Controllable synthesis of tricalcium phosphate (TCP) polymorphs by wet precipitation: Effect of washing procedure

In the present work, effect of processing conditions on the synthesis of tricalcium phosphate (TCP) polymorphs was investigated. Pure α- and β-TCP polymorphs were prepared by wet precipitation method at almost identical thermal conditions. It was shown that formation of the compound with desired crystalline structure can be achieved by applying a washing procedure with a certain solvent to as-prepared calcium phosphate precipitates. Effect of water, acetone, acetonitrile, ethanol and isopropanol on the crystallinity and crystal structure of the as-prepared and annealed powders was studied. It was demonstrated that type of the washing liquid strongly affects crystalline or amorphous nature of the as-prepared precipitates and formation of different TCP polymorphs after thermal treatment. Washing of the as-prepared precipitates with water and acetone leads to the formation of β-TCP, while washing with acetonitrile and alcohols leads to the crystallization of α-TCP. The thermal behavior of dried precipitates was investigated by thermogravimetric analysis (TGA). The crystallinity, crystal structure and structural changes were evaluated by X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) and Raman spectroscopy. Scanning electron microscopy (SEM) was used for the characterization of morphological features of the synthesized products.