Initial oxidation of zirconium in steam at 500 C (932 F), one atm is considerably accelerated by contamination deposited on metal surface during vacuum annealing in silica capsules. Radioactivation analysis shows that copper is transferred from silica to the zirconium. The layer of affected metal is less than 10μ thick, and may be removed by electropolishing. A “clean” surface with a low initial oxidation rate is produced by electropolishing, followed by rinsing in methanol.
Accelerated oxidation results when electropolished surfaces are dipped in aqueous solutions of several cations, including copper, or when they are given the normal HNO3/HF pickle followed by tap water rinsing. Simple immersion in tap or redistilled waters also can accelerate oxidation, probably due to the calcium present; but exposure to HF solution with rigorous exclusion of calcium, appears to have no effect.
Implications of these results for oxidation studies and corrosion testing are discussed.
