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, theywere often used as a secondary component. HAp-Al2O3 nano-composite powder combined the benefits of biocompatibility ofHAp 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 aluminateincreasing decomposition speed of HAp to TCP at higher degree than 1100-1200 oC temperatures; therefore, with the additionof additives to the powders, the decomposition reaction of HAp could be inhibited and the properties could be improved. Inthis 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 thatthe addition of different additives resulted in increase of the thermal stability and properties of HAp-Al2O3nano compositepowder. By replacement of Cl− and F−ions with OHinHAp structure, decomposition of HAp decreased and stability of HApat 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, replacementof Cl−and F−ions in the apatite structure limited the growth of the grains and decreased the crystallinity that led to a bettersolubility and bioactivity behavior of nano composite powder.

Keywords: Nano, Composite, HA, Alumina, Chemical precipitation