The Thermal Stability Research Of Fluoridated Hydroxyapatite And Synthesis Of Porous Structure

Fluoridated hydroxyapatite （FHA） was synthesized by sol-gel method with the chemicalcomposition of Ca₁₀（PO₄）6（OH）_2-2xF_2xand sintered at720oC,800oC,900oC,1000oC and1100oC,repectively. XRD, TGA, XRF and TEM were adopted to investigate the influence of F on themorphology, structure and the stability of Hydroxyapatite fore and after sintering. XRD resultssuggested that sintered the FHA decompose into Ca₃（PO₄）₂（TCP）. TEM studies showed thatrod-shaped particles with the lengths in the range of20-50nm and the widths in the range of10-13nm were produced in unsintered FHA, and the porous structure with about20nm diameterwas formed regularly in sintered FHA due to the decomposition from FHA into TCP. The TGAstudies confirmed that the weight loss of FHA, which was much less than HA, had four steps, theevaporation of the absorbed water, the loss of the crystal water, the loss of hydroxyls and thedecomposition of FHA into TCP. The XRF results showed that the weight percentage of F in thesamples was less than the theoretical value especially when x was more than0.5, which impliesthe hydroxyls in HA couldn’t be substituted by F completely. The mechanism of thedecomposition was analyzed from the crysral structure, the thermodynamic process and thedynamics process. The reaction of FHA decomposition became more difficult when the F contentwas more than0.5. The function of the decomposition temperature vs x was fitted. The increase ofthe decomposition temperature indicates that F ion can increase the thermal stability of HA.The FHA with porous structure was synthesized by combining it with PMMA. Biomaterialmust integrate with the human bone tissues quickly after being implanted into the human body,therefore the porous FHA can guarantee the tissues growing tightly with it. The porous FHAwas obtained by sintering at600oC with a heating speed of10oC/min. During the process, NH₄HCO₃was used as the foaming agent and PMMA was volatilized in gas. The product with100-300microns diameter was appropriate for the culture of human tissues.