Produção e caracterização de revestimentos de ligas metálicas Cu-Sn em banho eletrolítico contendo glicina: ensaios preliminares

Os problemas relacionados à corrosão são frequentes, podendo ocorrer nas mais variadas áreas, tais como,nas indústrias química, petroquímica, naval, de construção civil e automobilística, dentre outros setores produtivos.Portanto, métodos para prevenir a corrosão devem ser empregados para evitar a perda de materiais eo uso de revestimentos metálicos tem servido bastante a este propósito.A produção de revestimentos metálicos permite modificar a superfície do substrato levando à formação deum material funcional que apresenta as propriedades e características desejadas, no caso, resistência à corrosão.Contudo, esses revestimentos são geralmente produzidos usando banhos tóxicos a base de cianeto, o queeleva o custo do processo devido ao tratamento posterior dos rejeitos gerados.O presente trabalho propõe um estudo inicial para a produção de revestimentos de ligas de Cu-Sn com propriedadesanticorrosivas, a partir de banho eletrolítico menos agressivo, apresentando diferentes concentraçõesiônicas de cobre e estanho. Os revestimentos foram eletrodepositados em substrato de aço-carbono, utilizandoeletrólitos ácidos contendo CuCl2, SnCl2 e glicina. Estes revestimentos foram posteriormente caracterizadosatravés das técnicas de microscopia eletrônica de varredura (MEV), espectroscopia de raios X porenergia dispersiva (EDS), espectroscopia de impedância eletroquímica (EIE) e polarização potenciodinâmica.Os resultados de EIE mostraram que os filmes produzidos com maiores teores de cobre apresentaram umaumento nos valores da resistência de transferência de carga (Rtc). Contudo, os ensaios de polarização mostraramque estes filmes não atuaram como revestimentos protetores. As análises morfológicas evidenciaram aformação de revestimentos porosos, o que pode explicar seu pobre comportamento eletroquímico.Palavras-chave: Corrosão, glicina, liga Cu-Sn, revestiment

Carbon steel corrosion induced by sulphate-reducing bacteria in artificial seawater: electrochemical and morphological characterizations

In this work, the corrosion behavior of carbon steel AISI 1020 was evaluated in artificial seawater in the presence of mixed sulfate-reducing bacteria (SRB) culture isolated from the rust of a pipeline. The corrosion evaluation was performed by electrochemical techniques (open circuit potential (Eocp), polarization curves and electrochemical impedance spectroscopy (EIS)), while the formation of a biofilm and corrosion products were observed by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The presence of SRB in the medium shifted the open circuit potential to more positive values and increased the corrosion rate of the steel. Electrochemical and morphological techniques confirmed the presence of a biofilm on the steel surface. EDS spectra data showed the presence of sulfur in the corrosion products. After removing the biofilm, localized corrosion was observed on the surface, confirming that localized corrosion had occurred. The biogenic sulfide may lead to the formation of galvanic cells and contributes to cathodic depolarization. Keywords: sulphate-reducing bacteria, biofilm formation; carbon steel, electrochemical impedance spectroscopy, morphological characterization

Influence of cathodic current density and mechanical stirring on the electrodeposition of Cu-Co alloys in citrate bath

Cathodic polarization curves of Cu-Co alloys were galvanostatically obtained on a platinum net, using electrolytes containing copper and cobalt sulfates, sodium citrate and boric acid (pH values ranging from 4.88 to 6.00), with different mechanical stirring conditions. In order to evaluate quantitatively the influence of the applied current density and the mechanical stirring on the cathodic efficiency, the alloy composition for the Cu-Co alloy deposition process, and the average deposition potential, an experimental central composite design 2² was employed, and three current density intervals (0.11 to 0.60, 0.50 to 1.98 and 2.44 to 9.94 mA.cm-2) were chosen from the polarization curves for this purpose. The results indicated that the current density (mainly in the range between 0.11 and 0.60 mA.cm-2) affected significantly all the studied variables. In the intermediate range (0.50 to 1.98 mA.cm-2), only the average potential was influenced by the current density. On the other hand, the mechanical stirring had a significant effect only on the copper content, for both the lowest (0.11 to 0.60 mA.cm-2) and the highest current density range (2.44 to 9.94 mA.cm-2). Indeed, in the last range, none of the studied deposition parameters presented significant influence on the studied variables, except for the copper content. This could probably be explained by the direct incorporation of Cu-Citrate complexes in the coating, which was enhanced at high current values

The effects of aging time on the sol-gel properties and its relationship with the anti-corrosive performance of coatings prepared by sol-gel dip coating

This work evaluated the changes in the physicochemical properties (viscosity, surface tension, and zeta potential) of both alumina sol and boehmite solution at different aging times and their relationship with the corrosion resistance (in a saline solution) of the alumina film/boehmite conversion coating/carbon steel substrate systems prepared by sol-gel dip coating. The boehmite solution did not show significant changes in physicochemical properties throughout the studied time. As a result, the electrochemical behavior of the coating systems was independent of the aging time used to pretreat the substrate with the boehmite solutions. On the other hand, the changes in the physicochemical properties of the alumina sol with age were observed since the second week, causing an increase in the thickness (from 3.06 to 5.10 μm) and a decrease in the global resistance (from 138 to 30 kΩ cm2) of the systems. The most intense solvent evaporation effect and the macromolecules formed due to hydrolysis and condensation reactions during the studied aging period affected the properties of the alumina sol, leading to more heterogeneous and defective films when produced from sols with longer aging times

Electrodeposition of Composite Coatings of Cu/AlO(OH) Using Allyl Alcohol as an Additive

<div><p>In this work, composite coatings of Cu/AlO(OH) were produced by electrodeposition on steel substrates using a pyrophosphate-based bath containing allyl alcohol as an additive. The electrodeposition of the composite coatings was carried out using a 23 central composite design (CCD), aiming to verify the effects of the deposition parameters (previous stirring time (t), the stirring speed (S) and the current density (j)), considered the entry variables, on the electrochemical behavior of Cu/AlO(OH) coating, the response variables of the CCD. The results indicated that a decrease of the parameters j and S directly influenced the values of Rp and Rct, leading to the production of protective coatings. The best result (Rp = 211 Ω and Rct = 221 Ω) was obtained under conditions where t = 120 min, S = 1300 rpm and j = 7 A m-2. Dispersed bohemite particles could be noted on the surface of the composite coating.</p></div