Atomic emission spectroelectrochemistry study of the degradation mechanism of model high-temperature paint containing sacrificial aluminum particles

The atomic emission spectroelectrochemistry (AESEC) technique was used to monitor the degradation of a model silicone based galvanic paint system containing Al particles in 30 g/l NaCl electrolyte during spontaneous reaction and under polarization. The elementary degradation phenomena including the dissolution of the binder, the detachment and the dissolution of metallic pigment particles and the corrosion of the substrate were measured simultaneously and independently. Sharp peaks and a continuous increase of the background level under the peaks were observed on the Al dissolution profile (concentration vs. time) under applied cathodic potential. By comparing of the real coating with the model particle suspension, it was demonstrated that the peaks correspond to the release of Al particles from the coating due to the destruction of the binder. The continuous increase of the background level under the peaks during the coating degradation was related to the Al dissolution reaction due to the local pH increase near the surface. Standard solutions of Al particle suspensions were used so to demonstrate a quantitative analysis of particle release. It was determined that the dissolution of the silicate binder by cathodically generated hydroxide was related to the rate of particle release strongly suggesting that the dissolution of the Al particles and the Si binder are related competitive reactions.