Hydride formation on titanium surfaces by cathodic polarization

The formation of external layers of TiH2 on titanium metal by cathodic polarization was studied in buffers of oxalic, tartaric and of acetic acids. Reliable and reproducible hydride layers were obtained from pH 0.8 to 5.3. Variations in pH in this region had little influence. The thickness of the hydride layers increased with increasing current density in the range investigated from 0.14 to 6 mA cm−2. Air-formed titanium oxide film inhibited hydride formation for a period, which could last some hours at low current density. Thereafter the hydride layer thickness increased nearly proportionally with time, a typical value after 20 h treatment with 1 mA cm−2 being 13 μm. The roughness of the surface increased and formation of titanium nodules was observed after treatment with high current density. The current efficiency for hydride formation was approximately 1% at the lowest current densities and 0.15% at 6 mA cm−2. Tafel slopes in the range 0.3-0.4 V/decade indicated an exceptional electrochemical kinetics.