A Theoretical and Experimental Approach to E-pH Diagram for the Niobium-Water System

Abstract

Potential-pH (E-pH) diagrams are usually built from thermodynamic databases available in the literature or from specific software. However, depending on the conditions and the chemical species defined for elaborating a diagram, they may present completely different immunity, passivation, and corrosion domains. In order to obtain a result closer to a real system, experimental E-pH diagrams can be built from polarization curves obtained in the evaluated conditions. This work discloses the construction of a diagram for the Nb-H2O system at 25°C from theoretical study and the specific selection of chemical species in the solutions through computer simulations. The polarization curves for the construction of the experimental diagram were gathered without the use of buffer solutions and under pH monitoring in the solution bulk throughout all assays. The methodology proposed was considered adequate because, from experimental data, a final result compatible with the classic diagram for the Nb-H2O system and the excellent corrosion resistance of niobium in aqueous media were achieved.