Structures of silicate glasses with varying sodium and fixed iron contents

Abstract

Silicate glasses have been synthesised with a fixed 8 mol percent of Fe sub(3) O sub(4) and sodium oxide varying from 12 mol percent to 20 mol percent. The environment of the Fe ion was examined by Extended X-ray Absorption Fine structure and Mossbauer spectroscopy which have shown tetrahedral coordination of oxygen around Fe regardless of the oxidation state of iron. Mossbauer data indicate increasing; distortion of these tetrahedral units and Fe sup(3+) to Fe sup(2+) ratios, with increasing sodium concentration. Raman spectroscopic studies have shown the presence of Q sup(n) linkages for n=0 to n=4. For the sodium silicate glass without iron, the single most common linkage is Q sup(3) (~ 50 percent) suggesting the role of the alkali to be disruptive to the continuity of the silica random network. For the iron containing glasses, the main linkage is Q sup(2) (approx. 65 percent). However, in the latter glasses the fraction of Q sup(3) linkages although considerably less (approx. 10percent to approx. 20 percent) than Q sup(2) is shown to increase with alkali content due to the concomitant rise of Fe sup(3+) ions which are known to be network formers.