Physical and Structural Characteristics of Gel-Derived Glasses Prepared via Different Drying Procedures

The monolithic gels were prepared through different drying procedures including super critical, infrared wave lengths and traditional drying methods. Dense and transparent glasses with chemical composition of 66SiO2-18B2O3-7Al2O3-6K2O -3BaO (in wt.%) were obtained after controlled heat treatment of the dried porous xerogels at 950°C for 2 h in air atmosphere. The chemical bonding as well as different properties of the prepared gels and the relevant glasses were investigated by means of Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmitt-Teller (BET) and UV-Vis spectrometer. The results indicates that different drying conditions affect the average pore size and the total pore volume of the studied gels. The mean pore size was found to be 8.7, 2.4 and 3.2 nm for super critical, IR radiation and slow drying in air respectively. The glass network structure was significantly changed by heat treatment temperature such that the B-O-Si bonds were formed only after 450°C. It was found that the gel dried under super critical condition was unable to reach to its full density under the sintering conditions adopted in this study.