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
TRADITIONAL
ANTICORROSIVE
PIGMENTS
Chromate based
pigments
ALTERNATIVE NON CLASSIFIED AS HAZARDOUS
ANTICORROSIVE PIGMENTS
ZINC BASED
PIGMENTS
• Zinc Phosphate
ZINC FREE
PIGMENT
Calcium strontium
phosphosilicate
• Modified Zinc Phosphates
Zinc Chromate
Zinc Tetraoxychromate
Strontium Chromate
Barium Chromate
Red lead
Un/Modified with
organic surface
treatment
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
1
Anodic reaction:
Fe  Fe2+ + 2 e-
Cathodic reaction:
O2 + 2 H2O + 4 e-  4 OH-
2
e-
3
O2
Fe2+ Fe(OH)2
4
H2O
delamination
5
blistering
OH-
e-
Protective coating
OHFe
OH-
ee-
Metallic substrate (Fe)
Corrosion Process: reactions
Redox reaction:
Anodic reaction (oxidation): Fe  Fe2+ + 2 e-
Cathodic reaction (reduction): O2 + 2 H2O + 4 e-  4 OHGlobally:
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+, SO42-, Mg2+, COO-, etc
•Also: temperature
PROTECTION
How to Slow the Corrosion Process
1
e- flowing
O2
Fe2+
H2O
delamination
blistering
OHe-
Protective coating
OHFe
OH-
ee-
Metallic substrate (Fe)
It is impossible to interrupt the electron flowing (metal)
How to Slow the Corrosion Process
2
H2O / O2 in the
interface
O2
Fe2+
H2O
delamination
blistering
OHe-
Protective coating
OHFe
OH-
ee-
Metallic substrate (Fe)
It is possible to reduce water and oxygen flow through barrier effect
How to Slow the Corrosion Process
Cathodic reaction:
O2 + 2 H2O + 4 e-  4 OH-
3
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
O2
Fe2+
H2O
delamination
blistering
OH-
e-
Protective coating
OHFe
OH-
ee-
Metallic substrate (Fe)
How to Slow the Corrosion Process
Anodic reaction:
Fe  Fe2+ + 2 eAnodic passivation by metal and iron complexes
(phosphates, silicates, …) precipitation
O2
4
Fe2+ generation
in the anode
Fe2+
H2O
delamination
blistering
OH-
e-
Protective coating
OHFe
OH-
ee-
Metallic substrate (Fe)
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
Fe2+ Fe(OH)2
O2
H2O
Ionic mobility
delamination
5
blistering
OH-
e-
Protective coating
OHFe
OH-
ee-
Metallic substrate (Fe)
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
%
10
100
D(v,0.5)=1.15µ
%
10
100
90 N301 STD 5'-3
90 Nubirox 301
80 N 20 030829009 0'-1
80
70
70
60
60
50
50
40
40
0
0.01
30
30
20
20
10
10
0
0.1
1.0
10.0
100.0
Particle Diameter (µm.)
1000.0
0
0.01
0
0.1
1.0
10.0 100.0 1000.0
Particle Diameter (µm.)
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
SEM (scanning electron microscopy) 10000X
Zn free pigments: Calcium Strontium Phosphosilicates
O2 + 2 H2O + 4 e-  4 OH-
Cathodic reaction displacement
Barrier effect
aM*.bP2O5.cSiO2.xH2O
M= Ca, Sr
Anodic passivation:
Ca/Sr/Fe
phosphates&silicates
complexes
Cathodic
inhibition:
Ca/Sr
hydroxides
Metallic substrate (Fe)
CASE STUDY
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
Blistering
ISO 4628-2
“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
DOE: Pareto Plots
Thickness
Dose
DOE: interaction plot for oxidation at scribe
DOE: interaction plot for oxidation on the panel
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
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: Steps
ACET: Information
|Z|max(Ω)
|Z|min(Ω)
∆Z (Ω)
Emax (V)
Emin (V)
∆E (V)
Bode Graph
Definition
Effect
Maximum impedance value
Minimum Impedance Value
Impedance variation
Maximum Free Corrosion Potential
Minimum Free Corrosion Potential
Free Corrosion Potential Variation
Erelax vs trelax
Initial quality of the Coating
Coating Porosity
Coating Porosity & Adhesion
Coating Porosity & Adhesion
Coating Porosity & Adhesion
Activity in the Interface
Activity in the Interface, Adhesion & Porosity
ACET: Equivalent circuit
Equivalent circuit used to model EIS & ACET
Coating properties
Interface
Rpo
Cc
Rp
Cdl
Rs
Definition
Effect
Pore Resistance
Coating Capacitance
Polarization Resistance
Double Layer Capacitance
Degradation due to porosity increasing
Water Absorption
Corrosion in the Interface
Delamination
Electrolyte resistance
Panel Evaluation: Standard (SSC)
Blistering
ISO 4628-2
“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
Panel Evaluation: ACET
Impedance values:
Emax, Emin, ∆E and Bode
graph
Equivalent circuit parameters:
Rp and Cdl
Impedance values:
|Z|max, |Z|min and ∆Z
Equivalent circuit parameters:
Rpo and Cc
ACET: ANN
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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
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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 observation
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Oxidation
Zinc phosphate
Zn free
The finest particle distribution
SEM: cross-section observation
Zinc phosphate: Energy Distribution Spectroscopy Element Mapping (EDS
element mapping)
Fe
O
P
Si
Coating
Zn
Panel
SEM: cross-section observation
Zinc free pigment: Energy Distribution Spectroscopy Element Mapping (EDS
element mapping)
Fe
O
P
Si
Coating
Panel
Sr
Ca
Smaller particle size allows the pigment to have a
more direct interaction with the metal surface.
SEM: cross-section observation
Energy Distribution Spectroscopy Linescan (EDS Linescan)
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Panel
Coating
Zn free (line 2)
Zn free (line 1)
Panel
Coating
Panel
Coating
SEM: cross-section observation
Energy Distribution Spectroscopy Linescan (EDS Linescan)
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Panel
Coating
SEM: cross-section observation
Energy Distribution Spectroscopy Linescan (EDS Linescan)
Zn free (line 1)
Panel
Coating
SEM: cross-section observation
Energy 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
Cross cut test (ASTM D3359)
Mild steel
Cold rolled steel
SB015D
(Espancolor)
S-46 (Q-Panel)
Galvanized steel
SG015 (Espancolor)
Aluminum
3105H14 AA015D
(Espancolor)
Zinc Tetraoxychromate
5B
5B
4B
5B
5B
5B
3B
4B
Zinc free
SB Alkyd
Blank
6% Zinc Phosphate
6% Zinc free
•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 Alkyd
Blank
6% Zinc Phosphate
3% Zinc free
6% Zinc free
Zn free pigment shows better performance, even at lower dosage.
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 Epoxy
10 % Zinc Phosphate
6% Zinc free
1100 h
Blank
1320 h
Blank
10 % Zinc Phosphate
8% Zinc free
Zn free pigment shows
better performance,
even at lower dosage.
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
Hours
Blank
Zinc
Phosphate
Zn 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
•Powder Coating, Epoxy-Polyester
•Powder Coating, Epoxy-Polyester
•Substrate: Phosphated steel, Bonderite 1000
•90 
•1000 h Neutral Salt Spray ASTM B117
•Formulated at same:
•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)
•Anticorrosive Pigment Volume Content (2,3%)
•PVC/CPVC ratio (same free binder volume)
Blank
Blank
TESTED PANEL EVALUATION
Rusting on the panel (ASTM D610)
Zinc free
Zinc free
Blank
Zinc free 1
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%)
WB Acrylic DTM
Blank
4,5% Zinc Phosphate
4,5% Zinc free
Gloss 85º = 69
Gloss 85º = 57
Gloss 85º = 71
•WB Acrylic DTM
Zinc free:
 No gloss reduction
 Good anticorrosive activity
•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)
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
Blank
6% Zinc phosphate
6% Calcium
phosphate
6% Zinc free
•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)
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