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

sb244@buffalo.edu

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

Active-Passive Approach: Graphene-PEI Nanocomposite Coatings

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

Synthesis of Graphene

Graphite

UFG solution

UFG UFG

microstructure

Unfunctionalized Graphene (UFG)

Why Polyetherimides? Properties:

Hydrophobic

Low moisture permeation/water uptake

Solvent resistant

Temperature resistant

Formable

Flexible

Great adhesion to the steel surface

Polyamic acid

Process for Preparing Coatings UFG/PEI solutions

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

Coatings Blank steel PEI 0.05% wt UFG

0. 5% wt UFG 2.0% wt UFG 5.0% wt UFG

0.10% wt UFG

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

Tafel plot

Tafel plot

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.

Acknowledgements