nubiola Zn free pigments: How they work Dr. Ricard March Nubiola Protective Coatings, Düsseldorf, 12/13.9.2013
nubiola Agenda
Agenda Historical Evolution of Anticorrosive Pigments Corrosion Protection Zn free pigments Case Study Analytical experiments Additional systems tested Summary
nubiola Historical Evolution of Anticorrosive Pigments
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 Zinc Chromate Zinc Tetraoxychromate Strontium Chromate Barium Chromate Red lead Modified Zinc Phosphates Un/Modified with organic surface treatment
nubiola 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. + O 2 / + H 2 O Spontaneous!! Non spontaneous!! Entropy: Order Disorder
Corrosion Process: description 1 2 Anodic reaction: Fe Fe 2+ + 2 e - e - Cathodic reaction: O 2 + 2 H 2 O + 4 e - 4 OH - 3 4 Fe 2+ Fe(OH) 2 H 2 O O 2 5 delamination blistering e - Protective coating OH - OH - OH - Fe e - e - Metallic substrate (Fe)
Corrosion Process: reactions Redox reaction: Anodic reaction (oxidation): Fe Fe 2+ + 2 e - Cathodic reaction (reduction): O 2 + 2 H 2 O + 4 e - 4 OH - Globally: 2 Fe + O 2 + 2 H 2 O + 4 e - 2 Fe 2+ + 4 OH - + 4 e - Formation of rust: Fe 2+ + 2 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 2-4, Mg 2+, COO -, etc Also: temperature
nubiola Protection
Corrosion Process: how to slow 1 e - flowing Fe 2+ H 2 O O 2 delamination blistering e - Protective coating OH - OH - OH - Fe e - e - Metallic substrate (Fe) It is impossible to interrupt the electron flowing (metal)
Corrosion Process: how to slow 2 H 2 O / O 2 in the interfase Fe 2+ H 2 O O 2 delamination blistering e - Protective coating OH - OH - OH - Fe e - e - Metallic substrate (Fe) It is possible to reduce water and oxygen flow through barrier effect
Corrosion Process: how to slow Cathodic reaction: O 2 + 2 H 2 O + 4 e - 4 OH - High ph (OH - ) displaces the reaction to the left and helps hydroxides precipitation 3 OH - generation in the cathode Cathodic inhibition by metallic hydroxides and oxides precipitation Fe 2+ H 2 O O 2 delamination blistering e - Protective coating OH - OH - OH - Fe e - e - Metallic substrate (Fe)
Corrosion Process: how to slow Anodic reaction: Fe Fe 2+ + 2 e - Anodic passivation by metal and iron complexes (phosphates, silicates, ) precipitation 4 Fe 2+ generation in the anode Fe 2+ H 2 O O 2 delamination blistering e - Protective coating OH - OH - OH - Fe e - e - Metallic substrate (Fe)
Corrosion Process: how to slow Ionic mobility 5 Anodic reaction: Fe Fe 2+ + 2 e - Fe 2+ Fe(OH) 2 delamination Compounds precipitated in the cathode and the anode also avoid the ionic mobility blistering H 2 O Cathodic reaction: O 2 + 2 H 2 O + 4 e - 4 OH - O 2 e - Protective coating OH - OH - OH - Fe e - e - Metallic substrate (Fe)
nubiola 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 10 D(v,0.5)=1.15µ agglomerates up to <10µ % 0 0 0.01 0.1 1.0 10.0 100.0 1000.0 Particle Diameter (µm.) 100 90 80 70 60 50 40 30 20 10 10 % 0 0 0.01 0.1 1.0 10.0 100.0 1000.0 Particle Diameter (µm.) 100 90 N301 STD 5'-3 80 N 20 030829009 0'-1 70 60 50 40 30 20 10
Zn free pigments Higher specific surface area 21 m 2 /g vs 1 m 2 /g (std zinc phosphate) Minimizes moisture, oxigen 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 am*.bp 2 O 5.cSiO 2.xH 2 O M= Ca, Sr Anodic passivation: Ca/Sr/Fe phosphates&silicates complexes O 2 + 2 H 2 O + 4 e - 4 OH - Cathodic reaction displacement Barrier effect Cathodic inhibition: Ca/Sr hydroxides Metallic substrate (Fe)
nubiola Case study
DOE WB Styrene Acrylic Substrate: CRS, S-46 60-90 µ 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 2 4 (16 runs of 1 replica in one block): Pigment (qualitative): zinc phosphate zinc free Dose (quantitative): 3% - 6% Thickness (quantitative): 60 µ - 90 µ 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 µ 240 h Zn phosphate 6% 60 µ 240 h Zn free 6% 90 µ 1170 h Zn phosphate 6% 90 µ 1170 h
nubiola 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 µ 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 Blank Zinc phosphate Zn free Oxidation The finest particle distribution
SEM: cross-section observation Zinc phosphate: Energy Distribution Spectroscopy Element Mapping (EDS element mapping) Fe O Coating Zn P Si Panel
SEM: cross-section observation 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 observation Energy Distribution Spectroscopy Linescan (EDS Linescan) Blank Zn free (line 1) Zn free (line 2) Panel Coating Panel Coating Panel Coating
SEM: cross-section observation Energy Distribution Spectroscopy Linescan (EDS Linescan) Blank 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
nubiola Additional systems tested
SB Wash Primer Zinc Tetraoxychromate Zinc free 2K Etch/Wash primer: polyvinyl butyral epoxy modified Substrate: Galvanized Panels, SG015 20 µ (lower half only primer) 50 µ (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) Cold rolled steel S-46 (Q-Panel) Mild steel SB015D (Espancolor) Galvanized steel SG015 (Espancolor) Aluminum 3105H14 AA015D (Espancolor) Zinc Tetraoxychromate 5B 5B 4B 5B Zinc free 5B 5B 3B 4B
SB Alkyd Blank 6% Zinc Phosphate 6% Zinc free Solvent Based Alkyd Substrate: CRS, S-46 60 µ 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 µ 1100 h Neutral Salt Spray ASTM B117 Formulated at same: Anticorrosive Pigment Volume Content (6%) PVC/CPVC ratio (same free binder volume)
SB Epoxy Blank 10 % Zinc Phosphate 6% Zinc free 1100 h Blank 10 % Zinc Phosphate 8% Zinc free Zn free pigment shows better performance, even at lower dosage. 1320 h
SB 2K Polyurethane Blank 6% Zinc Phosphate 6% Zinc free Solvent Based 2K Polyurethane (acryl/polyisocianate) Substrate: CRS, S-46 60 µ 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 Substrate: Phosphated steel, Bonderite 1000 90 µ 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 µ 4000 h Neutral Salt Spray ASTM B117 Formulated at same: Anticorrosive Pigment Volume Content (2,3%) PVC/CPVC ratio (same free binder volume) Blank Zinc free Blank Zinc free 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%)
WB Acrylic DTM Blank 4,5% Zinc Phosphate 4,5% Zinc free Gloss 85º = 69 Gloss 85º = 57 Gloss 85º = 71 Zinc free: No gloss reduction Good anticorrosive activity WB Acrylic DTM Substrate: CRS, S-46 90 µ 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 µ 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 6% Calcium Blank 6% Zinc phosphate phosphate 6% Zinc free WB Styrene Acrylic Substrate: CRS, S-46 55 µ 478 h Neutral Salt Spray ASTM B117 Formulated at same: Anticorrosive Pigment Volume Content (6%) PVC/CPVC ratio (same free binder volume)
nubiola 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. All these macroscopic facts are related to the chemical composition and physical properties of the pigment.
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