Dissolution kinetic and structural behaviour of natural hydroxyapatite vs. thermal treatment

The dissolution kinetic and structural behaviour of natural hydroxyapatite (N-HA) and synthetic hydroxyapatite (S-HA) was studied vs. sintering temperature and using 'in vitro' experiments. Obtained results highlight the chemical stability of N-HA. Any structural modification was observed until 1200A degrees C. In the fact S-HA undergoes some modifications. XRD diagrams show the tricalcium phosphate (TCP) phase formation between 800 and 1100A degrees C and tetracalcium phosphate (TetCP) phase formation at 1200A degrees C. The 'in vitro' assay shows that the dissolution was occurred more in N-HA than in S-HA. The formed TCP activated the dissolution kinetic and then the precipitation phenomena when a continuous dissolution of TetCP leaded to slow down the kinetic precipitation.