Correlation Between Electronic States Of The Cathodes And Hydrogen Overpotential For Titanium-Based Alloys

In order to understand cathodic reactions of Ti-based alloys, local electronic states of the cathode were simulated by a DV-X-alpha-cluster method. The basis of the assumption of a local electronic cell model in which the anode was the titanium-matrix region and the cathode was the alloying-element containing region. The molecular orbital calculation shows that two conditions are required for the enhancement of the cathodic reaction in aqueous solutions: (1) the density of states near the Fermi level should be large enough to localize conduction electrons in the cathode region, and (2) the energy of the Fermi level should be high enough to discharge localized electrons so that the hydrogen evolution on the cathode surface proceeds smoothly. This conclusions were supported experimentally by a series of the measurements of polarization curves with Ti-0.1% (mole fraction) M alloys (M = W, Re, Ir, Pt, Au, Mo, Ru, Rh, Pd, Ag, Fe, Co, Ni and Cu) in 10% (mass fraction) H2SO4 solutions. An active cathodic reaction was observed when the alloy contained one of the elements that satisified the above conditions: Ir, Pt, Ru, Rh and Pd. The present results indicate that the simulation based on the molecular orbital theory is useful for describing the local electronic states of cathode in aqueous corrosion.