Bernard, M.C. Et Al. Investigation Corrosion Electrochemical Techniques. 2010

8/7/2019 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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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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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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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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C. Amatore in Electrochemistry at Ultramicroelectrodes, Physcal Electrochemistry 1995 Chap. 4


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-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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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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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



in situ300s

ex situ30s

Lepidocrocite-FeOOH


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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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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)


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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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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B

F F

F G

Cu20

Sn02

a-PbO 2PbCO3Pb(OH)2

PbClOHb-PbO


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10 cyclesin 10 g/L K2B4O7

10 mV s-1


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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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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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Electrochemical impedance at the corrosion potential

Diffusion of dissolved oxygen cannot be neglected


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Reactivity of the patina:oxygen reduction at the patinaredox couple formed by patina products


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C. Chiavari et al., Electrochim. Acta. 52 (2007) 7760

Possibility of performing layer by layer analysis


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- 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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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


- 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)

Documents

Bernard, M.C. Et Al. Investigation Corrosion Electrochemical Techniques. 2010