2012-01TU Delft - Advances in the Evaluation of Coating Corrosion Protection Performance

1

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

2

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

3

Corrosion impact

Indirect consequences of corrosion:

• Loss of product

• Loss of efficiency

• Reduced safety

• Overdesign

• Reputation

• Environmental effects, contamination

• Plant downtime

4

Corrosion issues…

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

7

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

55

NORSOK M501(Rev. 1, 1994)

offshore field test site, Snorre,Norwegian sector of the North Sea

14

Freeze/UV-condensation/Cyclic Salt Fog (non standardized)

marine exposure site, Sea Isle City,New Jersey, USA

4.16

10

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

11

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

12

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

13

Organic coating selection• From qualification through accelerated testing under severe testing

conditions….

‘Accelerated testing’

Mitigation of corrosion damage

14

Organic coating selection• …towards qualification under representative conditions

Mitigation of corrosion damage

Early detection using sensitive electrochemical methods

15

Electrochemical Methods

• Electrochemical Impedance Spectroscopy

Counter electrode

Reference electrode

Electrolyte

Working electrode

E

I

Emax

Imax

t

t

φ

16

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

17

metal/alloy

coating

Defect/micro-defect

aggressive environment

Local corrosion (protection) analysis

18

metal/alloy

coating

Local electrochemical techniques for the

study of corrosion (and healing) processes

aggressive environment

micro-probe

d

19

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

20

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

21

- 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

22

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

23

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

24

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

25

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

26

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

29

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

31

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

32

• 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

33

Thanks for your attention!!

For more information: [email protected]