Optimization of the Synthesis of Hydroxyapatite Powders for Biomedical Applications Using Taguchi's Method

A conventional method of chemical precipitation was used to produce hydroxyapatite (HAp) powders, with a molar ratio of Ca/P=1.67, for biomedical applications. The aim of this work was to study the effect of four control factors, namely pH, reaction temperature, reagent concentration and flow rate addition, at three levels, on the Ca/P ratio of the synthesized powders, using the Taguchi design of experiments method. Nine powders were synthesized using Ca(NO3)24H2O and (NH4)2HPO4 as starting reagents. The Ca/P molar ratio of each powder was determined by ICP-AES. Data obtained were used in the Taguchi’s design of experiments to optimize the Ca/P molar ratio. Results showed that the pH of the reaction is the main control parameter (74% contribution) affecting the Ca/P molar ratio of the powders. Therefore, attention should be paid to the control of the pH during the synthesis, in order to obtain HAp powders in a reproducible fashion. High pH values (9.5) and reaction temperature at 70 °C favoured the synthesis of HAp powders with a Ca/P ratio close to the target value of 1.67.