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Anticorrosive Zn Free Pigments: Their Performance

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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Anticorrosive Zn Free Pigments: Their Performance

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  1. Anticorrosive Zn Free Pigments: Their Performance PNWSCT 2014

  2. Agenda • Historical Evolution of Anticorrosive Pigments • Corrosion • Protection • Zn free pigments • Case Study • Accelerated cyclic electrochemical test • Analytical experiments • Additional systems tested • Summary

  3. Historical evolution of anticorrosive pigments Anticorrosive Zn Free Pigments: their performance Dr. Ricard March, Nubiola

  4. 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

  5. Corrosion

  6. 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

  7. 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)

  8. 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

  9. 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

  10. protection

  11. 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)

  12. 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

  13. 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)

  14. 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)

  15. 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)

  16. Zn free pigments

  17. 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

  18. 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

  19. 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)

  20. case study

  21. 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

  22. Panel Evaluation BlisteringISO 4628-2 “Cross cut” adhesionASTM D3359 Adhesion at thescribeASTM D1654 B Oxidation at thescribeASTM D1654 A Oxidationonthe panel ASTM D610

  23. DOE: ParetoPlots Exposure time Exposure time Thickness PIGMENT Dose Exposure time

  24. DOE: interaction plot for oxidation at scribe

  25. DOE: interaction plot for oxidation on the panel

  26. 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

  27. acet

  28. ACET: The need Accelerated Cyclic Electrochemical Technique (ACET) 24 h 100 - 10.000 h 4.400 – 25.000 h UNE 48315-1 ASTM B117

  29. ACET: Steps

  30. ACET: Information

  31. ACET: Equivalent circuit Equivalent circuit used to model EIS & ACET Coating properties Interface

  32. 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

  33. 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

  34. ACET: ANN Use of this methodology in the industry? Electrochemical Models? Artificial Neural Networks (ANN)

  35. ACET: correlation

  36. analytical experiments

  37. SEM: panel observation

  38. SEM: mapping

  39. 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)

  40. SEM: cross-sectionobservation Blank Zinc phosphate Zn free Oxidation The finest particle distribution

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

  42. 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.

  43. SEM: cross-sectionobservation Energy Distribution Spectroscopy Linescan (EDS Linescan) Zn free (line 2) Blank Zn free (line 1) Panel Coating Panel Coating Panel Coating

  44. SEM: cross-sectionobservation Energy Distribution Spectroscopy Linescan (EDS Linescan) Blank Panel Coating

  45. SEM: cross-sectionobservation Energy Distribution Spectroscopy Linescan (EDS Linescan) Zn free (line 1) Panel Coating

  46. SEM: cross-sectionobservation Energy Distribution Spectroscopy Linescan (EDS Linescan) Zn free (line 2) Panel Coating

  47. additional systems tested

  48. 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)

  49. 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

  50. 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)

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