Accession Number : ADA192184

Title :   Environmental Integrity of Coating/Metal Interface.

Descriptive Note : Annual progress rept. no. 1, 1 Feb 87-31 Jan 88,

Corporate Author : ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER

Personal Author(s) : Kendig, M ; Addison, R ; Jeanjaquet, S

PDF Url : ADA192184

Report Date : Jan 1988

Pagination or Media Count : 32

Abstract : Corrosion of polymer coated steel in neutral media entails the initiation of anodic dissolution of the metal at defects in the coating with the cathodic reduction of oxygen at the adjacent interface. The cathodic reduction of oxygen produces a buildup of NaOH at the interface which enhances adhesion loss which leads to the propagation of corrosion. In-situ acoustic microscopy of a coating undergoing cathodic disbonding at constant potential has allowed evaluation of both the kinetics and microscopic structure of the disbond front with detail not previously attained. Disbonding of a hydroxy-terminated polybutadiene coating from polished and degreased steel in 0.5 M NaCl has been examined in-situ as a function of applied potential. The results show that potentials more negative than -550 mV vs Ag/AgCl accelerate disbonding by the formation of a weak fluid boundary layer at the coating/metal interface just ahead of electroosmotically produced approximately 50 micro m blisters. Concentration of NaOH in the microblister weakens the polymer metal interface while the osmotic pressure in the microblisters provides the mechanical force necessary to rupture the coating/metal bond. Keywords: Organic coating, Corrosion, Cathodic disbonding, Acoustic microscopy, Polynbutadiene, Adhesion, Carbon steel.

Descriptors :   *BONDING, *COATINGS, *METALS, *POLYMERS, ACOUSTICS, ADHESION, BOUNDARY LAYER, CARBON STEELS, CORROSION, DEFECTS(MATERIALS), ENVIRONMENTS, FLUIDS, FORCE(MECHANICS), HYDROXYL RADICALS, INTERFACES, LOSSES, LOW STRENGTH, MEDIA, MICROSCOPY, NEUTRAL, ORGANIC COATINGS, OSMOTIC PRESSURE, POLYBUTADIENE, RUPTURE, STEEL, STRUCTURES

Subject Categories : Polymer Chemistry
      Coatings, Colorants and Finishes
      Fabrication Metallurgy

Distribution Statement : APPROVED FOR PUBLIC RELEASE