Developing an Elevated Temperature Pourbaix Diagram of Zirconium

Abstract

For applications that require robustness under extreme conditions, such as in nuclear reactors, zirconium and zirconium alloys are used due to their low neutron absorption cross sections, and good corrosion properties. Zirconium-based cladding in CANDU reactors can be exposed to aqueous temperatures ranging from 260-310°C, resulting in inevitable corrosion despite their high resistance. The corrosion susceptibility of metals can be investigated using a Pourbaix (potential/pH) diagram, which illustrate the stability domain of various metallic species in aqueous solution. This work will focus on obtaining the elevated temperature Pourbaix diagrams for zirconium, up to 100°C. Previously, Pourbaix diagrams have been developed for zirconium and other metals at room temperature. However, elevated temperature diagrams have only been constructed using extrapolation of current thermodynamic data or through computational methods. The elevated temperature data for these diagrams will be empirically obtained using in-situ pH and oxidation-reduction potential measurements in a batch vessel. The solubilities of these materials will be obtained at varying pHs, ranging from -1-14 pH, and the zirconium concentrations will be obtained using inductively coupled plasma spectroscopy (ICP). Solubility data will be used to calculated equilibrium constants and the Gibbs energies for the development of their respective Pourbaix diagrams.