Paint Inspection Lighting

Failure mechanism of phosphated adhesively bonded hot-dipped galvanized steel: a small-area XPS study

“…This has been discussed previously by Wiggle et al, 7 who, on investigating corrosion at scratches in paint films, reported that hydroxide produced by the cathodic corrosion reaction chemically dissolves the zinc phosphate, producing adhesion failure. Roberts et al 10 reported that there is a very strong dependence of the rate of removal of the phosphate coating with pH and has shown direct evidence that zinc phosphate degradation occurs by alkali attack.…”

“…7 By changing the nature of the substrate surface (e.g. chemistry or morphology) it is possible to reduce the rate of corrosion and bring a metallic surface to a condition that will favour the acceptance of a continuous and adherent protective organic coating; this is often achieved in practice by the application of a conversion coating.…”

Relative Contributions of Several Cathodic Reactions to the Anodic Dissolution of Electrogalvanized Steel

“…10 The popularly accepted cathodic delamination model explicitly states that oxygen reduction adjacent to the paint defect is the predominant cathodic reaction and implicitly assumes that red rust serves merely as a diffusion barrier for the transport of corrodents from the environment to the underlying steel. 8,[11][12] The present work probed the concept introduced by Roberts, et al, [13][14] and Jordan,[5][6] and supported by Franks 15 in which underfilm corrosion of painted electrogalvanized (EG) steel in the atmosphere is characterized by an incubation period followed by rapid paint delamination during a propagation period. During the incubation period, the effects of corrosion are confined to the paint defect area, no measurable creepback under the paint film occurs, and galvanic corrosion between zinc and iron is the primary behavior.…”

“…[4][5][6] Some models simply extend the cathodic delamination model proposed for painted non-metallic coated steel tested by the ASTM B 117 Standard Method of Salt Spray (Fog) Testing. [7][8] Cathodic delamination models involve the following steps:…”

Effects of residual white rust of inorganic zinc silicate primer on corrosion protection of epoxy-coated carbon steel

“…If bare steel is exposed at breaks in coating, corrosion begins to occur on the exposed metal, with an anode at the defect and cathodic reduction of oxygen on the steel surface beneath the coating at the edge of the defect. In solutions of alkali metal salts, an alkaline environment is soon created at the cathode, which results in disbonding of the coating [23][24][25][26][27][28]. Suggested mechanisms for disbonding include dissolution of the oxide film, degradation of the polymer, and failure of adhesion.…”