Strong-bonding calcium phosphate coatings on carbon/carbon composites by ultrasound-assisted anodic oxidation treatment and electrochemical deposition

The current work describes the ultrasound-assisted anodic oxidation treatment of carbon fiber-reinforced carbon (C/C) composites with H3PO4. The aim was to create chemical bonds between the surface-treated C/C composites and subsequently deposited calcium phosphate (CaP) coatings. The surface energy of C/C obviously increased after undergoing ultrasound-assisted anodic oxidation treatment at a current density of 50 mA/cm2 in aqueous 0.5 M H3PO4 solution (USAT–C/C-50). A large number of O-containing groups and some P-containing groups were found on the treated C/C substrate. The formation of O-containing groups may have been promoted by the energy input of the ultrasound and electric field. P-containing species could be bonded to C/C by Csingle bondPsingle bondO or Csingle bondOsingle bondP bonding. Among the species formed, the formation of (H2PO4)− on C/C was promoted by ultrasound. When USAT–C/C-50 was used as the substrate for CaP coatings deposited by ultrasound-assisted electrochemical deposition (USECD), the surface of USAT–C/C-50 acquired strong CaP induction ability, and large amounts of CaP were deposited on it during the initial deposition process. After USECD, very strong-bonding CaP coatings formed on USAT–C/C-50. The average shear bond strength of the coatings obtained on the USAT–C/C-50 substrate [(12.14 ± 1.30) MPa] was about twice that of the coatings obtained on untreated C/C [(6.78 ± 1.06) MPa].