Chapter 5 – Leady Oxide

Lead oxide (PbO) exists in two crystalline modifications: red tetragonal (α-PbO) and yellow orthorhombic (β-PbO). β-PbO is obtained at temperatures higher than 486°C and α-PbO, at lower temperatures. During thermal oxidation of lead, first a PbO layer forms on the metal surface, followed by an oxidation reaction that proceeds via a solid-state mechanism, i.e. by diffusion of oxygen vacancies through the PbO layer. In the battery industry, the lead powder used is oxidized to 75–85% and is called leady oxide. It is produced by two methods: Barton pot method. The molten lead (450°C) is fed into the reaction pot equipped with a rotating paddle, where it is pulverized and oxidized by humidified air flow. The oxidized particles are separated, coarse grains go back into the pot for oxidation and the fine particles are used for production of battery paste. Ball mill method. Lead balls are fed into a rotating steel drum. During rotation of the drum, the lead balls rub and strike against each other and get oxidized under the action of the heat generated by the friction and of the air flow drawn through the drum. The air flow carries out the oxidized particles and cyclone separators collect lead oxide grains of the desired size. The leady oxide produced by this method contains only β-PbO. The freshly produced leady oxide powder has elevated temperature and high reactivity. It has to be left to cool down for 3–6 days. If freshly produced leady oxide is used for paste preparation, the obtained paste will have granular structure. The effect of temperature, air flow humidity and flow rate on the properties of the leady oxides and on the productivity of the equipment is discussed. The Barton pot method is more productive, while the leady oxide produced by the Ball mill method is more reactive. An overview of the basic characteristics of leady oxides (crystal modification, chemical composition, water and H2SO4 absorption, specific density, particle size distribution and stability of the leady oxide) is presented. The influence of leady oxide properties on battery performance characteristics is discussed.