High Temperature Oxidation of Two Zirconium-Tin Alloys

The rate of oxidation of a zirconium‐1.5 wt % tin alloy followed a cubic law in the temperature range 600°–900°C at 1 atm pressure. However, two different energies of activation were obtained. In the range 600°–800°C the activation energy was calculated to be and the cubic rate constant in (ml/cm 2 ) 3 /sec can be expressed as . An activation energy of was obtained in the range 825°–900°C and the cubic rate constant is . For a zirconium‐2.5 wt % tin alloy, the rate of oxidation followed a parabolic law in the range 550°–900°C. The parabolic rate constant in (ml/cm 2 ) 2 /sec was calculated to be , where is the activation energy. Adherent gray‐black oxidation films were found to be N ‐type semiconductors and from this a mechanism for the oxidation of zirconium is proposed. The effect of tin in the zirconium is to increase the porosity of films and decrease the time before breakdown of the protective properties of the films.