RESUMO Em dutos que operam em regime turbulento, o processo corrosivo é acelerado e diretamente responsável por inúmeros prejuízos em plantas industriais, tais como paradas nas linhas de produção, falhas em equipamentos e elevados custos de manutenção. Embora haja poucos estudos laboratoriais nesta condição de escoamento, há um consenso entre inúmeros pesquisadores que o monitoramento e investigações nesta condição são essenciais, uma vez que simulam condições representativas da realidade industrial. Este trabalho investigou a influência do fluxo do meio eletrolítico sobre os parâmetros eletroquímicos do aço ABNT 1020 em solução NaCl 3% submetido a diferentes velocidades (0,21, 0,42, 0,62 e 0,84 m.s-1), relacionando os resultados obtidos por Espectroscopia de Impedância Eletroquímica (EIE) e Polarização Potenciodinâmica Linear (PPL). Os ensaios eletroquímicos foram realizados a partir de uma plataforma experimental construída para tal finalidade e acoplada às conexões do potenciostato, a fim de se obter curvas experimentais enquanto o eletrólito fluía dentro da célula e interagia com a superfície do metal. Os resultados mostraram que a variação da velocidade provoca mudanças notáveis nos principais parâmetros do ensaio e que as técnicas eletroquímicas corroboraram entre si mesmo em condições turbulentas de escoamento na plataforma de testes.

ABSTRACT In pipelines that operate in turbulent conditions, the corrosive process is accelerated and directly responsible for numerous losses in industrial plants, such as downtime in production lines, equipment failures and high maintenance costs. Although there are few laboratory studies in this flow condition, there is a consensus among countless researchers that monitoring and investigations in this condition are essential, since they simulate conditions representative of industrial reality. This work investigated the influence of the flow of the electrolytic medium on the electrochemical parameters of ABNT 1020 steel in 3% NaCl solution submitted to different speeds (0.21, 0.42, 0.62 and 0.84 ms-1), relating the results obtained by Electrochemical Impedance Spectroscopy (EIE) and Linear Potentiodynamic Polarization (LPP). The electrochemical tests were performed from an experimental platform built for this purpose and coupled to the connections of the potentiostat, in order to obtain experimental curves while the electrolyte flowed inside the cell and interacted with the metal surface. The results showed that the variation in speed causes notable changes in the main parameters of the test and that the electrochemical techniques corroborated each other in turbulent flow conditions in the test platform.

RESUMO O trabalho visa um estudo comparativo entre a eficiência do óleo de coco babaçu (Orbignya oleifera) utilizado como inibidor verde de corrosão e um inibidor comercial testados em aço ABNT 1020 em meio contendo ácido clorídrico. A avaliação foi realizada utilizando técnicas eletroquímicas de polarização linear aliado ao Método de Extrapolação de Tafel e Espectroscopia de Impedância Eletroquímica. As concentrações dos inibidores utilizadas foram 3, 4 e 5 g/L em solução contendo ácido clorídrico (HCl) 1M. Os resultados de espectroscopia de impedância eletroquímica mostraram que o Orbignya oleifera atua como inibidor de adsorção e que sua eficiência de inibição (56,45%) é superior comparado a eficiência do inibidor comercial (36,08%) na concentração de 3 g/L, uma vez que apresentou maior resistência de transferência de carga (47,3Ω) em comparação ao inibidor HPAA (32,23Ω). Os resultados de polarização linear mostraram que o óleo de Orbignya oleífera aumentou a eficiência de inibição no aço ABNT 1020 em solução de HCl 1M nas concentração de 3 e 4 g/L. A máxima eficiência inibidora do Orbignya oleífera neste ensaio foi de 48%, que pode estar associada a composição química desse óleo, na qual consta a presença do ácido láurico com concentração de 47%, o que pode ter contribuído para uma camada de inibição mais eficiente.

ABSTRACT The aim of this work is to compare the efficiency of babassu coconut oil (Orbignya oleifera) used as a green corrosion inhibitor and a commercial inhibitor tested on ABNT 1020 steel in hydrochloric acid medium. The search evaluation was accomplished with electromechanical techniques of linear polarizations and Tafel Extrapolation Method altogether with electrochemical impedance spectroscopy. The concentrations of the inhibitors were 3, 4 and 5 g/L in a solution of IM hydrochloric acid (HCI). The results of electrochemical impedance spectroscopy shows that Orbignya oleifera acts as an adsorption inhibitor and its inhibition efficiency value (56.45%) is higher when compared to the level of efficiency of the commercial inhibitor (36.08%) in the concentration of 3 g/L once that presented higher charge transfer resistance (47.3Ω) when compared to the HPAA (32.23Ω). The results of Linear Polarization Resistance shows Orbignya oleifera oil increased the inhibition efficiency in ABNT 1020 steel in 1M HCl solution at 3 and 4g/L concentrations. The level maximum inhibitory efficiency of Orbignya oleifera in this test was 48%. That percentage must be associated to chemical composition of that oil which contains lauric acid in a concentration of 47% - that probably contributed to a high efficiency of inhibition layer.

RESUMO As ligas de Alumínio são utilizadas para diversas finalidades e para a maioria dos casos a superfície desses materiais precisa ser modificada a fim de se melhorar propriedades como resistência ao desgaste e corrosão. Neste cenário, o processo de oxidação por plasma eletrolítico (PEO) surge como uma alternativa viável para produção de recobrimentos sobre esses substratos, já que o alumínio apresenta baixo ponto de fusão e este processo ocorre em baixas temperaturas. Neste trabalho, recobrimentos obtidos por plasma eletrolítico foram produzidos sobre a superfície de ligas de alumínio empregando diferentes parâmetros de forma a se comparar os recobrimentos obtidos. A caracterização foi feita por espectroscopia de impedância eletroquímica (EIE) com intuito de analisar o desempenho frente a corrosão. Modelo de circuito equivalente foi empregado para ajustar as curvas de EIE, de forma a melhor entender o comportamento da superfície. A partir dos resultados obtidos, foi possível constatar que em menor tensão (250 V), houve maior formação de filme sobre o substrato e consequentemente uma melhor proteção do mesmo. Quando comparado ao alumínio sem recobrimento, as amostras revestidas apresentaram uma melhora em termos de corrosão, apresentando maior resistência.

ABSTRACT Aluminum alloys are used for various purposes and in the most of cases the surface of such materials needs to be modified in order to improve properties such as wear resistance and corrosion. In this scenario, plasma electrolytic oxidation (PEO) process comes up as a viable alternative for the production of coatings on these substrates, since aluminum has low melting point and this process occurs at low temperatures. In this work, coatings obtained by PEO were produced on the surface of aluminum alloys, using different parameters in order to compare the properties of produced coatings. The coatings obtained were characterized by electrochemical impedance spectroscopy (EIS) in order to analyze the performance against corrosion. Equivalent circuit model was used to adjust the EIS curves, with a view to better understand the behavior of coatings. From the obtained results it was possible to verify that at lower voltage (250 V), there was a greater formation of film on the substrate and consequently a better protection of the same. When compared to uncoated aluminum, the coated samples presented an improvement of corrosion resistance.

AA 2024 aluminum alloy is widely employed in aeronautic and automobilist industries. Its hardness and low density are attractive properties for such industrial areas. However, since it contains copper, it undergoes severe corrosion in aggressive media as saline or low Earth orbit environments. In this work, it was investigated the properties of films deposited by PECVD on AA 2024 aluminum alloy as well as the corrosion resistance of the film/substrate systems under different corrosive atmospheres. Films were prepared in a plasma atmosphere composed of 50% of oxygen and 50% of hexamethyldisiloxane resulting in a total gas pressure of 4.0 Pa. Plasma ignition was promoted by the application of radiofrequency signal (13.56 MHz) to the sample holder while grounding the topmost electrode. The plasma excitation power, P, was changed from 10 to 80 W in the six different set of experiments. Film thickness, measured by profilometer, increases by 5 times as P was elevated from 10 to 80 W. As demonstrated by the infrared spectra of the samples, films are essentially organosilicons with preservation of functional groups of the precursor molecule and with creation of different ones. The oxide proportion and the structure crosslinking degree are affected by the plasma excitation power. According to the results obtained by sessile drop technique, hydrophilic to moderately hydrophobic films are produced with changing P from 10 to 80 W. The corrosion resistance, evaluated by salt spray and electrochemical impedance spectroscopy, EIS, experiments, in general increases after film deposition. It is demonstrated that film deposition improves, in up to 36 times, the resistance of the alloy to salt spray attack. It is also shown an improvement of about 240 times in the alloy resistance under NaCl solution by the EIS data. Micrographs acquired by Scanning Electron Microscopy after the corrosion tests furnish further information on the importance of the layer physical stability on its barrier properties. Furthermore, films highly protect the alloy against the oxygen attack. Interpretations are proposed based on the modification of the plasma kinetics with P, altering film structure, composition and properties.

Materials degradation due to simultaneous chemical and mechanical effects may occur under a variety of conditions. Galvanized and zinc-iron electrodeposited steels are widely used to protect automobile bodies against corrosion. In such applications, it is important to investigate the electrochemical and tribological behaviour of the coatings, in order to understand the behaviour of those surfaces in a tribological contact exposed to a corrosive environment. In the present paper, the evolution of open circuit potential, for both surfaces, was monitored during reciprocating sliding against an alumina pin in a 3% NaCl solution. The coatings are compared in terms of electrochemical behaviour by polarization tests, open circuit potential and friction coefficient during sliding; and loss of mass after sliding. The surface morphology, after sliding, was examined by SEM. Under the experimental conditions of the present study, the results found in terms of corrosion and wear resistance could be correlated to the differences in morphology, rugosity and composition of the two analysed surfaces.

The development of hybrids materials has been extensively investigated in recent years. The combination of a wide variety of compositions and production processes had permitted the use of these materials in different applications like coatings for corrosion protection of metals. In this work organic-inorganic hybrid materials have been prepared from the hydrolysis of tetraethylorthosilicate and silanol-terminated polidymetilmetoxysilane using a sol-gel process. These materials have been applied on galvanized steel and on steel electroplated with a ZnFe. In order to evaluate the degradation behavior of these coatings, electrochemical techniques (Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization) were used. EIS data was fitted to an equivalent circuit from which the electrochemical parameters were obtained. Results show a good protective character of the hybrid films, when compared with uncovered specimens. The overall performance of the coating systems appears to be highly dependent on the kind of metallic coating applied to the steel.