Ferrimagnetic bioglass ceramics in simulated body fluid: Electron, X-ray and neutron scattering studies

The effect of simulated body fluid (SBF) on the crystal structure and surface structure properties of Ferrimagnetic Bioglass Ceramics (FBC) as a function of the time of immersion in SBF was studied. The materials examined were prepared with a systematic variation of the composition of the oxides in the system [0.45(CaO, P2O5) (0.52-x)SiO2 xFe2O3 0.03Na2O] and the heat treatment temperature. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDX), neutron powder diffraction (NPD) and Rietveld refinement methods were used in our studies. The in vitro experiments demonstrated the bioactivity of the FBC through formation of hydroxyapatite (HAp). It varies with the composition of the FBC, annealing temperature, and time of immersion of the samples in SBF in a non-systematic way. SEM and EDX studies showed that pores appear on the surface of some specimens, while a surface layer of Si, P, and Ca partially covers the Fe, O dendrites of the original samples. Formation and size of pores was determined by the specific processing parameters of the samples. Quantitative phase analysis of the neutron diffraction patterns revealed a phase transition of the calcium phosphate from hexagonal to monoclinic, in weight percentages depended on the composition of the as-prepared FBC and time of immersion in SBF. The weight percentage of the ferrimagnetic phase [Fe3O4] is less affected by immersion in SBF. Inclusion of magnetic scattering of the neutrons in the Rietveld refinement process improved the quality of the fit between calculated and experimental diffraction patterns, resulting in a reduction of the weighted pattern residuals Rwp from 0.15 to 0.07.