Preparation and properties of high nitrogen content mixed alkaline-earth oxynitride glasses.
Sharafat Ali
A series of mixed alkali-earth element containing high nitrogen content oxynitride glasses (CaAESiON), with AE = Mg, Sr, Ba, and nominally equal (Ca/AE):Si:O:N ratios were prepared in order to investigate the compositional dependencies of physical properties on alkali earth element composition. The glasses were prepared by melting mixtures of AEH2, SiO2 and Si3N4 powders in nitrogen atmosphere at 1600–1700oC and characterized by X-ray powder diffraction and scanning and transmission electron microscopy. Cation and anion glass compositions were determined by respectively energy dispersive X-ray analysis and combustion analysis. The physical properties were found to vary linearly with the degree of substitution of Ca by the AE elements. The density of the glasses increases substantially with an increase in the AE atomic mass and slightly with an increase in nitrogen ratio. Ba containing glasses shows high value of density 3.99 g/cm3. Glass transition temperatures are found to be higher for Mg glasses, ca. 900C, in comparison with Ba glasses, ca. 850C. The hardness of Mg containing glasses shows high values ,up to 12.2 GPa, and decreases for Ca , Sr and Ba containing glasses. The refractive index increases upon substitution by Sr and Ba, up to 1.97, and decreases upon substitution by Mg. The observed response in the glass properties to changes in compositions appears to reflect modifications in the bonding within the glass network. Keywords: Oxynitride glass; mixed modifier; high nitrogen content; glass transition temperature; hardness;.