Structure and crystallization behavior of bioactive and mesoporous SiO2-CaO-P2O5-ZrO2 glass prepared via sol-gel method

Bioactive glasses containing ZrO2 have radiopaque property. Radiopacity is an essential feature of bioactive materials that allows easy follow-up of the treated patient under radiographic control. In this research، we synthesized 61. 2SiO2-24. 3CaO-4P2O5-10ZrO2 (mol%) via a simple sol-gel route. The sufficient heat treatment for converting dried gels into the glasses was determined using thermo-gravimetric and differential thermal analysis (TG/DTA) and X-ray diffraction (XRD). The structure of dried gels and glasses were investigated by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Specific surface area، pore volume، pore size and pore size distribution were evaluated by N2 adsorption/desorption technique and employing multipoint Brumauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. Differential scanning calorimetry (DSC) results were used to calculate the overall crystallization activation energy. Sol-gel process consisted of hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS)، triethyl phosphate (TEP)، Ca (NO3) 2. 4H2O and ZrO (NO3) 2. XH2O. Nitric acid was used to accelerate the hydrolysis step. The optimum H2O/TEOS+TEP ratio and nitric acid concentration were 15 and 0. 1 M، respectively. Structural analysis by NMR and FTIR revealed that glasses containing ZrO2 presents an amorphous structure in which Zr acts as a glass former and retards the crystallization of apatite. N2 absorption/desorption analysis exposed that the synthesized glasses are mesoporouse with average surface area and pore size of 133-160 m2/g and 2-4 nm، respectively. Additionally، upon adequate heat treatment at 1000 °C، the gel-glass containing ZrO2 converted into an apatite-wollastonite-zirconia glass-ceramic. Finally، ZrO2 addition increased the activation energy for apatite crystallization from 198 kJ/mol to 835 kJ/mol.