Effect of Addition of Some Organic and Inorganic Compounds on the Pitting Corrosion of Stainless Steel Electrodes

Abstract

The corrosion behavior of two stainless steel electrodes with different chemical compositions in different salt solutions of Cl¯ ions (NaCl, FeCl3 and HgCl2) was studied. The corrosion behavior in 3.5% NaCl with and without different concentrations of two different triazole derivatives, 3-amino-1, 2, 4 triazole (AT) and 4-amino-5-mercapto-1, 2, 4 triazole (AMT) and Na2S2O3 (50 to 200ppm.) was studied. Open circuit potential measurements, potentiodynamic cyclic anodic polarization (PCAP) and surface morphology techniques were used in this study. Obtained results showed that NaCl is more aggressive comparing with FeCl3 and HgCl2. As the concentration of sodium chloride increased, the (PCAP) curves indicated the presence of pitting or crevice corrosion breakdown potential which sustained the increase of anodic current density. The plots of pitting potential (Epit.), or protection potential (Ep) versus log [Cl¯] at 25 o C, for the two stainless steel electrodes were linearly decreased with the increase of the logarithm of chloride concentration. Also the increase of scan rate increases the localized pitting corrosion. The additions of sodium thiosulphate to 3.5% NaCl enhance pitting corrosion as compared with that found in pure sodium chloride solution. On the contrary, increasing concentration of (AT) and (AMT) in NaCl solution was found to greatly enhance IE%. The adsorptive behavior of the investigated inhibitors on the steel surface followed Langmiur-type isotherm. These results indicate the suitability of the use of the investigated inhibitors. Electrode type (I) has a greater tendency for pitting than electrode type (II) due to the percentage of nickel in electrode type (I) is half that of electrode type (II).