Analysis of corrosion resistance in simulated acid rain of Zn-Sn alloys

摘要

Zinc and tin, together with Zn-Sn alloys are used in industrial operations and steel coatings against corrosion. One of its most common uses is the galvanizing process for outdoor structures, which is affected by corrosion caused by acid rain. The aim of the study is to evaluate the electrochemical behavior of Zn-Sn alloys with respect to pure metals, in an aqueous simulated acid rain solution consisting of 31.85 mg/L H2SO4, 15.75 mg/L HNO3, 21.25 mg /L NaNO3, 46.20 mg/L (NH4)2SO4, 31.95 mg/L Na2SO4, 84.85 mg/L NaCl, at a pH between 3,5 and 4,0, at room temperature (25°C). Zn-Sn alloys samples were used with different percentages of tin (6 wt. % Sn, 10 wt. % Sn and 50 wt. % Sn), and pure metals samples. The samples were obtained by horizontal directional solidification. Samples of each of the revealed structures were taken and roughed with papers of SiC, of grain size between # 60 and # 1200. Subsequently, potentiodynamic polarization essays were performed in a conventional three electrode electrochemical cell and immersion tests. Each ones was examined by optical microscopy, before and after performing the tests. For cross sections of samples, in potentiodynamic curves was observed that increasing tin content in the alloy, the potential tend to nobler values. From immersion tests was observed that the columnar structure of zinc and alloys exhibit greater mass loss than other structures. Moreover, zinc and alloys have high corrosion rates on the first day of immersion, for all grain structures. The micrographs showed that zinc presents generalized corrosion.