Corrosion Inhibition of Stainless Steel Alloys in Phosphoric Acid Solution

THE CORROSION behavior of two stainless steel alloys in …...phosphoric acid solutions in the absence and in the presence of 3-amino-1, 2, 4-triazole (AT),4-amino-5-mercapto-1, 2, 4-triazole (AMT) and sodium orthophosphate corrosion inhibitors was studied using open circuit potential and potentiodynamic polarization techniques. Open circuit potential measurements of the two stainless steel electrodes in different concentrations of H3PO4 showed that the rates of film thickening of the two electrodes are independent of the solution concentration. Potentiodynamic polarization curves showed that the increase of Na3PO4 concentration in 0.5 M H3PO4 brought changes in the pH of solutions in the range 1.7-10.7 and decreases the corrosion rate. Electrode type (II) has inhibition efficiency more than the electrode type (I). AT compound (3-amino-1,2,4-triazole) has proven to be efficient inhibitor for pitting corrosion of stainless steel in phosphoric acid solutions. The inhibition efficiency may be argued to the formation of a compact Fe-AT complex film on the electrode surface.