Sol-gel Preparation of Fluoridated Hydroxyapatite in Ca(NO3)2-PO(OH)3− x (OEt) x -HPF6 System
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Fluoridated hydroxyapatite (FHA) has been successfully synthesized via sol-gel method with HPF6 as the fluorine containing reagent. The chemical reactions induced by HPF6 addition and the formation process of fluoridated hydroxyapatite (FHA) are investigated. The hydrolysis and alcoholysis of HPF6 release F ion into the solution which, in turn, reacts with Ca ion to form nanocrystalline CaF2 (nc-CaF2). These nc-CaF2 improves the gelation ability of the system through formation of F‒H hydrogen bonding between F in nc-CaF2 and H in P precursors. Increasing HPF6 leads to more nc-CaF2 thus less Ca(NO3)2 in the dried gel, or the presence of nc-CaF2 in the gel suppresses the formation of Ca(NO3)2. At elevated firing temperatures, the P containing groups react with each other to form condensed phosphate. These condensed calcium phosphate, nc-CaF2/Ca(NO3)2, reacts with the rest of the amorphous phase to form FHA phase at above 400°C.
KeywordsHPF6 CaF2 sol-gel processing fluoridated hydroxyapatite hydrogen bonding
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