CORROSION BEHAVIOR OF TBFECO MAGNETOOPTIC AL RECORDING FILMS WITH PROTECTION COATING IN AQUEOUS ENVIRONMENT

Corrosion behavior of sputter-deposited TbFeCo magneto-optical recordi ng films with protection coating has been studied in an aqueous soluti on. Specimens having Si3N4 (0 similar to 234 nm)/Tb0.33Fe0.48Co0.19 (7 4 nm)/glass structure were prepared and an immersion corrosion test an d an electrochemical impedance measurement of the specimens were perfo rmed in 1.0 kmol . m(-3) Na2SO4 of pH6.30. The corrosion morphology of the specimens in the solution was pitting, which started from pinhole defects in Si3N4 protection films. The morphology changed with the th ickness of the protection films. The selective dissolution behavior of alloying elements in TbFeCo films into the test solution also changed with the thickness of the protection films. Electrochemical impedance diagrams changed with the progress of pitting corrosion on the specim ens. After an analysis using an electrical equivalent circuit of the c orroding system, the values for the charge transfer resistance and the relaxation coefficient were found to decrease with the growth of pitt ing corrosion.