Abridged acid-base wet-milling synthesis of high purity hydroyapatite

Abstract

There is a plethora of routes to produce hydroxyapatite(HA) and in general calcium phosphates(CP) but production usually leads to a mixture of several phases. Besides ionic contamination, most of these methods are cumbersome, restricted to small volumes of product and require a lot of thermal energy. The acid-base route eliminates foreign ions or additives and its only byproduct is water. Heterogeneous reaction drawback is that solid reactants do not easily come in contact with each other and therefore addition and stirring times become very lengthy and still the product is a mixture. The synthesis started from calcium hydroxide and phosphoric acid (PA). Ball milling was used to favor kinetics and stoichiometry. Six sets of PA addition, paddle stirring and ball milling times were used. Products were evaluated by X ray diffraction (XRD), Fourier Transform Infrared (FTIR), scanning electron microscopy (SEM), X ray fluorescence (XRF) and Ca/P ratio. Chemical analysis for calcium proceeded through oxalate precipitate and phosphorus by the phosphomolibdate technique. A set of conditions yielding high purity HA was established.