Kinetic and Mechanistic Studies of Oxide Film Formation on Zircaloy- 4 in Lithium Hydroxide using Radio Tracer 32P

Viplav Duth Shukla²* and Ch. Anjaneyulu¹

¹Department of Chemistry, University College for Women, Osmania University, Koti, Hyderabad - 500 095 (India). ²Department of Chemistry, BJR Govt. Degree College, Bazarghat, Nampally, Hyderabad - 500 001 (India).

The kinetics of anodic oxidation of in 0.1M lithium hydroxide have been studied at a constant current density of 8 mA cm-2 and at room temperature. The conventional plots of formation voltage vs time and reciprocal capacitance vs time are found to be non-linear beyond a formation voltage of 180V. But with the addition of a millimole (mM)of sodium carbonate or sodium sulphates or sodium phosphate separately to 0.1M LiOH the conventional plots have became linear even upto breakdown voltage. This marked improvement in the kinetics can be attributed to the incorporation of anions (CO32-, SO42-, PO43-) into the oxide film. The phosphate ion incorporation was confirmed by radio-tracer studies using 32P isotope. The uptake and distribution of 32PO43-content in the film has suggested a mechanism for the growth of oxide film via interstitial movement of oxide ions. Migration of anion impurities from one layer to another layer in the oxide film has also been established by transferring the specimen from active to inactive solution of the electrolyte and vice versa and thinning subsequently. The amount of incorporation has been found to vary with experimental conditions. Radio-chemical experiments confirmed that the rate determining step is at the oxide /electrolyte interface.

Anodic oxide film; incorporation; anions; polarizing power; Radio-tracer technique