Controlled Synthesis And Growth Mechanism Of Porous Carbonated Hydroxyapatite By The Template-directed Homogeneous Precipitation Method

Carbonated hydroxyapatite(CHAp)is a multifunctional material of excellent bioactivity,biocompatibility,osteoconductivity and solid alkalescence,which is of significance in the fields of biology,medicine, environment and chemistry.The applications of synthetic porous CHAp are closely related to its size,morphology,surface state and pore structure.In this thesis,the template-directed homogeneous precipitation method was developed to prepare the porous CHAp spheres.The chemical component,crystal morphology,crystal orientation,the special surface area and the surface fractal demention of the products were investigated by XRD;FT-IR,XPS,SEM,TEM,the multipoint BET method and the calculational method of the surface fractal dimension.The results suggested that the product was a kind of micrometer sphere three-dimensionally structured by CHAp nanoflakes of high surface area and {10(?)0} surface characteristic.Parallel experiments and the corresponding crystallization thermodynamics analysis were carried out to study the initial concentration of Ca-P how to control the chemical component of the products.The results indicated that the lower concentration of Ca-P was prone to pure CHAp,and to keep the initial P concentration below 0.048 M was favorable to avoid dicalcium phosphate(DCPD).Batch experiments revealed that the morphology of the porous CHAp sphere was controlled by the concentration of urea.The results showed that too high concentration of urea would lead to disk congeries of overgrown nanoflakes,whereas too low concentration of urea would bring about irregular porous spheres,and 0.4 M was the optimal concentration of urea for regular porous spheres. The average aperture of porous CHAp spheres was well regulated from micrometer size to nanometer size via adding the template and the fractal conditioner and adjusting their concentrations. Correspondingly,the controlled growth mechanism was discussed in detail via analyzing the growth process and the template-directed growth kinetics.The results revealed that the growth process include three essential phases the nucleation and growth of octacalcium phosphate(OCP),interface phase translation of OCPâ†'CHAp and the growth of CHAp nanoflakes,furthermore that the higher concentration of the template leaded to the denser growth of CHAp nanoflakes on the surface of OCP and the smaller aperture,and also that the higher concentration of the fractal conditioner resulted in the more surface fractal dimension,the smaller aperture and the greater special surface area.