Anomalous high-temperature oxidation in the zirconium–copper system

The high-temperature oxidation of the Zr-3 mass % Cu alloy and Zr2Cu in oxygen is characterized by selective oxidation of zirconium while the excess of copper is accumulated at the alloy-oxide interface forming the Zr8Cu5 phase. The oxidation of Zr2Cu at elevated temperatures shows an anomalous decrease of the oxygen consumption rate in the temperature range 890-975 °C. The oxide layer consists of monoclinic ZrO2 mainly, with preferentially oriented crystallites in depth region at 900 °C and tetragonal ZrO2 on the surface below 600 °C, and small amounts of CuO and Cu2O. The reaction kinetics obeys a parabolic rate law. The activation energy of 117.5 kJ/mol and 54.4 kJ/mol has been estimated for the oxidation of the Zr-3 mass % Cu alloy and Zr2Cu, respectively.