Active corrosion protection of AA2024 aluminum alloy by sol-gel coating containing inhibitor-loaded mesoporous SBA-15

Abstract

Santa Barbara Amorphous-15 (SBA-15) silica were synthesized, and then aminated using 3-aminopropyl triethoxysilane (APTES). Afterward, Diclofenac Sodium (DFS) was loaded into the pores of the aminated SBA-15 before encapsulation in a polyelectrolyte shell. The SBA-15 showed a tubular morphology which did not influence by the amination and DFS loading. Spectrophotometric measurements showed that the release of the diclofenac sodium from the encapsulated substance is a pH-dependent process. The highest amount of the DFS molecules released at pH = 10 after about 2 h. The sol-gel coatings containing the appropriate concentration (1 g L−1) of the aminated and encapsulated SBA-15 were applied on the AA 2024 aluminum alloy. The SEM (scanning electron microscopy) images of the neat sol-gel coating showed structural micrometric cracks. However, the cracks were removed after adding 1 g L−1 of the aminated and encapsulated materials. Uniform distribution of the encapsulated material in the coating was approved by TEM (Transmission electron microscopy). In addition, a relative improvement in the thermal stability of the coating was observed after incorporating the encapsulated nanomaterial. The EIS (Electrochemical Impedance Spectroscopy) studies after 150 day of immersion in the simulated acid rain solution showed that the polarization resistance (Rp) of the sol-gel coating improved from 0.006 to 0.05 MΩ cm2 after incorporating the aminated SBA-15. Also, the polarization resistance was further enhanced to about 14.454 MΩ cm2 by incorporating the same concentration of the encapsulated SBA-15, indicating a significant improvement in the corrosion resistance. The polarization resistance of the coating containing encapsulated SBA-15 increased from 8.664 to 14.454 MΩ cm2 with increasing the immersion time from 120 to 150 days, likely due to intelligent release and subsequent adsorption of the diclofenac sodium on the active corrosion sites.