Mild steel surface pretreatment using phosphoric acid-inhibitor solution

In this study, a new mild steel surface pretreatment solution is introduced based on phosphoric acid containing a benzimidazole derivative as inhibitor. In this way, three different benzimidazole derivatives namely benzimidazole BI, 2-methyl benzimidazole 2MBI and 2-aminobenzimidazole 2ABI were studied in the 1M H3PO4 using DC and AC electrochemical techniques. Results revealed the better corrosion inhibition performance of 2ABI in the acidic medium. EDS analysis revealed that surface elemental composition of oxygen and phosphorus increased after pretreatment process, that could be attributed to formation of some compounds based on iron phosphate. EIS diagrams of the painted substrates showed that pre-treated mild steel using phosphoric acid-inhibitor provided higher corrosion protection performance than untreated mild steel during immersion in 3.5 w/w NaCl solution. Furthermore, acid wash process enhanced adhesion and cathodic disbonding resistance of painted mild steel.