DENSITY-STRUCTURE CORRELATIONS IN NA2O-AL2O3-SIO2 GLASSES

Density of Na2O-Al2O3-SiO2 glasses (with Al2O3/Na2O < 1) was analyzed to determine the volumes of structural units. Analysis is based on the assumption that for Al2O3/Na2O < 1 aluminum ions enter the structure in the form of AlO4 tetrahedra. There is a unique dependence of densit y on the ratio Na2O/SiO2 and the Al2O3 concentration has nearly no eff ect on density. In such glasses the change in density due to the struc tural units in the silicate network is always compensated with an oppo site and equivalent change due to the AlO4 groups. The resultant chang e in the rate of formation of the silicate structural units is also eq ual and opposite to the change in the rate of formation of AlO4 groups . The estimated volumes of the structural units help to calculate the density for different compositions. (C) 1998 Elsevier Science B.V. All rights reserved.