MINOR ELEMENTS IN LEAD MATERIALS USED FOR LEAD-ACID-BATTERIES .1. HYDROGEN-GASSING AND OXYGEN-GASSING CHARACTERISTICS

Minor elements are commonly present in the raw lead materials that are used to manufacture lead/acid batteries. Although certain of these el ements are known to exert, individually, a marked influence on the gas sing characteristics during charging, less is understood of their coll ective effects. As the first stage in an experimental campaign to obta in such information, the evolution of hydrogen and oxygen has been exa mined on both bare (grid) and doped/pasted electrodes. With the latter electrodes, different dopants (Ag, Bi, Cd, Cr, Ni, Sb, Se, Sn, Zn) ha ve been introduced at a level of 0.1 wt.%. The subsequent gassing rate s have been determined by application of either a potential-scan or a potential-step procedure. The latter has been conducted together with gas collection. The hydrogen-evolution characteristics on bare electro des are dependent on the chosen lead alloy. The rate increases in the order: Pb < Pb-0.09Ca < Pb-0.07Bi < Pb-0.09Ca-0.4Sn < Pb-0.09Ca-0.3Sn < Pb-0.09Ca-0.7Sn < Pb-2.2Sb < Pb-1.7Sb < Pb-5.7Sb. By comparison, the oxygen-gassing rate does not exhibit such a clear relationship with a lloy composition. In general, oxygen evolution above 1.7 V increases i n the order: Pb < Pb-0.09Ca-0.3Sn < Pb-2.2Sb < Pb-0.09Ca almost-equal- to Pb-5.7Sb < Pb-0.09Ca-0.7Sn < Pb-0.07Bi < Pb-0.09Ca-0.4Sn < Pb-1.7Sb . The Pb-0.09Ca-0.4Sn and Pb-1.7Sb electrodes exhibit abnormal hydroge n- and oxygen-evolution rates. This is probably due to the fact that t hese two alloys were made by a different manufacturer. The degree of h ydrogen evolution on untreated and doped negative-material (pasted) el ectrodes can be classified in terms of a low, a medium, or a high rate . For elements that give a low rate, gassing increases in the order: A g < Zn < untreated < Cd < Bi almost-equal-to Cr. The Sn- and Se-doped electrodes exhibit a medium evolution rate. Finally, Sb- and Ni-doped electrodes display the highest rate of hydrogen evolution; of these, n ickel exerts the stronger effect. All the dopants enhance oxygen evolu tion. The gassing rate increases in the order: untreated almost-equal- to Cd < Se < Sn < Bi almost-equal-to Cr < Ni almost-equal-to Zn < Sb < Ag. The hydrogen- and oxygen-gassing behaviour of the doped electrode s is discussed in terms of the operating characteristics of valve-regu lated batteries.