Property Variation in Alkali Alkaline-Earth Metaphosphate Glasses

Coefficients of helium migration, coefficients of thermal expansion, and glass-transition temperatures were measured for several series of alkali alkaline-earth phosphate glasses. The helium permeability decreases with the field strength of alkali or alkaline-earth ions in the order Na⁺ > Li⁺ and Mg²⁺ > Ca²⁺ > Ba2+. The glass-transition temperature increases and coefficient of thermal expansion decreases with increasing field strength of alkali or alkaline-earth ions. The relationship of lower molar volume, corresponding to decreased coefficients of helium diffusivity reported for other glass-forming systems, occurs in the phosphate glasses.