Crystallisation of a highly metastable hydrated calcium pyrophosphate phase

A simple and fast synthesis method was set up to obtain pure hydrated calcium pyrophosphate (CPP) phases of biological interest. This work focused on a specific phase synthesised at 25 °C and pH 4.5 in a stirred tank reactor. Powder X-ray diffraction, FTIR spectroscopy, scanning electron microscopy and thermogravimetric analyses revealed that the phase is unknown but presents similarities with a monoclinic tetrahydrated CPP phase (Ca2P2O7·4H2O, m-CPPT β phase) synthesised under the same conditions of pH and temperature. Characterisation of the unreferenced phase (u-CPP) has been performed, especially to better identify its composition, structure and stability, as well as its possible relation to the m-CPPT β phase or to other hydrated CPP phases.