Method for in-situ monitoring of corrosion in aluminum joints under Electrical Impedance Spectroscopy using a carbon nanotube-doped adhesive

Abstract

A novel monitoring technique based on in-situ electrical impedance measurements is proposed for the analysis of the corrosion process in bonded Al-Al joints. For the application of this technique, the adhesive is modified by embedding a carbon nanotube (CNT) dispersion able to generate an electrical percolation network. A correlation between the electrical response and the evolution of the corrosion of the adherents is investigated when the joints are immersed in a 3.5 wt% NaCl aqueous solution. It has been observed that the electrical behavior of the adhesive joint can be modeled by a series of resistance-capacitance (RC) and inductance-resistance-capacitance (LRC) elements. More specifically, the initial interface can be modeled with parallel RC elements. However, the ideal capacitive behavior of the interfaces becomes non-ideal when the immersion time increases, and the corrosion mechanism takes place at the interfaces. For short immersion times, the joint can be modeled by a Constant Phase Element (CPE), due to the formation of an Al₂O₃ layer and corrosion products, that promote a higher energy scattering. At longer immersion times the formation of spalled Al is observed, and the electrical model requires the inclusion of an additional R-CPE element within the interface, proving great potential for the in-situ evaluation of corrosion in such complex elements.