Sistema para avaliação de resistência à corrosão de revestimentos, método para a avaliação de resistência à corrosão de revestimento e uso da liga magnetoelástica

Universidade Federal do Rio Grande do SulEngenhariaDepositad

Monitoring the electrochemical behavior of hybrid coatings on magneto-elastic sensors using resonant frequency variations

In this work we present results for the protective performance of coatings used on magneto-elastic ribbons. It is found that monitoring the resonance frequency variation (Δf) of a magneto-elastic sensor can give useful electrochemical information. This method has the advantage of allowing one to monitor the electrochemical behavior of coatings without the need for direct access to the sample. A sensor developed from the FeNiMoB alloy (Metglas 2826MB3) was covered with hybrid coatings based on silicon alkoxide precursors. The results obtained from the magneto-elastic sensor test were correlated with the results obtained from electrochemical impedance spectroscopy (EIS). In general, it was observed that the Δf monitoring technique provided results consistent with those obtained by EIS, with the advantage that it does not need to have direct contact with the sample. Besides that monitoring the resonance frequency also allows one to evaluate the electrochemical behavior of the coating in the medium of interest

Electrochemical and mechanical behavior of UV curing paint on hybrid films modified with polyethyleneglycol plasticizer applied on tinplate

The objective of this work is to coat tinplate with a hybrid film obtained from a sol-gel process constituted by the alkoxide precursor tetraethoxysilane (TEOS) and 3-trimethoxysilylpropyl methacrylate (TMSM), with the addition of cerium nitrate (0.01 M) and polyethyleneglycol plasticizer (20 g.L-1) to the sol formulation. The films were obtained by dip-coating, applying one and two layers and curing them at different temperatures (60°C and 90°C) for 20 minutes, and adhering UV curing paint to each film respectively. The results showed that the double layered hybrid film obtained at 60°C had a higher layer of thickness and the best performance in the electrochemical assays, in other words, higher resistance to corrosion. Furthermore, in studies following the application of UV coating, the hybrid-film monolayer cured at 60°C wich had an organic coating of cured UV applied to it, achieved a performance similar to that of the pretreated alkyd greenhouse currently used in the metal packaging industry

Liga magnetoelástica metglas 2826MB3 revestida por processo sol-gel utilizada como plataforma para sensores de bactérias em leite

A detecção de bactérias em alimentos para consumo é feita por métodos clássicos que necessitam elevado tempo de resposta (dias) e pessoas qualificadas para a realização dos testes. Uma alternativa para viabilizar a rápida detecção de microrganismos em alimentos é a utilização de sensores magnetoelásticos (SME). Esses sensores permitem detectar e quantificar pequenos carregamento de massa, tendo como grande vantagem o fato de que o sensoriamento pode ser promovido sem a utilização de conexões físicas diretas (monitoramento wireless). Contudo, estas ligas magnetoelásticas são suscetíveis a corrosão quando expostas em meios agressivos. Por isso, os SME convencionais utilizam camadas de cromo e de ouro em sua superfície, a fim de proteger a liga da corrosão e facilitar a ancoragem de outros compostos específicos (funcionalização). O objetivo deste trabalho é desenvolver um sensor, não funcionalizado, para a detecção de bactérias no leite, a partir de uma liga magnetoelástica (Metglas 2826MB3) recoberta com revestimentos híbridos. Os revestimentos híbridos testados são à base dos precursores alcóxidos 1,2-bis(trietoxisilil)etano (BTSE) e tetraetoxisilano (TEOS) combinado ao 3- (trimetoxisilil)propilmetacrilato (MAP). A finalidade destes revestimentos é a proteção da liga magnetoelástica contra a corrosão, substituindo as camadas metálicas (cromo/ouro) convencionalmente utilizadas. Dentre os revestimentos testados, o desenvolvido a partir dos precursores TEOS-MAP apresentou-se compacto, uniforme e fortemente aderido ao substrato, o que proporcionou desempenho eletroquímico superior ao obtido para o revestido à base de BTSE. O sensor recoberto com o revestimento à base de TEOS-MAP foi testado quanto à detecção de bactérias (E. coli e S. aureus) em diferentes meios líquidos (PBS e em leite) por meio da técnica de variação da frequência de ressonância. Os resultados mostraram que o sensor, mesmo não funcionalizado, respondeu ao carregamento de massa permitindo detectar a presença de bactérias (E. coli e S. aureus) em diferentes concentrações. Os resultados permitiram concluir que o sensor desenvolvido a partir da liga magnetoelástica Metglas 2826MB3 recoberta com revestimento híbrido à base de TEOS-MAP mostrou-se eficaz na detecção da presença de bactérias em meios líquidos, mantendo-se íntegro durante todo o período de teste.The detection of bacteria in food for consumption is done by classical methods that require high response time. An alternative to enable rapid detection of microorganisms in food is to use of magneto-elastic sensors (SME). These media detect and quantify small mass loading, taking as a great advantage the fact that sensing can be promoted wirelessly whitout direct physical connections. However, these magnetoelastic alloys are susceptible to corrosion when exposed in aggressive medium. Therefore, conventional SME use layers of chromium/gold on their surface in order to protect the alloy from corrosion and facilitate anchoring of other specific compounds (functionalization). The objective of this work is to develop an unfunctionalized sensor for the detection of bacteria in milk, made from a magnetoelastic alloy (Metglas 2826MB3) with hybrid coatings. The hybrid coatings tested are based on precursor alkoxides 1,2-bis(triethoxysilyl)ethane (BTSE) and tetraethoxysilane (TEOS) combined with 3-(trimethoxysilyl)propylmethacrylate (MAP). The purpose of the coatings is a corrosion protection of the magnetoelastic alloy, replacing as conventionally used metallic layers (chromium/gold). Among the coatings tested, the one developed from TEOS-MAP precursors was compact, uniform and strongly adhered to the substrate, which provided superior electrochemical performance to that obtained for the BTSE coating. The sensor coated with the TEOS-MAP-based coating was tested for bacterial (E. coli and S. aureus) detection in different liquid media (PBS and milk) by means of the resonance frequency variation technique. The results showed that the sensor, even when it was not functionalized, responded to the mass loading by detecting the presence of bacteria (E. coli and S. aureus) in different concentrations. The results allowed to conclude that the sensor was developed from the alloy Metglas 2826MB3 with TEOS-MAP based coating showed to be effective in detecting the presence of bacteria in liquid medium, remaining intact throughout the test perio

Sistema para avaliação de resistência à corrosão de revestimentos, método para a avaliação de resistência à corrosão de revestimento e uso da liga magnetoelástica

Universidade Federal do Rio Grande do SulEngenhariaDepositad

Efeito do tratamento alcalino de fibras de Curauá sobre as propriedades de compósitos de matriz biodegradável

Neste trabalho avaliou-se a influência do tratamento alcalino das fibras de curauá, nas concentrações de 1, 5 e 10%(m/v) de NaOH, nas propriedades dos compósitos com matriz de PHBV e 20% m/m de fibras de curauá. Os compósitos foram moldados por extrusão e injeção e avaliadas suas as propriedades morfológicas, térmicas e mecânicas. Os resultados de FTIR mostraram que o tratamento alcalino promoveu modificações na estrutura das fibras de curauá, comprovadas pela remoção da hemicelulose e da lignina, evidenciadas pela ausência das bandas típicas destes compostos. Nos compósitos com fibras de curauá tratadas com solução de NaOH na concentração de 5% apresentaram um aumento de 30% na resistência à flexão e 12% na resistência ao impacto, quando comparados aos compósitos com fibras sem tratamento. Estes resultados indicam que o tratamento alcalino promoveu uma melhoria na adesão das fibras na matriz, o que melhorou significativamente as propriedades mecânicas dos compósitos

Revestimento híbrido a base de precursores silanos aplicado sobre uma liga magnetoelástica utilizada como plataforma para biossensores de carregamento de massa

Fundação Universidade de Caxias do SulUniversidade Federal do Rio Grande do SulEngenhariaDepositad

Anticorrosive performance of commercial nanoceramic coatings on AISI 1010 steel

The aim of this work was to study the corrosion behavior of three commercial nanoceramic coatings in comparison to zinc phosphate coatings applied on mild steel (SAE 1010). The coatings were evaluated by scanning electron microscopy (SEM), profilometry and hydrophobicity. The electrochemical behavior was evaluated by dynamic polarization. The results showed that the samples coated with nanoceramics presented contact angles greater than 100°, achieving hydrophobic behavior. Evaluating the electrochemical behavior under dynamic polarization revealed that the nanoceramic coating containing chromium (CHT) exhibited a higher corrosion potential and lower current than the other nanoceramic coatings tested, although its performance in a dilute sodium chloride solution was below that of the zinc phosphate-based coating. Although the nanoceramic coatings exhibited poor electrochemical behavior compared to the zinc-based coatings, they had a higher corrosion resistance when associated with an organic coating

Effect of the shot peening process on the corrosion and oxidation resistance of AISI430 stainless steel

Ferritic stainless steels are used in specific applications where corrosion resistance, oxidation resistance and a high mechanical resistance are required. Shot peening is a process applied to add residual compression stresses in metallic surfaces with the intent of improving the material when exposed to corrosion due to stress and fatigue. Some studies about the effect of the shot peening process on the fatigue resistance, bending fatigue behavior, and residual surface stress in the ferritic stainless steels have been performed. However, the effect of the shot peening process on the corrosion and oxidation resistance of the stainless steel is not well known. In this context, the purpose of this study is to evaluate the effect of the shot peening process on these superficial properties of ferritic AISI430 stainless steel. The obtained results showed that the ferritic AISI430 stainless steel samples treated with shot peening presented a significant modification on the surface morphology and an important decrease of oxidation and corrosion resistance, evidencing that the shot peening process compromises the chemical and physical properties of the surface