| Hydroxyapatite (HAP) has attracted significant interesting of many researchers in the past, because it is a bioactive material and the main mineral composition of human bone, and can reaction with the bone in its surface as implants. Performance of ceramic materials is closely related to size and distribution of crystal particle that is associated with size of raw powder, so it is important to prepare raw powder. The methods of HAP preparation contain sol-gel, solids state synthesis, precipitation method, mechanochemical route and so on. At present, nanometer HAP were synthesized by microwave irradiation and precipitation process, using Ca(NO3)2.4H2O and H3PO4 as raw materials. The results show that precipitation time, microwave irradiation time and microwave power has significant influence on thermal stability of HAP. HAP decompose CaO and β–Ca3(PO4)2 at 12000C, precipitating for 4h, 8h and 12h. HAP can exist stably at 12000C, precipitating for 24h. When microwave power is 700W, decomposition temperature of HAP irradiating for 5min and 30min is 12000C, composition of sample irradiating for 1h is pour HAP. When irradiating time is 1h, HAP synthesized at 70w microwave power decompose partly CaO and β–Ca3(PO4)2 at 12000C, few HAP synthesized at 210w microwave power decompose CaO and β–Ca3(PO4)2 at 12000C, and HAP prepared at 700 microwave power can exist stably at 12000C, which suggest that thermal stability of HAP enhanced with increase of microwave power. The optimal irradiation and precipitation time is 1h and 24h in the precipitation and microwave irradiation process, irrespectively. Preparation for thermally stable HAP with precipitation methods needs more time compared with synthesis of thermally stable HAP with microwave irradiation method, which is because mechanism of HAP formation is different between the microwave process and the precipitation. In the precipitation method, HAP was prepared by phase transformation from other amorphous calcium phosphate or hydrated orthophosphates, whose preparation process is slow and needs spontaneously prolonged time. However, in microwave synthesis, the HAP was directly obtained in water solution under the effect of microwave irradiation, and not involving crystallographic transformation. In our research, the influence of precipitation time, irradiation time and microwave power on the thermal stability of HAP was investigated in details. The aging time and irradiation time have significant effects on the thermal stability of HAP, due to HAP is a crystal with hexagonal structure, whose atoms occupy the special position in particular. Formation of perfect HAP crystal and the diffusion of the solution need the longer time. The results are that calcium deficient hydroxyapaptite (usually expressed as Ca10-X(PO4)6-X(HPO4)x(OH)2-X) were prepared in short time and higher energy solution, and Ca deficiency is responsible for the different thermal stability. Crystals prepared in short time have comparatively more Ca disfigurement in comparison with crystals synthesized in long time. The more Ca disfigurements of HAP polycrystal have, the worse thermal instability of HAP possess. The results show that microwave power has significant effects on thermal stability of HAP. Ca deficiency is responsible for the different thermal stability as analysed above. Microwave heat is a kind of body calefacion caused by medium ullage in the electric and magnetic field, substance molecule can move sharply in the microwave field. Dispersion of raw materials in solution system increases with improvement of microwave power. Input of the energy is more advantage to produce dispersion of raw materials, so reaction fulfilled drastically and more intact crystals were prepared. The preparation of nanometer composite material is important research direction in the 21 century, which is similar to the composition, structure andperformance of the body tissue. Development of the nanometer composite will provide bright future for the application of biomimetic tissue materials. In the present research, Magnesium doped hydroxyapatite/gelatin nanometer composite were prepared by biomimetic method in the first, using gelatin as template, which is similar to the composition of the dentine. Magnesium doped hydroxyapatite/gelatin nanometer composite is nanometer fibrils in the presence of gelatin, and pour HAP and HAP doped with 0.1 mol Mg are sphere nanometer particles in the absence of gelatin. The present result shows that morphology and size of HAP crystals were greatly influenced by the addition and amount of magnesium in aqueous solution. Particles size of samples decreased with the increase of Mg, due to Mg inhibits HAP crystallization in solution. The effects of the gelatin on the morphology and size of the HAP is critically dependent on the chemical interactions between the HAP and the functional groups (R-COO-) of gelatin. The carboxyl ion can be especially active site for the coordination of calcium ions to form ion complexes, these complexes can further interact with PO43-ions and from critical size nuclei for the growth of HAP nanometer crystals. After the nucleation, the HAP crystals will grow spontaneously with preferred orientation along gelatin, due to chemical interactions with pre-organized functional groups of the gelatin. The mechanical property of traditional HAP ceramics is poor, which enable the application of HAP to limit the lower loading position. Small size effect, surface and interface effect of the nanometer materials give rise to reduction of the porosity and defects, witch lead to the improvement of the ceramic mechanical property. At present, nanometer and traditional hydroxyapatite ceramics were prepared by sintering in the air ambience, whose mechanical performances were measured. The results show that porosity, water absorbability, density and compressing strength of nanometer hydroxyapatte ceramics is 0.3%, 1.4%, 3.12 g/cm3 and 195Mpa, irrespectively, and the porosity, water absorbability, density and compressing strength of traditional hydroxyapatte ceramics is 4%,10%,2.68 g/cm3 and 76Mpa, irrespectively. The...
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