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Agora exibindo 1 - 10 de 33
  • Resumo IPEN-doc 31002
    Synthesis and characterization of TiO2/GE nanocomposite films deposited on AISI 304 stainless steel
    2024 - SANTOS, THIAGO F. dos; COTINHO, SAMUEL P.; CORREA, OLANDIR V.; PILLIS, MARINA F.
    TiO2 and TiO2/exfoliated graphite (GE) films were prepared by the sol-gel method and applied to the surface of AISI 304 stainless steel using the cold spray technique. Initially, natural graphite was subjected to the liquid phase exfoliation process in an aqueous solution containing isopropanol and acetone under UVC irradiation, where expanded graphite was obtained. A solution containing titanium isopropoxide and ethanol was prepared to obtain the sol. The exfoliated graphite, after drying, was then added to the solution in concentrations between 2.5 and 10%, mass/volume ratio. The films were dried in an oven at 100ºC and heat treated at temperatures between 400 and 500 ºC in a tubular oven, under an argon atmosphere. Electrochemical techniques, field emission gun scanning electron microscopy (SEM-FEG), Raman spectroscopy and X-ray diffraction were used to characterize the coatings. The results confirm the formation of the anatase phase in all films and the presence of GE in the composite films. The films have a cracked morphology and TiO2 and GE particles on the surface of the sample were present. The samples were evaluated using potential x time and linear polarization techniques in a 3.5% NaCl aqueous solution at room temperature. The corrosion resistance of the samples increased compared to the substrate, suggesting that the coating act as a physical barrier [1].
  • Resumo IPEN-doc 30995
    Synthesis, characterization, and photocatalytic performance of nanostructured ZnO films under UV light
    2024 - COTINHO, SAMUEL P.; BENTO, RODRIGO T.; SANTOS, THIAGO F. dos; OLIVEIRA, LEANDRO da S.; SANTOS, CAMILA M.G.; SANTOS, DAVI R. dos; CORREA, OLANDIR V.; PILLIS, MARINA F.
    The limited natural water resources have been contaminated by effluents originating from both the industrial and domestic sectors. A large portion of the available water is consumed in chemical processes in various industrial sectors, including textiles, paper, and leather. Also, the inappropriate disposal of pharmaceuticals and dyes on a large scale results in effluent contamination. Methyl orange is one of the most widely used azo dyes on a large scale. Photocatalysis is a promising green alternative for the removal of organic dyes in wastewater. This research aimed to synthe and characterize nanostructured zinc oxide films to obtain a UV-light-activated photocatalyst capable of degrading organic compounds. The films were obtained using the sol-gel method. Zinc acetate, MEA, and ethanol were kept under constant stirring for 60 minutes at 70°C. The solution obtained was sprayed onto cleaned borosilicate glass substrates by using an airbrush. The samples were then heat treated at temperatures of 450 and 500°C for 45 minutes. The characterization of the films was performed using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), UV-Vis spectrophotometry and wettability. The efficiency of the films was determined by the degradation of a 5 mg.L-1 methyl orange dye water solution at neutral pH, at constant temperature of 20°C, and under two sources of ultraviolet radiation (λ=352 nm) for 300 minutes. The films exhibited hydrophilic characteristics and superficial morphology consisting of spherical nanoparticles. The films showed photoactivity when exposed to UVA radiation, with the best performance in removing methyl orange dye being 48.6% for the film treated at 500°C. This removal value can be attributed to the improvement in the homogeneity of the morphology and thickness of the film treated at 500°C.
  • Resumo IPEN-doc 30992
    Electrodeposition of high entropy FeCoCrNiMn coating on SAE 1020
    2024 - OLIVEIRA, LEANDRO da S.; COTINHO, SAMUEL P.; SANTOS, DAVI R. dos; GODOI, CAMILA; CORREA, OLANDIR V.; PILLIS, MARINA F.
    High entropy alloys (HEA) represent a relatively new class of metallic materials. They are composed of multiple components, without a predominance of elements, in an equiatomic form of five or more elements, with atomic concentrations between 5 and 35%. They present a distorted crystal structure and a combination of characteristics that affect their structure and functionality. These alloys exhibit excellent mechanical properties, such as high strength, hardness, wear and compression resistance, and chemical properties, including corrosion resistance. From the point of view of practical engineering applications, the and cost of components manufactured with HEA and produced by conventional casting methods are still considered a barrier. In this sense, coatings based on high entropy alloys have been gaining prominence in the scientific scenario to improve surface characteristics of conventional metallic alloys in a variety of applications, as resistance to corrosion and wear, when applied to low-cost metallic substrates, such as carbon steels and aluminum alloys. The electrodeposition process is considered advantageous in relation to the cost of equipment necessary for its execution and a more precise adjustment of the deposition conditions. In this study FeCoCrNiMn HEA coatings were electrodeposited on SAE 1020 steel. Process parameters as concentration of elements in the electrolyte, current-voltage values and process time of 15 and 30 minutes as well as substrate surface finish, were evaluated. The coatings obtained were characterized by X-ray diffraction, scanning electron microscopy and spectroscopy of dispersive energy. The electrochemical behavior in a 3.5 wt% NaCl aqueous solution was evaluated by the techniques of impedance spectroscopy and linear polarization. The results show the formation of a homogeneous coating on the steel surface and good corrosion resistance.
  • Resumo IPEN-doc 30291
    Corrosion analyses of anodized aluminum for biomedical purposes
    2023 - PIERETTI, EURICO F.; NEVES, MAURICIO D.M.; CORREA, OLANDIR V.; ANTUNES, RENATO A.; OLIVEIRA, MARA C.L.; PILLIS, MARA C.L.
    Introduction and objective: Anodic aluminum oxide has attracted a lot of interest due to the regular arrangement of nanopores, ease of control of the nanopores diameter, large specific surface area, low cost, good thermal stability, absence of toxicity and biocompatibility. The geometric arrangement of nanopores makes it possible to use alumina as a mold for the synthesis of various nanostructures, such as nanopores, nanotubes, nanorods and nanowires that have many advantages in advanced application areas due to their unique chemical, physical, mechanical, and optical properties [1,2]. The objective of this work was to study the corrosion susceptibility of anodized aluminum samples for biomedical applications. Methodology: In the present work, the localized corrosion resistance of AA6061aluminum alloy anodized in oxalic acid solution (C2H2O4) and sulfuric acid (H2SO4) was evaluated by electrochemical techniques. Prior to the anodization stage, the samples were electrolytically polished in a solution of perchloric acid and ethanol. Results and discussion: All samples showed a protective behavior on their surfaces, higher corrosion potentials in relation to the standard reference sample and a shift towards lower values of corrosion current densities in relation to the sample without passivation treatment. These results indicate that the anodizing treatments of AA6061 aluminum surfaces in oxalic or sulfuric acid are effective in producing surfaces resistant to localized corrosion and can therefore be used to coat this type of surface, ensuring an increase in the useful life of the devices. Conclusions: The results indicated superior corrosion resistance in the anodized samples in both conditions. Therefore, it is necessary to constantly advance research on the use of nanoporous anodic alumina coatings on biomaterials surfaces.
  • Resumo IPEN-doc 30290
    Surface investigation of a laser etched metallic biomaterial
    2023 - PIERETTI, EURICO F.; NEVES, MAURICIO D.M.; CORREA, OLANDIR V.; ANTUNES, RENATO A.; OLIVEIRA, MARA C.L.; PILLIS, MARINA F.
    Introduction and objective: Surface treatments are used to improve characteristics, such as: markings, texturing and polishing. The texturizations are produced to provide roughness and, consequently, adherence in specific locations of implantable medical devices of permanent character, that is, implants of prolonged use. Sometimes this process can generate stress concentrators and regions with probability for the occurrence of failures that can lead to fracture; in addition to damaging the passive layer, favouring the initiation of various forms of corrosion [1]. This work aims to evaluate the effect of the laser beam texturing technique in metallic implants on the corrosion resistance of ASTM 316L stainless steel. Methodology: Samples were prepared from the stainless steel textured by fiber optic laser doped with ytterbium (Yb) by changing the values of the frequency of the laser pulse cadence and keeping the other parameters constant. As a comparison, samples of the biomaterial without any type of laser treatment were also evaluated. The electrochemical tests performed consisted of open circuit corrosion potential (OCP) monitoring and cyclic potentiodynamic polarization measurements, determined after hours of immersion at 37°C body temperature. The scanning vibrating electrode electrochemical technique (SVET) was used as a tool to determine the corrosion current density in 0.1M NaCl solution. Results and discussion: The results obtained revealed the highest anodic current densities in the regions engraved by the laser beam and cathodic current densities in the regions farthest from the engravings, which indicates that laser engraving, in addition to increasing the roughness of the surfaces, makes them essentially anodic, changes the passive layer, affects the distribution of corrosion current densities and decreases the resistance to localized corrosion of this biomaterial. Conclusions: The change in the laser pulse frequency values is directly related to the behaviour observed on the analysed surfaces, indicating that the laser texturing treatment affects the passive layer of the material decreasing the resistance to localized corrosion.
  • Resumo IPEN-doc 30245
    Tribological characterization of nanoporous anodized anodic alumina coatings for biomedical applications
    2023 - PIERETTI, E.F.; CORREA, O.V.; NEVES, M.D.M.; OLIVEIRA, M.C.L.; ANTUNES, R.A.; PILLIS, M.F.
  • Resumo IPEN-doc 30159
    Raman spectroscopy applied on the structural characterization of TiO2/expanded graphite films
    2023 - BENTO, RODRIGO T.; ABE, IGOR Y.; CORREA, OLANDIR V.; PILLIS, MARINA F.
    Photocatalytic heterojunctions obtained from the use of titanium dioxide (TiO2) and carbon based materials are a promising way for the efficient water treatment [1]. The structural properties of the composite photocatalysts are an important characteristic that can influence their photocatalytic behavior [2]. Here, TiO2/expanded graphite (TiO2-EG) films were synthetized by sol-gel and deposited on borosilicate glass substrates by airbrush spray coating method at room temperature. Then, the hybrid films were heat treated at 350, 450 and 550 °C. Raman spectroscopy technique was applied to evaluate the effect of carbon amount and temperature on the structural properties of the films. The films heat treated at 350 °C exhibited a characteristic profile of amorphous material. Raman spectra of composite films heat treated at 450 and 550 °C showed well-defined peaks that can be attributed to anatase-TiO2phase. No peaks related to the rutile or other phases were observed. The investigation revealed that the G and 2D bands present a slight shift, as well as asymmetry, as the carbon content and heat treatment temperature increase – behavior that may be associated with the formation of the semiconductor-C heterojunction. Peaks deconvolution process demonstrated the presence of a second signal not found in the pure films. This effect may indicate a reduction of sp2 domains after the formation of semiconductor-C heterojunction, mainly due to the removal of oxygenated groups during heat treatment, and consequent Ti-C / Ti-O-C bonds formation [3]. The results suggested that the carbon amount and the temperature of heat treatment have great influence on the TiO2 -EG structural properties, which may contribute to the improvement of the photocatalytic activity of the composite films under visible light.
  • Resumo IPEN-doc 29412
    Síntese e caracterização de filmes nanoestruturados de ZnO para aplicação em fotocatálise
    2022 - COTINHO, S.P.; CORREA, O.V.; PILLIS, M.F.
    Os recursos naturais de águas têm sido contaminados por efluentes provenientes tanto do setor industrial quanto do setor doméstico. E ainda, grande parcela da água tratada é consumida em processos químicos em vários setores industriais, dentre estes os têxteis, de papel e de couro. Aproximadamente 70% dos corantes utilizados em larga escala nos vários processos correspondem a azo-corantes, sendo os principais o alaranjado de metila e o amaranto. Uma alternativa para a remoção de poluentes orgânicos se dá pela degradação fotocatalítica que tem se mostrado um método verde eficiente para eliminação de corantes orgânicos em águas residuais. Entre os semicondutores mais empregados, os óxidos TiO2, WO3 e ZnO têm se destacado. Algumas das características do ZnO que têm tornado esse material atrativo na área de fotocatálise são: boa estabilidade física e química, alta capacidade oxidativa, energia de band gap na região do UV ou do visível do espectro eletromagnético da luz, baixo custo e baixa toxicidade. Este trabalho de pesquisa objetivou a síntese e a caracterização de filmes nanoestruturados de óxido de zinco para obtenção de um fotocatalisador ativado por luz ultravioleta, capaz de degradar compostos orgânicos. Os filmes foram obtidos pelo método sol-gel dissolvendo-se 3,10g de acetato de zinco, 15ml álcool etílico e em seguida adicionando-se 0,86g de monoetanolamina (MEA). A solução obtida apresentou caráter básico (pH 8) e foi depositada por spray a frio em substratos de vidro borossilicato previamente preparados. As amostras foram tratadas termicamente nas temperaturas de 350°C, 400°C e 450°C nos tempos de 30, 40 e 60 minutos. A eficiência dos filmes foi determinada pela degradação do corante alaranjado de metila sob luz ultravioleta. A temperatura e o tempo de tratamento térmico influenciaram a atividade fotocatalítica, visto que a degradação do corante ocorre nas condições a partir de 400°C, sendo que após tratamento térmico a 450°C por 45 minutos foi observado o melhor desempenho.
  • Resumo IPEN-doc 29396
    Caracterização superficial de alumina anódica nanoporosa aplicada a revestimentos biomédicos
    2022 - PIERETTI, E.F.; CORREA, O.V.; NEVES, M.D.; ANTUNES, R.A.; PILLIS, M.F.; OLIVEIRA, M.C.
    As superfícies dos biomateriais utilizados como dispositivos médicos implantáveis e no ferramental cirúrgico devem ser adequadas à função que exercem; por este motivo a importância do estudo do acabamento superficial aumenta à medida que crescem as exigências do projeto, no que se refere ao regime de aderência entre o implante e o tecido humano adjacente e, requisitos de geometria e precisão nos implantes e nos utensílios cirúrgicos. Estes biomateriais, quando em contato com o tecido humano, estão sujeitos a falhas como desgaste, fadiga, micro movimentos, desprendimento de partículas e degradação, podendo causar hipersensibilidade, ou a necessidade de uma nova cirurgia para remoção e substituição. Consequentemente aumentam as despesas para os pacientes, convênios médicos e as instituições públicas de saúde. Óxido de alumínio anódico (OAA) tem atraído muito interesse devido ao arranjo regular de nanoporos, facilidade de controle do diâmetro dos nanoporos, grande área de superfície específica, baixo custo, boa estabilidade térmica, ausência de toxicidade e biocompatibilidade. Devido a essas características, as estruturas OAA têm sido utilizadas em aplicações como processos de filtração, biossenssores, sensores de oxigênio, catálise e fotocatálise. Além disso, o arranjo geométrico dos nanoporos torna possível utilizar a alumina como molde para a síntese de várias nanoestruturas, como nanoporos, nanotubos, nanobastões e nanofios que apresentam muitas vantagens em áreas de aplicação avançadas devido a suas propriedades químicas, físicas, mecânicas e ópticas únicas. Por isso, tornase necessário o constante avanço nas pesquisas sobre a utilização de revestimentos de alumina anódica nanoporosa sobre as superfícies dos biomateriais.
  • Resumo IPEN-doc 29395
    Avaliação da resistência à degradação do aço inoxidável AISI 316L revestido por filmes finos de TiO2
    2022 - PIERETTI, E.F.; CORREA, O.V.; PILLIS, M.F.; ANTUNES, R.A.; NEVES, M.D. das
    Os materiais metálicos utilizados na área de engenharia de biomateriais são geralmente materiais passivos e, dessa forma, estão sujeitos à corrosão localizada principalmente pela ação dos íons cloreto. Um dos tipos mais comuns de corrosão observados nestes materiais é a geração de pites. Os processos de produção envolvidos na fabricação de equipamentos para uso biomédico também afetam sua resistência à corrosão, especificamente aqueles que influenciam no acabamento de superfície. O aprimoramento de propriedades de superfície é uma exigência para os componentes metálicos utilizados em implantes e próteses. O objetivo deste trabalho foi investigar a influência películas finas de TiO2, de tamanho nanométrico, na resistência à corrosão do aço inoxidável austenítico AISI 316L, em uma solução de Ringer, que simula os fluidos corpóreos, a 25 °C . Os filmes foram depositados por CVD (deposição química em fase vapor). A resistência à corrosão foi avaliada utilizando-se métodos eletroquímicos como: monitoramento de potencial de circuito aberto (PCA), medições de espectroscopia de impedância eletroquímica (EIE) e polarização potenciodinâmica cíclica. A porosidade dos diferentes filmes também foi determinada utilizando-se um método eletroquímico. Análises de superfície e secções transversais foram realizadas por microscopia eletrônica de varredura (MEV). Os ensaios de corrosão mostraram que as amostras revestidas eram menos susceptíveis à corrosão do que as amostras sem recobrimento. Os revestimentos de TiO2 são finos, aderentes e conduzem a um comportamento mais capacitivo do filme passivo. Estes resultados sugerem que os filmes finos obtidos por este método podem ser empregados para a proteção contra a degradação deste aço inoxidável em ambientes agressivos.