Optimization of Chemical Pretreatment of Rusted Steel Surfaces by Solutions Based on Tannin and Phosphoric Acid Mixture

In this study، the electrochemical behavior of phosphoric acid and tannin mixture as rust converter solutions is investigated. Experimental design was carried out using taguchi method as a useful tool to interpret the results. Variables was studied comprising weight percentage of phosphoric acid and tannin، pH of pretreatment solutions and immersion time of rusted specimens in pretreatment solutions. Polarization test was utilized to measure the corrosion rate of conversion layer and optimization of pretreatment solutions in term of inhibition efficiency. Also، characterizing experiments including SEM-EDX،XRD and FT-IR were carried out on samples treated in optimum condition. Polarization test results showed that a solution containing no tannin and phosphoric acid (20 wt%) in pH=2 and immersion time equal to 5 hours exhibited the optimum condition in term of inhibition efficiency. XRD and FT-IR tests showed that a phase transformation of rust layer occurred after treatment and the conversion layer treated in optimum condition revealed suitable corrosion protection of metallic substrate. J. Color Sci. Tech. 6 (2012), 67-76© Institute for Color Science and Technology.