Performance Attributes of Organic Corrosion Inhibitors

Transcription

1 Performance Attributes of Organic Corrosion Inhibitors Additives 2012 Conference September 12-13, 2012 Sheraton Inner Harbor Baltimore, MD Nathan Kofira Technical Development Manager

2 Overview Requirements of Organic CI s Mechanism of Deposition Consequences of Placement 4 Synergies

3 Performance Attributes of Organic Corrosion Inhibitors 1. REQUIREMENTS OF ORGANICS

4 Inhibitive to Corrosion Of concern in coatings Flash Rust Galvanic Filiform Rapid, widespread corrosion seen during initial application. Contact between two alloys which promotes oxidation of the less noble metal. Differential aeration promotes this unique form of corrosion. Lambourne, R. (1999); Paint and Surface Coatings: Theory and Practice, 2 ed. (Lambourne, R. and Strivens, T.) England: William Andrew Publishing

5 Performance Attributes of Organic Corrosion Inhibitors 2. MECHANISMS OF DEPOSITION

6 Mechanisms of Deposition Migration Hydrophobicity Bond Strength The molecular design of selected Organic corrosion inhibitors focuses on the placement and effectiveness at the interface.

7 Organic Corrosion Inhibitors Migration Ionization potential creates lasting dipoles during paint cure which enable planar molecules to orient favorably at the interface Hydrophobicity Pore plugging with insoluble complexes of metallic ions Reduced permeability due to exclusion during film formation Chandler, D. (2005). Nature. Interfaces and thedriving force of hydrophobic assembly, 437,

8 Binding Energies of Paint Constituents Force Type example E (kcal/mol) Covalent 1 Organics Metal oxides 1 Oxide film Metallic 2 Metals H bonding 2 Water <12 Dispersion 2 Most Molecules <10 Dipole & Induction 2 Organics >1 to <5 Force Type example E (kcal/mol) Paint Film to Metal 2 DTM Coatings <25 Water to Metal 2 Coating Defect / Pore Sander, J. (2010); Anticorrosive Coatings. (Sander, J. et al Eds.) Germany: Vincentz Network

9 Performance Attributes of Organic Corrosion Inhibitors 3. CONSEQUENCES OF PLACEMENT

10 Organic Acid Anodic Inhibitors Key Benefits Improved Adhesion Binding energy modification Associative with additives and pigments Key Features Wetting out of substrate Decreased contact angle Stabilization of soluble corrosion products Improved gloss retention Low Mw liquid products Reduced H 2 O permeability Impedance gain No Ionic crosslinking Affinity for metallic ions

11 Organic Amine Mixed Inhibitors Key Benefits Mechanism is independent of dissolved O 2 Key Features Barrier to electron diffusion at Cathode Associative with additives and pigments Stabilization of soluble corrosion products Hydrophobic Efficient packing and layering High binding energy Displacement of water Shift in corrosion potential

12 Target Systems for Organic CI s Organic acids Coil applications Organic amines Marine and Pipe Heavy Industrial High humidity Epoxy Polyester melamine Modified acrylics Water-reducible Hi-solids Epoxy Alkyd systems Polyurethane & MCU Acrylic topcoats Corrosion inhibition is expanding with Synergy

13 Performance Attributes of Organic Corrosion Inhibitors 4. SYNERGIES

14 Types of Synergy Explored Sacrificial Anodic Passivation Cathodic Passivation Ion Exchange Ambiodic (Mixed) Hydrophobicity Precipitation Vapor Phase

15 Exploring Synergistic Partners Selection of partner is based upon the end-use environment and protection needs. Sol-Gel Complete acceptance of Organic acids and amine salts. Ion-Exchange Cationic Ion-Exchange Anionic INORGANIC Organic acids further reduce RedOx coupling impact of NH 4 + and other species. Organic amine salts prevail, as strong ionic charges are mitigated by reduced environmental Cl -. Thin film applications require reduced particle size Organo-metallic salts and surface treatments enhance dissolution control at the anode.

16 Organic amine salt and Anionic Ion-Exchange Ion-Exchange and Passivation Galvanized substrates Reduced dissolution rate of Zinc through adhesion force plus insoluble corrosion barrier product. Aluminum substrates Exclusion of water during film cure reduces potential for differential aeration gradient to establish.

17 Thin Film Application Synergies Enhancement of Key Technological Attributes Alkane Sulfonates Organic Additives Organo- Metallics Sol-Gel Adhesion and Durability are the most critical parameters. Film thickness dictates the need for small particle size Inorganic inhibitors for maximum corrosion protection.

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