Brian Hinderliter, Kenneth Croes, Xiaoning Qi, Victoria JohnstonGelling, Stuart G. CrollDepartment of Coatings and Polymeric Materials
LATERAL DIFFUSION IN COATING SYSTEMS
Department of Coatings and Polymeric MaterialsNorth Dakota State UniversityFargo, ND USA
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1. REPORT DATE FEB 2009 2. REPORT TYPE
3. DATES COVERED 00-00-2009 to 00-00-2009
4. TITLE AND SUBTITLE Lateral Diffusion in Coating Systems
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6. AUTHOR(S) 5d. PROJECT NUMBER
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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) North Dakota State University,Department of Coatings and PolymericMaterials,PO Box 6050,Fargo,ND,58105-5376
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12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited
13. SUPPLEMENTARY NOTES 2009 U.S. Army Corrosion Summit, 3-5 Feb, Clearwater Beach, FL
14. ABSTRACT
15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT Same as
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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18
REASON FOR RESEARCH “The total direct cost of corrosion was determined to be
$279 billion per year, which is 3.2 percent of the U.S. grossdomestic product (GDP). Indirect costs to the user (societycosts) are conservatively estimated to be equal to the directcosts.”1
Pollution Removed paint then repaint Removed paint then repaint
Volatile organic compounds Constituents of original paint (lead …)
Paint and corrosion products dissolved into environment Chromates, organics, metal (alloying components )
Safety
1. Federal Highway Administration (FHWA), Office of Infrastructure Research andDevelopment, Report FHWA-RD-01-156, September 2001
IS DIFFUSION IMPORTANT TOCORROSION? Corrosion is an electrochemical reaction of metals
with the liquid environment Why do we care about diffusion?
Corrosion requires electrical contact, electrolyte Corrosive ion transport, Cl- Corrosion inhibitors (chromates)
Corrosion inhibitors (chromates) Optimize drying cycles Design better accelerated testing protocols
What diffuses? Oxygen, water, chromates and other soluble inhibitors Residual solvent or hydrolysis products out UV absorbers, free radicals, pollutants
3
DIFFUSION IS IMPORTANT FOR:
Water and ion movementThrough coatingAround pigments, fillers and ion exchange
Movement of corrosion inhibitors
4
Movement of corrosion inhibitorsAcross substrate-coating interfaceThrough oxide layers
COATING AS A BARRIER
•Barriers, such as coatings,slow transport of water tosubstrate
•Delay onset of corrosion•Bottleneck for corrosion
5
Havard Undrum. (May 2006). SuperiorProtection. Coatings World, 43-48.
•Bottleneck for corrosionprogression
•Pigments and fillers make thediffusion path longer•Ion exchange can removeenvironmental hazard en route•Water acts as a conveyer forions
LATERAL DIFFUSION
Water advance water along the substrateThe advance of the water front includes a loss
term as the water diffuses up through thetopcoattopcoat
IMPACT OF LATERAL WATER DIFFUSION
Hydrolysis of adhesion bondsReaction with residual contaminants (Cl)
Osmotic pressure – blister formationCorrosion catalystCorrosion catalyst
Transport of active corrosion protectors
TRANSPORT AT COATING-SUBSTRATE INTERFACE
When corrosionbegins, diffusionoccurs in the plane ofthe coating. Diffusionis required to balancecharge.
8
J.H. Park, G. D., H. Ooshige, A.Nishikata, T. Tsuru. (2003).Monitoring of water uptake inorganic coatings under cyclicwet-dry conditions. CorrosionScience, 45, 1881-1894.
charge.Often salt required todefeat metal oxidelayer.(LeChartlier principle)
CORROSION NEEDS CONTINUITY
Corrosion needs:•Continuitybetween anodeand cathode•Focus on watermovement
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Craig R. Barrett, W. D..(1973). The Principlesof EngineeringMaterials. New Jersey:Prentice-Hall.
ASPECTS OF COATING SYSTEM THAT PROTECT
Surface topographySanding
Surface cleanlinessChlorides and sulfidesChlorides and sulfidesOils (protect metal, reduce adhesion)
PretreatmentPrimerTopcoat
TESTING METHODS FOR CORROSIONPROTECTION Gloss Color Contact angle Visual indication of blister formation
Difficult to test pretreatment or surface treatmentseparatelyTracers IndicatorsEIS (traditional setup tests directly below cell)
ORGANIC BARRIER COATINGS
Organic coating
Metallicsubstrate
H2O
O2
Prohesion test
12
Prohesion test
Wet step Dry step
CYCLIC DIFFUSION
Surface is exposed to water, then dry airReal-life and accelerated weathering
ASTM D58591 week of:
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1 week of: 4 hours UV exposure at 60C 4 hours of condensation at 50C
1 week of: 1 hour salt spray at 25C 1 hour dry at 35C
PHOTOCHEMICAL DEGRADATION(WATER AT SUBSTRATE)
Average wet exposure durationOverall fraction of time exposed to water
AFOSR Review 2009
0.300.40
0.00 0.05 0.10 0.15 0.20 0.25 0.300.00
0.05
0.10
0.15
0.20
0.25
Fra
ctio
nof
Tim
e
Water Concentration at Substrate
First CycleDayWeekMonth
-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Fra
ctio
nof
Tim
e
Water Concentration at Substrate
First CycleDayWeekMonth
EXPERIMENTAL SETUP
Working electrode connection
Counter Electrodes1
Scraped paint filledWith solution
Water diffusion12345
Water diffusion
TEST
Army PrimerArmy TopcoatHarrison solution
Conducting GelsConducting GelsEIS spectra
IMPEDANCE OF NEAREST CONTACT
1.00E+09
1.00E+10
1.00E+11
BK 1-1
1.5 Hours20.8 Hours44.8 Hours189 Hours
Initially impedance at high andlow frequency have high impedance
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
0.01 0.1 1 10 100 1000 10000 100000
Zmod
(Ohm
s)
Frequency (Hz)
189 Hours215 Hours239 Hours262 Hours333 Hours406 Hours525 Hours0 Hours1.5 Hours3.4 Hours
High and low frequencyImpedance drop as waterreaches
PHASE PLOT OF NEAREST CELL
-20
00.01 0.1 1 10 100
Phase Angles
0 Hours1.5 Hours3.4 Hours20.8 Hours44.8 Hours69.0 Hours
-100
-80
-60
-40
Phas
eA
ngle
(Deg
rees
)
Frequency (Hz)
69.0 Hours94.4 Hours121 Hours147 Hours164 Hours189 Hours215 Hours239 Hours262 Hours333 Hours406 Hours525 Hours741 Hours
IMPEDANCE TO SECOND CELL
1.00E+10
1.00E+11
1.00E+12
BK 1-2
0 Hours1.3 Hours3.7 Hours20.6 Hours44.6 Hours68.8 Hours94.2 Hours
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
0.01 0.1 1 10 100 1000 10000 100000
Zmod
(Ohm
s)
Frequency (Hz)
94.2 Hours120.8 Hours146.4 Hours163.8 Hours188.6 Hours214.8 Hours238.6 Hours263.5 Hours332.6 Hours412.7 Hours525 Hours741 Hours
IMPEDANCE TO 3RD CELL
1.00E+09
1.00E+10
1.00E+11
BK 1-3
0 Hours1.3 Hours2.5 Hours19.6 Hours43.3 Hours67.5 Hours93.4 Hours
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
0.01 0.1 1 10 100 1000 10000 100000
Zmod
(Ohm
s)
Frequency (Hz)
93.4 Hours119.4 Hours145.0 Hours162.4 Hours187.3 Hours213.4 Hours237.5 Hours263.3 Hours332.2 Hours411.3 Hours524.3 Hours740 Hours
SUMMARY
Lateral diffusion is being investigated to rank:Surface preparationsSurface cleaning technologiesPretreatmentsPretreatments
Testing is designed test complete systems
IMPACT OF LATERAL DIFFUSION
Corrosion advanceTime to connect cathodic and anodic regions
Concentration of the water needs to besufficient for ion transportsufficient for ion transportUnderstand metal surface treatment, surface
preparation, primer, topcoat (image thermal)
INTRODUCTION Accelerated weathering protocol
Need to test system designed to last for decades
Reciprocity shown based on dose (Chin et. al. 2005)But accelerated weathering protocols don’t always match
environmental exposuresenvironmental exposures
Simulations allow:physical processes can be combined (UV absorption and
diffusion)Results to be quickly analyzed unambiguouslyExperimental systems hard to design
COMPUTATIONAL TOOLS AND SELECTAPPLICATIONS
Finite element analysis Electromagnetic response (EIS and Dielectric spectroscopy) Diffusion Multiphysics (couple the above)
Monte Carlo – Coating as a composite breakdown
AFOSR Review 2009
Monte Carlo – Coating as a composite breakdown Finite difference – coupled photodegradation/ hydrolysis Molecular dynamics – simulate ion and water transport Quantum chemistry – polymer chain scission location
WHY DEVELOP MODELS OF COATINGSYSTEMS?
AFOSR Review 2009
Physically based equations/models allow: Extrapolation (Lifetime prediction) Understanding of processes impacting measurement
(Occam’s razor) – enhanced/optimized design Troubleshooting and new technology evaluation Compare various accelerated weathering standards with Compare various accelerated weathering standards with
various service environments Predicting service life and property changes with time Develop more realistic/representative accelerated tests Gain insights into degradation mechanisms
Modeling allows testing hypothesis that aredifficult or impossible to do experimentally.
SIMULATION
3/1/2009Army Corrosion ConferenceFebruary 2008
Substra
Applied voltage
Take pigment particlesize and number
Divide coating binderinto average coverage
27
ate
Ground plate
