- Author
-
Pommersheim, J. M.
|
Nguyen, T.
|
Zhang, Z.
|
Lin, C.
|
Hubbard, J.
- Title
- Mathematical Model of Cathodic Delamination and Blistering Processes in Paint Films on Steel.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
-
NIST TN 1293,
May 1992,
72 p.
- Distribution
- Available from National Technical Information Service
- Keywords
-
paints
|
mathematical models
- Abstract
- Conceptual and mathematical models are developed for processes which describe blistering of defect-containing coating on coated steel containing defets exposed to electrolytic solutions. The assumption is made that cations migrating along the coating/metal interface from an anode at the defect to cathodic sites are responsible for blistering. The cations are driven by both concentration and electrical potential gradients. The mathematical models are solved to predict ion fluxes and concentrations along the interface and within the blister. Solutions of the models are expressed in terms of dimensionless parameters. Model variables include blister size, distance between the blister and defect, ion diffusivity and potential gradients. To substantiate the models, an experiment was designed and conducted to measure the transport of cations along the coating/metal interface from the defect to the blister. Sodium ion concentration-time data within a blister were analyzed to determine model parameters. Under the experimental conditions employed, it was found that the transport of sodium ions is controlled by potential gradients rather than concentration gradients. Model results indicate that large blisters subject to a potential gradient are more likely to grow than small ones because higher concentrations can build up within them. Implications of this conclusion for maintaining the integrity of organic coatings are discussed.