Corrosion behavior of Pb-Ca-Sn alloys during charge/immersion cycling in high-temperature sulfuric acid solution

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 allo y. In this study, Pb-0.08 mass%Ca-Sn alloys with a wide range of Sn content s were prepared and the corrosion tests with charge/immersion cycling were carried out in 4.50 kmol m(-3) H2SO4 at 348 K for 604.8 ks. The total mass change during the corrosion test, which is the sum of mass change of the sa mple electrode and amount of suspended powder in the solution, increases wi th decreasing of the Sn content. For the Pb-Ca-Sn alloys with 0 similar to0 .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 th e Pb-Ca-Sn alloy. These data suggest that the corrosion attack has mainly o ccurred at the grain boundary of the alloy. Moreover, the analysis of the c harge reaction makes clear that about 97 similar to 99% of the charge curre nt is used for the oxygen evolution. Only 0.08 similar to2.75% of the curre nt is spent in formation of the corrosion layer consisting of PbSO4 and bet a -PbO2 and the ratio decreases as the Sn content increases.