Kinetics of zirconium conversion coating film formation on mild steel surface

Spectrophotometric technique was utilized to monitor the film formation kinetic of a zirconium conversion coating on a mild steel surface. For this reason, a metal-dyestuff complex was used to measure the zirconium ion concentration at different immersion times and temperatures. Results showed that the [Zr4+] rapidly decreased in the bath, reaching to a plateau region which could be attributed to formation a dynamic equilibrium between Zr ions in the solution and Zrcompounds on the surface. This indicates a self-limiting mechanism of the film formation. The obtained data revealed that an increase in conversion bath temperature caused an increase in zirconium ion consumption. Moreover, the precipitation rate of the conversion coating increased at higher temperatures.