Synthesis, structural, spectroscopic and thermoanalytical study of sol-gel derived SiO2-CaO-P2O5 gel and ceramic materials

tIn the present work bioactive powders of the ternary SiO2·CaO·P2O5systems, which differ in theCa/P molar ratio, were synthesized by means of a sol–gel route, using tetraethyl orthosilicate (TEOS,Si(OC2H5)4), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and triethyl phosphate (TEP, OP(OC2H5)3) asprecursors of SiO2, CaO and P2O5, respectively. In order to investigate the influence of the relative amountof each phase (in this study: SiO2, CaO and P2O5) the thermal properties of the synthesized gel-glass mate-rials were studied as a function of the Ca/P molar ratio using thermogravimetric and differential thermalanalysis (TG/DTA). After dehydration (in a single step), described from a kinetic point of view as a simplewater evaporation without rupture of chemical bonds, all gels undergo a complex multi-step decompo-sition with endo and exothermic effects, followed by crystallization of calcium silicate phases at about950◦C. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Scan-ning Electron Microscopy, coupled with energy dispersive spectroscopy (SEM/EDS), allowed us to detectthe chemical modifications induced by modifying the Ca/P molar ratio and the sintering. This processis obtained by thermal treatment of the gel-glass precursors after analyzing their thermal behavior inthe temperature range 600–1000◦C, with the aim to convert them into ceramic powders, suitable fortheir applications. The results revealed that when temperature is up to 900◦C, crystallization occurs andpseudowollastonite and wollastonite were formed. Finally, the amount of pseudowollastonite decreasedwith increasing the sintering temperature, while that of wollastonite increased.