MAS NMR studies of apatite formation on 50CaO.50SiO₂ glass in a simulated body fluid

²⁹Si and ³¹P MAS NMR spectra of 50CaO.50SiO₂ glasses before and after soaking in a simulated body fluid(SBF) for various periods were measured and the chemical processes leading to apatite formation were derived. The network of 50CaO.50SiO₂ glass consisted mainly of Q² group. The fraction of Qⁿ (n=2-4) group changes with immersion time in SBF. In the initial stage of apatite formation the Q² group comprising the 50CaO.50SiO₂ glass network dissolves or changes rapidly into the Q³ group by not only self condensation but also the polymerisation of the Q² group with phosphate ions with a few P-OH bonds in the SBF. The phosphate silicate matrix layer and hydrated silica gel layer formed on the glass surface mainly consist of the Q³ group. These layers provide the active sites where phosphate ions can be adsorbed easily and apatite nuclei can form. The local structure around a P atom may be very similar to that of hydroxyapatite or CaHPO₄.2H₂O crystals.