Hydroxyapatite is the most important bio ceramic, due to its structure and chemical composition which is similar to bone. Since feeble fracture toughness, brittleness and low tensile strength have restricted their use, for overcoming this problem, they were often used as a secondary component. HAp-Al2O3 nano-composite powder combined the benefits of biocompatibility of HAp and high strength of Al2O3. When HAp-Al2O3nano-composite powders were sintered at a higher temperature than 1100- 1200 oC, HAp was decomposed and converted to the second phase of TCP, due to the formation of calcium aluminate increasing decomposition speed of HAp to TCP at higher degree than 1100-1200 oC temperatures; therefore, with the addition of additives to the powders, the decomposition reaction of HAp could be inhibited and the properties could be improved. In this study the effects of alumina as reinforcement, pH, surfactant and different additives were investigated. At first, hydroxyapatite powder was synthesized. Then, the effect of different percentage of alumina (15, 20, 25), different pHs (9, 10, 11), different surfactants and different additives on HAp-Al2O3 nano-composite powder were studied. The results showed that the addition of different additives resulted in increase of the thermal stability and properties of HAp-Al2O3nano composite powder. By replacement of Cl− and F− ions with OH-in HAp structure, decomposition of HAp decreased and stability of HAp at higher temperatures was increased. Owing to the decomposition of HAp, the reaction between CaO and Al2O3 reduced; therefore, the amount of calcium alumina phases decreased something which resulted in Al2O3 phase. Moreover, replacement of Cl− and F− ions in the apatite structure limited the growth of the grains and decreased the crystallinity that led to a better solubility and bioactivity behavior of nano composite powder.
