Tin effects on conductivity of battery grids

Following the studies on pure lead [57,64], a great deal of work has been undertaken to determine the effects of tin on the corrosion layer of lead-calcium-tin alloys, which are the major alloys for VRLA batteries. One study [82] showed that the corrosion rate of lead-calcium alloys was significantly reduced by the addition of tin and the thickness of the a-PbO layer was substantially reduced. It was further found that tin enrichment at grain boundaries in cast alloys induced a high level of tin in the corrosion layer that was able to suppress passivation. Finally, it was suggested 

Tin has been shown to increase greatly the conductivity of the passive corrosion layer in lead-calcium alloys. The presence of tin can exercise an important influence on the corrosion resistance of lead-calcium-tin alloys, as well as on the thickness and conductivity of the passive layer formed on the alloys [91]. Tin additions of about 

% or more have been shown [90,92] to increase markedly the conductivity of the corrosion layer, particularly of the a-PbO, which can develop under deep-discharge conditions. Lead-calcium alloys show significant dilferences from pure-lead counterparts [65]. A lead-calcium alloy with 0.6wt.% Sn shows no enrichment of tin in the oxide layer [91], while an alloy with 1.2wt.% Sn exhibits only moderate enrichment. It is not until the tin concentration reaches 1.5wt.% that significant 

The phase diagram [97] presented in Fig. 2.10 shows the tin level above the V value of 9 1 that is sufficient to force the calcium within the cast matrix to react and produce continuous (PbSn)3Ca precipitates and dope the grain and interdendritic boundaries. The high tin content of the segregated boundaries enhances the localized doping of the corrosion product at the grid surface (Fig. 2.11). 

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