Improving Adhesion: Examining the Electrochemistry of rganic Inhibitors
Benefits of rganics Chemisorb onto metallic substrates Complex with metal ions at substrate Neutralize & absorb the corrodents Decrease permeability (barrier enhancement) Anodic passivators Improve wetting Promote adhesion Plug pores (defects)
All Coatings Made Here
Periodic Trends In general, Electronegativity increases to the right and increases upwards Greater ability to attract electrons to itself Close proximity to associated elements yields a dynamic sharing relationship among electrons Surface treatments allow for metals to associate with select elements in a sharing relationship that might otherwise not exist
Relative Electronegativities
CRRSIN CELL DIAGRAM 3/2 2 Water Droplet Rust Fe 2 3. H 2 3 n H 2 2 Fe 2+ 2 H 2 4 H + 2 2 2 Fe 4 e - 1 Iron Substrate Anodic Region Cathodic Region 1. xidation of Fe yields electrons which travel through the metal. 2. Electrons at the Fe (inactive) cathode reduce 2 to H 2. 3. The Fe 2+ migrates through the drop and reacts with H 2 to form rust.
Relative Bond Strengths Force Type example E (kcal/mol) Covalent 1 Most rganics 15-175 Metallic 1 Metals 27-83 H bonding 2 Water <12 Dispersion 2 Most Molecules <10 Dipole 2 Polar rganics <5 Induction 2 Non-polar rganics <0.5 Force Type example E (kcal/mol) Paint Film to Metal 2 DTM Coatings <25 Water to Metal 2 Coating Defect 40-65
Coating/Substrate Adhesion Promoter Resin rganic Corrosion Inhibitor Improved adhesion between coating and metal substrate Coating/Substrate interface
Adhesion Leads to Corrosion Protection Non-Skid Paint; 2K Solvent-borne Epoxy Polyamide With Poor Adhesion Non-Skid Paint needed better corrosion resistance. Needs to withstand 2000 hrs salt spray with minimal corrosion in the defect sites created by aircraft damage
Adhesion Leads to Corrosion Protection Primer w/o HALX Primer With HALX rganic severe corrosion creep reduced corrosion creep
Mechanism: Hydrophobic Film Formers Film Formers: Slow both anodic and cathodic reactions rganic Benzoates Amines Sulfonates Thiols Di-acids - NH 3 + - S - - S -
Multi-functional Anti-Corrosive (2) N S S (3) - - (1) (4) (1) Polar end: adsorption & strong affinity for M + / M leading to hydrophobic dense film formation. Also the Acid -Base reactivity site for modification (2) Electron donor site (3) Polycyclic aromatic: corrosion inhibition of non-ferrous substrates. Electron donors (N, S, ) (4) Non polar end: van der Waals interaction with multiple organic binders (Compatibility). Also electron donor to substrate
rientation of Molecule Impacts electron sharing capacity Dynamic action, changes during film formation and cure Imparts a surface tension gradient DTM adhesion Intercoat adhesion (pigment affinity)
Multi-functional Anti-Corrosive Adsorption of molecule forms a complex which increases the electrical resistance of the substrate Makes the oxidation of steel more difficult A form of active corrosion protection
Adhesion Promotion Electrons adjusting to lowest energy state (wetting) Dipoles formed during cure (intercoat) Polymer chains exhibit 1 bonding (coupling) Binder Substrate
WATER PERMEATIN (%) Barrier Properties No Inhibitor 4% BTTSA-amine 0 0 0 Reduced 34 Water 25 Permeation in 2K Epoxy System determined by EIS 52 36 70 60 50 40 30 5 54 42 52 41 52 43 10 54 45 54 44 57 45 15 57 43 56 44 59 45 20 62 43 61 44 62 43 25 62 42 63 43 63 41 2030 65 40 No Inhibitor 4% HALX rganic 10 0 0 5 10 15 20 25 30 TIME (days) 16
Coating Galvanized bjects Zn 2+ migration under film accelerates adhesion failure in susceptible systems Barrier type organic corrosion inhibition mechanism
18 RGANIC HYBRIDS 1. SILICNE ESTER HYDRLYZES T FRMS SILANL R Si R R H 2 R Si H R + RH 2. SILXANE BND FRMS R Si H R + H H H H SUBSTRATE R Si R Si SUBSTRATE + RH 3. GELATIN (CRSS-LINKING) PLYMER R Si R Si Si Si Si Si + H 2 + RH SUBSTRATE SUBSTRATE
Sol-Gel Treatment for Improved Adhesion Substrate: Hot dipped galvanized G70 70 U (ACT labs) Pretreatment application: 10% Hybrid Sol-Gel Cure: Air dry 24 hrs at RT Coating applied: Sherwin Williams high gloss water-based DTM at 50 µm DFT Accelerated test shown: 336 hrs salt spray
Ion-Exchange Notable Synergy
Ion-Exchange Inhibitors Significant release of energy by altering electron environment Decreases the densely packed electron structures of Alkali Metals Binds the strongest, most electronegative atoms and compounds, ex. Cl - and S 4 2- Significant synergy with Sol-Gel over Aluminum
Adhesion in Coil Coatings After 400h salt spray test ASTM B 117-90 Without Inhibitor Commercial system (SrCr 4 ) 4% HALX rganic 18.5% Ion-Exchange Substrate: hot dip galvanized steel Primer : TPA, phenolic resin, phosphoric acid pretreatment Topcoat: PES Melamine de-lamination at scribe (mm) 5 2 1 under-rusting at scribe (mm) 0 0 0 After 1500h Salt Spray Test ASTM B 117-90 Without inhibitor Commercial system (SrCr 4 ) 4% HALX rganic 18.5% Ion-Exchange Substrate: Al/Zn steel Primer : TPA, phenolic resin, phosphoric acid pretreatment Topcoat: PVC Plastisol de-lamination at scribe (mm) total 0 0 de-lamination at cut edge (mm) total 0 1.5 under-rusting at scribe (mm) 0 0 0 under-rusting at cut edge (mm) 3 1 1.5
Ion-Exchange CNTRL EXTENDER PIGMENTS rganic(2%) Ion-Exchange(9%) 500 hours Aluminum Filiform Corrosion Test (1.2 mil epoxy primer, 2.0 mil PU topcoat)
Hybrid Synergy with Ion-Exchange 3% Sol-Gel + 0.7% Ion-Exchange Solvent Based Polyester/Acrylic Hybrid coating Good gloss for Aluminum wheels The film thickness of 15-50 µm Filiform corrosion is < 1 mm
rganic Corrosion Inhibitors Anodic passivation (reduce rust & flash rusting) Improve adhesion Increase water resistance Reduce blistering Form protective films (adsorption) Increase coating flexibility (plasticize) Increase chemical resistance
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