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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.

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agenda
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
Historical evolution of anticorrosive pigments

Anticorrosive Zn Free Pigments: their performance

Dr. Ricard March, Nubiola

historical evolution of anticorrosive pigments1

ZINC FREE PIGMENT

Calcium strontium phosphosilicate

Un/Modified with organic surface treatment

Historical evolution of anticorrosive pigments

TRADITIONAL ANTICORROSIVE PIGMENTS

Chromate based pigments

ALTERNATIVE NON CLASSIFIED AS HAZARDOUS ANTICORROSIVE PIGMENTS

ZINC BASED PIGMENTS

  • Zinc Phosphate
  • Modified Zinc Phosphates

Zinc Chromate

Zinc Tetraoxychromate

Strontium Chromate

Barium Chromate

Red lead

corrosion1
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
Corrosion Process: description

1

Anodic reaction:

Fe  Fe2+ + 2 e-

Cathodic reaction:

O2 + 2 H2O + 4 e- 4 OH-

2

e-

3

O2

Fe2+

H2O

Fe(OH)2

4

delamination

5

blistering

OH-

Protective coating

OH-

OH-

e-

e-

Fe

e-

Metallic substrate (Fe)

corrosion process reactions
Corrosion Process: reactions
  • Redoxreaction:
      • 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
Corrosion Process
  • Other compounds can accelerate the reaction:
      • H3O+ (or changes in the pH)
      • SO2 (industrial environment)
      • NaCl (marine environment)
      • Other contaminants: NH4+, SO42-, Mg2+, COO-, etc
      • Also: temperature
how to slow the corrosion process
How to Slow the Corrosion Process

1

e-flowing

O2

Fe2+

H2O

delamination

blistering

OH-

Protective coating

OH-

OH-

e-

e-

Fe

e-

Metallic substrate (Fe)

It is impossible to interrupt the electron flowing (metal)

how to slow the corrosion process1
How to Slow the Corrosion Process

H2O / O2 in the interface

2

O2

Fe2+

H2O

delamination

blistering

OH-

Protective coating

OH-

OH-

e-

e-

Fe

e-

Metallic substrate (Fe)

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

how to slow the corrosion process2
How to Slow the Corrosion Process

Cathodic reaction:

O2 + 2 H2O + 4 e- 4 OH-

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

Cathodic inhibition by metallic hydroxides and oxides precipitation

OH- generation in the cathode

3

O2

Fe2+

H2O

delamination

blistering

OH-

Protective coating

OH-

OH-

e-

e-

Fe

e-

Metallic substrate (Fe)

how to slow the corrosion process3
How to Slow the Corrosion Process

Anodic reaction:

Fe  Fe2+ + 2 e-

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

O2

Fe2+

H2O

Fe2+ generation in the anode

4

delamination

blistering

OH-

Protective coating

OH-

OH-

e-

e-

Fe

e-

Metallic substrate (Fe)

how to slow the corrosion process4
How to Slow the Corrosion Process

Anodic reaction:

Fe  Fe2+ + 2 e-

Cathodic reaction:

O2 + 2 H2O + 4 e- 4 OH-

Compounds precipitated in the cathode and the anode also avoid the ionic mobility

O2

Fe2+

H2O

Fe(OH)2

Ionic mobility

delamination

5

blistering

OH-

Protective coating

OH-

OH-

e-

e-

Fe

e-

Metallic substrate (Fe)

zn free pigments
Zn free pigments

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

  • Lowparticlesize
  • Specialparticleshapecombination(acicular + spherical)
        • Elemental particles <1µ forming aggregates and agglomerates up to <10µ

D(v,0.5)=1.15µ

zn free pigments1
Zn free pigments
  • Higherspecificsurfacearea
  • 21 m2/g vs1 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
Zn free pigments: Calcium Strontium Phosphosilicates

O2 + 2 H2O + 4 e- 4 OH-

Cathodic reaction displacement

Barrier effect

SEM (scanning electron microscopy) 10000X

Cathodic inhibition: Ca/Sr hydroxides

aM*.bP2O5.cSiO2.xH2O

M= Ca, Sr

Anodic passivation: Ca/Sr/Fe phosphates&silicates complexes

Metallic substrate (Fe)

slide21
DOE
  • 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)
  • 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
panel evaluation
Panel Evaluation

BlisteringISO 4628-2

“Cross cut” adhesionASTM D3359

Adhesion at thescribeASTM D1654 B

Oxidation at thescribeASTM D1654 A

Oxidationonthe panel ASTM D610

doe pareto plots
DOE: ParetoPlots

Exposure time

Exposure time

Thickness

PIGMENT

Dose

Exposure time

faster activity and higher efficiency of zn free
Faster activity and higher efficiency of Zn free

Zn free

3%

60 

240 h

Zn phosphate

6%

60 

240 h

Zn free

6%

90 

1170 h

Zn phosphate

6%

90 

1170 h

acet the need
ACET: The need

Accelerated Cyclic Electrochemical Technique (ACET)

24 h

100 - 10.000 h

4.400 – 25.000 h

UNE 48315-1

ASTM B117

acet equivalent circuit
ACET: Equivalent circuit

Equivalent circuit used to model EIS & ACET

Coating properties

Interface

panel evaluation standard ssc
Panel Evaluation: Standard (SSC)

BlisteringISO 4628-2

“Cross cut” adhesionASTM D3359

Adhesion at thescribeASTM D1654 B

Oxidation at thescribeASTM D1654 A

Oxidationonthe panel ASTM D610

panel evaluation acet
Panel Evaluation: ACET

Impedancevalues:

Emax, Emin, ∆E and Bode graph

Equivalentcircuitparameters:

Rp and Cdl

Impedancevalues:

|Z|max, |Z|min and ∆Z

Equivalentcircuitparameters:

Rpo and Cc

acet ann
ACET: ANN

Use of this methodology in the industry?

Electrochemical Models?

Artificial Neural Networks (ANN)

sem cross section observation
SEM: cross-sectionobservation

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 observation1
SEM: cross-sectionobservation

Blank

Zinc phosphate

Zn free

Oxidation

The finest particle distribution

sem cross section observation2
SEM: cross-sectionobservation

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

Fe

O

Coating

Zn

P

Si

Panel

sem cross section observation3
SEM: cross-sectionobservation

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

Fe

O

Coating

Panel

Sr

Ca

P

Si

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

sem cross section observation4
SEM: cross-sectionobservation

Energy Distribution Spectroscopy Linescan (EDS Linescan)

Zn free (line 2)

Blank

Zn free (line 1)

Panel

Coating

Panel

Coating

Panel

Coating

sem cross section observation5
SEM: cross-sectionobservation

Energy Distribution Spectroscopy Linescan (EDS Linescan)

Blank

Panel

Coating

sem cross section observation6
SEM: cross-sectionobservation

Energy Distribution Spectroscopy Linescan (EDS Linescan)

Zn free (line 1)

Panel

Coating

sem cross section observation7
SEM: cross-sectionobservation

Energy Distribution Spectroscopy Linescan (EDS Linescan)

Zn free (line 2)

Panel

Coating

sb wash primer
SB Wash Primer

Zinc free

Zinc Tetraoxychromate

  • 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 primer1
SB Wash Primer

Cross cut test (ASTM D3359)

Aluminum

3105H14 AA015D (Espancolor)

Mild steel

SB015D (Espancolor)

Galvanized steel

SG015 (Espancolor)

Cold rolled steel

S-46 (Q-Panel)

Zinc Tetraoxychromate

5B

5B

4B

5B

Zinc free

5B

5B

3B

4B

sb alkyd
SB Alkyd

6% Zinc Phosphate

6% Zinc free

Blank

  • Solvent Based Alkyd
  • Substrate: CRS, S-46
  • 60 
  • 641 h Neutral Salt Spray ASTM B117
  • Formulated at same:
      • Anticorrosive Pigment Volume Content (6%)
      • PVC/CPVC ratio (same free binder volume)
sb alkyd1
SB Alkyd

Blank

6% Zinc Phosphate

3% Zinc free

6% Zinc free

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

sb epoxy
SB Epoxy

Blank

6% Zinc Phosphate

6% Zinc free

  • Solvent Based Epoxy
  • Substrate: CRS, S-46
  • 60 
  • 1100 h Neutral Salt Spray ASTM B117
  • Formulated at same:
      • Anticorrosive Pigment Volume Content (6%)
      • PVC/CPVC ratio (same free binder volume)
sb epoxy1
SB Epoxy

Blank

10 % Zinc Phosphate

6% Zinc free

1100 h

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

Blank

10 % Zinc Phosphate

8% Zinc free

1320 h

sb 2k polyurethane
SB 2K Polyurethane

Blank

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:
      • Anticorrosive Pigment Volume Content (6%)
      • PVC/CPVC ratio (same free binder volume)
sb 2k polyurethane pot life
SB 2K Polyurethane: pot-life

No effect on pot life / shelf life

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

Zinc free

Blank

Zinc free

Blank

wb acrylic dtm
WB Acrylic DTM

Blank

4,5% Zinc Phosphate

4,5% Zinc free

Gloss 85º = 69

Gloss 85º = 57

Gloss 85º = 71

  • WB Acrylic DTM
  • Substrate: CRS, S-46
  • 90 
  • 310 h Neutral Salt Spray ASTM B117
  • Formulated at same:
      • Anticorrosive Pigment Volume Content (4,5%)
      • PVC/CPVC ratio (same free binder volume)

Zinc free:

  • No gloss reduction
  • Good anticorrosive activity
wb alkyd
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:
      • Anticorrosive Pigment Volume Content (4,5%)
      • PVC/CPVC ratio (same free binder volume)
wb styrene acrylic
WB StyreneAcrylic

6% Calcium phosphate

6% Zinc phosphate

6% Zinc free

Blank

  • WB Styrene Acrylic
  • Substrate: CRS, S-46
  • 55 
  • 478 h Neutral Salt Spray ASTM B117
  • Formulated at same:
      • Anticorrosive Pigment Volume Content (6%)
      • PVC/CPVC ratio (same free binder volume)
summary1
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
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