| Nowadays the Technology of Ceramic Materials is one of the key technologies which have been promoting the development of the National Economy and the Bioceramics Materials is the important part of the new kinds of materials. As the Inorganic Biomedical Materials, the Bioceramics Material has been paid more attention and applied extensively just for nearly twenty years. The Bioceramics Materials are mainly applied for the substitution or the rebuild of the hard tissue of Human body which was damaged. Contrasted with metals and organic materials, the merits of the Bioceramics Materials are without poisonous by-effects, better biological compatibility with biological tissue and anti-decayed performance. Because of the many merits mentioned above, the Bioceramics Materials have been used clinically frequently. About forty kinds of Bioceramics Materials have been made about 50 kinds of substitutions on aspects of Medicine and Orthopedics and has come into the market. According to the activity, the Bioceramics Materials can be divided into three types: the Inert Bioceramics, the Active Bioceramics and the Absorbable Bioceramics. Hydroxyapatite is considered as the most valuable material by public. The molecular formula of hydroxyapatite is Ca10(PO4)6(OH)2, and also called HAP or HA, a kind of quaternion inorganic apatite and its crystal lattice parameter is a=b=0.9421nm,c=0.6882nm. And the ratio of Ca/P is 1.67 theoretically. HA is the most valuable active Bioceramics Materials for use, it is the main inorganic component of backbone animals'bones and teeth (70%-90% in human bones), and its structure is also like those animals'bones and teeth. HA has good biological compatibility, no biological noxious so that it can be used extensively as the substitution or the rebuild of the hard tissue of Human body, such as teeth plant, substitution of backbone, and it is better than metals and polymer. Therefore, HA is a kind of promising Active Bioceramics Materials. However, although owning so many advantages, HA is not perfect. HA is unfit for supporting heavy burden because of its low mechanical performance. As a kind of typical extreme condition, High-Pressure Method has been developed fast recent years on the aspects of big chamber and high pressure. The properties of High-Pressure Method are shortening the distances between the atoms effectively, changing the states of electrons and affecting phrases changing courses. In the condition of high pressure and high temperature the materials are given high energy. So the High Pressure Method is effective to synthesize new materials. However, now the High Pressure Method is reported rarely for study Bioceramics which have been studied in many way. In this paper, we select the valuable Biomceramics Material: Hydroxyapatite (HA) as an object to produce solid materials in the conditions of different pressures and temperatures though the High Pressure Method. We choose TG-DTA, XRD, Raman, IR and TEM to find the affects of the conditions to crystal structure and microstructure forapplications, offering experimental facts for creating better new Bioceramics Materials. The HA original powder is prepared in the Chemical Precipitation Method in this paper. We use 500 tons Belt High Pressure Machine, graphite which is responsible for heating up and fix the conditions on low pressure(1.25GPa), up to 300oC, 800oC; middle pressure(2.28GPa), up to 300oC, 800oC; high pressure(3.90GPa), up to 300oC, 800oC and keep the pressure and temperature 30 minutes every time. To test the thermo stability, the structure and the physical performance we use DTA/TG, XRD, Raman, FTIR, TEM, HV methods. Results & Discussion 1 The results of DTA/TG shows that the endothermal peak ranging from 50oC to 80oC which lose little mass usually reflects the escape of some impurity and moisture. While the three exothermic peaks ranging from 200oC to 540oC which lose much mass indicates the original HA powder can be changed in structure or crystallizes further. 2 The result of TEM shows that the original HA powder is made of some asymmetrical particles in size. The little ones adhere to each other and looks like floccules. The bigger ones have clear boundary. After 450oC sintered, the particles do not change clearly. While after 900oC, the floccules disappear and the size of the particles increase clearly, crystallizing better. 3 XRD shows that in the low pressure the diffraction peaks become narrower when the temperature go up, of which the third strong peak (112) divides from the most strong peak (211) gradually. This indicates that thiscondition can also help HA crystallize, like the normal pressure condition. It is the same when the pressure increases. However the color of samples changes from white to deep brown. 4 The result of the Raman shows that the original powder is HA but low crystallization, as the XRD. When heated in normal pressure, the group PO43-'s stretch peak changes following the temperature unlike XRD. The stretch peaks appear again. This means the microstructure inside changes. Some atomic group probably reset; the new microstructure appears in high temperature but now it is not sure based on the experimental results. After 1.25GPa and 2.28 GPa without heating, PO43-'s stretch peak become weak while the strength of this peak become strong again nearly to the original powder under the pressure of 3.90 GPa and no other peak appears. This can not be explained by the aberrance of PO43-due to the pressure without heat, which suggests the microstructure changes can be also brought by the pressure without heat. (It complies with the results of IR) After the process of the High Pressure and High Temperature, we can find that 1) all the Raman peaks (PO43-'s stretch) disappears when the original powder is under the different pressures, 300oC. 2) the Raman peaks appears again when the original powder is under the different pressure, 800oC. The intensity of the peaks changes due to the pressure. When 800oC, the crystallization is better in higher pressure. 3) There are always two widened peaks in 1331 cm-1 and 1598 cm-1 after the original powder is under different pressures, 800oC. Their positions, relative intensity and Full-Width Half-Maximum (FWHM) do not show obviousvariation accompanying with the pressure increasing. But the present experimental results are not enough to explain the two new peaks. 5 The results of IR show that the main phase of the original powder is HA. Some OH-in the original powder under normal pressure are of coordinative unsaturation. While some PO43 -have aberrances and vacancies. When the temperature increases, these OH-and PO43-decrease which cause the peaks stronger. The peaks located between 1100cm-1 and 3500cm-1 that cannot be recognized are not regular when the temperature increases. There are some other phases probably in the sample, which cannot be explained clearly and are needed further study. After normal temperature, 300oC and 800oC sintered in different pressure (1.25GPa and 3.90GPa), the IR peaks of OH-group of the sample change when the temperature increases although the rule of change is not clear. The shapes of IR peaks of PO43-group become sharper when the temperature increases, but the changes of the intensity and the change of the temperature do not show linear relationship (the sample under 1.25GPa, 300 oC is stronger than that under 1.25GPa, 800 oC). One of the reasons is: the pressure can affect the process that the coordinative unsaturated OH-turn into the coordinative saturated ones. Without the heat, the pressure can affect the peaks obviously located between 1100-3500cm-1, which shows some new microstructure come into being inside the sample. 6 The results of HV show that the average values of two samples'HV that are processed under 2.28GPa and 3.90GPa respectively are similar, and the change trend increases slightly when the pressure increase, but it is not...
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