FABRICAÇÃO E CARACTERIZAÇÃO DE ELETRODOS DE PbO2 ELETRODEPOSITADOS SOBRE TITÂNIO

Abstract

The aim of this work was to investigate the PbO2 electrodeposition process on the titanium substrate thermally modified by the rapid cooling method at the transition temperature to the beta phase of the metal. Measures in treated electrodes and simultaneous microscopic filming indicated contributions in the overlay process. The thermal treatment of the Ti substrate led to an increase in grain size and, eventually, depending on the treatment time and cooling speed, to the formation of the martensite phase. In all situations, heat treatment increases the strength of the oxide film and the charge transfer resistance. These effects lead to a decrease in the selective deposition process as well as decrease the oxygen release along the electrodeposition of PbO2, allowing the formation of more uniform deposits and more efficient coating. Some pre-treatments were analyzed, such as the use of oxalic acid, which proved to be interesting in the film anchoring process, but no decrease in the TiO2 layer was observed. Also, the influence of different granulometry sandpaper sizes was investigated, which did not had an influence on the growth of titanium oxide. Different current densities were considered for the growth of the PbO2 and TiO2 film, where the intermediate ones, above 2.5 mA.cm-2 and below 15 mA.cm-2 were more suitable for electrodeposition. During PbO2 deposition, three simultaneous processes were present: TiO2 growth, PbO2 deposition and oxygen deposition. The thermal treatment of the substrate, as well as the deposition currents were important factors that determined the interrelationship between these three processes.