Characterisation of phosphate coatings on zinc, zinc-nickel and mild steel by impedance measurements in dilute sodium phosphate solutions

摘要

Electrochemical Impedance Spectroscopy (EIS) was used in seeking a non-aggressive test solution for evaluation of phosphate coatings. Impedance measurements were performed at room temperature in na_2HPO_4 solutions of concentrations from 5x10~4 to 0.1 mol L~1 on steel and on electrodeposited Zn and Zn-12/100 Ni. It was found that 0.005 M Na_2HPO_4 was most appropriate as a test solution owing to its low aggressiveness and the ability to strongly differentiate electrochemical behaviour of phosphated and unphosphated materials.