The influence of the electronic properties of passive films on the corrosion resistance of Mo-Ta alloys - A photoelectrochemical study

Photoelectrochemical experiments have been carried out for characterizing p assive films on Mo-Ta sputtered alloys having different compositions, as we ll as on pure Mo and Ta metals. Both corrosion layers, formed by simple imm ersion in solution, and films grown anodically were investigated. The prese nce of Mo species in the passive layer anodically shifts the flatband poten tial with respect to pure Ta2O5 films. For high Mo contents the films chang e their behavior from an insulating to n-type semiconducting one. A variati on in the optical bandgap occurs due to the change of the Mo6+/Ta5+ ratio i nto the passive films. Cross experiments, performed in different solutions on the same film, suggest that a loss of Mo6+ ions occurs at the oxide/elec trolyte interface under anodic polarization. The influence of Mo content on the electronic properties of the passive films is invoked in order to expl ain its effect on the corrosion resistance of the different alloys. (C) 200 0 The Electrochemical Society. S0013-4651(99)05-032-6. All rights reserved.