Corrosion Behavior of Pb-Ca-Sn Alloys during Charge/Immersion Cycling in High-Temperature Sulfuric Acid Solution

Abstract

Sb free alloys, especially Pb Ca Sn alloys are the choice material for the grids of the valve regulated lead acid (VRLA) batteries. However, the grid is liable to be severely attacked, depending on the composition of the alloy. In this study, Pb 0.08 massCa Sn alloys with a wide range of Sn contents were prepared and the corrosion tests with charge/immersion cycling were carried out in 4.50 kmol m -3 H 2 SO 4 at 348 K for 604.8 ks. The total mass change during the corrosion test, which is the sum of mass change of the sample electrode and amount of suspended powder in the solution, increases with decreasing of the Sn content. For the Pb Ca Sn alloys with 0～0.20 massSn, the amounts of the total mass change during the corrosion test with charge/immersion are about 8 times as much as those with immersion. A proportional correlation between the total mass change and Ca dissolution can be recognized during the corrosion test, with charge/immersion or with immersion. And, high Sn contents tend to coarsen the grain structures of the Pb Ca Sn alloy. These data suggest that the corrosion attack has mainly occurred at the grain boundary of the alloy. Moreover, the analysis of the charge reaction makes clear that about 97～99 of the charge current is used for the oxygen evolution. Only 0.08～2.75 of the current is spent in formation of the corrosion layer consisting of PbSO 4 and b PbO 2 and the ratio decreases as the Sn content increases.