Influence of small concentration addition of tartaric acid on the 220 °C hydrothermal synthesis of hydroxyapatite

The synthesis of elongated hexagonal shape crystalline hydroxyapatite (HA) by chemical precipitation and crystallization by hydrothermal method at 220 °C is presented, with addition of tartaric acid (TA) in small concentrations. In order to study the influence of tartaric acid addition, it was added either at the end of the precipitation stage, or to the Ca precursor (before the P precursor addition), in different molar ratios to the Ca and P precursors, whose molar ratio was kept constant. The phase identification was performed by XRD and FTIR; size and morphology was studied by means of SEM and TEM. The crystallization took place along the c crystallographic axis, with formation of lamellar crystals with hexagonal habit, whose dimensions first decrease with rising tartaric acid concentration and then increase again. The morphology of the HA crystallites changes above a certain amount of tartaric acid admixture. The addition of TA to the Ca precursor, compared to the case of its addition to the already precipitated HA, leads to better results regarding crystallinity.