Corrosion of passive metals 2

Corrosion of passive metals

Jacek Banaś

University of Science and Technology (AGH-UST)

Faculty of Foundry Engineering

Effect of chemical composition on passive behaviour of the alloy

Stationary polarization curves of austenitic Fe-Cr-Ni alloys in 1M H₂SO₄ OH OH OH Cr H₂O OH OH OH O H₂ Cr OH OH OH Cr OH OH OH Cr OH OH OH OH Cr OH OH OH Cr OH OH OH Cr OH OH OH Cr OH OH OH OH OH OH OH OH OH Cr OH OH OH Cr OH OH OH Cr OH OH OH Cr OH OH OH H₂O O H₂

Model of passive film on pure chromium

Stationary polarization curves of Fe-Si alloys in 1M H₂SO₄

Effect of chromium on the structure of passive film on Fe-Cr alloys in neutral aqueous solutions

J.Kruger in Passivity of Metals, ed.by Electroche. Soc. Inc. Princetown ,N. Jersey 1978

Effect of chemical composition on passive behaviour of the alloy

lo

g

i

U

C r, Ti

M o , V

N i, M o , C u

C r, M o ,

P, V

C r, N i, M o ,

Ti, S i, V , W

S i> 2 %

M n

S

S

C r

Ti

C u

M o

N i

V

C r

N i

W

Ti

i

i

'

Corrosion of passive alloys

Pitting corrosion

Crevice corrosion

Inergranular corrosion

Stress corrosion

Corrosion-erosion degradation

Pitting corrosion

Mechanism of pitting corrosion in chloride containing media

Pitting corrosion of iron

in atmosphere polluted

Autocatalytic process occurring in a corrosion pit. The metal, M, is being pitted by an aerated NaCl solution. Rapid dissolution occurs in the pit, while oxygen reduction takes place on the adjacent metal surfaces.

Schematic of a polarization curve showing critical potentials and metastable pitting region. EP, pitting potential; ER, repassivation potential; Ecorr, corrosion potential.

Pitting corrosion

Pitting corrosion of Ti in CH

OH-LiCl

solutions

Pitting corrosion of Fe-18%Cr

alloy in CH3OH-H

SO

solutions

Effect of molybdenum on stability of passive film on stainless steels

N. Sato: Corrosion 45, 5, 354 (1989)

Adsorption of ions on hydrous metal oxide surface which provides the fixed charge whose determines the ion selectivity of the membranes.

Inergranular corrosion

Inergranular corrosion of NIROSTA 2202 steel (22%Cr,6%Ni,3%Mo) in 93.5 wt.% H₂SO₄ (1000_C)

Stress corrosion cracking

Surface mobility model of Stress corrosion cracking (SCC) according to Galvele

J.R. Galvele, Corrosion Science 27,1 (1987)

Crack velocity:

)

1

(

_



_e

L

D

v

D

– surface self diffusion coeficient

L – diffusion length

 – elastic surface stress at the crack tip