High Temperature Oxidation of Two Zirconium-Tin Alloys

Abstract

The rate of oxidation of a zirconium 1.5 wt % tin alloy followed a cubic law in the temperature range 600~176 at 1 atm pressure. However, two different energies of activation were obtained. In.the range 600~176 the activation energy was calculated to be 38,400:t: 1100 cal/mote and the cubic rate constant in (ml/cm~)~/see can be ex-pressed as k = 5.34 X 104 exp (--38,400/RT). An activation energy of 22,600 • 1400 cal/mole was obtained in the range 825~176 and the cubic rate constant is k = 87.2 exp (-22,600/RT). For a zirconium-2.5 wt % tin alloy, the rate of oxidation followed a parabolic law in the range 550~176 The parabolic rate constant in (ml/cm2)2/sec was calculated to be k = 2.63;4 103 exp (--32,400/RT), where 32,400 4- 1000 cal/mole 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.