Effective Parameters in Synthesis and Properties of Monolithic Oxynitride Glasses Prepared by Sol-gel Method

The monolithic oxynitride glasses in SiO2-Al2O3-B2O3 system were synthesized using sol-gel method. The porous, dried gels were heated in flowing ammonia for different times and varying temperatures. The nitrogen content of the oxynitride glasses was determined using an oxygen-nitrogen analyzer. The chemical bonding state and properties of glasses were investigated by means of Fourier transform infrared spectroscopy, dilatometry, and Vickers hardness methods. The crystallization behavior of glasses was studied with X-ray diffraction. Spectroscopic evidence indicated that nitrogen was chemically dissolved in the glass network. The results showed that the chemical composition of the glass has an effect on the nitridation processes. The nitrogen content of the glasses was increased to 3.8% wt. by increasing the soaking time of nitridation from 2 to 15h. The dilatometric softening point temperature of the glasses was increased approximately 25°C, the micro-hardness value reached 10.89 GPa and thermal expansion coefficient was decreased from 3.88×10-6 to 3.39×10-6 after the nitridation process at optimal composition. The X-ray diffraction pattern of the glasses confirmed that nitrogen does not enter the crystalline phase.