Passivityof metalsand metallic alloys. Jacek Banaś

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1 Passivityof metalsand metallic alloys Jacek Banaś

2 Wagner definition of passivation etal is passive when its corrosion in course of chemical or electrochemical reaction is lower at higher affinity of reaction than at lower affinity of chemical or electrochemical process C. Wagner: Corrosion Science 5, 751 (1965)

3 echanism of passivation e + n/m X -m ex n/m + ne solid state reaction precipitation mechanism

4 Oxide passivation Watermoleculeisa sourceof oxygen Ni + H O NiO + H + +e Cr + 3H O Cr O 3 + 6H + + 6e In anhydrous environments other molecules can be a source of oxygen (undissociatedmoleculesof oxy-acids: H SO 4, H 3 PO 4, HNO 3, HCO) Cr + H SO 4 CrHSO 4 ad + H + + e CrHSO 4 CrO + SO B. Stypuła, J. Banaś: Electrochim. Acta 38, 309 (1993) Fe + HCO FeO + CO + 3H + + e J. Banaś, B. azurkiewicz, W. Solarski, K. Banas: aterial Science Forum Vol , 845 (1995),

5 echanism of passivation in aqueous solutions + + H + + e e + + e HO dissolution + + e + H O e(h O) e + H e ad ad + H O intermediate e() H e passivation eo+ HO K. Schwabe, S. Hermann, W. Oelssner: Passivity of etals, Proc. of the Fourth Int. Symp. on Passivity, ed. by R.F. Frankenthal and J. Kruger, N.Y. 1977,

6 echanism of iron passivation in aqueous solutions I γfeo Fe Fe() A3 γfeo Fe 3 O 4 Fe 3O 4 Fe A1 A E C C1 Cyclic voltamperometric curve of iron polarization in neutral environment W.J. Lorenz, K. E. Heusler in Corrosion echanisms ed. arcel Dekker Inc. N. York 1987

7 High field mechanism (hfm) of oxide growth Electric field: E = Φ Φ 1 / Φ = d d / 3 d Electric field is a driving force for growth of oxide film. The anodic current related to growth of thefilm isan exponentialfunction of electric field: i = 0 β Φ i exp d i 0 W =ρχeν exp RT χaf β= RT etal (1) Oxide() Electrolyte(3) K.J. Vetter: Elektrochemische Kinetik, Springer Verlag 196

8 High field mechanism (hfm) of oxide growth i = 0 β Φ i exp d i 0 Q =ρχeν exp RT β = χaf RT ρ -surfacedensityof adatoms (mobile atoms) Χe - charge of theion ν oscillation frequency of metal atoms in crystalline lattice of oxide Q activationenergy of jumpof ionfrom one to other position a halfjumpdistance Activation energy of the ion migrating in oxide lattice without electric field Activation energy of the ion migrating inoxidelatticewithan electric field E

9 Point defects model - PD O χ/ etal Tlenek Roztwór χ' V (1) m + V χ' k1 + V + χe k4 δ+ χ' + V + (δ χ)e aq (4) () (3) m m k ' + V + χ i k 3 χ + VO + V O χe χe χ' i V k5 δ+ + (δ χ)e O aq k6 + H O O + H O + (5) (6) + k χ 7 δ+ Oχ/ + χh aq + HO+ (δ χ)e (7) etal Oxide Electrolyte D.D. acdonald, Electrochimica Acta 56, (011)

10 Oxide growth Relation describing oxide growth parabolic Charge q w necessary to oxide growth in the time t q w = k p t 1 Current density i w necessary to oxide growth in the time t Slope ' logarithmic q w = k l + k l ln t 1-1 i w i w = 1 = k k p l t t 1 1 echanism determining oxide growth diffusion exchange place, high field migration diffusion Growth of oxidefilm on iron surface inaqueoussolutions, ph K.E. Heusler, B. Kusian, D. cphail: Ber. Bunsenges. Phys. Chem. 94, 1443 (1990) high field migration

11 Spontaneous passivation(self passivation) active state (corrosion) i a I c < i p i p U U 3 U 1 U i k 1 i k i k i k 3 passivestate (protection by oxide film) I c > i p Effect of oxidant concentration on spontaneous passivation of metal

12 Passivity of metallic alloys Passivity promoters and dissolution moderators according to the synergy between the energy of the metal-metal bonds and heat of adsorption of oxygen P. arcus: Corr.Sci. 36, 155 (1994)

Effect of chemical composition on passive behaviour of the alloy Stationary polarization curves of austenitic Fe- Cr-Ni alloys in 1 H SO 4 Stationary polarization curves of Fe-Si alloys in 1 H SO 4 H

13 Effect of chemical composition on passive behaviour of the alloy Stationary polarization curves of austenitic Fe- Cr-Ni alloys in 1 H SO 4 Stationary polarization curves of Fe-Si alloys in 1 H SO 4 H O Cr Cr Cr H O Cr Cr Cr Cr Cr Cr H O Cr Cr Cr O H odel of passive film on pure chromium Effect of chromium on the structure of passive film on Fe-Cr alloys in neutral aqueous solutions J.Kruger in Passivity of etals, ed.by Electroche. Soc. Inc. Princetown,N. Jersey 1978

Oxidegrowth(Cr/Cr O 3 ) ST topographic images

75 L (a) and.5 L (b) of oxygen at 300 K.

formed by exposure of Cr(110) to 3.4 L (a), 7.

3 L (c) of oxygen at 65 K and subsequent

14 Oxidegrowth(Cr/Cr O 3 ) ST topographic images of the Cr(110) substrate after exposure to 0.75 L (a) and.5 L (b) of oxygen at 300 K. 7 C O ST topographic images of the oxide film formed by exposure of Cr(110) to 3.4 L (a), 7.5 L (b) and 11.3 L (c) of oxygen at 65 K and subsequent annealing at 95 K. 35 C + 65C annealing V. aurice, S. Cadot, P. arcus, Surface Science 458 (000)

15 Oxidegrowth(Cr/Cr O 3 ) At 300 K, a granular and non-crystalline oxide is formed, which grows with a constant ~Cr O 3 stoichiometry up to a limiting thickness of 0.9 nm. The film is hydrated with a water content of 10 0%, which decreases upon annealing. Nuclei of oxide with a lateral dimension of ~0.7 nm and a height of ~0. nm have been observed in the nucleation stage. These nuclei grow predominantly laterally and coalesce to fully cover the substrate surface prior to the thickening stage. At 65 K, a first stage of oxygen adsorption is observed in which stripes nm wide and parallel to the Cr[001] direction are observed after annealing in UHV. They correspond to narrow segments of mixed and close-packed planes of O atoms and ions having a geometry and orientation similar to those of the anions planes in the oxide crystals. Rows ofadatoms,possiblycr 3+ ionsofoxidenuclei,areobservedabovethestripes.thickeningat 65 K leads to the formation of a non-crystalline oxide, which grows up to a limiting thickness of 4.6 nm. The presence of Cr3+ vacancies related to a significant cation transport through the oxide film in this temperature regime is detected. After UHV annealing at 85 or 95 K, the film is anhydrous. The Cr3+ vacancies are accumulated at the metal/oxide film interface. The film crystallizes in epitaxy with the substrate in the followingorientation:α-cr O 3 (0001) Cr(110)andα-Cr O 3 [13:0] Cr[001]. V. aurice, S. Cadot, P. arcus, Surface Science 458 (000)

beginning of simulation process(a) and after simulation (b).

16 Passivation of alloys Fe Fe Cr Cr Fe ox Cr ox Simulation of the dissolution and passivation of Fe-%Cr alloy at the beginning of simulation process(a) and after simulation (b).legrand, B.Diawara, J.-J.Legrende, Ph.arcus, Corr.Sci, 44, (00)

3.2 Kinetics of Oxide Growth of Passive Films on Transition Metals

3.2 Kinetics of Oxide Growth of Passive Films on Transition Metals Katie Lutton, John R. Scully Center for Electrochemical Science and Engineering Department of Materials Science and Engineering University