| Summary: | 碩士 === 中華科技大學 === 機電光工程研究所碩士班 === 98 === Hydrothermal method was used to make nano carbonate (CaCO3) and diammonium hydrogen phosphate ((NH4)2HPO4) solution to react with each other and form a supercritical fluid under high pressure in a closed autoclave. A certain temperature was maintained for a fixed time to allow the reactant particles to fully interact with each other until an appropriate intermediate formed. To form nano hydroxyapatite (HAp) powder, the desired crystalline phase was obtained as the crystal took shape during the cooling process. Through the control of different Ca/P molar ratios, HAp of varied compositions and types could be derived. The results showed that purer HAp crystalline phase could be obtained when the following manufacturing parameters were used: temperature maintained at 250℃ for 8 hours, a pH value of 10 and NaOH as mineralizer. The derived HAp shows the regular rod-shape crystal. When Ca/P molar ratio was adjusted to be higher, which is 5:3 or 6:3, there would be a situation when CaCO3 failed to fully react and a few CaCO3 particles could be observed through an SEM. Observation was made to see if there were any changes of powder characteristics and appearances when the pH values of the solution were adjusted to 6 or 10 under the temperatures of 150℃, 175℃, 200℃, 225℃ and 250℃. When the solution's pH was adjusted to 10 and water temperature was maintained at 250℃ for 8 hours, the same result was obtained – an even, regular HAp in rod-shape with a few in needle-shapes. HAp nucleated and grew in solution. Its phase change and growth started from the surface of β-TCP. When water temperature rose to 250℃, the growth of β-TCP began to slow down. Only part of β-TCP could again dissolve in the solution and formed HAp. Consequently, when water temperature was high enough, most CaCO3 would change into HAp, leaving only a small amount of β-TCP residue.
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