RESUMO As telhas de aço usadas em galpões de fazendas expostas às intempéries ficam vulneráveis à degradação. A corrosão surge devido à diferença de potencial elétrico entre a superfície metálica e o meio, levando a um carregamento elétrico dessa superfície. Elas então necessitam da proteção de um recobrimento anticorrosivo, cujo objetivo é aumentar sua vida útil. Atualmente um recobrimento usado para diminuir os efeitos do sol e da chuva em telhas metálicas é o de zincalume, que consiste em uma liga de zinco e alumínio. Este recobrimento permite a combinação do zinco com alumínio, que alia a resistência por barreira do primeiro ao bom desempenho do segundo em proteger bordas e pequenas descontinuidades. Este produto mantém a força estrutural do aço-base e confere alta resistência à corrosão atmosférica, interrompendo a corrente elétrica. Neste trabalho foi analisada a degradação das telhas de aço recobertas com uma camada de zincalume sujeita à ação do tempo. Análises com fluorescência de raios X foram utilizadas a fim de se verificar a composição química das amostras estudadas. Foram realizadas também análises macrográficas e micrográficas, a fim de se avaliar a degradação das telhas.

ABSTRACT The steel roof tiles used in farm sheds are vulnerable to the action of weathering. The corrosion arises due to difference of electrical potential between the metallic surface and the environment, leading to an electrical load of this surface. They need a protection, an anticorrosive coating, whose purpose is to increase the lifetime. Zincalume is a kind of coating currently used to decrease the effects of sun and rain in the metal roof tiles. This coating consists of an alloy of zinc and aluminum. The Zincalume coating allows the combination of zinc and aluminum by combining the barrier resistance offered by the first one and the good performance of the second one in protecting edges and small discontinuities. This product maintains the structural strength of the steel base and provides high resistance to atmospheric corrosion leading to the interruption of the electrical current. The degradation of steel roofing coated with a layer of zincalume subject to weathering was analyzed in this work. Analysis with X-ray fluorescence was used to verify the chemical composition of the studied samples. Macrographic and micrographic analyzes were also carried out in order to evaluate the degradation of the roof tiles.

This work deals with the deposition of a thin layer of porous silica antireflective coating onto glass substrates. The films were deposited with different withdrawal speeds and heat-treated at 425°C for 30 minutes. The effects of heat treatment and film deposition rate on the films reflectance were evaluated. The diffuse reflectance was measured using ultraviolet-visible (UV-Vis) spectroscopy. Scanning electron microscopy (SEM) was used for microstructural evaluation of the films. The water contact angle upon the films surface was evaluated using a tensiometer and was based on the sessile drop technique. The mechanical characteristics of the films were evaluated by tape test and pencil hardness. The obtained sol-gel silica coatings were homogeneous and free of cracks. UV-Vis analysis of the glass substrate revealed a reflectance value of 3.86%, whereas the lowest reflectance value obtained for antireflective coatings was 2.72%. The contact angle measurement showed that, for all films, there was wetting of the film by water, characterizing them as hydrophilic. The adhesion of the films were 4B and the pencil hardness were 3H.

One of the applications of selective surfaces is to improve performance of solar absorbers. The purpose of this work is to produces selective coatings with high absorption of solar radiation in the range of UV/Vis/NIR. It was prepared a selective surface composed of black chromium (Cr/Cr2O3) deposited on substrates of AISI 304 stainless steel using the technique of electrolytic deposition for application in solar thermal absorbers. The great parameters for deposition consisted of a continuous electric current of 2A for 90s, at a constant temperature of 40°C. After deposition, the samples under went to a heat treatment at 600°C for 2h for oxidation. The coatings thicknesses were determined. From the SEM analysis coupled with EDS, it was found that the microstructures reported sample of cermets. The XRD results show diffraction peaks related to metallic chromium (Cr) and chromium oxide (Cr2O3). Spectral absorptance values more 90.0% were found.

Recobrimentos de Ni/NiO em substrato de alumínio têm sido utilizados para se desenvolverem superfícies seletivas com alto desempenho para aplicações fototérmicas. Industrialmente essas superfícies têm sido empregadas em coletores solares. No presente trabalho, amostras de alumínio foram recobertas com Ni/NiO por processos químico e eletrolítico seguidos de tratamento térmico para oxidação. Os filmes foram produzidos em camada dúplex, sendo a primeira constituída de Ni e a segunda de NiO, a camada de anti-reflexão (AR). As espessuras dos filmes depositados têm cerca de 1,0µm. As microestruturas das amostras foram examinadas ao microscópio eletrônico de varredura (MEV). Análises de difração de raios X (DRX) identificaram as fases presentes. As amostras foram caracterizadas quanto às propriedades óticas nas regiões do visível e do infravermelho próximo. A absortância solar média dos recobrimentos eletrolíticos oxidados atingiu picos de 97,5%, enquanto a refletância no infravermelho distante foi de 12%.

The investigation of Ni/NiO coatings in aluminum substrate has been realized to develop high performance selective surfaces for photothermal applications. These absorber surfaces have been designed for industrial production. The present work describes Ni/NiO coatings in aluminum substrate obtained by chemical and electrolytic processes. Thermal treatments were used for oxidation. The first layer is Ni, the second one is NiO, the layer is an antireflectant (AR). The layer thicknesses are 1.0µm. The microstructures of the samples were examined by scanning electronic microscope (MEV). The X-ray diffraction (XRD) was used to identify the present phases. The optical properties, in some regions of visible and near infrared, allowed peaks of 97,5% for solar absorption and reflection of 12% for the electrolytic process oxidation.

The effects of combustion thermal spraying parameters namely combustion pressure, feeding rate, and carrier gas on the wear resistance, friction coefficient, and Knoop hardness of poly (ethylene terephthalate) (PET) films were investigated. The PET coatings were characterized by measuring the wear coefficients by calowear-type testing, the friction coefficients by a pin-on-disk test, and Knoop hardness. The abrasive wear and friction coefficients of the coatings were compared with the values of a post consumer PET bottle chip reference sample. The structural characteristics of the coatings were investigated by X ray diffraction. Statistical analysis of the results allowed for the systematic characterization of the influence of the process variables mentioned above on the coating wear, friction, and microhardness values. Specifically, this study shows that the process parameters affect the wear coefficient and Knoop hardness significantly, but not the friction coefficient. The degree of crystallinity of the PET coatings varied from 20 to 26%.

Recobrimentos químicos de Ni-P têm sido observados em diversas aplicações, tais como ferramentas e matrizes, principalmente em condições de desgaste e em situações de corrosão. No presente trabalho, recobrimentos químicos de Ni-P com 8 e 10%P foram depositados, quimicamente, em aço ABNT 1020 e, posteriormente, tratados, termicamente, entre 300°C e 650°C por 1 hora. As microestruturas níquel e fosfetos foram examinadas ao microscópio eletrônico de varredura (MEV). Análises de calorimetria diferencial de varredura (DSC) foram realizadas para detectar reações e transformações de fases. Resultados do ensaio de riscamento constataram uma variação da adesão desses recobrimentos em função da temperatura de tratamento térmico, bem como da dureza ao risco, que atingiu um valor máximo a 400ºC.

Chemical coatings of Ni-P have been observed in various applications, such as, tools, molds and matrices, mainly to prevent wear and corrosion. In this present work, Ni-P coatings with 8 and 10%P were deposited on steel ABNT 1020 and heat-treated at temperatures between 300ºC and 650ºC for 1h. The microstructures, nickel and phosphates have been examined using a scanning electronic microscope (SEM). Analyses of Differential Scanning Calorimetry (DSC) has been carried out to detect reactions and transformations of the phases. The results of assay scratch revealed a variation of the adhesion of these coatings in function of the heat treatment temperature, as well as of the hardness to the scratch that reached a maximum value to 400ºC.