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 Chromate Zinc Tetraoxychromate Strontium Chromate Barium Chromate Red lead ZINC FREE PIGMENT Un/Modified with organic surface treatment Calcium strontium phosphosilicate Zinc Phosphate Modified Zinc Phosphates ZINC BASED PIGMENTS

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. + O 2 / + H 2 O Spontaneous !! Non spontaneous !! Entropy: Order  Disorder

Corrosion Process: description Metallic substrate (Fe) Protective coating H2OH2O O2O2 OH - Cathodic reaction: O H 2 O + 4 e -  4 OH - Fe 2+ Fe Anodic reaction: Fe  Fe e - e-e- e-e- e-e- e-e- delamination blistering Fe(OH)

Corrosion Process: reactions Redox reaction: Anodic reaction (oxidation): Fe  Fe e - Cathodic reaction (reduction): O H 2 O + 4 e -  4 OH - Globally: 2 Fe + O H 2 O + 4 e -  2 Fe OH e - Formation of rust: Fe OH -  Fe(OH) 2 4 Fe(OH) 2 + O 2  4 FeOOH + 2 H 2 O 2 FeOOH  Fe 2 O 3 + H 2 O

Corrosion Process Other compounds can accelerate the reaction: H 3 O + (or changes in the pH) SO 2 (industrial environment) NaCl (marine environment) Other contaminants: NH 4 +, SO 4 2-, Mg 2+, COO -, etc Also: temperature

PROTECTION

How to Slow the Corrosion Process Metallic substrate (Fe) Protective coating H2OH2O O2O2 OH - Fe 2+ Fe e-e- e-e- e-e- delamination blistering It is impossible to interrupt the electron flowing (metal) 1 e - flowing

How to Slow the Corrosion Process Metallic substrate (Fe) Protective coating H2OH2O O2O2 OH - Fe 2+ Fe e-e- e-e- e-e- delamination blistering It is possible to reduce water and oxygen flow through barrier effect 2 H 2 O / O 2 in the interface

How to Slow the Corrosion Process Metallic substrate (Fe) Protective coating H2OH2O O2O2 OH - Cathodic reaction: O H 2 O + 4 e -  4 OH - Fe 2+ Fe e-e- e-e- e-e- delamination blistering High pH (OH - ) displaces the reaction to the left and helps hydroxides precipitation Cathodic inhibition by metallic hydroxides and oxides precipitation 3 OH - generation in the cathode

How to Slow the Corrosion Process Metallic substrate (Fe) Protective coating H2OH2O O2O2 OH - Fe 2+ Fe Anodic reaction: Fe  Fe e - e-e- e-e- e-e- delamination blistering Anodic passivation by metal and iron complexes (phosphates, silicates, …) precipitation 4 Fe 2+ generation in the anode

How to Slow the Corrosion Process Metallic substrate (Fe) Protective coating H2OH2O O2O2 OH - Fe 2+ Fe Anodic reaction: Fe  Fe e - e-e- e-e- e-e- delamination blistering Cathodic reaction: O H 2 O + 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 D(v,0.5)=1.15µ

Zn free pigments Higher specific surface area 21 m 2 /g vs 1 m 2 /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 SEM (scanning electron microscopy) 10000X Metallic substrate (Fe) Barrier effect O H 2 O + 4 e -  4 OH - Cathodic reaction displacement Cathodic inhibition: Ca/Sr hydroxides Anodic passivation: Ca/Sr/Fe phosphates&silicates complexes aM*.bP 2 O 5.cSiO 2.xH 2 O M= Ca, Sr

CASE STUDY

DOE DOE : Full factorial experiment 2 4 (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  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

DOE: Pareto Plots Exposure time PIGMENT Dose Thickness

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 ASTM B117 UNE Accelerated Cyclic Electrochemical Technique (ACET) 24 h h – h

ACET: Steps

ACET: Information DefinitionEffect |Z| max (Ω) Maximum impedance valueInitial quality of the Coating |Z| min (Ω) Minimum Impedance ValueCoating Porosity ∆Z (Ω) Impedance variationCoating Porosity & Adhesion E max (V) Maximum Free Corrosion PotentialCoating Porosity & Adhesion E min (V) Minimum Free Corrosion PotentialCoating Porosity & Adhesion ∆E (V) Free Corrosion Potential VariationActivity in the Interface Bode Graph E relax vs t relax Activity in the Interface, Adhesion & Porosity

ACET: Equivalent circuit DefinitionEffect R po Pore ResistanceDegradation due to porosity increasing CcCc Coating CapacitanceWater Absorption RpRp Polarization ResistanceCorrosion in the Interface C dl Double Layer CapacitanceDelamination RsRs 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

Panel Evaluation: ACET Impedance values: |Z| max, |Z| min and ∆Z Equivalent circuit parameters: R po and C c Impedance values: E max, E min, ∆E and Bode graph Equivalent circuit parameters: R p and C dl

ACET: ANN Blankstd ZnPhZn-free CPV (%)034, |Z| max (Ω)1,45E+081,06E+081,55E+071,47E+089,81E+071,22E+088,39E+071,02E+086,92E+07 |Z| min (Ω)1,49E+042,57E+044,63E+032,38E+041,53E+049,26E+071,93E+072,67E+076,08E+07 E max (V)0,250,240,180,170,110,20,160,210,19 E min (V)-0,160,03-0,130,02-0,02-0,33-0,37-0,35-0,32 ∆E (V)0,410,210,310,160,130,520,540,550,51 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  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 Zn freeZinc phosphateBlank Oxidation The finest particle distribution

SEM: cross-section observation Fe Si O P Panel Coating Zn Zinc phosphate: Energy Distribution Spectroscopy Element Mapping (EDS element mapping)

SEM: cross-section observation O Fe SiCaSrP 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.

SEM: cross-section observation Zn free (line 1)Blank PanelCoatingPanelCoating Energy Distribution Spectroscopy Linescan (EDS Linescan) Zn free (line 2) PanelCoating

SEM: cross-section observation Blank PanelCoating Energy Distribution Spectroscopy Linescan (EDS Linescan)

SEM: cross-section observation Zn free (line 1) PanelCoating Energy Distribution Spectroscopy Linescan (EDS Linescan)

SEM: cross-section observation Energy Distribution Spectroscopy Linescan (EDS Linescan) Zn free (line 2) PanelCoating

ADDITIONAL SYSTEMS TESTED

SB Wash Primer Zinc Tetraoxychromate Zinc free 2K Etch/Wash primer: polyvinyl butyral epoxy modified Substrate: Galvanized Panels, SG  (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 steel S-46 (Q-Panel) 5B Mild steel SB015D (Espancolor) 5B Galvanized steel SG015 (Espancolor ) 4B Aluminum 3105H14 AA015D (Espancolor) 5B 3B4B Zinc Tetraoxychromate Zinc free Cross cut test (ASTM D3359)

SB Alkyd Blank 6% Zinc Phosphate6% Zinc free Solvent Based Alkyd Substrate: CRS, S  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 Phosphate6% Zinc free3% Zinc free Zn free pigment shows better performance, even at lower dosage.

SB Epoxy Blank6% Zinc Phosphate6% Zinc free Solvent Based Epoxy Substrate: CRS, S  1100 h Neutral Salt Spray ASTM B117 Formulated at same: Anticorrosive Pigment Volume Content (6%) PVC/CPVC ratio (same free binder volume)

SB Epoxy Blank10 % Zinc Phosphate6% Zinc free Blank10 % Zinc Phosphate8% Zinc free Zn free pigment shows better performance, even at lower dosage h 1320 h

SB 2K Polyurethane Blank6% Zinc Phosphate6% Zinc free Solvent Based 2K Polyurethane (acryl/polyisocyanate) Substrate: CRS, S  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 1Liquid 2 Thick liquidLiquid 3Thick liquidSolidThick liquid 4Solid No effect on pot life / shelf life

Powder coating Zinc free Blank Powder Coating, Epoxy-Polyester Substrate: Phosphated steel, Bonderite  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) TESTED PANEL EVALUATIONBlankZinc free 1 Rusting on the panel (ASTM D610) 8G (0.1%) 10 (none) TESTED PANEL EVALUATIONControlZinc 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 free Blank

WB Acrylic DTM Blank4,5% Zinc free4,5% Zinc Phosphate WB Acrylic DTM Substrate: CRS, S  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 Gloss 85º = 69Gloss 85º = 57Gloss 85º = 71

WB Alkyd Blank4,5% Zinc Phosphate4,5% Zinc free WB Alkyd Substrate: CRS, S  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 Substrate: CRS, S  478 h Neutral Salt Spray ASTM B117 Formulated at same: Anticorrosive Pigment Volume Content (6%) PVC/CPVC ratio (same free binder volume) 6% Calcium phosphate Blank 6% Zinc phosphate6% 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

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