IN SITU IMPEDANCE CHARACTERISTICS OF ZIRCONIUM ALLOY CORROSION IN HIGH TEMPERATURE AND PRESSURE WATER ENVIRONMENT

The electrochemical impedance spectroscopy (EIS) was used to analyze the corrosion evolution of pre- and post-transition of the annealed Zr-4 alloy in 0 01 mol/L LiOH aqueous solution at 360 degrees C/18 6 MPa. The results show that oxidation weight gain of Zr-4 alloy increases slowly before corrosion transition When Zr is oxidized into ZrO2, the stress appears in the oxide film clue to volume expansion. With gradually thickening of the oxide film; accumulation of micro-defects will relax the stress in outer layer of oxide film. As a result; the uniform and compact oxide layer turns into double layer with a porous outer layer and a. dense inner one Meanwhile the impedance spectra evolve from single arc into double capacitive arcs When the oxide film forms macro-defects such as cracks; corrosion transition takes place; giving rise to an acceleration of oxidation weight gain and the rapid drop of impedance and corrosion potential. Corrosion potential and electrochemical impedance spectroscopy are able to obtain in situ some information of the transition point