Preparation and performance of a composite epoxy coating based on modified hydroxyapatite

Abstract

Hydroxyapatite (HAp) has been widely used in modern medicine because of its good biocompatibility and has become an important coating material for biological implants. However, it is seldom used in traditional metal anticorrosion field. In this paper, a PDA-HAp@f-Al2O3/EP composite anticorrosive coating was synthesized by modifying the surface of hydroxyapatite (HAp) with polydopamine (PDA) and using amino functional group silane (KH550) doped nano Al2O3 particles for metal anti-corrosion. The introduction of polydopamine (PDA) and Al2O3 solved the problem of poor dispersion in the epoxy coating which can be obviously conducted from the decrease of agglomeration in the SEM images of both materials and composite coatings. Electrochemical impedance spectroscopy (EIS) showed that PDA-HAp@f-Al2O3/EP coating had the smallest change range of breakpoint frequency (fb) and the highest low frequency (f = 0.01 Hz) impedance value compared with other coatings in the experiment of immersing in 3.5 wt% NaCl solution. In particular, the impedance of pure EP is only 9.93 × 104 Ω cm2 and that of PDA-HAp@f-Al2O3/EP is up to 1.19 × 108 Ω cm2 after immersing in 3.5 wt% NaCl solution for 30 days, which is 4 orders of magnitude different. The data obtained by fitting the coating equivalent circuit model (QC, Qdl, RC, Rct) also show that the coating has excellent anticorrosion performance. Besides, the anticorrosion mechanism of the coating is also studied. PDA-HAp@f-Al2O3/EP composite anticorrosion coating plays a barrier role first when the corrosive medium begins to invade, and then protects the coating by extending the path of the corrosive medium into the coating and the release of corrosion inhibitor. This study provides a broad prospect for the application of hydroxyapatite (HAp) in traditional anticorrosive work.