1. Effect of hno3 and cl¯ on corrosion behaviour of cr-mn austenitic stainless steels
Authors : Nilay N. Khobragade, Awanikumar P. Patil
Pages : 113-120
DOI : http://dx.doi.org/10.21172/1.101.18
Keywords : Cr-Mn-Ni Austenitic Steels, Nitric Acid, Chloride, Corrosion Abstract :Due to rising cost of Ni, there is interest in low cost Ni-free (Cr-Mn) austenitic stainless steels for a few industrial applications. The present work deals with studying effect of HNO3/Cl¯ ratio on corrosion behaviour of Cr-Mn austenitic stainless steel (Cr-Mn ASS). Test methods used were potentiodynamic polarisation (PDP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis. Test solutions were 1000 ppm Cl¯, 0.01M HNO3+1000 ppm Cl¯, 0.1M HNO3+1000 ppm Cl¯ and 1M HNO3+ 1000 ppm Cl¯. From PDP plots it was found Cr-Mn ASS exhibited active corrosion in 1000 ppm Cl¯ and passivity in HNO3 containing test solutions. From EIS results it was found that polarisation resistance (Rp) decreased on addition of HNO3 for the both the test steel. This is attributed to effect of pH on stability of Cr2O3 film. The film of Cr2O3 is a p-type semiconductor and has vacancies in cation sub-lattice. When Cl¯ is incorporated in anion sub-lattice in sets in Schottky pair reaction by which anion vacancies are created. These vacancies allow migration of cations from metal-film interface to film-solution interface and anions in reverse direction by vacancy aided diffusion process. Therefore, the film forming on test alloys were characterised by Mott-Schottky analysis to find out cation and anion defect densities of passivating film in 1000 ppm Cl¯ and 0.1M HNO3+1000 ppm Cl¯ solutions. It was found that density of the cation vacancies in the film forming on Cr-Mn ASS in 1000 ppm Cl¯ solution was 12.6 x1020 per cm3, and increased to 87.5 x1020 per cm3 on addition of HNO3. This explains the role of HNO3 addition. It was also found that the density of oxygen (anion) vacancies for the test steel was 13x1020 per cm3 in 1000 ppm Cl¯ solution and increased to 29.6x1020 per cm3 for Cr-Mn ASS. The rise in defect densities is attributed to drop in pH on addition of HNO3.
Citing this Journal Article :Nilay N. Khobragade, Awanikumar P. Patil, "Effect of hno3 and cl¯ on corrosion behaviour of cr-mn austenitic stainless steels", Volume 10 Issue 1 - March 2018, 113-120
Click here to Submit Copyright Takedown Notice for this article.