Preparation of monolithic oxynitride glasses by sol-gel method

Monolithic aerogels and xerogels were obtained by drying gels at super critical condition and ambient pressure after aging at room temperature for various lengths of time. Heat treatment of porous xerogels at low temperature (<= 1000 degrees C) in air and flowing ammonia resulted dense, homogeneous oxide and oxynitride glasses, respectively. The chemical bonding state and properties of gels and glasses were investigated employing Fourier transform infrared spectroscopy (FTIR), dilatometry, and Brunauer-Emmitt-Teller (BET) methods. Nitrogen content of oxynitride glasses were determined by oxygen nitrogen analyzer. Based on the compressive strength measurement, the strength of gels was increased from 0.73 to 1.5 (Mpa) with aging time. The pore size distribution was also changed significantly during aging process via hydrolysis and condensation reactions; the latter is confirmed by the FTIR spectra. The dilatometric softening point temperature of glasses and their micro-hardness were increased after nitridation process. Spectroscopic evidence indicated that nitrogen was chemically dissolved in the network of glass and its content was increased from 0.67 to 2.08 (wt.%) after nitridation for 5 and 15 h, respectively. (C) 2014 Elsevier B.V. All rights reserved.