Surface hydrophilic modification for carbon/carbon composites and its effect on the bonding strength of hydroxyapatite coating

In order to improve the bonding strength of hydroxyapatite coating on carbon/carbon composites, a surface hydrophilic modification was performed on carbon/carbon composites using a combination of H₂O₂ and FeSO₄ · 7H₂O under ultraviolet irradiation. The hydroxyapatite coating was prepared by an ultrasound-assisted electrochemical deposition method. The results showed that the surface hydrophilic modification introduced a large number of oxygen-containing functional groups (C=O, C-O and COOH group) onto the surface of carbon/carbon composites. The surface hydrophily of the modified carbon/carbon composites was significantly improved with the water contact angle decreasing from 85.7 ± 4.1° to 11.9 ± 1.5°. The modified carbon/carbon composites had strong induction ability for the deposition of hydroxyapatite crystals. The hydroxyapatite showed a wavy-shaped crystal at initial deposition process and subsequently formed a compact and uniform coating. The bonding strength of hydroxyapatite coating on modified carbon/carbon composites (9.58 ± 0.40 MPa) was significantly higher than that of the coating on unmodified carbon/carbon composites (3.04 ± 0.20 MPa).