A Study of the Electrodeposition of Lead Dioxide from Alkaline Baths - Deposition Process and Coating Quality
Electrodeposition of lead dioxide from alkaline, acid and EDTA-based baths was studied (Figs.1-3, Tabl.1). Silicate additive included into the deposits in the amounts less than 1%, however, changes their structure (Fig.3). Bright, unstressed coatings were obtained at 333K and 50-200 A|m 2 (Fig.4). Unstressed coatings were not deposited from nitrate baths (Fig.5). Small additions of sodium silicate (0.015-0.02 M) improved also the quality of cathodic deposits of lead (Fig.6). The material of substrate for the anodic deposition of lead dioxide may be selected not only among materials with high oxygen overvoltage such as Pt and Ti, but also alloyed steel is suitable. Stability of PbO 2 coating in the course of an anodic etching is increased by 4-7.5 times due to the addition of 0.01-0.02M sodium silicate to EDTA bath. This bath (0.3M EDTA) has the highest throwing power (78%) as compared to the alkaline (75%) or nitrate (19%) baths (Fig.7). Contact of the solution with lead metal retards the formation of sludge, which is not formed at a certain ratio of cathode-to-anode surface. The latter is equal to 32 for the alkaline solution and to 6 for the EDTA one rising up to 6,35 in the presence of silicate additive. Bipolar anodes were prepared and tested successfully at a pilot-scale unit.