Electrochemical Characterization of Chromate Free Conversion Coatings on Electrogalvanized Steel

The chromate conversion treatment is widely used, but it requires highly toxic chromic acid solutions with the consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within European Union. The corrosion resistance of three alternative treatments applied on electrogalvanised steel, and immersed in aerated 0.3 M Na2 SO4 solution, pH 10, at 25 °C, was investigated using electrochemical techniques. Their performance was compared with the obtained using the traditional Cr6+-based treatment in the same conditions. The achieved results show that the alternative coatings exhibited discrete protective properties in the sulphate solution. The nitro-cobalt chemical conversion treatment showed similar protective properties than the traditional Cr6+-based treatment, while with the Cr3+-based treatment those were very poor. The phosphate treatment initially performed acceptably but as the time elapsed, its protective properties decreased.Facultad de Ingenierí

Characterization and corrosion resistance of galvanized steel/passivation composite/ polyurethane paint systems

The corrosion performance of electrogalvanised steel sheets pre-treated with a Cr3+ or Cr+6 -based conversion layer and then covered with polyurethane-waterborne topcoat paint has been studied. The pre-treated metallic panels were coated with one of the three tested polyurethane (PU) topcoat paints, in which the dispersion type was the formulation variable. The pigment was TiO2 (rutile) with a PVC value of 10. Before and after the immersion in 0.05 M NaCl (pH 5.70) or 0.1 M Na2SO4 (pH 6.36) solutions, replicates of the different samples were subjected to standardized tests (porosity, gloss and color, hardness, flexibility). During the immersion, blistering and rusting degrees were evaluated through periodical visual inspections, while the coated steel performance was monitored by Electrochemical Impedance Spectroscopy (EIS) measurements. Initial (dry) and final (wet) paint adhesion was also determined. EIS data were interpreted and discussed in terms of the time dependence of the electrical (paint coating) and electrochemical (steel substrate) parameters associated with interfacial processes describing the metal/paint system deterioration. According to the electrochemical properties, visual inspection and standardized tests results, it was concluded that the studied polyurethane-based polymeric films applied on pretreated electrogalvanised steel provided a very effective protection against corrosion as a result of their excellent barrier properties.Fil: Di Sarli, A. R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigación y Desarrollo En Tecnología de Pinturas (i); Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Elsner, Cecilia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigación y Desarrollo En Tecnología de Pinturas (i); Argentina. Universidad Nacional de La Plata. Facultad de Ingenieria; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Tomachuk, C. R.. Energy and Nuclear Research Institute; Brasi

Anti-Corrosion Performance of Cr+6-Free Passivating Layers Applied on Electrogalvanized

Hexavalent chromium-based passivation treatments have been successfully used as promoters of conversion coatings for many years. Their effectiveness is without question although there are many problems with regard to their environmental suitability. Hexavalent chromium compounds are carcinogenic and toxic. These problems have lead researchers to evaluate other potential systems, with lower toxicity, to ascertain if they can replace chromates as effective passivators. Researchers have proposed several alternative passivation treatments; these are processes based on molybdates, permanganates, titanates, rare earth metal and Cr3+ (considered to be non-carcinogenic) compounds. In this work, zinc coatings obtained from free-cyanide alkaline bath and submitted to a Cr3+ based passivation treatment with different colors were studied. The corrosion behavior was studied by polarization measurements and mainly by electrochemical impedance spectroscopy in 0.6 N NaCl solution. Morphological observations on the coatings surface were also performed. The results indicate that the green-colored Cr3+ passivated coatings have a good corrosion resistance followed by yellow and blue-colored passivation respectively. They could be a less polluting alternative to the traditional chromated coatings.Centro de Investigación y Desarrollo en Tecnología de Pintura

Anti-Corrosion Performance of Cr+6-Free Passivating Layers Applied on Electrogalvanized

Hexavalent chromium-based passivation treatments have been successfully used as promoters of conversion coatings for many years. Their effectiveness is without question although there are many problems with regard to their environmental suitability. Hexavalent chromium compounds are carcinogenic and toxic. These problems have lead researchers to evaluate other potential systems, with lower toxicity, to ascertain if they can replace chromates as effective passivators. Researchers have proposed several alternative passivation treatments; these are processes based on molybdates, permanganates, titanates, rare earth metal and Cr3+ (considered to be non-carcinogenic) compounds. In this work, zinc coatings obtained from free-cyanide alkaline bath and submitted to a Cr3+ based passivation treatment with different colors were studied. The corrosion behavior was studied by polarization measurements and mainly by electrochemical impedance spectroscopy in 0.6 N NaCl solution. Morphological observations on the coatings surface were also performed. The results indicate that the green-colored Cr3+ passivated coatings have a good corrosion resistance followed by yellow and blue-colored passivation respectively. They could be a less polluting alternative to the traditional chromated coatings.Centro de Investigación y Desarrollo en Tecnología de Pintura

Characterization and Corrosion Resistence of Galvanized Steel//Passivation Compositive/Polyuethane Paint Systems

The corrosion performance of electrogalvanised steel sheets pre-treated with a Cr3+ or Cr+6-based conversion layer and then covered with polyurethane-waterborne topcoat paint has been studied. The pre-treated metallic panels were coated with one of the three tested polyurethane (PU) topcoat paints, in which the dispersion type was the formulation variable. The pigment was TiO2 (rutile) with a PVC value of 10. Before and after the immersion in 0.05 M NaCl (pH 5.70) or 0.1 M Na2SO4 (pH 6.36) solutions, replicates of the different samples were subjected to standardized tests (porosity, gloss and color, hardness, flexibility). During the immersion, blistering and rusting degrees were evaluated through periodical visual inspections, while the coated steel performance was monitored by Electrochemical Impedance Spectroscopy (EIS) measurements. Initial (dry) and final (wet) paint adhesion was also determined. EIS data were interpreted and discussed in terms of the time dependence of the electrical (paint coating) and electrochemical (steel substrate) parameters associated with interfacial processes describing the metal/paint system deterioration. According to the electrochemical properties, visual inspection a standardized tests results, it was concluded that the studied polyurethane-based polymeric films applied on pretreated electrogalvanised steel provided a very effective protection against corrosion as a result of their excellent barrier properties.Centro de Investigación y Desarrollo en Tecnología de Pinturas (CIDEPINT

Electrochemical characterization of chromate free conversion coatings on electrogalvanized steel

The chromate conversion treatment is widely used, but it requires highly toxic chromic acid solutions with the consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within European Union. The corrosion resistance of three alternative treatments applied on electrogalvanised steel, and immersed in aerated 0.3 M Na2 SO4 solution, pH 10, at 25 °C, was investigated using electrochemical techniques. Their performance was compared with the obtained using the traditional Cr6+-based treatment in the same conditions. The achieved results show that the alternative coatings exhibited discrete protective properties in the sulphate solution. The nitro-cobalt chemical conversion treatment showed similar protective properties than the traditional Cr6+-based treatment, while with the Cr3+-based treatment those were very poor. The phosphate treatment initially performed acceptably but as the time elapsed, its protective properties decreased.Fil: Tomachuk, C. R. . National Nuclear Energy Commission; BrasilFil: Elsner, Cecilia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigación y Desarrollo En Tecnología de Pinturas (i); Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Di Sarli, A. R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigación y Desarrollo En Tecnología de Pinturas (i); Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentin

Characterization and Corrosion Resistence of Galvanized Steel//Passivation Compositive/Polyuethane Paint Systems

The corrosion performance of electrogalvanised steel sheets pre-treated with a Cr3+ or Cr+6-based conversion layer and then covered with polyurethane-waterborne topcoat paint has been studied. The pre-treated metallic panels were coated with one of the three tested polyurethane (PU) topcoat paints, in which the dispersion type was the formulation variable. The pigment was TiO2 (rutile) with a PVC value of 10. Before and after the immersion in 0.05 M NaCl (pH 5.70) or 0.1 M Na2SO4 (pH 6.36) solutions, replicates of the different samples were subjected to standardized tests (porosity, gloss and color, hardness, flexibility). During the immersion, blistering and rusting degrees were evaluated through periodical visual inspections, while the coated steel performance was monitored by Electrochemical Impedance Spectroscopy (EIS) measurements. Initial (dry) and final (wet) paint adhesion was also determined. EIS data were interpreted and discussed in terms of the time dependence of the electrical (paint coating) and electrochemical (steel substrate) parameters associated with interfacial processes describing the metal/paint system deterioration. According to the electrochemical properties, visual inspection a standardized tests results, it was concluded that the studied polyurethane-based polymeric films applied on pretreated electrogalvanised steel provided a very effective protection against corrosion as a result of their excellent barrier properties.Centro de Investigación y Desarrollo en Tecnología de Pinturas (CIDEPINT

Avaliação dos revestimentos de zinco com incorporação de partículas poliméricas

In the last 30 years, zinc plating had remarkable development due to the increasing demand for coatings with better corrosion resistance from the automotive industry. Hexavalent chromium compounds have been used to create conversion layers on zinc providing better anticorrosive protection as well as anchorage properties to painting systems. However, new and more severe environmental regulations impose elimination of these compounds on electrolytes for electroplating and passivation baths and its replacement by environmentally friendly products. In this work, the surface characteristics and electrochemical behavior of a zinc coating added with silicate nanoparticles included in a polymeric matrix were investigated with the aim of evaluating its effectiveness against corrosion. Then, to improve the coating protective properties a barrier waterborne polyurethane film was applied. The characteristics of the dried polymer film (such as adhesion metal/polymer, porosity, rusting degrees and blistering) were investigated using standardized tests while the corrosion resistance was evaluated by means of electrochemical techniques in solution 0.05 mol/L NaCl. The incorporation of silicate nanoparticles include in a polymeric matrix in the zinc coating provided good adhesion of the coating system without the need of applying an application of the passivation layer on the zinc coating.Revestimentos de zinco tiveram um desenvolvimento notável nos últimos 30 anos devido à crescente demanda das indústrias automobilísticas por produtos com boas propriedades protetivas. Compostos contendo íons de cromo hexavalente tem sido utilizados para obter uma camada de passivação sobre o zinco proporcionando melhor resistência à corrosão, além de aumentar as propriedades de adesão à pintura. Normas ambientais mais severas, no entanto, impõem a substituição desses compostos em eletrólitos de eletrodeposição e de passivação por produtos ambientalmente amigáveis. Neste trabalho as características superficiais e o comportamento eletroquímico de um revestimento de zinco com incorporação de nanopartículas de sílica incluídas em uma matriz polimérica foram investigadas com o objetivo de avaliar a eficácia frente à resistência à corrosão. Em seguida um filme de tinta poliuretânica de base aquosa foi aplicado e o seu desempenho foi investigado de acordo com os parâmetros de adesão do filme polimérico/revestimento de zinco, porosidade, avaliação visual do grau corrosão e empolamento. A resistência à corrosão foi avaliada, em solução de NaCl 0,05 mol/L, por meio de técnicas eletroquímicas. As partículas de sílica presente em uma matriz polimérica e incorporadas ao revestimento de zinco proporcionaram boa aderência do filme polimérico sem a necessidade de aplicação da camada de passivação sob o revestimento de zinco.Centro de Investigación y Desarrollo en Tecnología de Pintura

Kinetics of the simultaneous ZnCo electrodeposition

In order to be adopted by the industrial field, the alloys electrodeposition process must produce electrodeposits with the same composition and properties in as wide as possible electrodeposition parameters region. This implies the need to know not only the metals' electrodeposition kinetics in aqueous electrolytes containing both metals but also how that kinetics is affected by the metals relative concentration.Centro de Investigación y Desarrollo en Tecnología de Pintura

Corrosion Performance of Conversion Treatments for Electrogalvanised Steel Sheet

Chromate conversion treatments have been widely used due to their excellent corrosion resistance properties; however, their use is increasingly restricted because of the highly toxic chromic acid solutions required, with consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within most of the developed countries. In this work, the corrosion resistance of different alternative pretreatments applied on electrogalvanised steel sheet: 1) Cr(III) and Zr complexes layer, 2) Ce(III) layer, 3) Ce(III)/Ce(IV) double layer, 4) Cr(VI) chromating was investigated, and its results compared with those from the tests performed using bare electrogalvanized steel sheets as a substrate. These samples were exposed to aerated 0.05 mol/L NaCl or 0.1 mol/L Na2SO4 solutions. The electrochemical behavior of samples was studied by electrochemical techniques. For three days of immersion in the solution test, the experimental results have shown that, compared with the Cr(VI) protective properties, the Cr(III) + Zr complex layer presented similar performance. Even though the initial corrosion resistance was offered by the Ce(III) and Ce(VI)/Ce(III) conversion coatings was relatively good, it quickly decreased as a function of the exposure time.Fil: Di Sarli, Alejandro Ramón. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; ArgentinaFil: Elsner, Cecilia Ines. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería; ArgentinaFil: Palomino, L. E. M.. Universidade de Sao Paulo; BrasilFil: Tomachuk, C. R.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentin