Abstratc This work reports the production of low-tin Cu-Sn alloy coatings on carbon steel substrates using a bath containing CuCl2, SnCl2, and sodium citrate. In the first part of this study, the coatings were electrodeposited by direct and simple pulse current processes (DC and SPC, respectively). Different current density values were used, while the pulse frequency and duty cycle remained constant. Independent of the current mode used, low-tin Cu-Sn coatings, showing globular surface morphology and Cu6Sn5 as the main compositional phase, were produced. Both the current mode and the applied current density affected the anticorrosive properties of the coatings. The most protective DC and SPC coatings, showing Sn content < 3 wt.% and compact morphology, were prepared using j = 80 A m-2 and jc = 167 A m-2, respectively. High charge transfer resistance values were verified even after immersion for 24 h in 0.5 mol L-1 NaCl solution.

RESUMO 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 e o uso de revestimentos metálicos tem servido bastante a este propósito. A produção de revestimentos metálicos permite modificar a superfície do substrato levando à formação de um 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 que eleva 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 propriedades anticorrosivas, a partir de banho eletrolítico menos agressivo, apresentando diferentes concentrações iônicas de cobre e estanho. Os revestimentos foram eletrodepositados em substrato de aço-carbono, utilizando eletrólitos ácidos contendo CuCl2, SnCl2 e glicina. Estes revestimentos foram posteriormente caracterizados através das técnicas de microscopia eletrônica de varredura (MEV), espectroscopia de raios X por energia 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 um aumento nos valores da resistência de transferência de carga (Rtc). Contudo, os ensaios de polarização mostraram que estes filmes não atuaram como revestimentos protetores. As análises morfológicas evidenciaram a formação de revestimentos porosos, o que pode explicar seu pobre comportamento eletroquímico.

ABSTRACT The problems related to corrosion are frequent and may occur in many areas, such as the chemical, petrochemical, naval, civil construction and automobile industries, among other productive sectors. Therefore, corrosion prevention methods should be employed to avoid loss of materials and the use of metallic coatings has served well for this purpose. The production of metallic coatings allows a modification on the substrate surface leading to the formation of a functional material that presents the desired properties and characteristics, in this case, corrosion resistance. However, these coatings are generally produced using toxic cyanide-based baths, which increases the cost of the process due to further treatment of the generated wastes. The present work proposes an initial study aiming at producing of Cu-Sn alloy coatings, with anticorrosive properties, originated from a less aggressive electrolytic bath, presenting different copper and tin ionic concentrations. The coatings were electrodeposited on carbon steel substrate using an acidic electrolyte containing CuCl2, SnCl2 and glycine. These coatings were further characterized by scanning electron microscopy (SEM), X-ray spectroscopy energy dispersive (EDS), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results of EIS showed that the films produced with higher copper contents presented an increase in the values of the charge transfer resistance (Rct). However, the polarization experiments showed that these films did not act as protective coatings. The morphological analysis evidenced the formation of porous coatings, which may explain their poor electrochemical behavior.

Corrosive processes in acidic medium reduce the performance and durability of metallic materials, causing problems to several industries. Corrosion inhibitors are commonly used to decrease these effects. As these inhibitors must be ecologically friendly currently, this work evaluated the anticorrosive effect of natural extracts of coffee husks (Coffea arabica L.) in the protection of carbon steel in 1 mol L-1 HCl solution. Extractions were performed using water as the extraction solvent. The polyphenols content increased with the extraction temperature, and the extracts were produced using 100 ºC. Extract concentrations of 10, 20 and 30 % v/v were analyzed as inhibitors for carbon steel in acid medium, using weight loss and electrochemical tests, as well as scanning electron microscopy. There was an increase in the inhibition efficiency as the extract concentration increased, reaching values around 97 % using 30 %v/v of extract for the weight loss tests.

This work aims evaluate the use of biocides in the microbiologically-influenced corrosion (MIC) of AISI 1020 carbon steel by sulfate-reducing bacteria (SRB) in artificial seawater. A natural biocide (garlic oil) and a commercial biocide (glutaraldehyde) were used to control the corrosion caused by these bacteria in artificial seawater. Microbial growth on the steel surface was evaluated by quantifying the sessile SRB using the most probable number (MPN) method. The action of biocides in the biocorrosion process was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The biofilm formation and the corrosion products on the steel surface were observed by scanning electron microscopy (SEM). The results showed that, although it was not able to inhibit the growth of sessile SRB completely, garlic oil showed a greater reduction in the corrosion process when compared to glutaraldehyde, indicating its possible application as a natural biocide under these conditions.

Cu-Co alloys were electrodeposited on steel substrates from alkaline sodium tartrate electrolyte using direct and single pulsed current (DC and SPC, respectively). The electrodeposition bath was composed by 0.02 mol L−1 of CuSO4.5H2O, 0.10 mol L−1 of CoSO4.7H2O and 0.50 mol L−1 of Na2C4H4O6.4H2O. Using both kind of deposition processes, it was verified that the applied current density (j) affected the cathodic current efficiency (Ef), the copper and cobalt contents in the coatings (wt. % Cu and wt. % Co, respectively), the morphology and the anticorrosive performance of the coatings (based on the transfer charge resistance, (Rct) values). Comparing the results obtained for DC and SPC coatings, those produced by single pulsed current improved the Ef values and decreased the grain sizes. Concerning the conditions used in this work, the coating produced under the conditions of Experiment 4’, using jm = 40 A m-2 and SPC mode, presented 15.9 wt. % Co, the most compact morphology, the smallest grain size and the highest Rct value after 24 h of exposure in the saline medium.

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.

ABSTRACT 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.

Zn-Co alloy coatings were produced on carbon steel, at room temperature, from citrate baths (0.100 mol L-1) containing [Zn2+]= [Co2+] = 0.05 mol L-1. Coatings with %m/m Co > %m/m Zn were observed under all deposition conditions, except for I = 10 A m-2. As the current density (I) was increased, a significant decrease (p<0.05) in %m/m Zn was noted, and the highest value of % m/m Co was observed at 80 A m-2. The Co-rich coatings presented refined microstructure, with small grain sizes. The smallest Icorr of the studied substrate/coatings systems, 2.4 µA cm-2, was obtained at I = 10 A m-2. Under these conditions, the coatings contained ~ 30 % m/m Co and 70 % m/m Zn and only the γ-ZnCo phase was obtained. The Icorr found in the present work is smaller than those usually found in the literature for Zn-Co coatings with small Co content.

In the present work, cysteine and allyl alcohol were added to citrate baths as additives to Cu-Zn coatings on steel substrates. In order to verify the effects of the deposition parameters (current density, mechanical stirring speed, and additives) on the coating composition, electrochemical behavior, morphology, and microstructure properties of Cu-Zn coatings, the electrodeposition of the alloy was carried out using an experimental composite design 2³, in which these parameters were considered the entry variables and the measured properties were the response variables. The confidence level was 95% and the results were shown as response surface diagrams. It was possible to verify that the current density affected the zinc content in the coating, while the coating produced from cysteine-contained bath presented the worse anticorrosive performance. In a general way, it was possible to observe that the studied parameters affected the morphology, grain size, and the electrochemical behavior of these coatings, although only a few response variables were statistically influenced by them.

In the present work, stainless steel and Ni-Ti commercial orthodontic wires were immersed in artificial saliva solutions, containing or not F- ions, in different pH values, during 30 days. The weight loss and the Ni2+ content in the solutions at 15 and 30 days of exposition were evaluated using a composite design 2³ and response surface methodology. The open circuit potential (OCP) was measured over the same period of time. Polarization curves and morpHological analysis of the wires before and after the corrosion experiments were also carried out. The results showed that corrosion of the studied metal alloys depended on a combination among saliva pH, the exposition time, and the concentration of F- ions in the solution. The critical condition was observed for Ni-Ti wires at pH = 3.0, and high concentration of F- ions, causing a decrease in the OCP values and an increase in Ni dissolution and corrosion current density.

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 mixture of carboxylic acids present in petroleum oil and directly responsible for its acidity and corrosiveness in liquid phase during the refine process is denominated "naphthenic acids". These acids are also present in distilled fraction of petroleum, causing several problems in final products quality. A possible way to remove the carboxilic acids from petroleum distilled fractions is the adsorption in porous materials. However, the results obtained until now indicate that ion exchange resins would be the best adsorbents for this process, which would probably increase its cost. In this work, two commercial adsorbents (clay and activated alumina) were characterized by a set of physical-chemistry techniques and evaluated concerning their capacity of removing naphthenic acids from a light petroleum fraction. It was verified the influence of a thermal treatment previous to the adsorption in its physical-chemistry characteristics and its properties. A high reduction of the TAN values was verified in the residual oils from both adsorbent, although there was a competition among all the compounds present in the light oil fraction for the adsorption sites, which can be probably related to the thermal pre-treatment. These results were related to corrosion yield experiments, and it was observed that the adsorbent pretreatment also affected the reduction in corrosion yields for both alumina and clay.