Silicon oxynitride glasses produced by ammonolysis from colloidal silica

Abstract Silicon oxynitride glasses have been obtained by nitridation of two commercial colloidal silicas (Cab-O-Sil and Microsilica) and a SiO 2 –Na 2 O gel. The nitridation kinetics and the temperature influence over the nitridation process were studied. Crystallization and densification phenomena inhibit nitridation of SiO 2 –Na 2 O gel and Microsilica, while in the as-received Cab-O-Sil a maximum of nitridation around T g , along with an increase in T g with nitrogen were observed. The highest nitrogen contents obtained in Cab-O-Sil up to 19 wt% N are justified by its higher initial specific surface area S e . From this maximum nitrogen percentage, crystallization of α- and β-Si 3 N 4 occurs, and the powder maintains S s higher than 125 m 2 g −1 , corresponding to crystalline nanoparticles.