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8/7/2019 Cano, E. Electrochemical Protection System Mtal Artefacts. 2010
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Electrochemicalassessment of protection
systems for metalartefacts
Dr. Emilio Cano DazCentro Nacional de Investigaciones Metalrgicas
(CENIM)Consejo Superior de Investigaciones Cientficas
(CSIC)
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Outline
New protection systems for heritage? Pros and cons of electrochemical techniques Rp: fundamentals and applications EIS: fundamentals and applications Evaluation of innovative coatings in the
PROMET project.
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Need of new protection systems
Improved efficiency Lower toxicity Specific needs for cultural heritage
conservation: Reversibility/re-tratability Respect to original object and surface
Transparency, good visual aspect Reproducibility issues
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Testing new protection systems
Tests in laboratory coupons Difficult (impossible?) to reproduce composition
and corrosion layers
Tests in real objects: Not uniform in composition, microstructure and
patina/corrosion products Unique value of each object
Combination of both, specific protocols andnon-destructive and highly sensitivetechniques
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Testing new protection systems
Natural exposure Very reliable, but very slow
Accelerated tests in climatic chambers Fast, but too accelerated Well established for industrial applications (for
instance, salt fog test) Better for comparison purposes Not applicable to real objects
Electrochemical tests
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Electrochemical tests
Advantages Very high sensibility
Measure instantaneous corrosion rate and are notdestructive: evolution of protection/corrosion withtime
Measure in real conditions: even on real objects! Relatively simple and inexpensive equipment
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1 nA/cm 2Fe Fe 2+1 hour
1,04 10 -8 g
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Electrochemical tests
Disadvantages Usually need a bulk electrolyte: not real
atmospheric conditions
Interpretation might be not easy in some cases(EIS)
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Polarization resistance (Rp)
At Ecorr , the slope of the V/I curve isproportional to the corrosion rate
Stern and Geary (1957):
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Polarization resistance (Rp)
Potential sweep from +- 10 mV vs. Ecorr Usually not employed for coatings due to the
very high resistance of the coating Fast and easy to intrepret
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Electrochemical Impedance
Spectroscopy (EIS) Based on the application of a AC low
amplitude (typically 10 mV) potential signal
Frequency swept from 100 kHz to 1 mHz
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Perturbation: E(t)=E 0 cos( t)
System response : I(t)=I 0 cos( t- )
Response function: Z ( ) = E/I
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Electrochemical Impedance
Spectroscopy (EIS)
The most important technique for evaluationof corrosion protection coatings in the last 30years
Allows for the measurement of the propertiesof high resistance coatings
Can obtain information of differentprocesses/parts of your system: electrolyte,coating, corrosion processes, etc.
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History of use of EIS for CH
Pioneer work: Price, Hallam et al., Metal 95 In situ evaluation of CH objects (Letardi, Metal
98) Very important increase of the use of EIS in
CH in the last years
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PROMET project
PROMET:Innovative conservation approaches for monitoringand protecting ancient and historic metals collectionsfrom the Mediterranean basin 6 Framework Program E.U. INCO-MED November 2004 - April 2008 21 partners from 11 mediterranean countries
Spain: CENIM-CSIC & UAM
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Protocol to study new protectionsystems
Artificiallycorrodedcoupons
Newproductsselection
Study of realobjects
Naturallycorrodedcoupons
Real exposure
Final list ofproducts Application in real
heritage objects
Laboratorytests
Laboratorytests
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Experimental
Material: low carbon steel (0,14%) Coatings
New: Poligen ES91009 (BASF) Ready to use liquid poliethylene wax emulsion Dries in24 h. Non toxic and environmentally safe
Traditional: Paraloid B-72 and Renaissance With and without corrosion inhibitor additives Electrochemical tests (Rp and EIS)
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Coatings tested
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Experimental setup
Polarization resistance (R p) -10 +10 mV vs. OCP 0,16 mV/s
Electrochemical Impedance(EIS) 64 kHz 1mHz, 10 mV, 0 V vs. OCP
PAR 273A
Solartron 1250
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Experimental setup
Referenceelectrode
Platinummesh
(counterelectrode)
4.15 cm 2working
electrode
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Rp tests
Clean samplesID Coating
0 No coating (Blank)
1 Renaissance wax
2 Poligen ES 91009
2a Poligen ES 91009 + M435 inhibi tor
2b Poligen ES 91009 + M370 inhibi tor
3 Paralloid B-72 (15% Acetonae
3a Parallo id B-72 + M435 inhibi tor
3b Parallo id B-72 + M109 inhibi tor
3c Parallo id B-72 + Alkaterge-T
1
1
1
istance, cm
2
-2
0
2
46
8
10
12
14
16
1 2 2a 2b 3 3a 3b 3c
Sample
Thickness, micrometers
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Rp tests
Pre-corroded andaged samples
0
20
40
60
80
100
120
140
NC TC1 TC2 C1 C2 C3 C4 C5
Coating
Thickness, m
ReferenceAccelerated aged
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+051.0E+06
1.0E+07
1.0E+08
NC TC1 TC2 C1 C2 C3 C4 C5
Coating
Rp, cm
ReferenceAccelerated aged
* *
2
ID CoatingNC No coating (Blank)
TC1 15% Paraloid B-72 in acetone
TC2 Renaissance wax
C1 Poligen ES 91009
C2 Poligen ES 91009 + M370
C3 Poligen ES 91009 +M435
C4 15% Paraloid B-72 in acetone + Alkaterge-T
C5 15% Paraloid B-72 in acetone + M109
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R S
R 1
C dl
EIS results
10-1 100 101 102 103 10410010110210310410510610
7
Frequency (Hz)
|Z|
No coatingCoating 1Coating 2Coating 2aCoating 2b
10-1 100 101 102 103 104
-90
-45
0
Frequency (Hz)
theta
Sin recubrimiento
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EIS results
10-1 100 101 102 103 10410010110210310410510610
7
Frequency (Hz)
|Z|
No coatingCoating 1Coating 2Coating 2aCoating 2b
10-1 100 101 102 103 104
-90
-45
0
Frequency (Hz)
theta
Y 0F /cm 2 s
(1- )
2.8 10-3
0.74 2681
CPE 1
R 1 cm 2
jY Z CPE
0
1
CPE 1R S
R 1
Sin recubrimiento
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EIS results
10-1 100 101 102 103 10410010110210310410510610
7
Frequency (Hz)
|Z|
No coatingCoating 1Coating 2Coating 2aCoating 2b
10-1 100 101 102 103 104
-90
-45
0
Frequency (Hz)
theta
Rennaissance wax
Y 0 Y 0F /cm 2 s
(1- ) F /cm 2 s(1- )
0.4 10 -3 0.8 22.86 0 .3 10 -3 0.79 2960
R 2 cm 2
CPE 1 CPE 2 R 1
cm 2
CPE 1
CPE 2
R S
R 1
R 2
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EIS results
10-1 100 101 102 103 10410010110210310410510610
7
Frequency (Hz)
|Z|
No coatingCoating 1Coating 2Coating 2aCoating 2b
10-1 100 101 102 103 104
-90
-45
0
Frequency (Hz)
theta
Poligen ES 91009
Y 0 Y 0
F /cm 2 s(1- ) F /cm 2 s
(1- )
0.4 10 -3 0.76 2162 59 10 -3 0.51
1.17 10 -6 0.76 82442 2.7 10 -5 0.58
8.89 10 -9 0.96 280810 8.3 10 -7 0.47
CPE 1 CPE 2 R 1
cm 2
CPE 1
CPE 2
R S
R 1
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10-1 100 101 102 103 104100
101102103104105106107
Frequency (Hz)
|Z|
No coatingCoating 3Coating 3aCoating 3bCoating 3c
10-1 100 101 102 103 104
-90
-45
0
Frequency (Hz)
theta
EIS resultsParaloid B72
Y 0 Y 0
F /cm 2 s(1- ) F /cm 2 s
(1- )
2.95 10 -7 0.56 16725 4.6 10 -6 0.5 34825
0.39 10-3
0.5 407 1.2 10-3
0.82 1395
4.53 10 -7 0.65 32228 1.0 10 -6 0.63 1.29 10 6
2.14 10-7
0.65 8031 7 .6 10-6
0.54 28949
R 2 cm 2
CPE 1 CPE 2 R 1
cm 2
CPE 1
CPE 2
R S
R 1
R 2
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Conclusions
Electrochemical tests give a quantitativeinformation of the protection provided bydifferent coatings in a short time Rp provide quick and easy to interpret results EIS provide in-depth information on the corrosion
and protection mechanisms
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Conclusions
The addition of corrosion inhibitor additivesdid not provide and improvement of theprotection, and in some cases have a
negative effect. Poligen ES91009 provides better protection
than Paraloid B72 when applied in thick layers
Rennaissance provides very little protection
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PROMET: additional information
CSSIM conference proceedings Strategies forsaving our cultural heritage
Book Metals and Museums in the Mediterranean.
Protecting, preserving and interpreting
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Further reading Cano E, Bastidas DM, Argyropoulos V, Fajardo S, Siatou A, Bastidas JM, Degrigny C (2009) Electrochemical
characterization of organic coatings for protection of historic steel artefacts. Journal of Solid State Electrochemistry, 1- 11.
Cano E, Lafuente D, Bastidas DM (2009) Use of EIS for the evaluation of the protective properties of coatings formetallic cultural heritage: a review. Journal of Solid State Electrochemistry, 1-11.
Ellingson LA, Shedlosky TJ, Bierwagen GP, de la Rie ER, Brostoff LB (2004) The use of electrochemical impedancespectroscopy in the evaluation of coatings for outdoor bronze. Studies in Conservation 49, 53-62.
Letardi P, Beccaria A, Marabelli M, D'Ercoli G (1998) Application of electrochemical impedance mesurements as a toolfor the characterization of the conservation and protection state of bronze works of art. In 'Metal 98. InternationalConference on Metal Conservation '. Draguignan-Figanires (France). (Eds J Ashton and D Hallam) pp. 303-308.(James & James)
Loveday D, Peterspm P, Rodgers B (2004) Evalution of organic coatings with electrochemical impedance spectroscopypart 2: Application of EIS to coatings. JCT CoatingsTech 1, 88-93.
Mansfeld F (1995) Use of electrochemical impedance spectroscopy for the study of corrosion protection by polymercoatings. Journal of Applied Electrochemistry 25, 187-202.
Mansfeld F (2008) Fundamental aspects of the polarization resistance technique-the early days. Journal of Solid State Electrochemistry, 1-6. Murray JN (1997) Electrochemical test methods for evaluating organic coatings on metals: An update. Part III: Multiple
test parameter measurements. Progress in Organic Coatings 31, 375-391. Price C, Hallam D, Heath G, Creagh D, Ashton J (1995) An electrochemical study of waxes for bronze sculpture. In
'Metal 95. International Conference on Metal Conservation '. Semur-en-Auxois (France). (Eds ID MacLeod, SL Pennecand L Robbiola) pp. 233-241. (James & James)
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Acknowledments
Organizers of the workshop PROMET project E.U. Colleagues in the PROMET Prof. Jos Mara Bastidas