FORMATION AND DISSOLUTION BEHAVIOR OF ZRO2 FILM IN H3PO4 ACID-SOLUTIONS

The galvanostatic anodization of zirconium in phosphoric acid was studied. The results show that the rate of formation of the anodic oxide film on zirconium increases with increasing current density and acid concentration. The currentless dissolution of the oxide film in H3PO4 solutions was investigated using capacitance and potential measurements. The influence of the formation voltage, acid concentration and temperature on the dissolution rate of the oxide film was also studied. The dissolution behaviour of the oxide film in H3PO4 shows a two-stage dissolution process that seems to be related to the duplex nature of the oxide film; the outer layer is more susceptible to dissolution than the inner layer. The dissolution of the oxide film follows a zero-order rate equation. The average rate constant for dissolution of the entire oxide film KBAR was found to increase with increasing formation voltage and acid concentration. Also, an increase in temperature of the dissolving medium enhances the dissolution rate of the oxide film. The activation energy was found to be 37.4 kJ mol-1.