Nitridation and densification of SiO2 aerogels

Silica aerogels were nitrided by ammonia treatment at the range of temperat ures from 700 degreesC to 1300 degreesC. It was found that the amount of ni trogen incorporated in silica aerogel depends on the final temperature of a mmonolysis and on the time of heat treatment. The maximum amount of nitroge n introduced into the aerogel structure reached 33.1 wt%,. The specific sur face area of nitrided aerogels remains high and decreases with the temperat ure of ammonolysis and with nitrogen content. FTIR spectra of nitrided aero gels indicated that ammonia reacts with silica aerogels to form compounds i n which atoms of nitrogen are coordinated by three atoms of silicon. Nitrid ed aerogels can be converted into dense homogeneous oxynitride glasses cont aining 8.4-13.0 wt% of nitrogen by heat treatment at 1600 degreesC in vacuu m or in nitrogen atmosphere. (C) 2001 Elsevier Science B.V. All rights rese rved.