Nitridation and densification of SiO2 aerogels

Silica aerogels were nitrided by ammonia treatment at the range of temperatures from 700 degreesC to 1300 degreesC. It was found that the amount of nitrogen incorporated in silica aerogel depends on the final temperature of ammonolysis and on the time of heat treatment. The maximum amount of nitrogen introduced into the aerogel structure reached 33.1 wt%,. The specific surface area of nitrided aerogels remains high and decreases with the temperature of ammonolysis and with nitrogen content. FTIR spectra of nitrided aerogels indicated that ammonia reacts with silica aerogels to form compounds in which atoms of nitrogen are coordinated by three atoms of silicon. Nitrided aerogels can be converted into dense homogeneous oxynitride glasses containing 8.4-13.0 wt% of nitrogen by heat treatment at 1600 degreesC in vacuum or in nitrogen atmosphere. (C) 2001 Elsevier Science B.V. All rights reserved.