Surface Modification of Aluminum Flakes with Amino Trimethylene Phosphonic Acid: Studying the Surface Characteristics and Corrosion Behavior of the Pigment in the Epoxy Coating

Aluminum flakes were modified with 0.25 M amino trimethylene phosphonic acid (ATMP) to enhance their corrosion resistance. The surface chemistry of the unmodified and modified pigments was evaluated by x-ray photo electron spectroscopy (XPS), Fourier transform infrared spectroscopy, thermal gravimetric analysis, and a contact angle measuring device. Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion resistance of aluminum flakes in 3.5 wt% NaCl solution. Results obtained from XPS analysis revealed that the ATMP molecules adsorbed on the surface of the aluminum flakes via acid-base interaction in a bi-dentate conformation. Also, the corrosion resistance of the pigment was significantly enhanced after surface modification. Results showed that the maximum adsorption of ATMP on the surface of the pigment was observed after 12 h of treatment. The electrochemical measurements showed higher corrosion resistance of the modified particles than the unmodified ones. The effects of the addition of unmodified and modified pigments on the corrosion protection properties of the epoxy coating were also studied by EIS and salt spray test. It was shown that the unmodified Al pigment did not provide promising corrosion protection properties but the surface modified pigment promoted the corrosion resistance of the coating significantly.