2008 年 59 巻 5 号 p. 326
Cathodic polarization of niobium specimens that have been anodized galvanostatically up to Ea=100V, and then potentiostatically at Ea=100V has been investigated in a neutral borate solution. During potetiostatic cathodic polarization below Ec=−2.36V (vs. RHE) in both aerated and deaerated solutions, the cathodic current increased rapidly initially, and then increased gradually until it reached a steady value. Hydrogen gas evolution was observed during cathodic polarization below Ec=−2.36V with no formation of blisters and pits, suggesting that H+ reduction occurs mainly at the film surface. GD-OES spectra revealed that hydrogen species are enriched in the niobium substrate near the interface between anodic oxide films and the substrate at potentials below Ec=−2.36V, and that the trend is pronounced at lower potentials. Chemical shift was observed on Nb 3d and O 1s peaks in XPS spectra for the specimen at Ec=−3.36V, suggesting the formation of Nb2O3(OH)2.
Mechanism for the reaction during cathodic polarization in a neutral solution is discussed in terms of the proton reduction at the interfaces both between oxide films / solutions and between oxide films / substrates.