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This thesis presents: 1) literature review on adhesive bonding technologies in aviation industry including surface pretreatments (pre-preparation), surface quality assurance, and surface chemistry analysis methods; and 2) development and study of a novel solid-state electrochemical sensor for surface chemistry analysis of composite surfaces. The performance of an adhesive bonding is greatly determined by the adherend?s surface pretreatments which could increase surface tension, surface roughness, and change surface chemistry thereby increasing bond strength and durability of polymer composite adhesive joints. The primary goal of the surface pretreatments is to increase the surface roughness, surface energy, chemical activity, and cleanliness of the composite adherend as much as possible. Methods of surface pretreatments are reviewed in this paper, including: (1) abrasion/solvent cleaning; (2) grit blasting; (3) peel-ply; (4) tear-ply; (5) acid etching/anodizing; (6) corona discharge treatment; (7) plasma treatment; (8) flame treatment; (9) laser treatment; (10) others. One of the critical issues in aviation industry for an adhesive bonding is to analyze the prepared composite surfaces using a nondestructive inspection (NDI) or nondestructive test (NDT) method to determine whether the quality of surfaces are ready for the following bonding processes. Existing NDI methods include: (1) Near-Infrared; (2) Electrical potential; (3) Transient thermal NDT; (4) Electrical Impedance Spectroscopy (EIS); (5) Neutron radiography; and (6) X-ray Photoelectron Spectroscopy (XPS). However, up till now, these methods cannot provide definitive analysis or online and in-field analysis. Because of the non-availability of an on-line, in-field NDI method for surface chemistry analysis, excess or inadequate surface treatment and quality control processes may exist in the current aircraft manufacture processes incurring either a high cost or potentially weak adhesive bonds. Electrochemical reactions usually occur in liquid electrolyte or on conducting electrode but not on non-conducting composite. Conventional electrochemical sensors involve liquid electrolytes which will cause contamination on composite surfaces when they are used for surface chemistry analysis. In this work, we explore an all solid-sate electrochemical sensor technology. Redox pairs or mediators are combined into a solid-state electrolyte, NafionTM. The mediators can pass electrons to or from the composite surfaces causing slight reduction or oxidation of the composite surfaces. The output current in response to cyclic polarization (cyclic potential scanning) is used as the indication of the surface contamination level. The sensors included a working or sensing electrode with mediated Nafion clusters, Nafion membrane, Pt catalyzed carbon counter electrode, and Ag|AgCl reference electrode. The working electrode and counter electrode were attached to the Nafion membrane from different sides. The sensors were tested on different kinds of surfaces: original, polished, and sulfuric acid treated acrylic samples and pristine peel ply prepared, polished, and sulfuric acid treated composite laminate surface samples. The sensors showed a high sensitivity to the surface contamination. The performances and possible mechanisms related to the electrochemical sensors are discussed.

Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-16T13:29:16Z No. of bitstreams: 1 TeseRKH.pdf: 7966483 bytes, checksum: 075f420f66971bcdd35c8dbfe1d3c37c (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:45:53Z (GMT) No. of bitstreams: 1 TeseRKH.pdf: 7966483 bytes, checksum: 075f420f66971bcdd35c8dbfe1d3c37c (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:45:58Z (GMT) No. of bitstreams: 1 TeseRKH.pdf: 7966483 bytes, checksum: 075f420f66971bcdd35c8dbfe1d3c37c (MD5) / Made available in DSpace on 2016-09-16T19:46:05Z (GMT). No. of bitstreams: 1 TeseRKH.pdf: 7966483 bytes, checksum: 075f420f66971bcdd35c8dbfe1d3c37c (MD5) Previous issue date: 2015-02-26 / Não recebi financiamento / The research proposal was found low cost alternative solution to automatize the classification and selection process to recognize fruit ripeness level using biologic behavior instead of human visual inspection. The goal was to develop low cost and disposable solid state sensor made of office paper with respective equipment for odor monitoring. The concept used to development this sensor was replace the interdigitated electrode with a conductive track using office paper impregnated with an electrolyte that "turns" cellulose fiber in an electrical conductor under gas action. In order to get gas adsorbing surface property for odor monitoring were tested some electrolytes like: Magnesium Chloride, Potassium Iodide, Calcium Hydroxide and others. This configuration replaced the interdigitated electrode per cellulose fiber doped with an electrolyte, it´s the originality of this research. In the fruit ripening process, the major enzymes involved are pectinase to crack the cell walls responsible for the fruits softening, amylase which degrades carbohydrates to simple sugars responsible for the flavor and hydrolase which reduces the amount of chlorophyll responsible for the fruit color change. The reaction that produces ethylene gas (C2H4) is lipids oxidation, the main gas exhaled during the fruits ripening process. The equipment adopted to pick up electrical signal is based on resistance and capacitance measuring that showed reversible electrical signal variation basically due the track geometry and cellulose fiber doping with an electrolyte. Another feature found was the office paper sensor decrease resistivity with fruit odors presence. The sensor manufacturing process is simple, basically consist in printing a mask with a negative image of the track by laser printing and office paper impregnation by an electrolyte. / A proposta da pesquisa foi buscar uma alternativa de baixo custo para automatizar o processo de seleção e classificação do nível de maturação da banana, utilizando-se do reconhecimento de gás exalado no processo de maturação via biológica, em vez da inspeção visual humana. O objeto da pesquisa foi desenvolver um sensor de estado sólido, de baixo custo e descartável, à base de papel sulfite, com o seu respectivo equipamento de monitoramento de odor. O conceito utilizado no desenvolvimento do sensor foi eliminar o eletrodo condutor interdigitado e substitui-lo por uma trilha condutora via dopagem do papel sulfite, impregnando com um eletrólito que “transforma” a fibra de celulose em um condutor elétrico sob a ação de gás. Visando conferir a propriedade de adsorção superficial dos gases no processo de monitoramento de odor, foram testados os seguintes eletrólitos: Cloreto de Magnésio, Iodeto de Potássio, Hidróxido de Cálcio entre outros. Essa configuração de substituir o eletrodo interdigitado por fibra de celulose dopada com um eletrólito traduz a originalidade desta pesquisa. No processo de amadurecimento das frutas, as principais enzimas envolvidas foram: pectinase, que quebra as paredes celulares, responsável pelo amolecimento das frutas; amilase, que degrada carboidratos em açúcares simples, responsável pelo sabor e a hidrolase, que reduz a quantidade de clorofila responsável pela mudança de cor da fruta. A reação que produz o gás etileno (C2H4) é a oxidação de lipídios, principal gás exalado durante o processo de amadurecimento das frutas. O equipamento de captação de sinal elétrico do sensor de estado sólido foi baseado na medição de resistência e capacitância, que apresentou variação de sinal elétrico reversível, basicamente em função da geometria da trilha e da dopagem da fibra de celulose com um eletrólito. Outra característica do sensor de papel sulfite foi a queda da resistividade com a presença de odores da fruta. O processo de fabricação do sensor é simples: consiste basicamente em uma impressão a laser de uma máscara com imagem negativa da trilha e a impregnação do papel sulfite com um eletrólito.