A simplified process for preparing adhesive hydroxyapatite coatings on carbon/carbon composites

Abstract

A monetite (CaHPO4) coating prepared by hydrothermal electro-deposition technology (HET) owned a well adhesive strength on Carbon/Carbon (C/C) composites, showing a promising prospect in orthopedic and teeth implants. However, hydrophobic C/C surface had to be pre-treated by solutions containing oxidants, such as H2O2, (NH4)2S2O8, to form chemical bonding with the calcium phosphate coating before the deposition, which is a time-consuming and tedious procedure. To simplify the CaHPO4 preparation, H2O2 was directly added into an electrolyte for depositing a well-bonded CaHPO4 coating by HET, denoted as H-CaHPO4, on naked C/C composites. For comparison, another CaHPO4 coating was prepared on H2O2 pre-treated C/C by HET under the same conditions, designated by N-CaHPO4. Both the CaHPO4 coatings were converted to HA coatings via a post-hydrothermal treatment in an ammonia solution, correspondingly defined as H-HA and N-HA. Interestingly, scratch tests showed H-HA coating on C/C through the simplified HET method had a critical load of 29 N, nearly twice as high as N-HA coating. And H-HA coating on naked C/C showed a more compact microstructure and a lower Ca/P atomic ratio in comparison with N-HA coating on H2O2 pre-treated C/C. The reasons for the change in the microstructure and the improvement in the adhesion of the coatings on C/C were discussed. Besides, in-vitro SBF tests and cell experiments indicated that H-HA coating had a better bioactivity and cell biocompatibility than N-HA coating.