1. Studies on passivation of aisi 304 stainless steel in 0.4n/0.5n h2so4 and effect of oxidizer (mno4-) addition
Authors : N.n. Khobragade, Dr. A.p.patil
Pages : 101-105
DOI : http://dx.doi.org/10.21172/1.92.17
Keywords : SS 304, KMnO4 , H2SO4 , corrosion Abstract :Austenitic stainless steel, particularly SS 304 is a popular material for application in chemical and fertilizer industry. It has excellent corrosion resistance in sulfuric acid owing to formation of a fine and compact Cr2O3 film. Sulfuric acid is an oxidizing acid but when its concentration is low, the film is not stable and does not heal by itself quickly, if damaged. Therefore, if film is damaged by turbulences or erosion, the alloy suffers from accelerated corrosion. The situation can be salvaged by addition of an oxidizer. Present study is aimed at finding out how the passivity in dilute acidic solution can be restored so that the SS 304 does not suffer from accelerated corrosion. Test solutions were 0.4N and 0.5N H2SO4 without or with an oxidizer (0.1, 0.2, 0.5,1 and 2% KMnO4). Test method was potentiodynamic polarization with scan range of 1V from open circuit potential. It is found that in absence of oxidizer the cathodic part shows instability and few segments of cathodic/anodic switch over; indicating thereby that active and passive states are stable simultaneously. This means that the passivity is not truly stable and there is risk of accelerated corrosion in case of damage to the film. On addition of oxidizer, the Ecorr shifts in noble direction and the feature of simultaneous presence of active and passive state is removed. It is found that the cathodic plot has linear region extending more than two order of magnitude of current; this part is used to workout cathodic current density at OCP (icorr). Anodic part of the plots containing 0.1 KMnO4 has no passive phase and the icorr obtained from cathodic part is highest. On increasing KMnO4 addition further, few plots exhibit two segment; first limiting current region and second typical passivation region. However, the current density in this region is too high for this to term as true passivity. The current density in limiting current region is also higher than icorr obtained from cathodic part. Thus, corrosion of stainless steel in these test solutions is under cathodic control. The optimum amount of KMnO4 both the solutions is 1%. It means, on additions 1% KMnO4 to 0.4N and 0.5N H2SO4 solutions, the passivity will become stable. However, corrosion will remain under cathodic control.
Citing this Journal Article :N.n. Khobragade, Dr. A.p.patil, "Studies on passivation of aisi 304 stainless steel in 0.4n/0.5n h2so4 and effect of oxidizer (mno4-) addition", Volume 9 Issue 2 - November 2017, 101-105
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