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CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

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Chapter 7<br />

observed with increase in immersion time, instead surface became stained with degraded<br />

passive film and corrosion products with increase in root mean square roughness from 15 nm<br />

in as polished condition to 52 nm after immersion for 27 h.<br />

2. Potentiodynamic polarization study in 0.1 M, 0.5 M, 0.6 M, and 1 M nitric acid showed<br />

increase in passive current density and corrosion current density, and decrease in transpasive<br />

potential with increase in concentration of nitric acid. Passive current density increased by one<br />

order, corrosion current density increased by two order, and transpassive potential decreased<br />

by 150 mV vs. Ag/AgCl from 0.1 M to 1 M nitric acid.<br />

3. In-situ passive film surface morphology study in 0.1 M, 0.5 M, 0.6 M, and 1 M nitric acid<br />

using EC-AFM showed the growth of passive film in the form of platelet like structure at<br />

lower concentration of 0.1 M and 0.5 M nitric acid. At concentration of 0.6 M and 1 M nitric<br />

acid the platelet like structures got agglomerated, homogenized and started depleting from the<br />

surface leading to selective dissolution and opening up of oxide boundaries.<br />

4. X-ray photoelectron spectroscopy analysis of passive film as observed in in-situ study in 0.1<br />

M, 0.5 M, 0.6 M, and 1 M nitric acid revealed the presence of hydroxide and oxide layer on<br />

304L SS at lower concentration of 0.1 M and 0. 5 M nitric acid. Towards higher<br />

concentrations of 0.6 M and 1 M nitric acid, presence of oxide layer was observed. Overall, the<br />

passive film at lower concentration consists of hydroxide and oxide layer, and at higher<br />

concentration it consists of oxide layer only.<br />

7.2 Conclusions from the study on corrosion behaviour of nitrogen ion implanted AISI<br />

304L stainless steel in nitric acid medium<br />

Followings are the major conclusions from the study on “corrosion behaviour of nitrogen<br />

ion implanted AISI 304L stainless steel in nitric acid medium” to understand the effect of subsurface<br />

modification on the corrosion behaviour of 304L SS in nitric acid medium.

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