Viscosity of high-nitrogen content Ca-Si-O-N glasses

The viscosity of three high-nitrogen content Ca-Si-O-N glasses, with 30-58 e/o N and 36-39 e/o Ca, was determined by micro-indentation. The measurements were made using an automated set-up, designed and built in-house, capable of measurements up to 1200 degrees C with applied loads of 0.01-15 N. The viscosity increases significantly with the nitrogen content and reaches viscosity values close to reported values for rare-earth silica oxynitride glasses. The glass transition temperatures range between 878 and 995 degrees C and are in very good agreement with values measured by differential thermal analysis. The apparent viscosity activation energies are very high, ranging from 855 to 2170 kJ/mol. The glasses can accordingly be classified as being both very refractory and very fragile. Implications of the viscosity values and mechanical properties of the glasses for their structures are discussed. (c) 2010 Elsevier Ltd. All rights reserved.