportados em alumina ou nanofibras de carbono (NFC) foram utilizados para estudo da WGSR. Os catalisadores foram preparados através da impregnação de nitrato do metal nos suportes, sendo 5% em massa o valor nominal de teor metálico empregado. Os materiais foram secados, calcinados e caracterizados através de Microscopia Eletrônica de Varredura (MEV), Difração de Raios X (DRX), Adsorção Física de Nitrogênio e Espectrometria de Emissão Óptica por Plasma Indutivamente Acoplado (ICP OES). Depois de calcinados, os catalisadores foram carregados no reator, reduzidos e então testados na WGSR a baixas temperaturas (125 - 300 °C). Os gases que saíram do reator foram analisados online por Cromatografia Gasosa (CG). Houve produção de CO2, H2 e, provavelmente, de coque em pequenas quantidades. A pressão parcial de CO variou entre 4,64 e 11,35 kPa, e a pressão parcial de água variou entre 20,01 e 47,44 kPa. As condições de reação mais favoráveis para 5% Cu/Al2O3 foram pH2O = 38,64 kPa e pCO = 11,35 kPa, em todas as temperaturas reacionais empregadas. Já para 5% Cu/NFC as condições mais favoráveis foram pH2O = 20,01 kPa e pCO = 6,56 kPa, correspondendo a uma razão molar H2O:CO de 3,05. Outra variável testada foi corrente elétrica aplicada em 5% Ni/NFC, com o objetivo de verificar sua influência na atividade do catalisador. Entretanto, diferentes intensidades de corrente elétrica (entre -1,4 e 1,4 A) não alteraram a taxa ou a seletividade da WGSR. Dentre os catalisadores testados, 5% Cu/Al2O3 foi o mais ativo em todas as condições reacionais, devido à alta dispersão das partículas metálicas no suporte. Níquel suportado em Al2O3 se mostrou pouco ativo, porque as partículas metálicas estavam muito dispersas e, provavelmente, não foram reduzidas pelo H2. Ni/NFC e Cu/NFC apresentaram baixas conversões de CO, devido à hidrofobicidade do suporte. A energia de ativação aparente calculada para a WGSR foi de 86,05 kJ/mol para 5% Cu/Al2O3 e de 69,80 kJ/mol para 5% Cu/NFC. O mecanismo de reação proposto para Cu/NFC foi redox de cooperação e as ordens aparentes de reação obtidas foram 0,64 em relação ao CO e aproximadamente zero em relação à água / Abstract: The water gas shift reaction (WGSR) is widely used in the production of hydrogen, by the conversion of carbon monoxide into CO2 and of water into H2. In the present work, copper and nickel catalysts supported on alumina or carbon nanofibers (CNF) were used to study the WGSR. The catalysts were prepared by impregnating metal nitrate in the supports, with a nominal mass metallic content of 5%. The solids were dried, calcined and characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Nitrogen Adsorption and Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). After calcination, the catalysts were loaded into the reactor, reduced and then tested in the WGSR at low temperatures (125 - 300 °C). The gases from reactor were analyzed online by Gas Chromatography (GC). The products were CO2, H2 and, probably, small amounts of coke. The CO partial pressure varied between 4.64 and 11.35kPa, and the water partial pressure varied between 20.01 and 47.44 kPa. The most favorable reaction conditions for 5% Cu/Al2O3 were pH2O = 38.64 kPa and pCO = 11.35 kPa, for all reaction temperatures used in this work. For 5% Cu/CNF the most favorable conditions were pH2O = 20.01kPa and pCO = 6.56 kPa, corresponding to a molar ratio H2O:CO of 3.05. In a different experiment, electrical current was used in the 5% Ni/CNF bed, in order to verify its influence on the catalyst activity. The electrical current was varied between -1.4 and 1.4 A and no change was observed in the rate or selectivity of the WGSR. Among the catalysts tested, 5%Cu/Al2O3 was the most active under all conditions used in this work, due to the high dispersion of the metal particles on the support. Nickel supported on Al2O3, under reaction conditions studied, was less active, because the metal particles were widely dispersed and, probably, were not reduced by H2. Ni/CNF and Cu/CNF had low CO conversions, due to the support hydrophobicity. The apparent activation energy calculated for the WGSR was 86.05kJ/mol for 5% Cu/Al2O3 and 69.80 kJ/mol for 5% Cu/CNF. For Cu/CNF a co-operative redox reaction mechanism was proposed, and apparent reaction orders were 0.64 in relation to CO and approximately zero in relation to water / Mestrado / Desenvolvimento de Processos Químicos / Mestra em Engenharia Química

Corrosion of steel tendons is a major problem for post-tensioned concrete, especially because corrosion of the steel strands is often hard to detect inside grouted ducts. Non-metallic tendons can serve as an alternative material to steel for post-tensioning applications. Carbon fiber reinforced polymer (CFRP), given its higher strength and elastic modulus, as well as excellent durability and fatigue strength, is the most practical option for post-tensioning applications. The primary objective of this research project was to assess the feasibility of the use of innovative carbon fiber reinforced polymer (CFRP) tendons and to develop guidelines for CFRP in post-tensioned bridge applications, including segmental bridges and pier caps. An experimental investigation and a numerical simulation were conducted to compare the performance of a scaled segmental bridge model, post-tensioned with two types of carbon fiber strands and steel strands. The model was tested at different prestress levels and at different loading configurations. While the study confirms feasibility of both types of carbon fiber strands for segmental bridge applications, and their similar serviceability behavior, strands with higher elastic modulus could improve structural performance and minimize displacements beyond service loads. As the second component of the project, a side-by-side comparison of two types of carbon fiber strands against steel strands was conducted in a scaled pier cap model. Two different strand arrangements were used for post-tensioning, with eight and six strands, respectively representing an over-design and a slight under-design relative to the factored demand. The model was tested under service and factored loads. The investigation confirmed the feasibility of using carbon fiber strands in unbonded post-tensioning of pier caps. Considering both serviceability and overload conditions, the general performance of the pier cap model was deemed acceptable using either type of carbon fiber strands and quite comparable to that of steel strands. In another component of this research, creep stress tests were conducted with carbon fiber composite cable (CFCC). The anchorages for all the specimens were prepared using a commercially available expansive grout. Specimens withstood 95% of the guaranteed capacity provided by the manufacturer for a period of five months, without any sign of rupture.

La demande mondiale des composites à fibres de carbone est en forte croissance. Les résidus qui en découlent augmentent également. Le procédé de solvolyse a été étudié pour recycler les fibres de carbone et valoriser la résine décomposée dans la phase liquide. L’étude se focalise sur l’impact du procédé batch (température et temps de réaction) sur la disparition de la résine dans l’eau sous- et supercritique. Le procédé batch n’est pas limité par la pénétration de l’eau dans un lit de composite, mais par contre, la haute teneur en composés organiques semble initier un phénomène de repolymérisation. Aux conditions optimales (350°C, 30 min et 400°C, 15 min) les fibres sont dépourvues de résine PA6, et les propriétés mécaniques sont proches des fibres vierges. Les analyses de diffraction des rayons X montrent une modification des distances inter-réticulaires des empilements de graphène, et la spectroscopie Raman met en évidence des modifications de la structure turbostratique des fibres. Ainsi le procédé de solvolyse a conduit à des changements nanostructuraux. Les valeurs de résistance à la traction sont assez proches de celles des fibres vierges. Ainsi, les fibres peuvent être réutilisées dans la reformulation de nouveaux composites. Enfin, l’étude cinétique basée sur les valeurs d’énergie d’activation en eau sous-critique (77,79 kJ/mol) et en eau supercritique (78,51 kJ/mol) montre qu’il s’agit du même schéma mécanistique régissant la réaction de dépolymérisation de la résine. La composition de la phase liquide montre la récupération de 70 % de monomère caprolactame et de la formation de produits plus lourds dans les temps de réaction relativement long (>45min). Ceci a été expliqué par un phénomène de repolymérisation. L’utilisation du CeO2 a permis d’une part de limiter des réactions indésirables et d’autres part d’améliorer la conversion de la résine PA6 en son monomère dans les temps de réaction courts. / The global demand of carbon fibers reinforced composites increases greatly, resulting in an increase of its residues. The solvolysis process has been studied in the framework of the recycling of carbon fibers and the recovery of the resin decomposed in the liquid phase. First, the study focuses on the impact of the batch process (temperature and reaction time) on the resin removal under subcritical and supercritical water. Although the batch process is not limited by the water diffusion into the composite bed, a large amount of organics results in a repolymerization phenomenon. The optimal conditions (350 °C, 30 min and 400 °C, 15 min) led to achieve the PA6 resin removal and the mechanical properties of recovered carbon fibers are similar to the virgin ones. The X-ray diffraction patterns show a modification of the inter-reticular distances of the graphene stacks, and Raman spectroscopy analysis reveal a modification in the turbostratic structure. Therefore nanostructural changes have occurred due to solvolysis process. Tensile strength values are quite similar to those of the virgin fibers, thus the fibers can be reused in the reformulation of new composites. Finally, the kinetic study based on the values of activation energy in subcritical water (77.79 kJ / mol) and in supercritical water (78.51 kJ / mol) shows that the same mechanistic scheme is governing the resin depolymerization reaction. The composition of the liquid phase shows the recovery of 70 % the monomer (caprolactam) and the production of heavier products in long reaction times (>45min). This has been explained by a repolymerization phenomenon. The use of CeO2 was efficient to limit undesirable reactions and to improve the conversion of the PA6 resin into its monomer in short reaction times.

No description available.

Carbon fiber reinforced plastic (CFRP) composites have extensive value in the aerospace, defense, sporting goods, and high performance automobile industries. These composites have huge benefits including high strength to weight ratios and the ability to tailor their properties. A significant issue with carbon fiber composites is the potential for catastrophic fatigue failure. To better understand this fatigue, there is first a huge push to measure strain accurately and in-situ to monitor carbon fiber composites. In this paper, piezoresistive nickel nanostrand (NiNs) nanocomposites were embedded in between layers of carbon fiber composite for real time, in situ strain monitoring. Several different embedding methods have been investigated. These include the direct embedding of a patch of dry NiNs and the embedding of NiNs-polymer matrix nanocomposite patches which are insulated from the surrounding carbon fiber. Also, two different polymer matrix materials were used in the nanocomposite to compare the piezoresistive signal. These nanocomposites are shown to display repeatable piezoresistivity, thus becoming a strain sensor capable of accurately measuring strain real time and in-situ. This patch has compatible mechanical properties to existing advanced composites and shows good resolution to small strain. This method of strain sensing in carbon fiber composites is more easily implemented and used than other strain measurement methods including fiber Bragg grating and acoustic emissions. To show that these embedded strain gages can be used in a variety of carbon fiber components, two different applications were also pursued.

Yes / In view of high-performance, multifunctional and low-carbon development of infrastructures, there is a growing demand for smart engineering materials, making infrastructures intelligent. This paper reports a new-generation self-sensing cementitious composite (SSCC) incorporated with a hierarchically structured carbon fiber-carbon nanotube composite filler (CF-CNT), which is in-situ synthesized by directly growing CNT on CF. Various important factors including catalyst, temperature, and gas composition are considered to investigate their kinetic and thermodynamic influence on CF-CNT synthesis. The reciprocal architecture of CF-CNT not only alleviates the CNT aggregation, but also significantly improves the interfacial bonding between CF-CNTs and matrix. Due to the synergic and spatially morphological effects of CF-CNT, i.e., the formation of widely distributed multiscale reinforcement networks, SSCCs with CF-CNTs exhibit high mechanical properties and electrical conductivity as well as excellent self-sensing performances, particularly enhanced sensing repeatability. Moreover, the SSCCs with CF-CNTs are integrated into a full-scale maglev girder to devise a smart system for crack development monitoring. The system demonstrates high sensitivity and fidelity to capture the initiation of cracks/damage, as well as progressive and sudden damage events until complete failure of the maglev girder, indicating its considerable potential for structural health monitoring of infrastructures. / The work described in this paper is supported by grants from the National Science Foundation of China (51978127 and 51578110) and grants from the China Postdoctoral Science Foundation (2022M710973 and 2022M720648).

Pyrograf IIITM,/sup> fibers (PR-19-PS, Applied Sciences, Inc.) with 100-300 nm diameters and ~ 10-100 ìm lengths were used with a low viscosity aliphatic epoxy resin (Clearstream 9000, Clearstream Products, Inc.) to produce composites. The VGCFs were oxidized in 69-71 wt% nitric acid (115°C) for various times (10 min to 24 h) to modify the surface to enhance fiber/matrix adhesion. Remarkably, little fiber weight loss was detected even after 24 h of oxidation. Composites containing 19.2 volume percent (29.4 weight percent) VGCFs were prepared. Their flexural strengths and flexural moduli were obtained. The flexural strengths did not increase using oxidized VGCFs. Fiber surfaces were characterized using N2 BET, CO2 DR, XPS, SEM, TEM and base uptake measurements. Increasing the oxidation time produced only small initial increases in surface area up to a limit. Significant surface oxygen was present before oxidation and the amount increased initially, though not continuously, with nitric acid oxidation.