Energetics of oxidation of RE-Si-Al-O-N glasses

Enthalpies of drop solution in molten 52 wt.% LiBO₂-48 wt.% NaBO₂ at 1078 K were measured for RE_1.1Si_1.7Al_0.6O_6-1.5xN_x (x = 0, 0.2, 0.4, 0.6, 0.8) glasses for RE = Nd, Gd, Dy, Er, and Y. Linear relations between enthalpies of formation from elements and nitrogen content indicate that, within the experimental composition range, sites occupied by nitrogen ions are approximately equivalent in energy for a given substitutional series. The energetics of different rare-earth SiAlON glasses appears to be dominated by differences in the acid/base character of the cations. The onset glass-transition temperature increases linearly with increasing nitrogen content for the same rare earth and with decreasing rare-earth ionic radius for the same nitrogen content.