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PARTICLE LEACHING FROM POLYMERIC COATINGSA Combined Experimental and Simulation Study
Eugenio Bonetti –AkzoNobel, Malmö, SE and CEAS, The University of Manchester, UK Ander Cervellera-Dominguez – AkzoNobel, Sassenheim, NED and School of Materials, The University of Manchester, UKPeter Visser – AkzoNobel, Sassenheim, NEDSimon Gibbon – AkzoNobel, Felling, UKProfessor Xiaorong Zhou – School o Materials, The University of Manchester, UKFlor R. Siperstein – CEAS, The University of Manchester, UK
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IntroductionActive corrosion protection by organic coatings in AerospaceCorrosion in modern world• Corrosion cost: 2.5 trillion US$ - 4% percent of the global Gross Domestic Product (GDP)• 20-35% of this loss could have been saved by implementing better corrosion preventing
practices.
In the aerospace industry corrosion impacts• Cost • Aircraft availability • Safety• Social
German, T. & Section, N. Corrosion news. 140 146 (2018).
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October 1992, The Netherlands:Fatigue corrosion cracking
https://aviation-safety.net/database/record.php?id=19921004-2
April 1988, Hawaii: Fatigue corrosion crackinghttps://faculty.up.edu/lulay/me401/aloha_flight_243_a_new_direction.pdf
Organic coatings provide corrosion protection
Key steps for corrosion inhibition via leaching
1. Water uptake2. Dissolution of active pigment3. Transport and delivery of active species through
the polymeric matrix to de defect area4. Fast, effective, and irreversible passivation
O Gharbi et al. Npj Materials Degradation, 2, 12 (2018)
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IntroductionActive corrosion protection by organic coatings in Aerospace
Challenge
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Develop coatings that are:
Environmentally friendly
Sustainable
Efficient
Cost effective
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Approach
Replacing toxic chemicals (chromates)
Use renewable materials
Understand and optimise performance
Minimise use of expensive materials
UNDERSTAND LEACHING OF INHIBITORS FROM ORGANIC COATINGS
UNDERSTAND THE RELATIONSHIP BETWEEN LEACHING AND PERFORMANCE
IntroductionLithium leaching technology protection concept
Provide fast, effective, and irreversible corrosioninhibition
1. Leaching of lithium ions2. Lithium ion transport to defect area3. Formation of a protective layer on the
aluminium substrate
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Visser et al. Faraday Discuss. 180, 511-526 (2015)
Fitting with physical model• Oxide layer provides corrosion protective properties
Visser et al. Journal ofThe Electrochemical Society, 164 (7) C396-C406 (2017)
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The effect of the PVC Systems of study and microstructure analysis
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Epoxy model system with PVCs between 7.5 – 37.5%Pigment ratios constant
Before exposure
30 PVC
30 PVC 30 PVC
30 PVC
After 2 weeks exposure to 3.5% NaCl solution
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The effect of the PVC Lithium leaching and corrosion protection properties
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0
0.5
1
1.5
2
2.5
0 100 200 300 400 500 600
mg/
L
Time (h)
Leaching rate of lithium from the matrix
7.5 PVC
15 PVC
22.5 PVC
30 PVC
37.5 PVC
37.5 PVC22.5 PVC7.5 PVC
Epoxy model system with PVCs between 7.5 – 37.5%Pigment ratios constant
0
0.1
0.2
0.3
0.4
0.5
0.6
7.5%PVC
15%PVC
22.5%PVC
30%PVC
37.5%PVC
MΩ
Oxide layer resistance Polarization resistance
Active corrosion properties
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The effect of the PVC
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Higher pigment volume concentration result in higher leaching rates and faster exhaustion of the system• Larger network of interconnected pigment clusters
Increase of pigment volume concentration decrease the barrier properties of the coating• Formation of defects through the polymeric matrix which enhance water permeation
Slower dissolution rate leads to higher Roxid and Rpol – Better active corrosion protection
Can we control the rate of release?
Can we control the amount released?
Develop a model that describes the leaching of inhibitors with sufficient
accuracy to explore the formulation space and inform what are the desirable features or properties of the coating and inhibitor
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Release of corrosion inhibitors
Binder properties
Particles microstructure
Pigment volume concentration
Inhibitor solubility
Fillers
Inhibitor dissolution rate
Cellular Automata Model is a good compromise to model the release of inhibitors:
Can capture different physical phenomena Can be related to real physical properties of the system Computationally efficient
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Microstructure generation• Pigment volume concentration• Particle size distribution
Permeable heterogeneities
Clusters formation
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Release simulation
DissolutionPolymer
Solid inhibitor
Water
Dissolved inhibitor
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Release simulation
DissolutionPolymer
Solid inhibitor
Water
Dissolved inhibitor
Diffusion
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Results
Random distribution of inhibitor particles results in unique connectivity profiles.Averages are needed over multiple configurations to represent real systems
Total and connected inhibitor concentration Release curves
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Effect of PVC
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
0 5 10 15 20 25
Num
ber o
f cel
ls re
leas
ed
Time / days
PVC = 30%
PVC = 22.5%
PVC = 15%
PVC = 7.5%
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Effect of solubility
Solubility
S = 0.13 g/cm3
S = 0.013 g/cm3
S = 0.0013 g/cm3
0
0.00002
0.00004
0.00006
0.00008
0.0001
0.00012
0.00014
0.001 0.01 0.1 1 10 100
Mas
s re
leas
ed p
er u
nit a
rea
/ g c
m-2
Time / log(days)
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Effect of particle distribution
Spatial heterogeneity can affect the connectivity between inhibitor particles
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PVC = 7.5%
PVC = 15%
PVC = 22.5%
PVC = 30%
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20 25
Con
cent
ratio
n / g
cm
-3
Time / days
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Comparison with experimental data
Simulated data
Experimental data
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Conclusions
• The release of corrosion inhibitors from primer coatings can be modelled using the CA approach
• Models can show the influence of microstructure and pigment properties on the release, enabling control on the factors that affect the process
• Simulations can provide important insight on the structure-property relationship in complex coatings to enable optimal formulation design
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Acknowledgments
Dr. Yanwen Liu
Ms Maria Georgiades
Assistance given by the IT Services and the use of the Computational Shared Facility at the University of Manchester.
University of Manchester – AkzoNobel Corrosion Protection Partnership
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 721451
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