2012-01TU Delft - Advances in the Evaluation of Coating Corrosion Protection Performance
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Advances in the evaluation of coating corrosion protection performance
Arjan Mol
NVVT
24 January 2012
Faculty 3mE, Department of Materials Science and Engineering Surfaces & Interfaces Group, Corrosion Technology and Electrochemistry
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Corrosion Technology and EC
Corrosion associated cost in the western world
The NetherlandsEstimated possible
reduction
3.5% GNP (gross national product)
17.5 billion €/yr(GNP=500 billion €)
1100 €/yr/inhabitant
5 billion € in The Netherlands (30% of total)
anode
cathode
2e-
MM2++2e-
M(OH)2
M →→→→ M2++2e-
1/2O2 + H20+2e-
Double layer
SOLUTION
anode
- Anode (for M oxidation or anodic reaction)
- Cathode (for H+ or O2 reduction or cathodic reaction)
- Electrolyte (ion conduction)
- Electrical contact between anode and cathode (e- conduction)
Progress in corrosion protection as a requirement for technical progressMaterials and Corrosion 60 (7) 2009, 481-494W. Fürbeth, M. Schütze
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Corrosion impact
Indirect consequences of corrosion:
• Loss of product
• Loss of efficiency
• Reduced safety
• Overdesign
• Reputation
• Environmental effects, contamination
• Plant downtime
5
PROTECTION BY ORGANIC COATINGS
1. Barrier (polymer) Metal
2. Adhesion(polymer)
RR'
OH
RR'
OH
Metal
RR'
OH
RR'
OH
RR'
OH
RR'
OHRR'
OH
RR'
OH
RR'
OH
RR'
OH OxidesRR'
OH
RR'
OH
RR'
OH
RR'
OH
Primer
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OHRR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
RR'
OH
3. Sacrificial orinhibitive pigments(charges)
Metal
Protection mechanisms
6
Coating – Metal(oxide) interaction
Metal
Coating
Inte
rfa
ce
Ox
ide
Co
ati
ng
Aspects determining the protection efficiency: coating chemistry: constitution, composition,...
Interface: (Mixed) oxide surface and bulk properties
- acid-base properties - hydroxyl fraction- surface energy- surface contamination- stability- IEP
- composition- structure- stability- electronic properties
Interfacial bonding
Delamination: local (electrochemical) activity
Wet
de-adhesion
Wet
de-adhesionCorrosive
de-adhesion
Corrosive
de-adhesionMobility
Mobility of
water
Mobility of
ions and charge
transfer
De-adhesion of polymers
on metals
De-adhesion of polymers
on metals
Explanation of
complex mechanisms
of de-adhesion
Explanation of
complex mechanisms
of de-adhesion
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Accelerated testing
• Accelerated testing aims to reproduce, in an accelerated manner, degradation processes without changing the degradation mechanism.
• Performed by increasing the physical and chemical stress conditions (temperature, salt concentrations, pressure…)
8
Review accelerated tests
Acceleration of accelerated exposure tests compared to outdoor exposure
Acceleration factor:
test
field
field
test
t
t
x
xA ⋅=
where:
A = acceleration factor [-]
xtest = response from accelerated test, e.g. creep [mm]
xfield = response from field exposure, e.g. creep [mm]
tfield = duration of field exposure [h]
ttest = duration of accelerated test [h]
9
Review accelerated tests
Acceleration of accelerated exposure tests compared to outdoor exposure
Accelerated test Outdoor Environment Acceleration factor (A)
ASTM B 117 marine exposure site, Sea Isle City,New Jersey, USA
12.5
Cyclic Salt Fog(modified version of ASTM G85)
marine exposure site, Sea Isle City,New Jersey, USA
10.6
NORDTEST NT BUILD 228(cyclic salt spray, ASTM G85)
offshore field test site, Snorre,Norwegian sector of the North Sea
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NORSOK M501(Rev. 1, 1994)
offshore field test site, Snorre,Norwegian sector of the North Sea
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Freeze/UV-condensation/Cyclic Salt Fog (non standardized)
marine exposure site, Sea Isle City,New Jersey, USA
4.16
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Review accelerated tests
∑ ∑
∑−−
−−=
22 )()(
))((
yyxx
yyxxr
ii
ii
x
y
where:
r = correlation coefficient [-]
xi = single response value from test A, e.g. creep [mm]= average response value from test A, e.g. creep [mm]
yi = single response value from test B, e.g. creep [mm]
= average response value from test B, e.g. creep [mm]
A value of r = 0 indicates no linear relationship, whereas a value of r = 1.0 or r = -1.0
suggests a strong linear relationship between the two tests.
Correlation factor:
Correlation of accelerated exposure tests with 12 months of outdoor exposure
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Review accelerated tests
TestDelamination, corrosion
ASTM D1654Rusting
ASTM D610Blistering
ASTM D714
Salt fog -0.173 0.045 0.058
Cyclic Salt Fog -0.050 0.315 0.769
Prohesion -0.122 0.541 0.688
Prohesion/QUV 0.519 0.481 0.782
Outdoor exposure(intercorrelation exposure sites)
0.693 - -
Correlation of accelerated exposure tests with 12 months of outdoor exposure
Spearman rank correlation factors
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Review accelerated tests
• Standardized visual evaluation techniques are subjective, depend on operator
• Test conditions are non-representative for outdoor, practical conditions
• Scribe test panels do not provide information on the important coating barrier properties
• All (accelerated) exposure tests, including outdoor exposure, are relative tests
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Organic coating selection• From qualification through accelerated testing under severe testing
conditions….
‘Accelerated testing’
Mitigation of corrosion damage
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Organic coating selection• …towards qualification under representative conditions
Mitigation of corrosion damage
Early detection using sensitive electrochemical methods
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Electrochemical Methods
• Electrochemical Impedance Spectroscopy
Counter electrode
Reference electrode
Electrolyte
Working electrode
E
I
Emax
Imax
t
t
φ
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EIS - Equivalent Circuit Modeling
Re Qc
Re Qc
Rc
Re Qc
Rc Qdl
Rct
Re Qc
Rc Qdl
Rct Ws
cathodeanode
e-
conductive pathway
OH-Fe2+
H2O, O2 NaCl
H2O, O2, NaCl
coating
steel
hydrophilic
region
cathodeanode
e-
corrosion products
Na+, OH -Fe2+
H2O, O2 NaCl
cathodeanode
e- Na+, OH -
Fe2+
H2ONaCl
Na+, OH -
corrosion products
e-
cathode
O2
O2
O2
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metal/alloy
coating
Local electrochemical techniques for the
study of corrosion (and healing) processes
aggressive environment
micro-probe
d
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Self-healing coatings
Prevention of corrosion
Polymeric coatings
Corrosion inhibitors >1900
Gap filling >2006
CrVI
S.J. García, H.R. Fischer, S. van der Zwaag, ”A critical appraisal of the potential of self healing polymeric coatings”, Progress in Organic Coatings 72 (2011) 211– 221
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Self Healing Coating
Encapsulated system
One healing agent: silyl ester
S.J. García, H. Fischer, P. White, J. Mardel, Y. González-García, J.M.C. Mol, A.E. Hughes , Prog. Org. Coat. 70 (2011) 142Y. González-García, S.J. Garcia, A.E. Hughes, J.M.C. Mol, Electrochem.Comm. 13 (2011) 1094
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- Reacts with H2O and adheres to M-OH
“Hydrophobic” and barrier protection
- Healing agent wets the surface
- Healing agent released
- Capsules break
- Coating is damaged
Autonomic and Reactive healing
Silyl Ester
One healing agent: silyl ester
S.J. García, H.R. Fischer, P.A. White, J. Mardel, Y. González-García, J.M.C. Mol, A.E. Hughes , Prog. Org. Coat. 70 (2011) 142
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Protection of coated AA2024
EIS (NaCl 0.05M)
Protects
10-2
10-1
100
101
102
103
104
105
103
104
105
106
107
108
109
Clearcoat 2h
Clearcoat 1d
SH System 2h
SH System 1d
Clearcoat
SH system
|Z| /
Ω
Frequency / Hz
EIS to damaged coatings
Immersion in 0.05M NaCl solutionDefect of ~100µm width
10-2
10-1
100
101
102
103
104
105
103
104
105
106
107
108
109
Clearcoat 2h
Clearcoat 1d
SH System 2h
SH System 1d
Clearcoat
SH system
|Z| /
Ω
Frequency / Hz
S.J. García, H.R. Fischer, P.A. White, J. Mardel, Y. González-García, J.M.C. Mol, A.E. Hughes , Prog. Org. Coat. 70 (2011) 142
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Local electrochemical techniques for
the study of self-healing efficiency
Scanning vibrating electrode technique (SVET)
Scanning electrochemical microscopy (SECM)
S.J. García, H.R. Fischer, P.A. White, J. Mardel, Y. González-García, J.M.C. Mol, A.E. Hughes , Prog. Org. Coat. 70 (2011) 142
Y. González-García, S.J. García, A.E. Hughes, J.M.C. Mol, Electrochem. Comm. 13 (2011) 1094
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epoxy sleeve
Metal
0.1 M NaCl solution
Ionic currentSVET
SECMUME
Counter
electrodeReference
electrode
Substrate
Electrolyte
Vi
O Re-
UMECounter
electrodeReference
electrode
Substrate
Electrolyte
Vi
O Re-
UMECounter
electrodeReference
electrode
Substrate
Electrolyte
Vi
O Re-
Redox-competition
mode
Feedback imaging
mode
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Corrosion protection
SVET(NaCl 0.05M)
(a) (b) (c)
a – 1hb – 1 dayc – 2 days
Clearcoat
Doped self healing coating
Immersion in 0.05M NaCl solution
Defect of ~100µm width
Scanned area: 2x4 mm2
(a) (b)
SVET experiment
S.J. García, H.R. Fischer, P.A. White, J. Mardel, Y. González-García, J.M.C. Mol, A.E. Hughes , Prog. Org. Coat. 70 (2011) 142
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SVET – long term immersion and wider defect(NaCl 0.05M)
1 day
2 days15 days
DopedSelf healingcoating
0.05M NaCl solution
Defect of ~160µm width
Scanned area: 2x5mm2
Corrosion protection
defect
SVET experiment
S.J. García, H.R. Fischer, P.A. White, J. Mardel, Y. González-García, J.M.C. Mol, A.E. Hughes , Prog. Org. Coat. 70 (2011) 142
27
long term immersion and wide defect(NaCl 0.05M)
Immersion in 0.05M NaCl solutionDefect of ~200µm width
SECM experiment
Line scan in feedback mode. Topography
1 day
Protection of coating defect on AA2024
Y. González-García, S.J. García, A.E. Hughes, J.M.C. Mol, Electrochem. Comm. 13 (2011) 1094
28
long term immersion and wide defect(NaCl 0.05M)
Immersion in 0.05M NaCl solutionDefect of ~200µm width
SECM experiment
Line scan in feedback mode. Topography
Line scan in redox-competition mode. Oxygen Concentration
1 day
Protection of coating defect on AA2024
Y. González-García, S.J. García, A.E. Hughes, J.M.C. Mol, Electrochem. Comm. 13 (2011) 1094
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long term immersion and wide defect(NaCl 0.05M)
Immersion in 0.05M NaCl solutionDefect of ~200µm width
SECM experiment
after 3 days
3 days
clear coating
Protection of coating defect on AA2024
Y. González-García, S.J. García, A.E. Hughes, J.M.C. Mol, Electrochem. Comm. 13 (2011) 1094
30
long term immersion and wide defect(NaCl 0.05M)
Protects: self-healing !Immersion in 0.05M NaCl solutionDefect of ~200µm width
SECM experiment
Oxygen profile shows topography. No cathodic activity at the defect
15 days 30 days!
Oxygen profile shows transition from
redox-competition to
electrochemical mediator behavior of oxygen by
inactivity in the defect area
Protection of coating defect on AA2024
Y. González-García, S.J. García, A.E. Hughes, J.M.C. Mol, Electrochem. Comm. 13 (2011) 1094
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Conclusions
• Accelerated corrosion tests show bad correlation to real life performance:
• Aggressive non-representative conditions
• Subjective analysis
• Relative performance at most
• Electrochemical methods like EIS allow early detection of coated metal degradation before final failure under representative conditions
• Pre-qualification
• In-situ analysis
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• Presentation of the SVET and SECM as a new alternative inthe local study and evaluation of corrosion protection andhealing properties of coating systems at high spatialresolution.
• The SECM provide specific information about corrosionreaction taking place on the surface.
• Local electrochemical techniques becoming powerfulmethods for the evaluation of local corrosion and healingefficiency
Conclusions
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