Non-classical nucleation in magnesium phosphate cement reaction

In-situ synchrotron X-ray powder diffraction and small-angle scattering allowed to describe the setting reaction as controlled by the nucleation of nanoparticles which organize themselves into an intermediate amorphous precursor of the crystalline final product. This intermediate precursor already contains the structural motives of the crystalline counterpart, as previously suggested by nuclear magnetic resonance. An amorphous-amorphous transformation occurs through relatively minor structural rearrangements which increase the long-range order, eventually leading to crystallization [3]. This multi-step pathway is compatible with non-classical crystallization mechanisms described in Ca-carbonates, Ca-phosphates and recently proposed for C-S-H in Portland cement.