Estudo das variáveis PH e densidade de corrente na obtenção da liga ternária Zn-Fe-Ni por eletrodeposição.

Abstract

Electrodeposition is a very efficient technique for obtaining metallic coatings, it has a low cost and excellent reproducibility, since it is possible to control several parameters such as, for example, pH, current density, temperature, degree of agitation and chemical composition of the electrolyte. In view of these various parameters, the use of factorial planning is fundamental, as it allows the analysis of variables in a quick and simple way from a mathematical model, in addition to observing the behavior of the experiment within the defined variables combined with the technique of the methodology of the surface of answer. It should be noted that the chemical elements Zn, Ni and Fe are already widely used in metallic coatings and binary alloys. Zn-Metal alloys can present a phenomenon called anomalous co-deposition, in which zinc deposits preferentially in relation to more noble metals. In this work, a 22 factorial design plus two central points was used to evaluate the pH and current density factors in the obtained coatings. The coatings showed great variations in relation to the chemical composition, at the lowest levels of pH (2) and current density (10mA/cm2), a higher percentage of Zn deposit was observed, as well as the highest current efficiencies, about 38%, at the highest levels of pH (7) and current density (60mA/cm2), a greater deposit of Ni and Fe was observed, which inhibited the deposition of Zn, at these points the current efficiency was the lowest, reaching 15%. Surface morphology and energy dispersive spectroscopy maps showed coatings with unique features containing cracks and nodules that tend to repeat. According to the X-ray diffractograms, the experiments showed noble phases Ȗ Ni2Zn11 and Fe3Ni2 as well as phases of low nobleness (Zn phase). For the corrosion tests in saline solution (NaCl 3.5%), experiments 4 and 5 were the best and worst, respectively, experiment 4 obtained at pH 7 and current density of 60mA/cm2 had the highest resistance to polarization of 46.01 KΩ.cm2, and one of the lowest corrosion current densities 1.22 x10-3 mA/cm2, justified by the exclusive presence of the noblest phases Ȗ Ni2Zn11 and Fe3Ni2, unlike experiment 5 which obtained the lowest resistance to polarization β.11 KΩ .cm and the highest corrosion current density, 3.42x10-3 mA/cm2, due to the low presence of the noble phase Ȗ Ni2Zn11 and the presence of the Zn phase considered of low nobility.