Abstract Frequently stainless steel AISI 316L aseptic tanks have their passivity and corrosion resistance properties degraded by biofilm formation and localized corrosion processes. Thereby, maintenance projects are performed to repair the surface in food-grade product contact to obtain an aseptic property as defined by ASME BPE. However, the on-site non-destructive testing are limited to the liquid penetrant examination and the average roughness measurement. The on-site open circuit potential and on-site cyclic polarization measurements were conducted using a portable electrochemical minicell. The level of passivation was quantified on the tank surface, and it was performed before and after the repairing maintenance protocol be made. The results of the on-site electrochemical measurements showed a clear difference between as-degraded and repaired surfaces, indicating a sensible response to aseptic surface inspection. The on-site open circuit potential together with the on-site cyclic polarization were considered an advanced tool to support the maintenance projects of the AISI 316L aseptic surfaces.

Abstract This work aims at investigating the charge transfer resistance (RCT) of the two membranes derived from vegetable oils which are intended to protect materials against corrosion. The membranes were characterized by thickness measurement (328±1 μm and 491± 1 μm), atomic force microscopy (AFM) to estimate of roughness (<0.5 μm), Raman spectroscopy while the RCT values were evaluated by electrochemical impedance spectroscopy (EIS) in 0.1 mol/L KCl solution. EIS was used to measure the impedance at low frequency (Z0.01Hz ≅ 109 Ω cm2), RCT ≅ 109 Ω cm2 and exchange current density (i0 ≅ 10-11 Ω cm2), employing simple instrumentation. The thickness of the membrane must be considered for coherent interpretation of the impedance results. The study of electrolytes permeation in membranes is important to previously estimate the lifetime offered to a substrate over the time of immersion even before being applied to the metallic surface. The impedance measurements demonstrated that the most resistant membrane to permeation presented a RCT around 2 GΩ cm2. This EIS measurements approach enables the optimization of membrane fabrication by conveniently identifying the best formulation.

RESUMO Avaliou-se o grau de passivação da superfície de tanques de bioprocessamento em aço AISI 316L com polimento mecânico e rugosidade média de 0,8 μm. Os tanques foram inspecionados após a sua construção e em diferentes condições de superfície: (i) após 12 meses em operação industrial, (ii) com a adesão de biofilme, (iii) após o tratamento de passivação química. O aparelho PassivityScan foi utilizado nas inspeções in situ do grau de passivação aplicando as técnicas de potencial de circuito aberto e polarização potenciodinâmica cíclica. Os resultados indicaram que a superfície interna polida do tanque como fabricado gerou um grau de passivação relativamente baixo (Eprot–Ecorr<150 mV) e elevada cinética de corrosão. Após 12 meses de operação reduziu-se o grau de passivação da superfície e consequentemente sua durabilidade. Notou-se um agravamento com a presença de biofilme, dado que a superfície não possuía mais a capacidade de repassivação. É importante ressaltar que o tratamento de passivação química elevou o grau de passivação para 520 mV(Ag|AgCl|KCl 3 mol/L), reduzindo a densidade de corrente de passivação de 20 para 0,7 μA cm–2. Conclui-se que um tanque passivado quimicamente apresenta melhor confiabilidade operacional, e que o tratamento de passivação a cada 12 meses restaura as propriedades de resistência da superfície.

ABSTRACT The passivation level of AISI 316L bioprocessing tanks of roughness average of 0.8 μm mechanically polished was assessed. The on-site inspections were performed after tanks manufacturing and in distinct surface conditions: (i) after 12 months of industrial operation, (ii) with biofilm adhesion, (iii) after chemical passivation treatment. The PassivityScan inspection instrument was used in on-site measurements of passivation level applying the open circuit potential and cyclic potentiodynamic polarization techniques. The results showed that the tank inner surface in as-built condition obtained a relative low passivation level (Eprot–Ecorr < 150 mV(Ag|AgCl|KCl 3 mol/L) and high corrosion kinetic. The passivation level and durability of the surface were reduced after 12 months of operation. A worst-case scenario was noted with biofilm adhesion given that the surface was not able to repassivate. It worth to emphasize that the passivation treatment increased the passivation level to 520 mV(Ag|AgCl|KCl 3 mol/L) and reduced the passivation current density from 20 to 0.7 μA cm–2. It was concluded that a passivated AISI 316L tank reach a better operational reliability, and also the chemical passivation treatment should be done every 12 months in order to restorage the passive film resistance.

The construction and optimization of a device that can be applied to electrochemical studies in flat micro regions are described. This was developed as an attempt to study small regions of metallic samples, whose properties may differ completely from its macroscopic behavior and for studies in highly resistive medium. Some results were obtained for individual grains of polycrystalline samples, welded regions, pure copper, platinum, glassy carbon, single crystals of Cu-Zn-Al alloy, and steel in biodiesel without electrolyte intentionally added. The device showed to be useful for the proposed purpose, allowing to be automated and has potential possibilities of other applications.

Measurements at high temperature using liquid solutions require special cells and materials which are able to support the temperature and pressure developed inside. The constructed cell was designed to support pressures up to 20 bar, temperatures relatively high up to around 200 ºC, depending on the pressure developed inside the system. It also supports aggressive solutions since its inner wall is made of Teflon. The electrolyte has no contact with the metallic body of the cell. Then, it is supposed that this work represents a great contribution to the electrochemical studies of materials in solutions at high pressure and temperature

Este trabalho descreve a preparação de eletrodo de pasta de carbono (EPC) em minicavidade de contato sólido e sua avaliação quando a pasta de carbono contém ou não partículas sub-micormétricas de SiO2(Eu3+ 2%) e SiO2(Eu3+ 2%)-lisina. Nestes estudos, medidas de voltametria cíclica e impedância eletroquímica foram realizadas em PBS (0,1 mol L-1 pH 7,4) contendo as espécies redox Fe(CN)6-3/-4. Os resultados de impedância foram interpretados baseados na reação de transferência de carga envolvendo as espécies Fe(CN)6-3/-4 e/ou oxigênio em frequências mais altas e, difusão das espécies eletroativas e características da pasta de carbono a baixas frequências. EPC-minicavidade é apropriado para eletroanálises usando pasta de carbono modificada.

This work describes the preparation of carbon paste electrode (EPC) in a solid-contact minicavity and its evaluation when containing carbon paste without and with SiO2(Eu3+ 2%) and SiO2(Eu3+ 2%)-lysine sub-micrometrics particles. For this study cyclic voltammetry and electrochemical impedance measurements were performed at pH 7.4 in 0.1 mol L-1 PBS containing Fe(CN)6-3/-4 redox species. The impedance results were interpretated based on a charge-transfer reaction involving Fe(CN)6-3/-4 species and/or oxygen at higher frequencies and, diffusion of the electroactive species and carbon paste characteristics at lower frequencies. EPC-minicavity is suitable for electroanalysis using modified carbon paste.

The electrochemical study of glass like tungsten oxide derivatives requires the construction of special electrodes due to the fact that these glasses are not conductive. Electrodes modified with WO3 change their color when submitted to some potential perturbation. The color change of the electrochromic materials was observed in situ by coupling an electrochemical cell to a stereomicroscope. The constructed cell is versatile and may represent a great contribution to the electrochemical studies of materials, especially in the systems where it is interest to observe the working electrode surface during the electrochemical experiment.

In the present work, the electrochemical behavior of WC-CoCr coatings with 10 (W10), 15 (W15) and 20 (W20) torch passes sprayed by High Velocity Oxygen-Fuel (HVOF) flame on AA7050 aluminum alloy substrate, evaluated in 3.5% NaCl solution, were compared using open-circuit potential (E OC) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coating surfaces and their cross sections were characterized by X ray diffraction and the Rockwell-C hardness test, and also by optical (OM) and scanning electron microscopy (SEM) before and after the corrosion tests. The electrochemical data showed that sample W10 presented higher corrosion resistance than the others in chloride solutions. In some tests, aluminum salts on the coating surface were identified by EDS, indicating the corrosion of the substrate. And using aluminon, aluminum ions were detected and analyzing the surface via stereomicroscopy, hydrogen bubbles were observed, both showing that the electrolyte reached the substrate and galvanic corrosion possibly occurred. The physical characterization showed that sample W10 presented a lower number of cracks and pores, justifying its higher corrosion resistance.

O setor automotivo é um dos mais competitivos e um grande consumidor de materiais ferrosos, que exigem uma eficiente proteção contra a corrosão. Esta proteção é alcançada aplicando revestimentos adequados. Para se aplicar revestimentos se requer uma cuidadosa preparação da superfície que pode ser feita por ataque químico. Neste trabalho, determinou-se a velocidade de reação do aço extra-doce, SAE-AISI 1005, laminado a frio (CFF) utilizando várias soluções ácidas, de baixo custo, baixa agressividade ao meio ambiente e que geram pouco hidrogênio. O estudo cinético foi realizado medindo-se a perda de massa (deltam/mg cm-2) de chapas de aço CFF em função do tempo (s) de reação nas diferentes soluções, com e sem agitação, a 30ºC. Os resultados foram interpretados considerando-se os efeitos de transporte de massa, o efeito oxidante dos íons Me3+ e inibidor dos íons Fe2+. Dentre as várias soluções estudadas a que apresentou maior velocidade de reação foi a solução de H2SO4 2 M + MeCl3 1 M, v = 15,44 x 10-6 g cm-2s-1 para tempos até 1800 s.

The automotive sector is one of the biggest consumers of ferrous materials, which require an efficient protection against corrosion. This protection can be reached applying adequate coatings. A careful surface preparation is required to apply any kind of coatings on surfaces. The surface preparation can be done by a chemical attack. In this work, reaction rates of cold-rolled steel with different acid solutions were determined. The solutions used have low cost, are environmental friendly and some of them generate low quantity of hydrogen. The kinetic study was performed measuring the loss of mass (deltam/mg cm-2) of cold-rolled steel samples with time (s) reaction in the different solutions, with and without solution stirring, at 30 ºC. The results were interpreted considering the mass transfer effect, the Me3+ oxidizing and Fe2+ inhibitor effects on the steel dissolution. Among the different solutions studied, the 2 M H2SO4 + 1 M MeCl3 solution was the one that showed the highest rate, v = 15.44 x 10-6 g cm-2 s-1 for times up to 1800 s.

Estudou-se a influência de adições de 2, 6 e 8% Ag, em peso, na resistividade elétrica da liga Cu-5%Al, utilizando-se o método dos quatro pontos e um sistema de registro contínuo de variação da resistividade elétrica com a temperatura. Os resultados obtidos indicaram que a resistividade elétrica da liga aumenta com o aumento da concentração de prata e que as inflexões observadas nas curvas de variação da resistividade com a temperatura de aquecimento podem ser atribuídas à solubilização da prata na matriz de Cu-Al. Observou-se também que a velocidade de aquecimento da amostra é um fator importante na intensidade e forma dos eventos observados.

The influence of additions fo 2, 6, and 8 wt. % Ag on the electrical resistivity of the Cu-5 wt. %Al alloy was studied by the four-probe d.c. method and an automated recorder system. The results indicated that the electrical resistivity of the alloy increases with silver concentration and that the inflexions on the curves of electrical resistivity changes with temperature may be ascribed to silver solubilization on the Cu-Al matrix. It was also observed that the sample heating rate may change the shape of the curve recorded.