Grid alloy composition additives

If thermopassivation is a result of changes in composition of the corrosion layer, then the grid alloy composition will affect the semiconductor properties of the oxides in this layer through the dopants formed as a result of oxidation of the grid alloying additives. The latter s ions will modify the electrical properties of the oxides in the corrosion layer (Table 13.1) [5,6]. 

The rates of the self-discharge reactions also depend on temperature, additives to the active mass, electrolyte formulation, and grid alloy composition. As the surface of the electrodes is covered by PbS04 (the product of the self-discharge reactions), the state of charge of the electrodes begins to affect the rate of the self-discharge process. 

The rate of grid corrosion is influenced by the composition of the grid alloy and the manufacturing process. Selection of appropriate alloying additives is important to reach the desired service fife. 

In an attempt to improve the properties of Pb—low Sb—Sn alloys and increase the productivity of the grid-casting process, different additives to these alloys have been tested. Selenium has proved to be one of the most efficient additives. Alloys with the composition Pb—3.0 wt% Sb—1.3 (or 1.5) wt% Sn—0.05 wt% Se have been in British Naval and British Rail use for over 20 years with very good results [29]. 

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