Anticorrosive Zn Free Pigments: Their Performance PNWSCT 2014.

Anticorrosive Zn Free Pigments:

Their Performance

PNWSCT 2014

Agenda

Historical Evolution of Anticorrosive Pigments

Corrosion

Protection

Zn free pigments

Case Study

Accelerated cyclic electrochemical test

Analytical experiments

Additional systems tested

Summary

HISTORICAL EVOLUTION OF ANTICORROSIVE

PIGMENTS

Anticorrosive Zn Free Pigments: their performance

Dr. Ricard March, Nubiola

Historical evolution of anticorrosive pigments

ALTERNATIVE NON CLASSIFIED AS HAZARDOUS ANTICORROSIVE PIGMENTS

TRADITIONAL ANTICORROSIVE PIGMENTS

Chromate based pigments

Zinc ChromateZinc TetraoxychromateStrontium ChromateBarium ChromateRed lead

ZINC FREE PIGMENT

Un/Modified with organic surface treatment

Calcium strontium phosphosilicate

• Zinc Phosphate

• Modified Zinc Phosphates

ZINC BASED PIGMENTS

CORROSION

CORROSION

What the corrosion is? Corrosion is a gradual spontaneous process as a result of a chemical reaction with the environment that damages the original metal, typically iron.

+ O2 / + H2O

Spontaneous !!

Non spontaneous !!

Entropy: Order Disorder

Corrosion Process: description

Metallic substrate (Fe)

Protective coating

H2OO2

OH-OH-

OH-

Cathodic reaction:O2 + 2 H2O + 4 e- 4 OH-

Fe2+

Fe

Anodic reaction:Fe Fe2+ + 2 e-

e-

e-

e-e-

delamination

blistering

Fe(OH)2

1

2

3

4

5

Corrosion Process: reactions

Redox reaction:

Anodic reaction (oxidation): Fe Fe2+ + 2 e-

Cathodic reaction (reduction): O2 + 2 H2O + 4 e- 4 OH-

Globally:

2 Fe + O2 + 2 H2O + 4 e- 2 Fe2+ + 4 OH- + 4 e-

Formation of rust:

Fe2+ + 2 OH- Fe(OH)2

4 Fe(OH)2 + O2 4 FeOOH + 2 H2O

2 FeOOH Fe2O3 + H2O

Corrosion Process

Other compounds can accelerate the reaction:

• H3O+ (or changes in the pH)

• SO2 (industrial environment)

• NaCl (marine environment)

• Other contaminants: NH4+, SO4

2-, Mg2+, COO-, etc

• Also: temperature

PROTECTION

How to Slow the Corrosion Process


Protective coating

H2OO2

OH-OH-

OH-

Fe2+

Fee-

e-e-

delamination

blistering

It is impossible to interrupt the electron flowing (metal)

1 e- flowing



Protective coating

H2OO2

OH-OH-

OH-

Fe2+

Fee-

e-e-

delamination

blistering

It is possible to reduce water and oxygen flow through barrier effect

2 H2O / O2 in the interface



Protective coating

H2OO2

OH-OH-

OH-

Cathodic reaction:O2 + 2 H2O + 4 e- 4 OH-

Fe2+

Fee-

e-e-

delamination

blistering

High pH (OH-) displaces the reaction to the left and helps hydroxides precipitation

Cathodic inhibition by metallic hydroxides and oxides precipitation3 OH- generation in

the cathode



Protective coating

H2OO2

OH-OH-

OH-

Fe2+

Fe


e-

e-e-

delamination

blistering

Anodic passivation by metal and iron complexes (phosphates, silicates, …) precipitation

4 Fe2+ generation in the anode



Protective coating

H2OO2

OH-OH-

OH-

Fe2+

Fe


e-

e-e-

delamination

blistering

Cathodic reaction:O2 + 2 H2O + 4 e- 4 OH-Compounds

precipitated in the cathode and the anode also avoid the ionic

mobility

Fe(OH)2

5

Ionic mobility

Zn FREE PIGMENTS

Zn free pigments

Calcium Strontium Phosphosilicates: aM*. bP2O5 . cSiO2 . xH2O, for M = Ca, Sr

• Low particle size

• Special particle shape combination (acicular + spherical)• Elemental particles <1µ forming aggregates and

agglomerates up to <10µ

P artic le D iam eter (µ m .)

%

0

10

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1.0 10.0 100.0 1000.0

N ubirox 301D(v,0.5)=1.15µ

P artic le D iam eter (µ m .)

%

0

10

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1.0 10.0 100.0 1000.0

N 301 S TD 5'-3

N 20 030829009 0'-1

Zn free pigments

• Higher specific surface area 21 m2/g vs 1 m2/g (std zinc phosphate)

• Minimizes moisture, oxygen and ionic species diffusion.• Microscopical reinforcing action• Better adhesion to the metal surface• Better dispersion capability• More active surface (allows lower pigment dosage)• Better performance in thin film systems• Low effect on gloss

Zn free pigments: Calcium Strontium Phosphosilicates

SE

M (

scan

ning

ele

ctro

n m

icro

scop

y) 1

0000

X


Barrier effect

O2 + 2 H2O + 4 e- 4 OH-

Cathodic reaction displacement

Cathodic inhibition:

Ca/Sr hydroxides

Anodic passivation: Ca/Sr/Fe

phosphates&silicates complexes

aM*.bP2O5.cSiO2.xH2OM= Ca, Sr

CASE STUDY

DOE

• DOE: Full factorial experiment 24 (16 runs of 1 replica in one block):• Pigment (qualitative): zinc phosphate – zinc free• Dose (quantitative): 3% - 6%• Thickness (quantitative): 60 - 90 • Exposure time (quantitative): 240 h – 1170 h

• Exit parameters:• Oxidation at scribe• Oxidation on the panel• Adhesion at the scribe

• WB Styrene Acrylic• Substrate: CRS, S-46• 60 - 90 • 240 - 1170 h Neutral Salt Spray ASTM B117• Formulated at same:

• Anticorrosive Pigment Volume Content (3% - 6%)• PVC/CPVC ratio (same free binder volume, 0,47)

Panel Evaluation

“Cross cut” adhesion ASTM D3359

Adhesion at the scribe ASTM D1654 B

Oxidation at the scribe ASTM D1654 A

Oxidation on the panel ASTM D610

Blistering ISO 4628-2

DOE: Pareto Plots

Exposure time

Exposure time

Exposure time

PIGMENT

DoseThickness

DOE: interaction plot for oxidation at scribe

DOE: interaction plot for oxidation on the panel

Faster activity and higher efficiency of Zn free

Zn free3%60

240 h

Zn phosphate6%60

240 h

Zn free6%90

1170 h

Zn phosphate6%90

1170 h

ACET: The need

ASTM B117

UNE 48315-1

Accelerated Cyclic Electrochemical Technique (ACET)

24 h

100 - 10.000 h

4.400 – 25.000 h

ACET: Steps

ACET: Information

Definition Effect|Z|max(Ω) Maximum impedance value Initial quality of the Coating|Z|min(Ω) Minimum Impedance Value Coating Porosity∆Z (Ω) Impedance variation Coating Porosity & AdhesionEmax (V) Maximum Free Corrosion Potential Coating Porosity & AdhesionEmin (V) Minimum Free Corrosion Potential Coating Porosity & Adhesion∆E (V) Free Corrosion Potential Variation Activity in the Interface

Bode Graph Erelax vs trelax Activity in the Interface, Adhesion & Porosity

ACET: Equivalent circuit

Definition EffectRpo Pore Resistance Degradation due to porosity increasingCc Coating Capacitance Water AbsorptionRp Polarization Resistance Corrosion in the InterfaceCdl Double Layer Capacitance DelaminationRs Electrolyte resistance

Coating properties

Interface

Equivalent circuit used to model EIS & ACET

Panel Evaluation: Standard (SSC)

“Cross cut” adhesion ASTM D3359

Adhesion at the scribe ASTM D1654 B

Oxidation at the scribe ASTM D1654 A

Oxidation on the panel ASTM D610

Blistering ISO 4628-2

Panel Evaluation: ACET

Impedance values:

|Z|max, |Z|min and ∆Z

Equivalent circuit parameters:

Rpo and Cc

Impedance values:

Emax, Emin, ∆E and Bode graph

Equivalent circuit parameters:

Rp and Cdl

ACET: ANN Blank std ZnPh Zn-free

CPV (%) 0 3 4,5 6 8 3 4,5 6 8

|Z|max(Ω) 1,45E+08 1,06E+08 1,55E+07 1,47E+08 9,81E+07 1,22E+08 8,39E+07 1,02E+08 6,92E+07

|Z|min(Ω) 1,49E+04 2,57E+04 4,63E+03 2,38E+04 1,53E+04 9,26E+07 1,93E+07 2,67E+07 6,08E+07

Emax (V) 0,25 0,24 0,18 0,17 0,11 0,2 0,16 0,21 0,19

Emin (V) -0,16 0,03 -0,13 0,02 -0,02 -0,33 -0,37 -0,35 -0,32

∆E (V) 0,41 0,21 0,31 0,16 0,13 0,52 0,54 0,55 0,51

Use of this methodology in the industry?

Electrochemical Models?

Artificial Neural Networks (ANN)

ACET: correlation

ANALYTICAL EXPERIMENTS

SEM: panel observation

SEM: mapping

SEM: cross-section observation

Blank Zn Phosphate Zn free

• Water Based Styrene Acrylic• Substrate: CRS, S-46• 70 • 450 h Neutral Salt Spray ASTM B117• Formulated at same:

• Anticorrosive Pigment Volume Content (6%)• PVC/CPVC ratio (same free binder volume)

SEM: cross-section observationZn freeZinc phosphateBlank

OxidationThe finest particle distribution


Fe

Si

O

P

Panel

Coating

Zn

Zinc phosphate: Energy Distribution Spectroscopy Element Mapping (EDS element mapping)


OFe

SiCaSr P

Panel

Coating

Zinc free pigment: Energy Distribution Spectroscopy Element Mapping (EDS element mapping)

Smaller particle size allows the pigment to have a more direct interaction with the metal surface.


Zn free (line 1)Blank

Panel CoatingPanel Coating

Energy Distribution Spectroscopy Linescan (EDS Linescan)

Zn free (line 2)

Panel Coating


Blank

Panel Coating



Zn free (line 1)

Panel Coating


SEM: cross-section observationEnergy Distribution Spectroscopy Linescan (EDS Linescan)

Zn free (line 2)

Panel Coating

ADDITIONAL SYSTEMS TESTED

SB Wash Primer

Zinc Tetraoxychromate Zinc free

• 2K Etch/Wash primer: polyvinyl butyral epoxy modified

• Substrate: Galvanized Panels, SG015• 20 (lower half – only primer)• 50 (upper half – primer & intermediate)• 300 h Neutral Salt Spray ASTM B117• Formulated at same:

• Anticorrosive Pigment Volume Content (9%)

• PVC/CPVC ratio (same free binder volume)

SB Wash Primer

Cold rolled steelS-46 (Q-Panel)

5B

Mild steelSB015D (Espancolor)

5B

Galvanized steelSG015 (Espancolor)

4B

Aluminum3105H14 AA015D (Espancolor)

5B

5B 5B 3B 4B

Zinc Tetraoxychromate

Zinc free

Cross cut test (ASTM D3359)

SB AlkydBlank 6% Zinc Phosphate 6% Zinc free

• Solvent Based Alkyd• Substrate: CRS, S-46• 60 • 641 h Neutral Salt Spray ASTM B117• Formulated at same:


SB AlkydBlank

6% Zinc Phosphate 6% Zinc free3% Zinc free

Zn free pigment shows better performance, even at lower dosage.

SB EpoxyBlank 6% Zinc Phosphate 6% Zinc free

• Solvent Based Epoxy• Substrate: CRS, S-46• 60 • 1100 h Neutral Salt Spray ASTM B117• Formulated at same:


SB EpoxyBlank 10 % Zinc Phosphate 6% Zinc free

Blank 10 % Zinc Phosphate 8% Zinc free

Zn free pigment shows better performance, even at lower dosage.

1100

h13

20 h

SB 2K PolyurethaneBlank 6% Zinc Phosphate 6% Zinc free

• Solvent Based 2K Polyurethane (acryl/polyisocyanate)

• Substrate: CRS, S-46• 60 • 385 h Neutral Salt Spray ASTM B117• Formulated at same:


SB 2K Polyurethane: pot-life

Hours BlankZinc

PhosphateZn free 2

1 Liquid Liquid Liquid

2 Liquid Thick liquid Liquid

3 Thick liquid Solid Thick liquid

4 Solid Solid Solid

No effect on pot life / shelf life

Powder coating

Zinc freeBlank

• Powder Coating, Epoxy-Polyester• Substrate: Phosphated steel, Bonderite

1000• 90 • 1000 h Neutral Salt Spray ASTM B117• Formulated at same:

• Anticorrosive Pigment Volume Content (2,3%)• PVC/CPVC ratio (same free binder volume)

• Powder Coating, Epoxy-Polyester• Substrate: Aluminium, 3105H14• 90 • 4000 h Neutral Salt Spray ASTM B117• Formulated at same:


TESTED PANEL EVALUATION Blank Zinc free 1

Rusting on the panel (ASTM D610)8G

(0.1%) 10 (none)

TESTED PANEL EVALUATION Control Zinc free 1

Rusting at the scribe (ASTM D1654)7

(1.5mm) 9 (0.5mm)

Rusting on the panel (ASTM D610) 6G (1%) 9G (0.03%)

Zinc freeBlank

WB Acrylic DTM

Blank 4,5% Zinc free4,5% Zinc Phosphate

• WB Acrylic DTM• Substrate: CRS, S-46• 90 • 310 h Neutral Salt Spray ASTM B117• Formulated at same:


Zinc free: No gloss reduction Good anticorrosive activity

Gloss 85º = 69 Gloss 85º = 57 Gloss 85º = 71

WB Alkyd

Blank 4,5% Zinc Phosphate 4,5% Zinc free

• WB Alkyd• Substrate: CRS, S-46• 90 • 500 h Neutral Salt Spray ASTM B117• Formulated at same:


WB Styrene Acrylic

• WB Styrene Acrylic• Substrate: CRS, S-46• 55 • 478 h Neutral Salt Spray ASTM B117• Formulated at same:


6% Calcium phosphateBlank 6% Zinc phosphate 6% Zinc free

SUMMARY

Summary

• Zinc free pigments are an effective environmentally friendly option to zinc phosphate based products.

• Compared to anticorrosive zinc phosphate based products, they show• an adhesion improvement on cold rolled steel.• a lower effect on gloss.• a lower reactivity in WB and SB polyurethane systems.

• Accelerated evaluation have been used and correlated with results obtained in classic evaluation methods like Salt Spray test.

• All these macroscopic facts are related to the chemical composition and physical properties of the pigment.

• Proper adjustment of paint formula variables is a complex procedure. The expertise and skill of a reputable paint company and their staff of paint chemists is invaluable for the long term performance of a coating system

Thank you for your attention

Anticorrosive Zn Free Pigments: Their Performance PNWSCT 2014.

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Transcript of Anticorrosive Zn Free Pigments: Their Performance PNWSCT 2014.