The Coating Adhesion of Lead Dioxide Anode on Titanium Substrate

The Coating Adhesion of Lead Dioxide Anode on Titanium Substrate

Titanium is the usual substrate for lead dioxide anode. Adhesion of the PbO2 coating to titanium is, however, a problem. Certainly, the titanium, usually in the form of a plate or expanded metal mesh, must be pretreated before the anodic plating process in order to remove the existing TiO2 scale from the surface and roughen the surface and prevent passivation. This pretreatment commonly involves, first sandblasting, then an alkaline degrease followed by etching in heated oxalic acid or hydrochloric acid for at least 30 minutes. Even this may be insufficient and various undercoats have been proposed—gold, platinum, tin dioxide, TiO2/Ta2O5, and TiO2/RuO2 are examples of such thin undercoats applied to titanium before deposition of the lead dioxide.

Another approach has involved the use of multilayers of lead dioxide based materials with different compositions; the bottom layer is selected for good adherence and the top layer for the properties desired for the electrode reaction and/or stability to corrosion in the electrolysis medium.

For example, (a) the Ti is first coated with a thermally formed TiO2/Ta2O5 undercoat, then a stress free a-PbO2 layer and finally a b-PbO2/Ta2O5 particle composite. (b)Doped PbO2 coatings on Ti are prepared with an initial layer F-doped material to give good adhesion and stability and a top layer of Bi- or Fe-doped lead dioxide to give the desired electrocatalytic activity. Graphite is also degreased and sometimes oxidised and roughened, either mechanically before deposition or, for example, by electroplating from a bath containing fine silica sand.