Figure Thus, to better understand these differences and the effect of milling process in material structure, the milled samples were calcined to characterize the solid fractions after each main loss mechanism (280 °C, 420 °C and 710 °C) (Fig. ). In all cases, a similar thermal behavior related to crystalline phases formation was identified -except for milling during 2 h at 600 rpm, this sample has an unclear phosphate phase, but after thermal treatment at 280 °C it slightly changes matching with K3CaH(PO4)2 phase (Supplementary Material, Fig. ). For the other samples, the treatment at 280°C did not affected the phase K3CaH(PO4)2 (PDF database n° 22-1218), confirming that the mass losses observed in Fig. regard to unbounded water. On the other hand, the thermal treatment at 420°C converted the samples to KCaPO4 (PDF database n° 33-1002), which confirms that the related mass loss is associated to recrystallization by the partial thermal dehydration of the K3CaH(PO4)2 phase that may still be present in the samples. After thermal treatment at 710 °C, the patterns correspond to KCaPO4 phase in all cases indicating the complete conversion: The 31 P NMR MAS spectra of the precursor KH2PO4 shows a single intense signal at δ = 3.74 ppm, characteristic of monosubstituted phosphate (Fig. ). The shift at δ = 3.28 ppm (2 and 6 h at 600 rpm) and at δ = 2.82 ppm (24 h at 600 rpm) are reported to calcium phosphates compounds, for example, hydroxyapatite (Ca10(PO4)6(OH)2) and octocalcium phosphate (Ca8H2(PO4)6.5H2O) . In addition, the signal at δ = 0.74 ppm is related to disubstituted phosphate, suggesting H(PO4)2 5-species agreeing with the KCaPO4 formation.