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An in-situ spectroelectrochemistry study of
the response of artificial chloride corrosion
layers on copper to remedial treatment
Mieke Adriaens1, Mark Dowsett2
1
Ghent University, Belgium2 University of Warwick, UK
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Christian Degrigny
Mieke AdriaensMark Dowsett
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archaeological copper artefacts recovered from wet saline
environments corrode at accelerated rate in oxygen-rich air
storage in a solution
tap water sodiumsesquicarbonate
solution
Photo © Western Austrialia’s Maritime Museum
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Photo © Western Austrialia’s Maritime Museum
artefacts often show a certain instability
(e.g. chemical transformation of the natural patina
and development of active corrosion)
monitoring the treatment remains necessary
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Present monitoring method
determination of the chlorideconcentration in solution using volumetric
analyses
– change of solution when
predetermined value is
exceeded– repetition until value low enough
disadvantages
– time consuming
– indirect monitoring method
– no idea of potential side reactions
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Objective
investigate the use of corrosion potential measurements(Ecorr) to monitor the behaviour of copper based alloys
during their storage and stabilization
benefits
– simple tool
– inexpensive to conservators
– direct monitoring method of the metal surface
– more complete reaction profile when combined with the
analysis of the solution
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Corrosion potential
potential difference between metal object and reference electrode
depends on
– metal composition
– solution
– interface metal – solution
hypothesis: surface composition is stable when the corrosion
potential measurements do not change as a function of time
referenceelectrode
Photo © EVTEK
object(porthole)
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Strategy
Corrosion simulation Evaluate corrosion products
Immerse sample into sodium sesquicarbonate solution
Perform corrosion potential measurements as a function
of time and monitor the surface of the electrode
simultaneously
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Corrosion simulation
Electrodes– reference materials with known composition
• copper
• copper-tin alloy
• copper-tin-lead alloy
Corrosion products
cuprite nantokite atacamite atacamite and
paratacamite
metal surface
(12 mm diameter)
epoxy resin
electrical connection
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eCell
webcam
incoming X-rays
detector
SRS 6.2
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Nantokite (CuCl) protocol*
Immersing pure coppersamples for one hour in a
saturated CuCl2.2H2O
solution
Rinsing with deionised water
Exposure to atmosphere
over night
1 mm
C. Lamy (1997) Stabilisation d’Objects Archéologiques Chlorurés en Alliage Cuivreux – Définition des Conditions d’une PolarisationCathodique à Potentiel Constant en Solution de Sesquicarbonate de Sodium 1%, Rapport du Stage, Université de Nantes ISITEM.
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Nantokite
Cuprite
Cuprite
C
opper
XRD data – nantokite coated copper in 1% sodium sesquicarbonate
K. Leyssens et al., Electrochemistry Communications 7 (2005) 1265.
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Elapsed time / minutes
0 50 100 150 200
Relativepeakar
ea/percent
0
20
40
60
80
100
Nantokite (29.6o)
Cuprite (37.7o)
Cuprite (43.8o)
Copper
Nantokite (49.3o)
Cuprite (43.8o) corrected for Cu
Elapsed time / minutes
0 50 100 150 200
Relativepeakar
ea/percent
0
20
40
60
80
100
Ecorr/V
-0.22
-0.20
-0.18
-0.16
-0.14
-0.12
-0.10
-0.08
-0.06
-0.04
Nantokite (29.6o)
Cuprite (37.7o)
Copper
Nantokite (49.3o)
Cuprite (43.8o) corrected for Cu
Corrosion Potential (Ecorr)
XRD dataEcorr data
K. Leyssens et al., Electrochemistry Communications 7 (2005) 1265.
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XRD conclusions
Corrosion potential measurements need to be treated withcaution
Further investigations needed
• E.g. which reactions take place?
– CuCl -> Cu2O
– CuCl -> Cu -> Cu2O
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Can XAS data provide additional information?
An independent means of surface characterization whichis sensitive to the presence and evolution of amorphous
compounds
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XAS data from powder samples (references)
Energy / keV
8.96 8.98 9.00 9.02 9.04 9.06 9.08 9.10
normalized (E)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
8.97 8.98 8.99 9.00
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Atacamite
Copper
Cuprite
CuCl
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XAS data from corroded copper samples
Energy / keV
8.96 8.98 9.00 9.02 9.04 9.06 9.08 9.10
normalized
0.0
0.2
0.4
0.6
0.8
1.0
1.2
8.97 8.98 8.99 9.00
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Atacamite
Cuprite
Nantokite
Copper
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XAS data from corroded copper samples in solution
Energy / keV
8.96 8.98 9.00 9.02 9.04 9.06 9.08 9.10
normalized (
E)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
8.97 8.98 8.99 9.00
0.0
0.2
0.4
0.6
0.8
1.0
1.2Copper
Atacamite
Nantokite
Cuprite
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“atacamite” (Cu2(OH)3Cl isomers ) protocol*
prepare a solution of 15.07g (NH4)2CO3.NH3 and 10.02 g
NH4Cl in 100 mL deionised
water
wet coupons twice a day
with this solution repeat procudere for 5 days
between each application,
the samples were left to dry
to the air
C. Lamy (1997) Stabilisation d’Objects Archéologiques Chlorurés en Alliage Cuivreux – Définition des Conditions d’une PolarisationCathodique à Potentiel Constant en Solution de Sesquicarbonate de Sodium 1%, Rapport du Stage, Université de Nantes ISITEM.
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Time dependence – “atacamite” on copper in 1% sodium sesquicarbonate
8.9 9.0 9.1 9.2 9.3 9.4 9.5 9.6
0
10
20
30
4012
11
10
9
8
1
(E) normalized to the first scan
Energy (keV)
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8.90 8.95 9.00 9.05 9.10
Energy (keV)
CuCO3
atacamite
CuCl2.2H20
Bour sample
* Add 50 mL 0.1 M Na2CO3 solution dropwise to a stirred solution of 100 mL 0.1 M CuCl2.2H2O. Boil at reflux. After 5 h filter the slurry,
wash and dry at 333 K. Crush the samples to a very fine powder.
C. Lamy (1997) Rapport du Stage, Université de Nantes ISITEM.
*
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“atacamite” coated copper in 1% w/w sodiumsesquicarbonate
Time dependence
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Two theta
20 40 60 80
Intens
ity
0
2000
4000
6000
8000
10000
12000
“atacamite” as obtained from protocol
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Two theta
20 40 60 80
Intens
ity
0
2000
4000
6000
8000
10000
12000
“atacamite” as obtained from protocol
after rinsing
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Two theta
20 40 60 80
Intensity
0
2000
4000
6000
8000
10000
12000
“atacamite” as obtained from protocol
after rinsing
XRD reference of atacamite
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Time dependence – “atacamite” on copper in 1% sodium sesquicarbonate
8.9 9.0 9.1 9.2 9.3 9.4 9.5 9.6
0
10
20
30
40 12
11
10
9
8
1
(E)
normalized to the first scan
Energy (keV)
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time/hours
0 10 20 30 40
Corrosionpote
ntial/V
(vsAg/AgClref)
-0.08
-0.06
-0.04
-0.02
0.00
Simulaneous Ecorr measurement
Fluid
change
Fluid
change
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Overall reaction
Cuprite forms at the chloride/copper interface
The insoluble chlorides fall off or remain physically but not
chemically attached
The corrosion potential becomes
characteristic of a passive cuprite
covered surface but chlorides may
remain to cause further problems
Corrosion potential measurements
need to be treated with caution!
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Summary simulated chloride species
Nantokite– Converts to cuprite
“Atacamite”
– Surface converts to cuprite
– “Atacamite” becomes detached
Paratacamite/atacamite
– Protocol also produces nantokite
– Nantokite converts to cuprite and can coat the hydroxychlorides
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Future
Address the suitability of simulated alloys/corrosionproducts
More complex systems
– Bronzes
– Multi-layers
Long term experiments in portable cells
Photo: Paola Letardi
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Acknowledgments
Karen Leyssens, Bart Schotte and Gareth Jones Pieter Van Hoe, Derrick Richards, Adrian Lovejoy
Dr. Manolis Pantos, Dr. Tony Bell, Dr. Chris Martin, SRS
Dr. Laurence Bouchenoire, Dr. Sergey Nikitenko, ESRF
Dr. Christian Degrigny, SARL Germolles
COST Action G8 - http://srs.dl.ac.uk/arch/cost-g8/
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Further reading
K. Leyssens, A. Adriaens, M. Dowsett, B. Schotte, I. Oloff, E. Pantos, A. Bell andS. Thompson, Simultaneous In-situ time Resolved SR-XRD and Corrosion
Potential Analyses to Monitor the Corrosion on Copper, Electrochemistry
Communications 7 (2005) 1265-1270.
K. Leyssens, A. Adriaens, C. Degrigny, E. Pantos, Study of Corrosion Potential
Measurements as a Means to Monitor the Storage and Stabilization Processes
of archaeological Copper Artefacts, Analytical Chemistry 78(8) (2006) 2794-
280.
M. Dowsett, A. Adriaens, Cell for Simultaneous Synchrotron Radiation X-ray and
Electrochemical Corrosion Measurements on Cultural Heritage Metals and Other
Materials, Analytical Chemistry 78(10) (2006) 3360-3365.
A. Adriaens, M. Dowsett, K. Leyssens, B. Van Gasse, Insights into electrolytic
stabilization with weak polarization as treatment for archaeological copper
objects, Analytical Bioanalytical Chemistry 387(3) (2007) 861-868.
A. Adriaens, M. Dowsett, G.K.C. Jones, K. Leyssens, S. Nikitenko, An in-situ X-ray
absorption spectroelectrochemistry study of the response of artificial chloride
corrosion layers on copper to remedial treatment, J. Anal. At. Spectrom. 24(1)
(2009) 62-68.