The effect of nitrogen on viscosity of La-Si-Mg-O-N glasses by compressive creep and dilatometry

Viscosity as a function of temperature and nitrogen content and the
glass transition temperature (T-g) were investigated in
20La-6OSi-20Mg-O-N glasses with nitrogen contents varying from 0 to 28
eq.% (e/o) using compressive creep and dilatometric experiments.
Although T-g obtained from dilatometry were 6-12 degreesC lower than
the lower limit of the transition temperature range from creep, both
methods revealed identical and linear dependencies of T-g on N content.
The average activation energy was 1184 +/- 36 kJ/mol and viscous flow
remains the deformation mechanism in all glasses regardless of nitrogen
content. Addition of 28 e/o N in oxide glass resulted in an increase of
T-g by 94-105 degreesC and an increase in viscosity of around 5 orders
of magnitude. These changes are greater than those reported in similar
Al-containing glasses. Linear increase of T-g and compactness of the
glass with nitrogen content result from enhanced cross-linking of the
glass network.