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Do Hyung Kim , Hyun Hwi Lee, Sang Soo Kim, Hyon Chol Kang, Hyo Jung Kim, Do Young Noh, Kwangju Institute of Science and

In-situ x-ray specular reflectivity study of the passive films formed on stainless steel. Do Hyung Kim , Hyun Hwi Lee, Sang Soo Kim, Hyon Chol Kang, Hyo Jung Kim, Do Young Noh, Kwangju Institute of Science and Technology KOREA Hyun Jung Kim, Dong Ryeol Lee, Sunil K. Sinha

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Do Hyung Kim , Hyun Hwi Lee, Sang Soo Kim, Hyon Chol Kang, Hyo Jung Kim, Do Young Noh, Kwangju Institute of Science and

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  1. In-situ x-ray specular reflectivity study of the passive films formed on stainless steel Do Hyung Kim, Hyun Hwi Lee, Sang Soo Kim, Hyon Chol Kang, Hyo Jung Kim, Do Young Noh, Kwangju Institute of Science and Technology KOREA Hyun Jung Kim, Dong Ryeol Lee, Sunil K. Sinha Argonne National Laboratory USA

  2. Mn+ Mn+ transpassive state active state passive state Passivation of Metal Electrodes Protect metals and alloys from corrosion CURRENT DENSITY The importance of passivity Need the understanding of the electronic and physical properties of passive films APPLIED POTENTIAL (V)

  3. -Fe2O3(n-type) Cr2O3(p-type) SS The passive film on Stainless Steels • Stainless steels (SS) : iron-based alloy (  10%Cr) • Duplex structure  an inner Cr oxide • and an outer Fe oxide • Electronic properties •  the Cr oxide behave like a p-type semiconductor • and the Fe oxide like a n-type semiconductor Passive film (N. E. Hakiki et al., J. Electrochem. Soc., 145, 3821, 1998) • Electronic properties • Oxide Growth mechanisms • Protectiveness of the passive films Chemical composition of stainless steels

  4. The Cabrera-Mott Model -The inverse-logarithmic law Assumptions : 1. Growth is by cation migration. 2. A large uniform electric field (E=V/L) lowers the activation energy W for the movement of a cation. where the oxide thickness is L,time t, number of potentially mobile ions N, activation energy W, voltage across the oxide V, ion-jump distance 2a, frequency of vibration v, initial oxide thickness L0, and oxide volume per ion .

  5. Ssurf. Sinter. d 0.0 0.1 0.2 0.3 0.4 X-ray Specular Reflectivity : A powerful tool for analysis of surfaces and thin film interfaces. X-ray reflectivity represents the interference pattern of the reflected x-rays from the surface and interface Intensity -1 Q ( Å ) z

  6. z Parratt’s formalism for analysis of x-ray specular reflectivity : employing Fresnel reflection and transmition coefficients as derived from electromagnetic wave-propagation theory • Fresnel reflection coefficient, • From Parratt’s recusive formula, Reflectivity

  7. Anomalous X-ray Specular Reflectivity Near Fe K-absorption edge • Atomic scattering factor depending on the photon energy • Index of Refraction : X-ray where

  8. solution Experimental Details • In-situ Electrochemical Cell • Working electrode : SS430(Fe-18%Cr) • Reference electrode : Ag/AgCl electrode • Counter electrode : Pt wire • Solution : pH8.4 Boric Borate buffer solution 7.07gl-1H3BO3+8.17gl-1Na2B4O7•10H2O

  9. Cyclic Voltammogram In-situ X-ray reflectivity during pretreating cathodically • Experimental Procedures •  cathodic pretreatment •  under open circuit condition •  apples potentials for oxide growth An insoluble Cr oxide on SS430

  10. Anomalous X-ray Specular Reflectivity  Depth profiles of chemical compostions in the oxide film Transpassive film Passive film near Fe K-absorption edge (7.112 keV)

  11. Anomalous X-ray Specular Reflectivity Oxide film Passive Film SS430 Oxide film Transpassive Film SS430

  12. Fe2O3&Cr2O3 Fe2O3 Fe2O3 & Cr2O3 Cr2O3 SS SS Depth profiles of chemical compostions • Passive film • Transpassive film Cr2O3  CrO42- Intial Cr oxide dissolution M The Growth of the transpassive film  Anion diffusion mechanism The Growth of the passive film  Cation diffusion mechanism

  13. The Growth Kinetics  X-ray Specular Reflectivity E (vs. EAg/AgCl) = 0, 200, 400, 600, 800 mV

  14. X-ray Specular Reflectivity • The quasi-equilibrium states • with potentials • Real-time measurement

  15. The Growth Kinetics • Thickness vs. Time • Thickness vs. Potentials

  16. The Growth Kinetics : The C-M model If (R. Ghez, J. of Chem. Phys., 1973) where

  17. The C-M model If Z = 3 & a = 4Å, • does not obey the C-M model which the driving force for the reaction is the voltage set up across the oxide film

  18. q qs qm q qs qm q(V0-Va) q(m-s)=qV0 q(m-) q(m-) qVa Rectifying Contact Va - + (I) qVa q(V0+Va) q(s-m)=qV0 Metal p-type semiconductor Va - + (II) Metal n-type semiconductor

  19. -Fe2O3(n-type) Cr2O3(p-type) SS The Electronic properties of the passive film Rectifying contacts • The Cabrera-Mott theory : • V   Growth rate  • Cation diffusion mechanisms p-type Cr oxide semiconductor

  20. O2- O2- – – – – – – – + – + + + + + + + + O2- O2- Metal Metal O2- O2- O2- O2- O2- O2- Discussion • Anion diffusion mechanism • Cation diffusion mechanism p-type n-type

  21. Conclusions

  22. The Point Defect Model (PDM) The processes that generate and annihilate vacancies at the metal/film and film/solution interfaces of the barrier layer The metal/film and film/solution interfaces are in electrochemcal equilibrium Assumptions : where

  23. The Point Defect Model (PDM) where

  24. The PDM • 2 : Transfer coefficient (0~1) • : Cation valence  : Constant  : Electric field strength If 2 = 0.05,

  25. The PDM

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