Obtainment and characterization of a silicon alkoxides-based coating applied to a substrate of stainless steel 316L for use in biomaterials

The silicon alkoxides-based coating is an alternative to control the release of cytotoxic ions through metal implants. This study evaluated the influence of the number of layers of a hybrid coating on the surface of austenitic stainless steel AISI 316L on the corrosion resistance. This coating was produced from the precursors of silicon alkoxides 3-(trimethoxysilyl)propyl methacrylate (MAP) and tetraethoxisylane (TEOS) obtained by sol-gel process, and easily applied by dip-coating. Results indicated that a single layer of coating in the substrate showed a better protection than two layers. This single layer developed by the combination of the precursors TEOS-MAP was enough to create a compact and uniform film with good adherence to AISI 316L and higher electrochemical development. A single layer of TEOS-MAP coating is more adequate as a protective coating for the AISI 361L than the sample subjected to two layers and the non-coated substrate, because this film ensures its integrity in an aggressive environment

RESISTÊNCIA A CORROSÃO EM DIFERENTES TRATAMENTOS DE SUPERFÍCIE SOBRE LIGAS DE ZINCO UTILIZADOS EM METAIS SANITÁRIOS

Entre as ligas não ferrosas, as ligas de zamac são as mais utilizadas para a fundição e vêm sendo aplicadas na substituição de peças de latão, utilizadas industrialmente em metais sanitários. O zamac apresenta propriedades mecânicas semelhantes às do latão, porém com custo inferior. Entretanto, a alta porosidade destas ligas, impede que tratamentos superficiais garantam bom acabamento e resistência à corrosão. Visando melhorar o desempenho, frente à corrosão de peças de zamac, o objetivo do presente trabalho é avaliar o processo de diferentes tratamentos de superfície dos metais sanitários produzidos em zamac. As amostras foram injetadas sobre pressão e submetidas a diferentes tratamentos superficiais (tratamento mecânico, tratamento químico, cobre alcalino, cobre ácido, níquel, cromo). Os corpos de prova foram expostos a um meio agressivo, por meio de nevoa salina a fim de analisar a resistência à corrosão das peças, além de análises de polarização, metalografia e microdureza. Observou-se que a maior incidência de corrosão ocorreu nas partes de injeção e solda da peça, as amostras tratadas com níquel e cromo demonstraram o melhor desemprenho frente a resistência a corrosão.Palavras-chave: Zamac. Metais sanitários. Corrosão.ABSTRACTAmong the non ferrous alloys, zamak are the most used for casting and have been applied to substitute brass parts, industrially utilized in sanitary metals. The zamak presents mechanical properties similar to brass, however with lower cost. Meanwhile, the high porosity of these alloys hinders the superficial treatments ensure good finishing and corrosion resistance. Aiming to improve the performance against corrosion of zamak parts, this work evaluates the process of different superficial treatments of sanitary metals produced with zamak. The samples were injected under pressure and submitted to different superficial treatments (mechanical, chemical, alkaline copper, acid copper, nickel and chromium). The specimens were exposed to an aggressive medium through salt spray test to evaluate the corrosion resistance, and the following analysis: polarization, metallography and microhardness. It was observed that the higher corrosion incidence occurred on the injection and weld regions. The samples treated with nickel and chromium demonstrated better performance of corrosion resistance. Keywords: Zamak. Sanitary materials. Corrosion

INFLUÊNCIA DOS PARÂMETROS DE ELETRODEPOSIÇÃO DE COBRE E NÍQUEL SOBRE O ZAMAC

A camada de cobre alcalino confere proteção ao zamac nos processos químicos posteriores, enquanto que a camada de cobre ácido confere nivelamento bem como a camada de níquel que confere brilho e proteção à peça. Neste sentido, esse trabalho tem por objetivo avaliar a influência dos parâmetros do processo de eletrodeposição das camadas de cobre e níquel na resistência à corrosão do zamac 5. Para tanto, camadas de cobre foram eletrodepositadas em amostras de zamac, com aplicação de 2V por 30 minutos e de 1V por 5 minutos + 2V por 40 minutos. Em cima desses depósitos, camadas de cobre ácido foram eletrodepositadas com aplicação de 2V por 30 minutos. Por último, sobre as camadas de cobre foram eletrodepositadas camadas de níquel com aplicação de 4V por 8 minutos e 4V por 20 minutos. O zamac sem e com revestimentos foi avaliado por Microscopia Eletrônica de Varredura (MEV), e quanto ao desempenho corrosivo por testes eletroquímicos (polarização). Os resultados mostraram que a diferença de tensão aplicada na eletrodeposição (1V e 2V) e o aumento de tempo (5min. e 40 min.), possibilitaram a obtenção de uma camada de cobre alcalino mais homogênea e uniforme e consequentemente mais resistente à corrosão do zamac em relação à camada de cobre alcalino com voltagem e tempo constante (2V por 30 min.). Palavras-chave: Corrosão. Eletrodeposição. Zamac. Cobre. Cristais. Porosidade.ABSTRACTThe alkaline copper layer provides zamac protection for subsequent chemical processes, while the acidic copper layer imparts leveling and the nickel layer imparts luster and protection to the part. In this sense, this work has the objective of evaluating the influence of the parameters of the electrodeposition process of copper and nickel layers on the resistance to the corrosion of zamac 5. For this, copper layers were electrodeposited in zamac samples, applying 2V by 30 minutes and 1V for 5 minutes + 2V for 40 minutes. On top of these deposits, layers of acid copper were electrodeposited with 2V application for 30 minutes. Finally, on the copper layers were electrodeposited layers of nickel with application of 4V for 8 minutes and 4V for 20 minutes. Zamac without and with coatings was evaluated by Scanning Electron Microscopy (SEM), and for the corrosive performance by electrochemical tests (polarization). The results showed that the voltage difference applied in the electrodeposition (1V and 2V) and the increase of time (5min and 40min) allowed to obtain a more homogeneous and uniform alkaline copper layer and consequently more corrosion resistant zamac in relation to the alkaline copper layer with voltage and constant time (2V for 30 min.).Keywords: Corrosion. Electrodeposition. Zamac. Copper. Crystals. Porosity

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

Hydrolysis time influence in obtaining hybrid film with addition of cerium ions for protecting galvanized steels

Las películas hibridas actúan como una barrera entre el substrato y el medio, reduciendo la velocidad de entrada del agua, electrolito, oxígeno y la penetración deiones agresivos hasta el metal, disminuyendo la velocidad de corrosión del substrato. Los principales factores que influyen en la resistencia a la corrosión de las películas híbridas son: el tiempo de curado, la concentración del baño, el pH de la solución de hidrólisis y el tiempo de hidrólisis. En este trabajo, se realizaron las pruebas con cuatro diferentes tiempos de hidrólisis (1, 3, 24 y 48 horas), el acero galvanizado fue revestido con una película híbrida obtenida a partir de un sol constituido por los precursores alcohoxidos 3-(trimetoxisililpropil) metacrilato (TMSPMA) y Tetraetoxisilano (TEOS) con adición de nitrato de cerio [0,01 M]. La caracterización de las películas fue realizada por MEB, perfilometria, ángulo de contacto, polarización y espectroscopia de impedancia electroquímica. Los resultados muestran que el tiempo de hidrólisis interfiere en la obtención de la película híbrida y consecuentemente en las propiedades protectoras de la película.The hybrid films act as a barrier layer between the substrate and the environment. This kind of coating reduces the electrolyte permeability, decreasing the corrosion rate of the substrate. However, many variables influenced the corrosion resistance of hybrid coating. The main factors that influence the thickness of the films are: temperature, curing time, the concentration alcooxide precursors on the bath, the pH of the hydrolysis and the hydrolysis time. In this study, the galvanized steel was coated with and hybrid film obtained from precursors consisting of a sol alcooxide 3-(trimetoxisililpropil) methacrylate (TMSPMA) and tetraethoxysilane (TEOS) with cerium nitrate addition [0,01 M]. The hydrolysis time was varied in four levels of (1, 3, 24 and 48 hours). The characterization of the films was performed by SEM, profilometry, contact angle determination, polarization and electrochemical impedance spectroscopy measurements. Results showed that the hydrolysis time presented influence on the hybrid film properties and consequently on the protection

Surface treatment of galvanized steel with hybrid films formed by 3-(trimethoxysilyl) methacrylate (TMSPMA) and tetraethoxysilane (TEOS)

Acero galvanizado fue revestido con una película híbrida a partir de una solución formada por los precursores silanos 3-(trimetoxisililpropil) metacrilato (TMSPMA) y tetraetoxisilano (TEOS) con adición de cerio. El uso de capas hibridas orgánico-inorgánico representa una alternativa ambientalmente aceptable para mejorar la resistencia de una serie de materiales metálicos frente a los procesos corrosivos. Se emplearon tres tiempos de inmersión (2, 10 y 15 minutos) y se caracterizaron las películas mediante microscopia electrónica de barrido, evaluando también el carácter hidrofóbico de las películas. El comportamiento electroquímico de los revestimientos obtenidos fue determinado por el monitoreo del potencial de circuito abierto, polarización potenciodinámica e impedancia electroquímica. Los resultados que se obtuvo evidenciaron el efecto del tiempo de permanencia dentro de la solución en la uniformidad de la película y consecuentemente sobre la resistencia a la corrosión del mismo.Galvanized steel was coated with a hybrid film obtained from a solution formed by silane precursor 3-( trimethoxysilyl) methacrylate (TMSPMA) and tetraethoxysilane (TEOS) with addition of cerium. The use of hybrid organic-inorganic layers represents an environmentally friendly alternative to improve resistance against corrosion of a series of metallic materials. Three immersion times (2, 10 and 15 minutes) were used and the films were characterized by scanning electron microscope evaluating film wetability was at the same time. The electrochemical behavior of the coatings obtained was evaluated by open circuit potential, potentiodynamic polarization and electrochemical impedance. The results showed the effect of immersion time in the solution on the film uniformity and consequently on the corrosion resistance of these films

Tratamento térmico em Zamac visando diminuir defeitos de porosidade

O Zamac tem sido utilizado na indústria galvânica, principalmente, devido ao seu baixo ponto de fusão, o que permite a obtenção de peças com riqueza de detalhes, tais como peças do setor moveleiro, moda e metais sanitários. No entanto, os processos de sua obtenção, por injeção sob pressão e injeção centrífuga, geram porosidade e, consequentemente, aumento de sucata. Por outro lado, estudos mostraram que fusão por gravidade não apresenta tais problemas. Nesse sentido, o objetivo deste artigo foi tratar termicamente peças de Zamac injetadas sob pressão, com a finalidade de obter comportamento semelhante às peças fundidas por gravidade. Para tanto, peças injetadas sob pressão foram tratadas termicamente, abaixo da temperatura de fusão. A caracterização morfológica dessas amostras foi obtida por MEV. Observou-se que o tratamento térmico acima da temperatura eutetoide apresentou melhor resultado com respeito à porosidade observada.The Zamac has been used in the galvanic industry mainly due its low fusing point properties, which allows obtaining very detailed parts, like parts for furniture industry, fashion and health metals. However, its production processes, like pressure injection and centrifugal injection, generate an increase in porosity as well as waste. On the other hand, studies show that die casting leaked Zamac doesn’t show the same problems. In this sense, the goal for this work is to perform heat treatment in Zamac parts produced by pressure injection in order to obtain similar properties as the ones produced by die casting leakage. For this, the parts injected under pressure were thermally treated under their fusion temperature. It was observed that thermic treatment over the eutectoid temperature showed the best result, regarding the observed porosity

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