Advanced Electrochemical Rolf Gubner Swedish Corrosion Institute Kräftriket 23A 10405 Stockholm Sweden Tel: +46 8 674 1745 Fax: +46 8 674 1780 Rolf.Gubner@corr-institute.se www.corr-institute.se Methods for Studying Biocorrosion: : Part II -Localised Techniques-
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
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)
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?).
Introduction T Processes influencing the electrochemical metal dissolution Formation of aeration cells Formation of ion concentration cells Acidic metabolite interactions Extra-cellular enzymatic interactions
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)
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)
Pourbaix diagram thermodynamic predictions for corrosion, passivity, immunity dependent on an oxide s heat of formation and solubility (Hugh Isaaks, BNL)
(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
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)
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)
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
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)
Potential transients with Stainless Steel (Hugh Isaaks, BNL)
(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
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
Scanning Vibrating Electrode Technique Potentiostat vibrating electrode CE RE WE r
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
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
Scanning Vibrating Electrode Technique
Scanning Vibrating Electrode Technique. Applications. T Sterile vs. non-sterile carbon steel T Pseudomonas sp on carbon steel T Stainless steel in marine enviroments
mild steel in Cl - /SO 4 2- current density maps potential changes (Hugh Isaaks, BNL)
STERILE AERATED MEDIUM carbon steel following immersion current density maps after 3 h after 32 h corrosion potential (Hugh Isaaks, BNL)
INOCULATED AERATED MEDIUM A C current density maps B D corrosion potential A B C D (Hugh Isaaks, BNL)
Pseudomonas sp on carbon steel Current mapping Autoradiography
Pseudomonas sp on carbon steel Current mapping Autoradiography
Pseudomonas sp on carbon steel Current mapping (abiotic) Autoradiography
Pseudomonas sp on carbon steel T SVET combined with autoradiography provide a spatial and temporal information of localized corrosion due to MIC
Stainless steel in seawater. The ennoblement of the corrosion potential
Effect of temperature
The ennoblement of the corrosion potential
The ennoblement of the corrosion potential
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)
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)
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)
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)
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
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
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
IMPEDANCE MAPPING In Phase Z Quadrature Z (Hugh Isaaks, BNL)
Localized Electrochemical Impedance Spectroscopy Pt-disk
Localized Electrochemical Impedance Spectroscopy Pt-disk
Localized Electrochemical Impedance Spectroscopy Deconvolution of signal reveals real electrode shape
Localized Electrochemical Impedance Spectroscopy
Localized Electrochemical Impedance Spectroscopy Passive surface Active surface
Localized Electrochemical Impedance Spectroscopy Corroding surface
Localized Electrochemical Impedance Spectroscopy
Localized Electrochemical Impedance Spectroscopy
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,
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
Scanning Ion-selective Electrode Technique Electrolyte Ionophore - LIX 10 µm
Scanning Ion-selective Electrode Technique
Scanning Ion-selective Electrode Technique
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
Scanning Kelvin Probe
Scanning Kelvin Probe http://www2.rgu.ac.uk/subj/skpg/kptech.htm
Scanning Kelvin Probe
Scanning Kelvin probe Sample for the measurements shown on the next pages
Scanning Kelvin probe
Scanning Kelvin probe
Scanning Kelvin probe T Changing of Atmosphere (removal of O 2 )
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.
T If you are interested in using these techniques, visit us in Stockholm! Invitation Rolf Gubner Swedish Corrosion Institute Kräftriket 23A 10405 Stockholm Sweden Tel: +46 8 674 1745 Fax: +46 8 674 1780 Rolf.Gubner@corr-institute.se www.corr-institute.se
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