Methods for Studying Biocorrosion: : Part II -Localised Techniques-

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1 Advanced Electrochemical Rolf Gubner Swedish Corrosion Institute Kräftriket 23A Stockholm Sweden Tel: Fax: Rolf.Gubner@corr-institute.se Methods for Studying Biocorrosion: : Part II -Localised Techniques-

2 Content T Introduction T Scanning Vibrating Electrode Technique T Localized Electrochemical Impedance Spectroscopy T Scanning Ion-selective Electrode Technique T Scanning Kelvin Probe T Conclusions

3 Introduction "Microbially Influenced Corrrosion (MIC) refers to the influence of microorganisms on the kinetics of corrosion processes of metals, caused by microorganisms adhering to the interfaces (usually called "biofilms" biofilms"). Prerequisites for MIC is the presence of microorganisms.. If the corrosion is influenced by their activity, further requirements are: (I) an energy source, (II) a carbon source, (III) an electron donator, (IV) an electron acceptor and (V) water" (Task 1 MIC of Industrial Materials network, H-C H Flemming)

4 Introduction T MIC is (mostly) of electrochemical nature and therefore electrochemical methods are generally useful tools to study reactions at the metal/biofilm interface. T Due to the localized character of MIC, localized electrochemical technique would be most powerful for MIC investigations (but seldom used?).

5 Introduction T Processes influencing the electrochemical metal dissolution Formation of aeration cells Formation of ion concentration cells Acidic metabolite interactions Extra-cellular enzymatic interactions

6 Localized Corrosion Examples of localized corrosion chloride induced stress assisted metallurgical causes pitting corrosion (metallurgical causes for passivity loss) crevice corrosion waterline corrosion filiform corrosion bacterial atmospheric stress corrosion cracking intergranular weld decay (Hugh Isaaks, BNL)

7 Localized Corrosion Electrode surface area: T Overall current may be low as measured using conventional potentiostatic techniques e.g. 1 µa cm -2. T Localised currents may be much larger! (pit initiation at 1% of surface area => 100 µa)

8 Pourbaix diagram thermodynamic predictions for corrosion, passivity, immunity dependent on an oxide s heat of formation and solubility (Hugh Isaaks, BNL)

9 (Hugh Isaaks, BNL) BIOCORR, Summer School Portsmouth July 2002 Localized Corrosion INITIATION pitting PROPAGATION changes in solution ph and composition REPASSIVATION loss of corrosive environment

10 current flow between pit and passive area initiation metastable repassivation loss of anolyte occurs at inclusions pits repassivate easily when small solution ionic current pit intrinsic rates electronic current metal slow cathodic oxygen reduction reaction fast anodic metal dissolution reaction (Hugh Isaaks, BNL)

11 passive surface behavior passive film growth Potential t 2 cathodic anodic t 1 O 2 + H 2 O + 4e- 4OH - [current] M + 1½ H 2 O ½ M 2 O 3 + 3H + + 3e - (Hugh Isaaks, BNL)

12 passive surface behavior Potential Potential t 2 (Hugh Isaaks, BNL) anodic [current] t 1 cathodic M M 2 O 3 + 3e - O + H 2 2 O + 4e- 4OH - open circuit or free potential Time

13 the passive film grows and the potential increases E OC E OC R passive Ω M M 2 O 3 + 3e - O 2 + H 2 O + 4e- 4OH - t C interface (Hugh Isaaks, BNL)

14 Potential transients with Stainless Steel (Hugh Isaaks, BNL)

15 (Hugh Isaaks, BNL) E OC RBIOCORR, Summer School Portsmouth July 2002 passive Ω C interface E pit R pit Ω E OC E E OC R passive Ω C interface E pit R pit Ω during pitting t C interface after pitting stops

16 Scanning Vibrating Electrode T Advantages Technique In-situ and non-destructive Separation of anodes and cathodes at the micro- scale Qualitative and quantitative information of localized corrosion Lateral resolution in the range a 10µm

17 Scanning Vibrating Electrode Technique Potentiostat vibrating electrode CE RE WE r

18 Scanning Vibrating Electrode Ohm s Law: U U I = = κ ; R = R r i DC E = κ r r κ Technique E sin ωt vibrating electrode equipotential lines r current lines i DC anodic site

19 Scanning Vibrating Electrode Technique Video Camera Microscope Focus 3D Stepper Motor Translator 2 D Vibrator assembly CMC4 Motor Controller Probe Position x y x oscillator y oscillator Frame Grabber Parallel Port ASET Computer (Windows) D/A A/D Bath Vibrating Probe - Differential Pre Amp + x PSD y PSD IN-PHASE QUADRATURE Ref. Electrode

20 Scanning Vibrating Electrode Technique

21 Scanning Vibrating Electrode Technique. Applications. T Sterile vs. non-sterile carbon steel T Pseudomonas sp on carbon steel T Stainless steel in marine enviroments

22 mild steel in Cl - /SO 4 2- current density maps potential changes (Hugh Isaaks, BNL)

23 STERILE AERATED MEDIUM carbon steel following immersion current density maps after 3 h after 32 h corrosion potential (Hugh Isaaks, BNL)

24 INOCULATED AERATED MEDIUM A C current density maps B D corrosion potential A B C D (Hugh Isaaks, BNL)

25 Pseudomonas sp on carbon steel Current mapping Autoradiography

26 Pseudomonas sp on carbon steel Current mapping Autoradiography

27 Pseudomonas sp on carbon steel Current mapping (abiotic) Autoradiography

28 Pseudomonas sp on carbon steel T SVET combined with autoradiography provide a spatial and temporal information of localized corrosion due to MIC

29 Stainless steel in seawater. The ennoblement of the corrosion potential

30 Effect of temperature

31 The ennoblement of the corrosion potential

32 The ennoblement of the corrosion potential

33 The ennoblement of the corrosion potential MIC? Cathodic current distribution over SAF 2507 after 1 day exposure To Baltic seawater (E pol = -800 mv vs. SCE)

34 The ennoblement of the corrosion potential MIC? Cathodic current distribution over SAF 2507 after 50 days exposure to Baltic seawater (E pol = -800 mv vs. SCE)

35 The ennoblement of the corrosion potential MIC? Cathodic current distribution over SAF 2507 after 50 days Exposure to Baltic seawater (E pol = -800 mv vs. SCE)

36 The ennoblement of the corrosion potential MIC? Cathodic current distribution over SAF 2507 after 50 days exposure to Baltic seawater with addition of 1% NaN 3 a) Without b) 5 min. c) 145 min. d) 565 min. (E pol = -800 mv vs. SCE)

37 Localized Electrochemical Impedance Spectroscopy T Advantages Same as SVET» In-situ and non-destructive» Separation of anodes and cathodes at the micro- scale» Qualitative and quantitative information of localized corrosion» Lateral resolution in the range a 10µm Mechanistic information on localized corrosion may also be obtained

38 Localized Electrochemical Ohm s Law: κ i( ω ) = φ( ω) d Local Impedance: z( ω) = V i( ω) Impedance Spectroscopy equipotential lines applied d h Probe Ф(ω) i(ω) i(ω) 2r o Low impedance site

39 Localized Electrochemical Impedance Spectroscopy Video Camera Microscope Focus 3D Stepper Motor Translator 2 D Vibrator assembly CMC4 Motor Controller Probe Position x oscillator y oscillator Frame Grabber Parallel Port ASET Computer (Windows) D/A A/D Bath - Differential Pre Amp + x PSD y PSD IN-PHASE QUADRATURE Electrochemical Interface

40 IMPEDANCE MAPPING In Phase Z Quadrature Z (Hugh Isaaks, BNL)

41 Localized Electrochemical Impedance Spectroscopy Pt-disk

42 Localized Electrochemical Impedance Spectroscopy Pt-disk

43 Localized Electrochemical Impedance Spectroscopy Deconvolution of signal reveals real electrode shape

44 Localized Electrochemical Impedance Spectroscopy

45 Localized Electrochemical Impedance Spectroscopy Passive surface Active surface

46 Localized Electrochemical Impedance Spectroscopy Corroding surface

47 Localized Electrochemical Impedance Spectroscopy

48 Localized Electrochemical Impedance Spectroscopy

49 Scanning Ion-selective Electrode Technique T Originally designed for biological use T Extremely sensitive (1 µv gradients) T High spatial resolution (ca 10µm) T Ions: Ca, K, H,

50 Scanning Ion-selective Electrode Technique Ag-AgCl Agar Bridge Video Camera Microscope Bath Focus Ion Selective Probe 3D Stepper Motor Translator Headstage CMC4 Motor Controller Probe Position Bath Potential Subtraction - Differential Amp + Frame Grabber Parallel Port ASET Computer (Windows) D/A Electrode Signal Bath Potential x100 A/D

51 Scanning Ion-selective Electrode Technique Electrolyte Ionophore - LIX 10 µm

52 Scanning Ion-selective Electrode Technique

53 Scanning Ion-selective Electrode Technique

54 Scanning Kelvin Probe T Potential distribution on metal surface T In-situ and non-destructive T Lateral resolution in the range of 50 µm. T Separation of anodes and cathodes

55 Scanning Kelvin Probe

56 Scanning Kelvin Probe

57 Scanning Kelvin Probe

58 Scanning Kelvin probe Sample for the measurements shown on the next pages

59 Scanning Kelvin probe

60 Scanning Kelvin probe

61 Scanning Kelvin probe T Changing of Atmosphere (removal of O 2 )

62 Conclusions T SVET, LEIS and the Scanning Kelvin probe have a high potential for applications in laboratory investigations of MIC. T The informnation obtained with this techniques combined with other techniques (optical, spectroscopical, chemical sensors ) should provide new possibility in understanding the mechanisms of MIC.

63 T If you are interested in using these techniques, visit us in Stockholm! Invitation Rolf Gubner Swedish Corrosion Institute Kräftriket 23A Stockholm Sweden Tel: Fax: Rolf.Gubner@corr-institute.se

64 Thanks to: T Hugh Isaaks,, BNL T Al Shipley, Applicable Electronics T Feng Zou,, (former PhD student at SCI) T Dominique Thierry T Iwona Beech and the organising committee