Bernard, M.C. Et Al. Investigation Corrosion Electrochemical Techniques. 2010
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Transcript of Bernard, M.C. Et Al. Investigation Corrosion Electrochemical Techniques. 2010
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Local Investigation of Corrosion Processes byCoupled Electrochemical and Spectroscopic
Techniques
M-C. Bernard, S. Joiret, V. Vivier
Laboratoire Interfaces et Systmes lectrochimiquesCNRS UPR 15 (Paris France)[email protected]@upmc.fr
Electrochemistry in Historical and Archaeological Conservation Leiden 11-15 January 2010
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Objectives
Monument to Francis Garnier, Paris
Coin of post-Roman Empire Vth IIIrd A.D.found in Morocco
- Characterization of corrosion products (Ramanspectroscopy, SEM, X-Ray diffraction,electrochemical techniques )
- Characterization of corrosion processes:electrochemical techniques coupled withspectroscopy
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Outline
How to perform electrochemistry on tiny amount ofpowder materials?
1. Electrochemical tools for studying powder materials2. Cavity microelectrode Interest of decreasingelectrode size3. Coupling with Raman spectroscopy
4. Analysis of corrosion products- iron- bronze
5. Conclusion
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Electrochemical tools for powder materials
Composite or carbon paste electrode
Electrode dimension
diameter ~ 5 - 10 mmmass ~ 5 100 mg
Use of graphite for electrical conductivity
and a binder (Teflon) for mechanical properties
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Electrochemical tools for powder materials
micromanipulator / abrasive electrode
I. Uchida, H. Fujiyoshi and S. Waki, J. Power sources, 68 (1997) 139.
M. Perdicakis, N. Grosselin and J. Bessire, Electrochim. Acta, 42 (1997) 3351 D.A. Fiedler, J. Solid State Electrochem., 2 (1998) 315
1 mm
scratches
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Cavity microelectrode
Electrode dimension
diameter ~ 50 mdepth ~ 25 m
volume ~ 5 10-8 cm3
half of the cavity is filledV ~ 2.5 10-8 cm3
density of the material 1-10
mass ~ 25 250 ngC. S. Cha, C. M Li, H. X. Yang, and P. F. Liu, J. Electroanal Chem., 368 (1994) 47V. Vivier, C. Cachet-Vivier, C.S. Cha, J-Y. Nedelec, L.T. Yu, Electrochem. Comm. 2 (2000) 180.C. Cachet-Vivier, V. Vivier, C.S. Cha, J-Y. Nedelec, L.T. Yu, Electrochim. Acta. 47 (2001) 181
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Cavity microelectrode
Let us assume m = 100 ng
and a specific surface area of10 1000 cm2g-1
Select = 100 m2 0.01 mm2
e totE=U-R iOhmic drop:
ic 0 0
e e 0
E -ti =vC + -vC exp
R R C
Capacitive current:
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Interest of decreasing electrode dimension
reversible electrochemical system
D = 10-5 cm2s-1
k0 = 1 a = 0.5
Cox = 10 mM
r0 = 5 mm
V = 100 Vs-1
Re = 2 W
Cdl = 50 F
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Interest of decreasing electrode dimension
Significant parameters : Re
and Cdl
For a usual working electrode (disk-electrode) smaller than the counter electrodethe current is then forced to flow through a conical volume delimited by the twoelectrodes.
Ohmic drop
Time constant
04
eR
r
2
0dlC r
2
0toti r
0e totR i r
0e dlR C r
workingelectrode
counterelectrode
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Interest of decreasing electrode dimension
Significant parameters : Re
and Cdl
For a very small working electrode (microelectrode), edge effects and non planardiffusion control the mass transport to the electrode interface.
Ohmic drop independent of the electrode size
Time constant
04
eR
r
2
0dlC r
0toti r
e totR i
0e dlR C r
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Interest of decreasing electrode dimension
C. Amatore in Electrochemistry at Ultramicroelectrodes, Physcal Electrochemistry 1995 Chap. 4
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Cavity microelectrode
-0.2 0.0 0.2 0.4
-2
-1
0
1
2
3
4
5
(c)(b)
E / VSCE
(a)
-0.2 0.0 0.2 0.4
-2
-1
0
1
2
3
4
5
I/A
E / VSCE
-0.4 0.0 0.4 0.8
-100
-50
0
50
100
I/mA
E / VSCE
Pani powder as an example (0.5 M H2SO4)
10 cycles
at 2 Vs-1
1 cycle
at 0.5 mVs-1
1 cycle
at 0.02 Vs-1
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Outline
How to perform electrochemistry on tiny amount ofpowder materials?
1. Electrochemical tools for studying powder materials2. Cavity microelectrode Interest of decreasingelectrode size3. Coupling with Raman spectroscopy
4. Analysis of corrosion products- iron- bronze
5. Conclusion
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Coupling with Raman spectroscopy
250
200
150
100
50
0
200 400 600 800
Wavenumber (cm-1)
Wavenumber
Energy of vibration
The Raman spectra isa material signature
IntensityLaser
Notch
Filter
Lens(x80)
CCDdetector
potentiostat
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Analysis of corrosion products
Iron: nail from Bois lAbb Gallo Roman site in France
Layered structure
Outer layer
Inner layer
Massive iron
M.C. Bernard, S. Joiret, Electrochim. Acta. 54 (2009) 5199
Is this structure is protective? How does Iron corrode?
What can we say about the model of iron dissolution?
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Analysis of corrosion products
Layered structure
Outer layer
Inner layer
Massive iron
The process of metallic corrosion associates dissolution of the metal asanodic reaction and a counter part the cathodic reaction. In moisture air thiscan be the reduction of oxygen into hydroxyle anions, in water this can be thereduction of water to hydrogen gas. For long duration buried artefacts,
oxygen is supposed to be absent close to the object and iron cannotspontaneously reduce water in soils.
One hypothesis have been proposed: the reduction of already formed ironoxides, which can take place and allowed further corrosion process without
any oxygen intervention.
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Analysis of corrosion products
M.C. Bernard, S. Joiret, Electrochim. Acta. 54 (2009) 5199
50
60
70
80
LengthY(m)
60 80 100
Length X (m)
00 400 600 800
Wavenumber (cm-1)
00 400 600 800
Wavenumber (cm-1)
500 1000
Wavenumber (cm-1)
500 1000
Wavenumber (cm-1)
Goethitea-FeOOH
MagnetiteFe3O4
Maghemite-Fe2O3
carbonate
Ferrihydrite(Fe2O3,5H2O)
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200 400 600 800
Wavenumber (cm-1)
-1A 2hrsE=-1.3
-1A 1hrE=-1.3
-0.5A 1hrE=-1.1
Borate buffer
60 E=-1.1
40 E=-1.1
30 E=-1.1
15 E=-1.05
2 E=-1.02
Sulphate solution
400 600 800Wavenumber (cm-1)
Fe3O4
0 400 600 800
Wavenumber (cm-1)
Fe3O4
SO42-
i=-500nA
-500nA/ 1heure = 20 x the theoretical charge for the whole reduction
Analysis of corrosion products
M.C. Bernard, S. Joiret, Electrochim. Acta. 54 (2009) 5199
in situ300s
ex situ30s
Lepidocrocite-FeOOH
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Analysis of corrosion products
M.C. Bernard, S. Joiret, Electrochim. Acta. 54 (2009) 5199
0 400 600 800 1000
Wavenumber (cm-1)
-0.5a 4 heuresv=-1.35
-0.3a 2heuresv=-1.21
-50nA 3hrsV=-1.2
500
0
500
Wavenumber (cm-1)
dpart
50nA 1hrV=+1
50nA 3hrsV=+1
Goethitea-FeOOH
Maghemite / Magnetite-Fe2O3 / Fe3O4
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Analysis of corrosion products
150
100
50
0
400 600 800 1000
Wavenumber (cm-1)
-50 nA1heure E = -0.96 V
-50 nA
10 minutes E = -0.93 V
Taking (ex situ)
M.C. Bernard, S. Joiret, Electrochim. Acta. 54 (2009) 5199
Reduction of synthetic lepidocrocite to magnetite and of goethite from patina(easier than pure goethite) is taking place only during hydrogen evolution fromwater reduction. This mecanism is not responsible of ferrous objects
corrosion.
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 50 (2005) 4699
Cu Sn Pb Fe Al
at.% 80.0 7.75 10.9 0.74 0.54
wt.% 61.1 11.1 27.2 0.24 0.36
Alloy composition of the Roman coin bronze
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 50 (2005) 4699
B
F F
F G
Cu20
Sn02
a-PbO 2PbCO3Pb(OH)2
PbClOHb-PbO
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 50 (2005) 4699
10 cyclesin 10 g/L K2B4O7
10 mV s-1
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 54 (2005) 4699
Raman spectra collected during CV experiments
Cu20 ; Sn02a-PbO2
Cupric formCu(II)
Reduction tometallic species
Cu20but lost ofcristallinity
SnO2
Chemicaldisso
lution
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 50 (2005) 4699
10 cyclesin 10 g/L K2B4O7
10 mV s-1
Cu(II)/Cu(0)Cu(I)/Cu(0)
Cu(II)/Cu(I)
PbO2/Pb
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 50 (2005) 4699
Electrochemical impedance at the corrosion potential
Diffusion of dissolved oxygen cannot be neglected
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Analysis of corrosion products
M. Serghini-Idrissi et al., Electrochim. Acta. 50 (2005) 4699
Reactivity of the patina:oxygen reduction at the patinaredox couple formed by patina products
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Analysis of corrosion products
C. Chiavari et al., Electrochim. Acta. 52 (2007) 7760
Possibility of performing layer by layer analysis
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Analysis of corrosion products
C. Chiavari et al., Electrochim. Acta. 52 (2007) 7760
Possibility of performing layer by layer analysis
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Analysis of corrosion products
C. Chiavari et al., Electrochim. Acta. 52 (2007) 7760
Possibility of performing layer by layer analysis
- No electrochemical reactivity at pH = 5.6- Same behavior for sample FG1 & FG2 (same layer)- Copper dissolution during the first cycle- Fluorescence for Raman spectroscopy
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Analysis of corrosion products
C. Chiavari et al., Electrochim. Acta. 52 (2007) 7760
Possibility of performing layer by layer analysis
Same model than for the bronze coinOxygen reduction + diffusion
Patina = redox couple
the inner layer (with Cu/Zn) exhibits a similar behavior than the bronze coin
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Conclusion
M. Serghini-Idrissi et al., Electrochim. Acta. 54 (2005) 4699
- Cavity microelectrode allows studying few amount of material (~100 ng)
- Possibility to perform Raman spectroscopy and electrochemistrysimultaneously
- We can scrap off corrosion product layer by layer
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Acknowledgments
M-C. Bernard, S. Joiret (LISE)H. Takenouti (LISE)
L. Robbiola (ENSCP Toulouse)