Avaliação do desempenho à corrosão do revestimento de zinco com verniz poliuretano e passivadores em substituição ao níquel brilhante em uma indústria de acessórios para moda

Abstract

Metallic coatings have several applications, among them, the use in jewelry and accessories for fashion. The bright nickel (Ni) coating has great use as a final finish due to its protection and bright, however, in some people, skin contact directly with Ni can cause allergies. In this context, the objective of this work was to evaluate the corrosion resistance of electroplated metallic coatings of bright Ni, zinc (Zn) with passivator, Zn with passivator plus sealant and Zn with passivator plus polyurethane varnish (PU), with the purpose to replace the bright Ni eliminating allergenic problems. For this purpose, a visual evaluation of the metallic coatings was carried out, salt spray test, saturated moisture test, immersion test in solution with bleaching detergent, scanning electron microscopy analysis by field emission (MEV/FEG), dispersion spectroscopy in (EDS) and monitoring of open circuit corrosion potential (OCP). By visual assessment, metallic coatings showed different aspects in terms of color, but the Zn coating with passivator plus PU varnish showed high gloss. In the salt spray test the bright Ni coating showed red corrosion in 24 hours of testing, the Zn coatings with passivator and Zn with more sealant passivator showed white corrosion with 24 hours of testing and the Zn coating with passivator plus varnish PU obtained the best result, starting corrosion with 48 test gardens. In the saturated moisture test, the Zn coating with a passivator plus PU varnish showed bubbles on the surface, in contrast, the bright Ni coating showed no visual change after 360 hours. In the bleach detergent immersion test, no metallic coating showed corrosion over 48 hours. In the MEV/FEG analyzes it was found that the bright Ni coating has less flaws and defects, while the other coatings with Zn showed some flaws along the surface. The EDS analyzes showed a higher incidence of the chemical element Zn for Zn coatings with passivator and Zn with more sealant passivator, observing the failure to protect the Zn coating, whereas in the Zn coating with passivator plus PU varnish, a higher incidence was obtained of the chemical element of carbon (C) related to the deposition of a high layer of PU varnish on the Zn coating. In the open circuit potential monitoring test, the bright Ni coating showed a potential of -204,5 mV at the beginning and stabilizing with the reduction of the potential by -428,3 mV, showing red corrosion at the end of the test, in the other coatings of Zn with passivator, Zn with passivator plus sealant and Zn with passivator plus PU varnish showed potential close to each other around - 1,010 V, observing that the coatings did not show resistance to corrosion throughout the test. Therefore, in the results presented, the Zn coating with passivator plus PU varnish showed the best results, demonstrating the potential to replace the bright Ni coating, however, changing the bright Ni process is not indicated before further studies, to guarantee the use of the Zn coating with greater safety in relation to corrosion performance. [resumo fornecido pelo autor]