EFFECT OF ZNO ON THE PROPERTIES OF (100-X)(NAPO3)-XZNO GLASSES

Glasses of the (100-x)(NaPO3)-xZnO system with 0 less than or equal to x less than or equal to 33.3 mol% have been prepared with a conventio nal melting procedure. The density and index of refraction of (100-x)( NaPO3)-xZnO glasses increases linearly with x, in accordance with the network modifying behavior of ZnO. For x less than 15%, the glass tran sition temperature, the activation energy for viscous flow and the aqu eous durability are affected by the decrease in phosphate chain length , owing to the very weak zinc-oxygen bonding energy. For larger x (15 less than or equal to x less than or equal to 33.3), these properties increase because the covalent character of zinc-oxygen bonds enables t he formation of a mixed zinc-phosphate network. (C) 1998 Elsevier Scie nce B.V.