The use of Tafel back extrapolation to clarify the influence of ruthenium and palladium alloying on the corrosion behaviour of titanium in concentrated hydrochloric acid

Tafel back extrapolation of the cathodic reaction was used to interpret polarization data obtained for titanium alloyed with small amounts of ruthenium and palladium in concentrated hydrochloric acid. It was found that the ruthenium and palladium stimulated the cathodic reaction, but that the anodic behaviour of the titanium was unchanged. The results indicate that the corrosion of the titanium is increased by the small amount of alloying as the catalysis of the hydrogen reduction reaction was not strong enough to cause passivity of the titanium under these conditions. This was even so at longer times of exposure when significant enrichment of the ruthenium and palladium occurred on the surface of the titanium. Thermodynamic data were used to give further perspective to the results. Although excellent Tafel behaviour was found for the cathodic reaction, the exchange current densities and Tafel slopes obtained, are specific to the prior exposure time and surface enrichment of the alloying elements, and should not be interpreted as steady state data.