Oxide growth mechanism of Zr alloys in aqueous alkali hydroxides

The autoclave corrosion test was performed on the zirconium alloys in various aqueous solutions of LiOH. NaOH, KOH, RbOH and CsOH. The oxide growth mechanism at metal-oxide interface was evaluated using SEM on the samples which were prepared to have an equal oxide thickness at pre-transition regime and post-transition regime. At a low concentration (4.3 mmol), the corrosion rate was gradually decreased as the ionic radius of cation increased. However, at a high concentration (32.5 mmol), the corrosion rate was significantly accelerated in LiOH solution and slightly in NaOH solution. The morphologies and the growth rates of the oxides at metal-oxide interface were dependent on the ionic radius of cation even if the samples have an equal oxide thickness in LiOH, NaOH and KOH. The grain orientation in Zr matrix also controlled the growth rates and the morphologies of the oxides. Therefore, it is considered that the oxide growth mechanism of Zr alloys can be controlled by the cation incorporation into zirconium oxide