Preparation and characterization of fluoridated hydroxyapatite coatings on HT-C/C composites

Monetite-like coatings were deposited from a solution containing Ca and P ions onto H2O2 treated Carbon/Carbon composites (HT-C/C) by ultrasonic induction heating (UIH) and subsequently subjected to ammonia hydrothermal treatment to form hydroxyapatite (HA). Subsequently, this HA coating was placed in a NaF solution and hydrothermally treated to produce fluorinated hydroxyapatite (FHA) coatings. The structure, morphology and chemical composition of the HA and FHA coatings were characterized by SEM, XRD, XPS, EDS and FTIR, and the adhesiveness and dissolution rate were examined by a scratch test and an immersion test respectively. The results showed that incorporation of F into HA led to an increase in the adhesiveness but a decrease in the dissolution rate of HA coating on C/C. With increasing hydrothermally fluoridation temperature, the F content in the FHA coatings increased and their dissolution rate decreased. However, the adhesiveness of these FHA coatings on C/C first increased from 42.7 N to 54.2 N as the hydrothermal fluoridation temperature increased from 353 K to 393 K, and then decreased to 18.3 N at 413 K. The reasons for changes in the adhesiveness and dissolution rate of the coatings were discussed.