resulted from the in homogeneous curing reaction. Addition of nanoparticles causes less corrosive electrolyte diffusion into the coating matrix due to its great barrier performance. In fact, the presence of nanoparticles at low cross-linking density areas leads to a decrease in the electrolyte diffusion into the coating matrix. As a result, less hydrolytic degradation occurs on the nanocomposite compared to the blank sample. The second reason is that Al2O3 nanoparticles may behave like an inhibitive pigment at alkaline condition. Electrochemical reactions occur beneath the coating resulting in hydroxyl ions (OH.) creation. The ions produced can diffuse into the bulk of the coating catalyzing hydrolytic degradation and etheric bonds cleavage [33]. In the case of using nanoparticles, the following reaction may occur:
2H2O
+
O2 +
4e
จ
4OH. (pH
ช) (6)
Al2O3 +
OH.จ
2AlO2
. +
H+ (pH
ซ) (7)Eq. (7) shows that nanoparticles could react with OH.ions leading to decrease in pH in the coating matrix [32]. As a result, less coating degradation occur in presence of the nanoparticles.
4. Conclusion
Epoxy/polyamide nanocomposites were prepared using various loadings of nano-alumina particles. The effects of addition of nanoparticles on the corrosion resistance and hydrolytic degradation of the nanocomposites were studied on AA1050 substrate. Results showed that the nanoparticles dispersed in the coating matrix uniformly even at high loadings. Results obtained from EIS and salt spray test measurements suggested the beneficial role of nano-alumina particles in the corrosion resistance improvement of the coated samples. Nanoparticles improved the barrier properties and the coating resistance against hydrolytic degradation.The coating corrosion resistance was increased more by increasing the nanoparticles concentration. The epoxy nanocomposites showed more capacitive behaviour compared to the blank sample. Lower number of defects and holes produced on the surface ofthe nanocomposite containing 3.5 wt% nanoparticles.