Chromium fluoride-containing bioactive glasses: Structure and properties

Abstract

Bioglasses in the system 24.5Na₂O.24.5CaO.6P₂O₅.xCrF_2.(45-x)SiO₂ have been studied in the composition region of x= 0-10 mol%. CrF₂. Glass of molar ratio (Ca+Na)/SiO₂ ~1.1 is the base material for the glasses containing different CrF₂ concentrations. X-ray diffraction (XRD), differential scanning calorimetriy (DSC), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Vicher hardness (H_v) measurements have been carried out. Crystalline feature of the glasses is followed up by XRD spectroscopy. It is found that crystallinity was enhanced via CrF₂ addition. More enhancement was confirmed via thermal heat treatment process.  Increasing CrF₂ and sintering temperature will induce new ordered phases which will be distributed in the main glassy phase. Well formed flouroapatite (Ca₅(PO₄)₃F and wollastonite Ca₃Cr₂(SiO₄)₃ phases containing fluorine and chromium ions are evidenced in CrF₂ containing glasses. Increasing glass transition temperature T_g and hardness number H_v upon increasing CrF₂ concentration was discussed on bases of formation of additional bonds by the effect of CrF₂ molecules. The measured temperature window between T_c and T_g was found to have a great influence in material structure. Wide window is a feature of amorphous glass which free from CrF₂.  The window scale is found to quickly decrease with increasing CrF₂, since crystalline phases are already formed in glasses containing CrF₂.  Formation of crystalline intermediate phases with more shielded silicate and phosphate structural is considered as the main reason for increasing T_g and (H_v) of the glasses.  EDS as well as XRD analyzed spectra confirm that crystalline wollastonite of calcium inosilicate mineral (CaSiO₃) phase is well formed. The wollastonite species is evidenced to contain small amounts of chromium and fluorine ions which are substituting for calcium cations. Wollastonite phases with Cr/Si=1 is the most dominant type. This ratio is a characteristic feature of crystalline CaSiO₃ species. Small concentration from fluorine ions are involved in apatite phases. Presence of both crystalline apatite and wollastonite in the sample matrix promotes its biocompatibility, particularly orthopedic bioactivity. As a consequence, some of investigated glasses are recommended to be applicable in dental field of applications. This depends on its own crystallinity, hardness, its apatite and wollastonite concentration as biocompatible phases in the crystallized glass