Abstract: The nano carbonate-containing hydroxyapatite(CHAP) with different CO₃^2- contents (WCO₃^2-)
was prepared by a sol-gel process. DTA, TG, XRD, FTIR, TEM,dynamic absorption test and crystalline density measurement were used to study substitution
structure, phase tranversion and absorbing F- action of the CHAP. Test results indicate that the CHAP is with AB mixed-type substitution structure.
When WCO₃^2-<3.34%, RI increases and capacities absorbing F^- decrease with the increasing of CO₃^2- contents, and the CHAP has
preferentially a tendency of absorbing CO₃^2- to enter its lattice in absorbing F^- process, and a phase tranversion from the CHAP to Ca-deficient
HAP takes place at 150～776℃, then the HAP occurs dehydroxy phase tranversion at 776℃. When WCO3^2-=3.34%, RI has maximum
value, a phase tranversion from the CHAP to Ca-stoichiometric HAP takes place at 150～776℃, so the dehydroxy phase tranversion of HAP can
not occur at 776℃. When 3.34%<WCO₃^2-≤7.52%, RI decreases and capacities absorbing F^- increase with the increasing of CO₃^2- content, and the CHAP has preferentially a tendency of absorbing
F^- to enter its lattice and exchanging out CO₃^2- in absorbing F^- process, and a phase tranversion from the CHAP to Ca-surplus HAP takes place
at 150～776℃, so the dehydroxy phase tranversion of HAP can not occur at 776℃. The nano CHAP crystals have a behavior of dissolving along crystal length, and 2～3 times capacities absorbing
F^- of the pure HAP, and show an effect of dissolving-precipitating adsorption in nanoscale.

Key words: absorption effect in nanoscale, carbonate hydroxyapatite（CHAP）, substituted struc-ture, phase tranversion, absorbing F-action