Description
To protect metal constructions from corrosion, organic coatings are widely applied. However, these coatings can be prone to breakdown when exposed to aqueous environments during prolonged periods of time. The initial step of failure of a coating when it comes into contact with water is water uptake. This water uptake has been studied extensively in literature [1, 2] by Electrochemical Impedance Spectroscopy (EIS) and/or gravimetry. With EIS, the coating capacitance is followed as a function of time, and the dielectric constant of the coating over time is extracted. The water uptake can then be estimated by either using the Brasher-Kingsbury equation [2] or the linear relationship [3]. This method to determine water uptake from EIS results, takes as an assumption that water only diffuses perpendicular to the surface, while lateral diffusion could also occur from a theoretical standpoint.In this work, the validity of this assumption is investigated, by not only measuring the capacitance change of the coating surface exposed to electrolyte, but also at surfaces that are not directly exposed. The capacitance will be monitored through odd random phase electrochemical impedance spectroscopy (ORP-EIS). The test will be performed on model coatings, which are based on acrylic and/or methacrylic backbones. From initial research, it is found that the water uptake in these coatings has to be measured immediately after the immersion of the coating as it is a very fast process. This rapid water uptake in the coatings is monitored using the time-resolved instantaneous impedance calculation [4] from ORP-EIS measurements. To identify the lateral diffusion, the impedance is measured simultaneously at the immersed surface and at a surface that is not in direct contact with the solution. This measurement is performed using a custom-made dual potentiostat that shares the working electrode, which is the metal substrate underneath the coating. Results show that there is indeed a measurable capacitance increase in the measured surface outside of the immersed surface, indicating the lateral diffusion of water. The lateral diffusion coefficient can be calculated and compared to the perpendicular diffusion coefficient.
[1] Deflorian, F. et al, Electrochimica Acta 44 (1999) 4243-4249
[2] Brasher, D.M. and Kingsbury, A.H., Journal of Applied Chemistry 4 (1954) 62-72
[3] Nguyen, A.S. et al., Progress in Organic Coatings 112 (2017) 93-100
[4] Breugelmans, T. et al., Electrochimica Acta 76 (2012) 375-382
| Period | 3 Sep 2020 |
|---|---|
| Event title | 71st Annual Meeting of the International Society of Electrochemistry |
| Event type | Conference |
| Degree of Recognition | International |