Anti-Corrosive Graphene Coatings: An Active—Passive
Alternative to Hexavalent Chromium Coatings
Robert V. Dennis, Vincent Lee, Lasantha Viyannalage, Steven M. Henderson and Sarbajit Banerjee
Department of Chemistry
University at Buffalo
Graphene: The New Carbon Age
The “Rust Belt” and Hexavalent Chromium
Graphene Nanocomposites for Corrosion Protection: The Story so Far
Commercialization and Outlook
Outline
Corrosion – deterioration of a material due to reactions with
its surrounding environment
Fe
H2O
O2
O2
O2 + 2 H2O + 4 e- → 4 OH-
2 Fe → 2 Fe2+ + 4 e-
2 Fe + O2 + 2 H2O → 2 Fe(OH)2
2 Fe(OH)2 + ½ O2
+ H2O →
2 Fe(OH)3
Fe2+/3+ Rust
Fe2O3
Requirements for rust
formation
o Iron
o Oxygen
o Water
o Electrolytes
Iron oxide does not form
passivating layer
Degrades mechanical
strength
Na+ Cl-
The “Rust” in the “Rust Belt”
The cost of corrosion on the US economy is roughly $300 billion annually
Chromium-Based Coatings Chromium-based coatings
used heavily for the better part of the last century
Ease of plating technology
Excellent corrosion and wear resistance
Lustrous surface finish
Potent carcinogen
Hard chrome electroplating has lead to dangerously high levels of Cr(VI) across the USA
Increased regulations require development of a new “greener” alternative.
Regulating agencies include: Environmental Protection Agency (EPA), Occupational Safety and Health (OSHA), NIOSH, and Environment Canada
http://www.ewg.org/chromium6-in-tap-water/full-report
http://www.ec.gc.ca/
Zinc Coatings
Zinc galvanization is widely used to prevent corrosion on iron and steel surfaces
Excellent corrosion and wear resistance
Steel companies don’t want to be held hostage by fluctuating costs of Zn
An alternative to Zn would greatly reduce the use of Zn and lower costs for steel companies
http://www.slamresources.com/investor-center/market-outlook/
Passive: The coating serves as a “barrier layer” precluding permeation of corrodants to the metal surface.
Active: An effective passivation layer is formed, which impedes corrosion half-reactions. “Schottky barrier” at interface leads to depletion of electrons.
Self-Healing (future): pH-sensitive leachable components that are deposited as precipitates upon initiation of rust formation.
The Active—Passive Approach
Graphene to the Rescue Graphene is a single layer of graphite in a honeycomb lattice
Geim and co-workers synthesized graphene in 2004 through mechanical exfoliation (Nobel Prize in Physics, 2010)
Geim, A. K.; Novoselov, K. S. Nat Mater 2007, 6, 183-191.
Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.;
Firsov, A. A. Science 2004, 306, 666-669.
Brian J. Schultz, Christopher J. Patridge, Vincent Lee, Cherno Jaye, Patrick D. Lysaght, Casey Smith, Joel
Barnett, Daniel A. Fischer, David Prendergast,* Sarbajit Banerjee,* Nature Commun., 2011, 2, 372/1-372/8.
High electrical conductivity
(mobilities >200,000 cm2/Vs)
Excellent mechanical strength
Tensile strength of ~1 TPa
Light weight
Hydrophobic
Heat resistant
Why Polyetherimides? Properties:
Hydrophobic
Low moisture permeation/water uptake
Solvent resistant
Temperature resistant
Formable
Flexible
Great adhesion to the steel surface
Polyamic acid
Polyamic acid
0.05% wt UFG
0.10% wt UFG
0. 5% wt UFG
2.0% wt UFG
5.0 % wt UFG
UFG/polyamic acid solutions
Day 1
Day 3
1.7% wt. UFG
PEI 1.3% wt. UFG
Blank Steel
1.0% wt. UFG
1.7% wt. UFG PEI
1.3% wt. UFG Blank
Steel
1.0% wt. UFG
Day 10
Day 14
1.7% wt. UFG PEI
1.3% wt. UFG
Blank Steel
1.0% wt. UFG
1.7% wt. UFG PEI
1.3% wt. UFG
Blank Steel
1.0% wt. UFG
Corrosion Rate g
𝑚2ℎ
An order of magnitude
improvement with a small loading of
UFG!
Tested using ASTM G1
Steel sample size: 4 cm x 4 cm
Testing Corrosion-Resistance
Potentiodynamic polarization resistance measurements
Standardized by ASTM G59
Working electrode:
Coated steel plate
Reference electrode:
Saturated calomel electrode
Counter electrode:
Pt strip
Electrolyte:
3.5% NaCl
𝑪𝒐𝒓𝒓𝒐𝒔𝒊𝒐𝒏 𝑹𝒂𝒕𝒆 𝑪𝑹 =𝑰𝒄𝒐𝒓𝒓 × 𝑲 × 𝑬𝑾
𝝆
K = 3.27 x 10−3 mm g/μA cm yr EW - Equivalent weight = 27.92 for steel ρ = 7.87g/cm3 for steel
Conclusions and Outlook Graphene-polyetherimide
coatings provide enhanced corrosion resistance to low alloy steel as verified by qualitative, semi-quantitative, and quantitative tests
An active-passive mechanism for corrosion inhibition is proposed.
PCT International filed
Outlook & Future Directions
Self-healing particles that are released in response to external stimuli (crack formation, initiation of rusting).
Extension of methodology to replace chromate conversion coatings on aluminum.
Nanostructured Mg-based coatings.