Electrochemical Behavior of Steel Alloys as Affected by Phosphoric Acid

Abstract

The behavior of two steel alloys in phosphoric acid solutions alone and with addition of organic and inorganic compounds was studied using open circuit potential and potentiodynamic polarization techniques. Open circuit potential measurements of the two stainless steel electrodes in different concentrations of H 3 PO 4 showed that the rates of film thickening of the two electrodes are independent of the solution concentration. Potentiodynamic polarizations illustrate that, upon increasing Na 3 PO 4 concentration in 0.5M H 3 PO 4 the pH of the solutions changed in the range from 1.7 to 10.7 and the corrosion rate decreases. Electrode type (II) has inhibition efficiency more than 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 was increased by increasing the inhibitor concentration. The inhibitive property may be argued to the formation of a compact FeAT complex film on the electrode surface.