Influence of Sn content on the corrosion behavior of Pb-Ca-Sn alloys in high-temperature sulfuric acid solution

Pb-0.08 mass%Ca-Sn alloys with a wide range of Sn contents were prepared, a nd then immersed in 4.50 kmol m(-3) H2SO4 at 338 K to elucidate the influen ce or Sn content on their corrosion behavior. Under natural immersion, the corrosion current of the Pb-Ca-Sn alloys is governed by the cathodic reacti on, which involves the consumption of dissolved oxygen. The anodic reaction consists mostly of PbSO4 formation and Sn dissolution. For the Pb-Ca-Sn al loys with 0 similar to 0.2 mass%Sn, 99% of the anodic current is used in th e former reaction. The formation of the sulfate, which is noticeably fragil e and low in strength, can be assumed to be one cause for the serious corro sion damage to the low-Sn alloy grids in high-temperature sulfuric acid sol ution. On the other hand, the current for the PbSO4 formation decreases lin early with increasing Sn content in the alloys at about 0.3 mass% Sn or mor e. For the high-Sn alloys such as Pb-0.08 mass%Ca-1.2 mass%Sn, the ratio of PbSO4 formation to the anodic current is lowered by the Sn content, and th e mechanical strength may be maintained at a high level to prevent serious corrosion.