REVISITING WET-CHEMICALLY SYNTHESIZED β-TRICALCIUM PHOSPHATE: SOLID-STATE NMR STUDY OF LOCAL STRUCTURE

抄録

Several parameters, including the pH, ripening time, temperature, and Ca/P molar ratio, affect the crystal phase of wet-chemically synthesized beta-tricalcium phosphate (β-TCP). In previous studies, optimal synthesis conditions for β-TCP have been established. However, the local structure and dissolution of β-TCP remain unclear. As such, we investigated the effects of the ripening time on the local structure and dissolution of β-TCP. Wet-chemical synthesis at 25 °C, a pH of 7.0, and a Ca/P molar ratio of 1.50 over a ripening time of 48 h resulted in the formation of single-phase β-TCP. A solid-state nuclear magnetic resonance analysis revealed two distinct local structures of β-TCP: the conventionally reported broad resonances’ local structure under a ripening time of 48 h and 16 narrow-linewidth resonances’ local structure over a ripening time of 48 h. The narrow-linewidth resonances indicated the ordered vacancies of Ca(4) sites in the β-TCP structure, in contrast to previously reported randomly ordered Ca(4) vacancies. In a buffer solution with a pH of 5.5, the dissolution was higher and heterogeneous for β-TCP with ordered Ca(4) vacancies than for β-TCP with randomly ordered Ca(4) vacancies, and in a buffer solution with a pH of 7.3, the opposite was observed.