Preparation And Properties Of Fluoride And Carbonate Composite Substitute Apatite

Hydroxyapatite（abbreviated HA）has widely applied as bone implant material in medicine field owing to its excellent bioactivity and biocompatibility.However,hydroxyapatite in the natural bone is non-stoichiometric and contains many other ions,in which carbonate(CO₃^2-)is the most abundant dopant ions.Since the composite substitution can compensate for each other to optimize the structure and performance of apatite,many researchers focus their reserach on the composite substitution on the basis of mono-substitution.The substitutions of carbonate and fluorine have different effects on apatite’s structure and performance;therefore,the comprehensive performance can be controlled by adjusting the substitution of carbonate and fluorine.In this paper,carbonate and fluoride co-substituted hydroxyapatite powder（CFHA）are prepared via chemical precipitation method.The effects of preparation parameters on the substitution are investigated.CFHA bulk and powder are conducted by heat treatment and the effects of carbonate and fluoride co-substitution on structure and properties of apatites are characterized via test measures such as XRD,SEM,TEM,FTIR,DTA/TG,etc.The CFHA powders are synthesized by chemical precipitation method.The effect of reaction temperature,pH value,initial concentration and adding order of carbonate and fluoride components,adding timing of alkali,co-substitution of Na⁺ ion and n（Ca）/n（P）molar ratio on the carbonate and fluoride substitute,structure and morphology of apatite are invesitaged in detail.Results showed that:（1）particle size and aspect ratio increases with reaction temperature;particle size and aspect ratio of nano-HA are reduced with pH value,and alkaline system favors the crystallization and substitution of HA.（2）Fluorine concentration has little effect on the morphology of apatite.The particle size and aspect ratio of apatites reduce accordingly as carbonate concentration increases.The high concentration of fluoride and carbonate favor the B-type substitution.The fluoride and carbonate contents in CFHA crystals increase nonlinearly with initial concentration,the measured value for carbonate is higher than the theoretical value,whereas the measured value for F-is far lower than the theoretical value.（3）The way of adding lye before reaction causes too fast nucleation rate,giving rise to the clustering phenomenon of crystals,the crystal prepared via the way of adding lye after reaction exhibits plate-like structure.（4）The existence of Na⁺ favors the growth of apatite crystals,and the co-substitution of Na⁺/CO₃^2-is conductive to the carbonate B-type substitution.（5）[Ca]/[P] molar ratioof raw materials will affect the carbonate substitution and the final phase composition of CFHA.The CFHA powder and bulk are conducted heat treatment in a wet CO₂ atmosphere.The effect of carbonate and fluoride co-substitution on the thermal stability of CFHA powders,sintering properities,coefficient of thermal expansion（CET）and flexural strength CFHA bulk are studied.Results showed that:（1）the thermal stability of CFHA has been improved in a wet CO₂ atmosphere;carbonate and fluoride co-substitution has no obvious effect on thermal decomposition of the samples.（2）When heat treatment temperature is fixed at 850 ℃ in wet CO₂ atmosphere,sintered density for CFHA samples increases with the carbonate contents.And when the temperature is fixed at 950℃,carbonate and fluoride co-substitution has no obvious effect on sintered density of the samples.（3）The CET of CFHA samples increases with increasing temperature,but decreases with the increase of the carbonate and fluoride substitution content.（4）Flexural strength of CFHA samples increases with the carbonate and fluoride substitution content.