Investigation of phosphate coating formation by electrochemical impedance spectroscopy

In this investiAation, an attempt has been made to use electrochemical impedance spectroscopy as a tool for monitoring the phosphate coating formation, especially the involvment of hase metal in the coating fornlation. Results of the studies have been presented in the foml of Nyquist plot.. of various immersion time which shows a depressed semicircle and the diameter and degree of depression increase with time. Charge transfer resistance and the int~rfacial capacitance of steel in phosphatin~ solution are parameters of impedance study which helps in assessing and optimizing the conditions of phosphating. The result.. also show that presence of crystal refiner and/or accelerator accelerate the base metal dissolution at the initial stJlge of coating formation and the crystal refiner modifies the coating properties hy lowering tbe porosity by redissolution and deposition