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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.

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1 正会員 工博 早稲田大学理工学術院教授（〒 169-8555 東京都新宿区大久保 3-4-1） 学生会員 早稲田大学大学院創造理工学研究科（同上） 学生会員 早稲田大学創造理工学部社会環境工学科（同上）The main purpose of this study is to understand the evolution process of river bed in case that the sediment size distribution is extremely wide. In this fundamental experimental study, the bed is composed of three groups of sediment, and one of the grain size is completely different from each other. One is L-particle which cannot move at all in the stream, and constitutes a bed frame. And M-particle or S-particle exists in the space surrounded by L-particles, and moves as bed load or suspended load, respectively. Hiding effect of L-particle on M and S-particles was evaluated, and the vertical structure of bed was also made clear in the evolution process toward a static equilibrium state. In addition to these, it was found that the arrangement of L-particle cannot affect the state of equilibrium state.