Reaction mechanism of magnesium potassium phosphate cement with high magnesium-to-phosphate ratio

3D microstructure of magnesium potassium phosphate ceramics from X-ray tomography: new insights into the reaction mechanisms

“…Phase composition has been controlled with X-ray powder diffraction (diffraction spectra are reported in Online Resource 2), and the presence of only MKP as crystalline reaction product has been confirmed, in agreement with results from MPC samples with different w/s ratio [8,16,18]. Previous results of quantitative phase analysis indicated that MKP largely prevails over the amorphous phase [13,14,18].…”

“…Previous results of quantitative phase analysis indicated that MKP largely prevails over the amorphous phase [13,14,18]. The compact microstructure exhibited by sample MPC_044_15d confirms that, at low w/s ratio, the crystals are densely packed and embedded in the amorphous phase from which they crystallized [16,17,25,49]. Few large pores (size [ 200 lm) of irregular shape are observed.…”

“…Commonly, effective formulations contain an excess of MgO [11,12], resulting in a molar ratio between MgO and potassium di-hydrogen phosphate (KH 2 PO 4 , KDP) higher than 1. The first reaction product is amorphous/paracrystalline [13][14][15], and even if at w/s = 5 an intermediate phase (Mg 2 KH(PO 4 ) 2 Á15H 2 O) has been detected, from 30 min on, the only crystalline phase present in the system is MKP [16]. The strength seems to be driven mostly by the progressive development of a network of elongated or tabular crystals of MKP in the ceramic volume [17,18].…”

“…1; a lower content would leave a fraction of unreacted reagents and any excess should be segregated in pores within the volume. Studies on pastes and suspensions with large water contents have been frequently reported [16,[19][20][21][22], and Mg-P-based materials with excess of water have been considered for specific applications, like in the fabrication of injectable biomedical cements [23] (w/s up to 1). However, detailed characterization of the role of water in defining the microstructure in MPC is lacking.…”

“…In general, it is of practical importance to verify the role of water on the development of the coarse microstructure of MPCs (up to mm in pore size), because it may help to shed light on the reaction mechanisms, and, ultimately, help in product design. In fact, different reaction sequences have been reported in function of MPC formulation [16,20,22,26]. There is indication that this occurs in reason of the degree of supersaturation achieved in solution in the first stages of the reaction.…”