Protection of Metallic Substrates Protection of Metallic Substrates through Electropolymerizationthrough Electropolymerization

International Conference on Material Sciences (SCICON' 16), December, 19-21, 2016

Need for Surface ProtectionNeed for Surface Protection Surfaces of all materials are corrosion-prone due Surfaces of all materials are corrosion-prone due

to Climatic conditions & Chemical factorsto Climatic conditions & Chemical factors Destruction of materials leads to economy lossesDestruction of materials leads to economy losses Direct & Indirect losses due to corrosion amounts Direct & Indirect losses due to corrosion amounts

to $13 billions per yearto $13 billions per year

Need for Surface ProtectionNeed for Surface Protection……

Prime concern is Conservation of MaterialsPrime concern is Conservation of Materials World’s supply of materials is limited &World’s supply of materials is limited &

wastage / loss of materials leads to loss of wastage / loss of materials leads to loss of energy, cost escalation etc.,energy, cost escalation etc., Surface coating is an important strategy to Surface coating is an important strategy to

protect materials which are prone to decayprotect materials which are prone to decay

Impacts of CorrosionImpacts of Corrosion

Copper – An Engineering MaterialCopper – An Engineering Material Copper has been commonly used in a wide range

of applications in heat conductors, heat exchangers because of its excellent thermal conductivity and mechanical workability.

Copper generally shows resistant against atmospheric corrosion and other forms of corrosion.

However, copper becomes very susceptible to corrosion in a significant rate in media that contain chloride ions.

Corrosion Protection MethodsCorrosion Protection MethodsBarrier Protection

Cathodic Protection

Corrosion Resistant Materials

Provided by a protective coating that acts as a barrier between corrosive elements and the metal substrate.

Materials inherently resistant to corrosion in certain environments.

Employs protecting one metal by connecting it to another metal that is more anodic, according to the galvanic series.

It is a polymerisation of organic molecules in the presence of an

electrical current.

It is a relatively new technique involving aspects of electrochemical

engineering, polymer science, organic chemistry and

coating/plating technology.

ElectropoIymerizationElectropoIymerization

Prevention of corrosion in copper has attracted many Researchers and many strategies have been developed to protect copper.

Among the available methods, electropolymerization techniques have become prominent nowadays due to its simplicity and wide range of applications.

ElectropoIymerization…ElectropoIymerization…

Protection through Electropolymerization Electropolymerization of an organic

compounds (usually the heterocyclic compounds) under the influence of current.

Electrodeposition of polymeric films at the surface of an electrode has opened up a new field at the convergence between two rich domains: Electrochemistry of modified

electrode Conjugated systems

Simple process

Doesn’t require any toxic solvent

Films thickness can be controlled

Different morphology can be produced by varying the scan rate

It is enough to impose a sufficiently positive potential on a metallic electrode.

By passing of an anodic current through the solution of monomer, film of the

corresponding polymer progressively grows at the electrode surface.

General Aspects of Electropolymerization

Solvent Electrolyte Bath composition and temperature pH Monomer concentration Hydrodynamic conditions (e.g., stirring or its

absence) Pretreatment of its surface Electrode surface area Shape of the working electrode Current density

Factors Affecting Electropolymerization

Conjugated Polyheterocycles

Electrodeposition can be done by any of the following methodsCyclic Voltammetry

The working electrode potential is ramped linearly versus time. These cycles of ramps in potential may be repeated as many times

as needed. The current at the working electrode is plotted versus the applied

voltage

Chronoamperometry

Cont…

Potential of the working electrode is stepped and the resulting

current from faradaic processes occurring at the electrode is

monitored as a function of time.

The current density at the working electrode is plotted versus

time.

The rate of change of potential at an electrode is

measured at constant current.

The working electrode potential is plotted

against time.

ChronopotentiometryCont…

Work done in our lab...Electrosynthesis of poly-3-amino-1,2,4-triazole/TiO2 (3-ATA/TiO2) on copper

Electropolymerization of 3-amino-Electropolymerization of 3-amino-1,2,4-triazole (3-ATA)1,2,4-triazole (3-ATA) Monomer Concentration - 0.1 M Electrolyte - 0.1M Methanol/NaOH Scanning potential - ˗ 0.2 to 1.6 V vs SCE Scan rate - 30 mV/s

CV of 3-ATA on Cu in MeOH-NaOH CV of monomer –free Cu in MeOH-NaOH

CV of 3-ATA with various concentrations of TiO2

Addition of TiO2 increases the peak current values suggesting the increase of rate of polymerization

Schematic representation of electropolymerization of 3-ATA

FT-IR Studies XRD pattern of (a) p-3-ATA (b) p-3-ATA/TiO2

For bare TiO2, the strong absorption at 686 cm-1 could be obtained due to Ti-O stretching .

This band is weak in p-3-ATA+TiO2 composites due to the interaction of polymer with TiO2

XRD pattern of p-3-ATA showed a peak at 25o. This could be due to the polymer.

The 2Ө values at 37o, 47o and 55o showed the presence of Ti in the polymeric matrix and these values proved that the crystalline behavior of TiO2 particles was not affected during electropolymerization.

SEM Suggests the incorporation of TiO2 particles in the polymeric matrix.

The average particle size of TiO2 is 0.67 µm.

The incorporation of TiO2 particles into the polymeric matrix was also confirmed by EDX analysis.

The intense peak at 0.40 and 4.5 keV confirms the presence of Ti.

SEM image of p-3-ATA/TiO2

EDAX spectra of p-3-ATA/TiO2

Ti

Nyquist plots Polarization plots

Materials Rct

(Ω cm-2 )

IE (%) Icorr (µA cm-2)

IE (%)

Bare 1043 --- 97.94 -0.1 M 3-ATA 5051 95.3 18.4 81.20.1 M 3-ATA + 10-3 M TiO2 11549 98.8 0.982 98.9

Thus, the study revealed that the incorporation of TiO2 at lower concentration decreases the porosity of the polymer and significantly increases the inhibition efficiency

Work done in our lab...

Electropolymerization of 4-methyl-3-Electropolymerization of 4-methyl-3-mercapto-1,2,4-triazole (MMTAmercapto-1,2,4-triazole (MMTA))

NN

N

SH

CH3

slow

NN

N

S

CH3

e

NN

N

S

CH3

NN

N

S

CH3

nH

fast ne

H

NN

N

S

CH3

NN

N

S

CH3n

(peak A)

(peak B)

Monomer Concentration - 0.1 M Electrolyte - 0.5M Methanol/NaOH Scanning potential - 0 to 1.7 V vs SCE Scan rate - 10 mV/s

FT-IR spectrum of (a) TiO2, (b) p-MMTA and (c) p-MMTA/TiO2

CV of p-MMTA over copper surface

As the number of cycles were increased, the anodic current values decreased.

This suggested the formation of insulating polymeric films.

The strong absorption at 694 cm-1 is due to Ti–O stretching. This band appeared weak in the IR spectrum of the composite. This result strongly suggested the interaction of TiO2 with polymer.

CV of poly-MMTA on Cu FT-IR spectrum

The 2θ values at 35, 55, 60, 63 and 70 indicated the presence of TiO2 in the polymeric matrix. It also confirmed the crystalline nature of the incorporated TiO2.

XRD pattern of poly-MMTA/TiO2

Corrosion Inhibition Studies of poly-MMTA/TiO2

Materials Rct

(Ω cm-2 )

IE (%) icorr(µA cm-2)

IE (%)

Bare/Cu 1081 --- 70.12 ---p-MMTA/Cu 2450 55.4 33.12 52.7p- MMTA/TiO2/Cu 5201 79.1 15.62 77.7

Nyquist plots Polarization plots

The increase in Rct values and decrease in icorr values suggested the higher IE of p-MMTA/TiO2 composite on copper

Bare Cu

Bare Cu

p-MMTA/TiO2/Cup-MMTA/TiO2/Cu

M. G. Sethuraman et al. Res. Chem. Intermed., 41 (2015) 8041-8055

Electrochemical synthesis of poly-3-amino-5-mercapto-1,2,4-triazole (AMTA) on copper and its protective effect in 3.5% NaCl medium (Res. Chem. Intermed.)

Electropolymerization of Electropolymerization of 3-amino-5-mercapto-1,2,4-triazole (AMTA)AMTA) Monomer Concentration - 0.1 M Electrolyte - 0.5M Methanol/NaOH Scanning potential - ˗ 0.7 to 1.2 V vs SCE Scan rate - 10 mV/s

AMTA

CV of AMTA

Schematic representation of electropolymerization

of AMTA on Cu

As the cycle increases, anodic peak current decreases, suggesting the formation of polymer film at the electrode surface

Schematic representation

FT-IR spectra of (a) AMTA and (b) p-AMTA film

The disappearance of

S-H stretching for

p-AMTA suggested the

formation Cu-S

linkage.

Effect of scan rate on electropolymerization of AMTA

The anodic current density increases with the increase of scan rate

suggested the polymerization process is diffusion controlled in

nature.

Electrodes icorr IE

(µAcm−2) (%)

A 39.87 -- B 13.63 65.8 C 11.73 70.5 D 7.02 82.3 E 4.97 87.5 F 3.14 92.1

A – Bare Cu; B – poly-AMTA-Cu; C – poly-AMTA-La2O3-Cu; D – poly- AMTA-CeO2-Cu; E – poly-AMTA-TiO2-Cu; F – poly-AMTA-nano TiO2-Cu

Effect of Various Oxides on Corrosion Protection

From the above results, it is clear that the incorporation on nnao TiO2 into

polymeric matrix enhanced the protection efficiency. This is because, TiO2 being a metal oxide additive in the composite, could give

better dispersion of the particles and also enhance the barrier properties of the

coatings.

Evaluation of Corrosion Protection of Poly-4-amino-1,2,4-triazole and Its Composites

We have studied the effect of various inorganic oxides

(La2O3, CeO2, TiO2 and nano TiO2) on the

electropolymerization of 4-amino-1,2,4-triazole (4-ATA).

EIS Studies

Nyquist plots for (a) bare; (b) poly-4-ATA; (c) poly-4-ATA-La2O3; (d) poly-4-ATA-CeO2; (e) poly-4-ATA-TiO2 and (f) poly-4-ATA-nano TiO2 copper electrode in 3.5% NaCl

Bare Cu

p-4-ATA + nano TiO2

Nano TiO2

incorporated

composite coatings shows higher Rct value compared to other inorganic oxides.

Electrodes Rct

(Ω.cm2)

IE (%)

Bare Cu 1184 --poly-4-ATA 3508 56.2poly-4-ATA-La2O3 4450 73.3poly-4-ATA-CeO2 5673 79.1poly-4-ATA-TiO2 9893 88.0poly-4-ATA-nano TiO2 12435 90.4

EIS Studies…

Addition of inorganic oxide particles have increased the Rct

values which in turn increased the inhibition efficiency (IE).

Nano TiO2 composite coatings could reduce the porosity of the

coatings to a larger extent thereby increasing the IE.

Polarization Studies

Potentiodynamic polarization curves for (a) bare; (b) poly-4-ATA; (c) poly-4-ATA-La2O3; (d) poly-4-ATA-CeO2; (e) poly-4-ATA-TiO2 and (f) poly-4-ATA-nano TiO2 copper electrode in 3.5% NaCl

From the polarization curves, it is clear that the addition of nano TiO2 particles into polymeric matrix decreased the corrosion current values (icorr) vales.

Polarization Studies…

Electrodes icorr

(µAcm−2) IE (%)

Bare Cu 71.24 --poly-4-ATA 39.07 45.1poly-4-ATA-La2O3 12.52 72.4poly-4-ATA-CeO2 3.03 78.7poly-4-ATA-TiO2 2.15 86.9poly-4-ATA-nano TiO2 0.98 92.6 The decrease in icorr value suggested the prevention of

attack of corrosive chloride ions onto electrode surface.

Nano TiO2 composite coatings showed higher IE.

Reason for the higher IE of Composites

Higher corrosion protection performance of the

composites could be due to the filling-up of oxide

particles in the pores/defects of the coatings.

The use of inorganic oxide particles reduced the

porosity and defects in the coatings thereby

hindering the diffusion of corrosive ions onto the

electrode surface.

Reason for the higher IE of Composites…

Among the investigated oxides, nano TiO2

incorporated composite coatings showed greater

corrosion resistance property.

This is because, TiO2 being a metal oxide additive

in the composite, could give better dispersion of

the particles and also enhance the barrier

properties of the coatings.

Reason for the higher IE of Composites…

Another plausible reason for the enhanced protection

ability is polymer being the p-type offers large barrier

for electron transport onto electrode surface, while

TiO2 being n-type causes an obstruction against hole

transport across the interface in the polymeric

composites.

The nano-sized particles could be easily impregnated

into pores of the polymeric matrix and thus reduced

porosity which could enhance the protection

performance.

Copp

er

pores/defects in the polymer coating inorganic oxides

Copp

erComposite coatings

diffusion of chloride ions prevention of diffusion of chloride ions

Plausible schematic representation of protection mechanism

The pores/defects of the coatings are filled by the inorganic oxides

thereby prevents the diffusion of corrosive ions onto the electrode

surface

Electro catalysisElectro catalysis

SensorsSensors

Biosensors Biosensors

Energy storage ( batteries and supercapacitors)Energy storage ( batteries and supercapacitors)

AnticorrosionAnticorrosion

Semiconductors Semiconductors

ElectrochromismElectrochromism

Applications of Electropolymerization