Corrosion beneath a blister with high impedance
- PDF / 2,877,367 Bytes
- 7 Pages / 595.276 x 790.866 pts Page_size
- 72 Downloads / 150 Views
Corrosion beneath a blister with high impedance Vinod Upadhyay , Luke Wiering, Zachary Bergseth, Xiaoning Qi, Dante Battocchi
Ó American Coatings Association 2019 Abstract In this work, the effect of blisters on the performance of protective coatings was investigated. Artificial blisters were generated by potentiostatic DC polarization of an epoxy-coated aluminum substrate and characterized using optical microscopy, electron microscopy (SEM), scanning electrochemical microscopy, as well as by scanning Kelvin probe (SKP) measurement. Impedance measured above blisters displayed high values, typical of an intact undamaged coating. SKP measurement above the blister identified regions of likely corrosion beneath it, which was verified by SEM. SEM images showed pitting-like corrosion beneath the blisters, implying that high impedance measured on delaminated coatings may correspond to the delaminated polymeric film. SKP was also able to identify regions of invisible delamination. Keywords Coating, Corrosion, Blister, Electrochemical impedance spectroscopy, Delamination, Scanning Kelvin probe, Scanning electrochemical microscopy, Epoxy
Introduction Organic coatings are widely used to protect structural surfaces of buildings, bridges, automobiles, aircrafts, electronic devices, and many others. They form a This paper was presented at the 15th Coatings Science International Conference on June 24–29, 2019, in Noordwijk, the Netherlands. V. Upadhyay (&), L. Wiering, Z. Bergseth, X. Qi, D. Battocchi Coatings and Polymeric Materials, North Dakota State University, Fargo, ND 58102, USA e-mail: [email protected]
barrier between the external aggressive corrosive species (such as water, oxygen, and ion) and the substrate surface and prevent their interaction.1 For lifetime extension, incorporation of corrosion inhibitors into organic coatings can be performed.2–6 However, barrier protection remains the primary means for which organic coatings are employed. Failure in barrier protection may lead to electrochemical activity at the substrate-coating interface, inducing substrate corrosion. Coatings, therefore, must be defect free to ensure adequate protection. Common electrochemical indication of coating failure includes low coating resistance or high current activity at the metal coating interface of the substrate under protection. Before any final application, a coating must be tested for protective performance to verify if it meets the desired performance requirements. Such requirements may be of various types such as high impedance, high chemical and solvent resistance, scratch resistance, flexibility, and adhesion. A good coating adhesion is of paramount importance for a coating to function properly. Adhesive failure can be in the form of blisters, cathodic delamination, and anodic undermining. However, whether such delamination and blistering result in protection loss, and the concurrent effect on the substrate beneath, is not well investigated. The effect of delamination/blister on the performance of an organic coating was un
Data Loading...
