New Routes For Metal Protection Combining Conducting ... · New Routes For Metal Protection...

New Routes For Metal Protection Combining Conducting Polymers with SAMs

Luísa M. AbrantesCQB, Departamento de Química e Bioquímica

WorkshopElectrochemistry in Historical and

Archaeological Conservation January 11-15, 2010

Leiden

Contents

�� Introduction to Conducting Polymers

Basic aspects: polymerization, doping and conductiv ity

CP as Corrosion protective coatings- Why ?

CP film formation on metal surfaces

Corrosion protection ability of CP coatings

�� Conducting Polymers: A Versatile Route for novel an ti-corrosion coatings

�� Combining Conducting Polymers with Self-assembled M onolayers


Self-assembled adhesion promoters

Densely packed polymeric assemblies chemisorbed on solid surfaces

Incorporation of metal microparticles in CP matrice s

�� Concluding Remarks

From Plastics to Electronically Conductive Polymer s (ECP)

1960’s

“There can be no such things as Conducting Organic M aterials or Polymers ”

Introduction

19771977Oxidation of PA

� ‘doped ’ PA (conductivity 105 S/m)

A J. Heeger, A G. MacDiarmid and H. Shirakawa

2000 NOBEL Prize for Chemistry

“For the discovery and development of Conductive Pol ymers ”

Conducting Polymers – Most studied systems

Introduction

Conducting electric current ⇔⇔⇔⇔ free movement of electrons

PA

‘Doping ’

Introduction

Electrons removed / introduced

Oxidation with halogen (p-doping):

[CH]n + 3x/2 I2 → [CH]nx+ + xI3

-

Reduction with alkali metal (n-doping):

[CH]n + xNa → [CH]nx- + xNa +

Electrons removed / introduced

Need of “holes” for balloon propagationCharge can migrate along the polymer

Polymerization

Introduction

‘Dopant ’ not bound but ‘ near ’ the polymeric chain

Ionic participation assure the electroneutrality

The formed polymer is electrically charged

Conducting ( doped ) state can be reversibly reduced to the neutral fo rm

Conductivity of most known Conducting Polymers

Introduction

Conducting Polymers as Corrosion Protective Coating s

CP for novel anti-corrosion coatings

Why ?

•••• Reversible oxidation / reduction behaviour

•••• Reduced (neutral) form : semiconductor and hydropho bic

•••• Positive value of redox potential

�� coating gets noble character�� coating gets noble character

•••• Catalytic activity for oxygen reduction and simulta neous ability

to form a passivating oxide layer

•••• Metal dissolution and oxygen reduction processes se paration

�� prevent local pH increase



•••• Addition of an oxidant to the solution ( e.g. FeCl 3)

�� suspension of polymer particles or colloids

Oxidative treatment of a monomer solution

•••• Anodic oxidation at the envisaged substrate

��polymer formed as a film on the electrode material

Oxidation potential of most monomers is in the range of metal dissolution

�

Metal dissolution competes with monomer oxidation



Polymerization in the presence of passivating agent soxalic acid

p-toluene-sulphonic acid

sodium oxalate

sodium citrate

... /...

Substrate pre-treatment

PolymerSubstrate

PAni , PPy, PTh, PEDOTh, P(Amino -naphtol )

Iron /Steel

... /...

The inter-layer (pseudo-passive) supresses the metal dissolution

without preventing the electropolymerization process

P(Amino -naphtol )

PAni , PPy, PThAluminium

PPyZinc

PPyCopper

PAni , PPyTitanium

PAniNickel

PPyMagnesium


Electrosynthesis of PPy on Copper

Cyclic voltammogram of a copper electrode A1 : Cu 2O; A2 : Cu(II) species

Chelating agent

precipitated layerdiffusional barrierpartial inhibition

A3, A4 : adsorbed S, S ion oxidation0.1M sodium salicylate ( SS) 0.1M sodium salicylate ( SS) υυυυ=20mV/s (*)

1 M SS + 0.5 M Pyυυυυ=20mV/s (**)

_______________(*) A.C.Cascalheira, L.M. Abrantes, Electrochim. Acta 49 (2004) 5023(**) A.C.Cascalheira, S. Aeiyach, J. Aubard, P-C Lacaze,L.M. Abrantes, Russian J.Electrochem. 40 (2004) 294

In the presence of SS the oxidation of PPyoccurs at ~0.55 V

• before the oxidation of SS species

• after the surface modification

Successful polymerization

0.5 M pyrrole in 1 M sodium salicylate at 0.6 V vs. SCE

80

60

40

20

0

-20-1.0 -0.5 0.5 1.00 1.5

E / V vs. SCE

Polymer growth

I/ µ

A c

m-2

In-situ contact mode AFM



in-situ AFM

globular morphology developinginto the typical “cauliflower”structure with film thickening(5 µµµµm x 5 µµµµm)

_______________A.C.Cascalheira, A.S. Viana, L.M. Abrantes, Electrochim. Acta 53 (2008) 5783

no corrosion observed

PPy / Cu PPy / Pt



Polymer electrochemical behaviour not influenced by the substrate nature

Comportamento redox em SS 1 M; υυυυ =50 mV / s (*)

_______________(*) A.C.Cascalheira, Ph.D. Thesis, Univ. Lisboa (2004) (**) L.M.Santos, J.C. Lacroix, K.I. C. Ching, L.M. Abrantes, P-C Lacaze, J.Electroanal Chem. 587 (2006) 67

10 µµµµm

PPy deposited at 100 mA/cm 2 (600 mC/cm 2) (**)from SS tartrate

Polymer thickness depends on the growth conditions

Typical polarisation curves



PPy /Cu Polyaniline / steelPolymer prepared with 25 and 300 mC cm -2 (*)

NaCl 3.5%Coated steel

Polymer prepared from soluble doped PAni (Monsanto) (**)

NaCl 3 %

-0,1

0,0

0,1

0,2

Uncoated CuThin film(Thick film

vs.

SC

E

Ig = 1 mA cm-2

Bare steel

10 -9 10 -8 10 -7 10 -6 10 -5 10-4 10-3 10-2-0,5

-0,4

-0,3

-0,2

E /

V v

s.

I / A

_______________(*) A.C.Cascalheira, L.M. Abrantes, Corrs. Prot. Mater.,23 (2004) 6(**) D.E.Tallman, Y.Pae, G.P. Bierwagen, Corrosion,. 55 (1999) 779

Corrosion potential :shift to more positive values

Oxidation current: accentuated decrease

Anodic peak (CuCl formation): decreasesubstrate isolated from the aggessive anions

Combination of SAMs with CPs

Bifunctional molecules

� � Polymerizable terminal group

Densely packed polymeric assemblies

� head group

appropriate for self-assembly

_______________E. Jaehne et al., Progress in Organic Coatings.,61 (2008) 211

Bifunctional molecules

�� Surface reaction of the terminal reactive group with further monomers

The introduction of polymerizable terminal groups allows in-situ surface polymerization


Strongly bond layer

Densely packed polymeric assemblies chemisorbed ont o solid surfaces

Combination of SAMs with CPsModified copper electrodes

i) Adsorption of self-assembled monolayers (SAM) on Co pper

NN N N1 mM

solution

Cu substrates polished with alumina (down to 0.05 µm); washed in ultrasonic bath and transferred to the SAM adsorption solution.Cu


S

S

O

O

H

O

O

S SH

O

O

S SH

O

O

S SH

Cu

solution

~ 20 h

pyrrole lipoic acid derivative

(Py )

hexanethiol (C6), Py SAM C6 SAM

S-H

CH3

CuS

CH3

S

CH3

S

CH3

S

CH3

S

CH3

Electrochemical Characteristion of SAM modified cop per electrodes

0.1 M NaOH; 20 mV s-1Bare Copper

0.0

0.4

i / m

A c

m-2

Copper Modified with SAMs

0.0

0.3

0.6

i / m

A c

m-2

Cu / C6 SAM

Cu / Py SAM



IEp red = - 0.460 V; IIEp

red = - 0.955 V C6 SAM : Ep

red = - 1.150 VPy SAM : Ep

red = - 0.980 V

-1.6 -1.2 -0.8 -0.4 0.0 0.4

-1.2

-0.8

-0.4

i / m

A c

m

E / V vs. SCE

I

II

C6 and Py derivative SAMs inhibit the copper oxide peaks

-1.6 -1.2 -0.8 -0.4 0.0

-1.2

-0.9

-0.6

-0.3

i / m

A c

mE / V vs. SCE

reduction peaks: SAMs reductive desorption

Combination of SAMs with CPsii) potentiostatic deposition of polypyrrole thin films onto

the Copper modified with Py SAM

N NN N NN

Pyrrole monomer


O

O

S SH

O

O

S SH

O

O

S SH

O

O

S SH

O

O

S SH

Cu

Potentiostatic polymerisation

Cu

0.5 M pyrrole em 1M sodium salicylate; Eg = 0.6 V

1.0

1.5

2.0

i / m

A c

m-2

CuCu / Py SAM

Cu / PPy



0 20 40 600.0

0.5

t /s

Similar growth charges used to deposit Polypyrrole on bare copper (55 mC cm -2) and on

copper modified with Py SAM (57 mC cm -2). AFM images revealed thetypical globular morphologyobtained for polypyrrole films

Cu / Py SAM / PPy

Current transients for the potentiostatic depositio n of PPy


Combination of SAMs with CPsiii) Corrosion protection evaluation

-0.16

-0.14

-0.12

-0.10

Cu Cu/ PPy Cu/ SAM Py / PPy

E /

V v

s. S

CE

Open circuit potential

-0.2

-0.1

0.0

0.1

0.2

E /

V v

s. S

CE

Cu Cu/ PPy Cu/ Py SAM / PPy

Polarisation curves 0.5 M NaCl

0 750 1500 2250 3000 3750-0.22

-0.20

-0.18

-0.16

E /

V v

s. S

CE

t / s1E-9 1E-7 1E-5 1E-3 0.1

-0.5

-0.4

-0.3

-0.2

E /

V v

s. S

CE

i / A cm-2

ECA / V Ecorr / V i /(A cm -2) at - 0.075 V

Cu -0.204 -0.268 4.37 x 10 -4

Cu/ PPy -0.149 -0.180 7.02 x 10 -5

Cu/ Py SAM / PPy -0.115 -0.169 4.83 x 10 -5

best protection against Cu dissolution

PPy - PySAM /CuCorrosion protection evaluation (AFM analysis)

PPy / PySAM/Cu

3x3 µµµµm2

after polarisation curves in NaCl 0.5 M

2x2 µµµµm2

after 2 days in NaCl 0.5 M pH 1

3x3 µµµµm2


topography (z = 60 nm) Phase ( z = 44 º)

5x5 µµµµm2

z = 500 nm

1.7x1.7 µµµµm2 1.7x1.7 µµµµm2

bare copper after polarisation curves in NaCl 0.5 M : evident corrosion

Typical PPy morphology is obtained after the polari sation curvesPPy coating is still present after two days under h arsh conditions

Granular deposit might arise from corrosion of the underlying copper

5x5 µµµµm2

z = 80 nmCu

2x2 µµµµm 3x3 µµµµm

Incorporation of metal particles into CP films

Transition from active dissolving Fe-Cr alloy to th e passive state possible when the cathodic current ( reduction of oxygen or proton )

exceeds the critical anodic current necessary for t he alloy passivation

Protection of stainless steel (ss)

Acid solutions :

Combining CP with SAMs

considerable overpotentials for ORR and HER on ss

�� Fe-Cr alloys dissolve fairly

Decrease of overpotential in acid solution

�� small additions of Pt or Pd (0.1-0.5%) to Fe-Cr alloys

very efficient but too expensive

Incorporation of metal particles into CP films

The polymeric layer serves as a conducting matrix w hich supports, separates and stabilizes the metal clusters

PPy / Fe

Py electropolymerization from aqueous oxalic acid so lution PPy

Strongly adherent, smooth film

Physical barrier

Shift the potential of the coated metal ��

Lower the kinetics of corrosion

CP films incorporating metal microparticles

to stabilize the corrosion potential in the passive range

Cu2+ + Fe →→→→ Cu + Fe2+

mCu 2+ + 2PPyn+ →→→→ mCu + 2PPy (n+m)+

Cu – PPy / FeCementation process

Physical barrier��

Lower the kinetics of corrosion

Cu particles accelerate reduction of both protons a nd dissolved oxygen

SAMs

Ease adsorptionSelf-organization

Terminal reactive

CP

Work as oxidants New bifunctionalsystems

in -situ surface

Combining CP and SAMs

Concluding Remarks

Terminal reactivegroup

-SH, -S-S-, LA, Phophonic

thiophene, pyrrole

Passivation filmon metals

Steels, Al, Cu

Dopant anion, bi-layers, composites

in -situ surface polymerization

versatile corrosion resistant coatings

Novel anti-corrosion coatings

Acknowledgements

Joana Cabrita

António Cascalheira

Luís Santos

Franz-Peter Montforts

Pierre-Camille Lacaze

Ana Viana

Joana Cabrita

Christoph Eberle

Nina HeidaryFranz-Peter Montforts

Isabel Tissot

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