Properties of Na2O-Al2O3-B2O3 glasses

The density and transformation temperature of (30 - y)Na2O . yAl(2)O(3). 70 B(2)O(3) glasses show a minimum at Al2O3Na2O approximate to 1. The molar vo lume increases with increasing Al2O3 concentration and it seems to be const ant for Al2O3/Na2O greater than or equal to 1. There is a slight increase i n the thermal expansion coefficient up to Al2O3/Na2O approximate to 0.9 fol lowed by a fast decrease. It is assumed that up to Al2O3/Na2O = 1. Na2O ass ociates preferentially with Al2O3 to form AlO4 tetrahedra. Infrared spectra are consistent with this assumption, There is a linear dependence between the electric resistivity and the activation energy. Both of these quantitie s increase with increasing Al2O3 content. It is concluded that the conducti on parameters are determined by the Na+ - Na+ distance. (C) 2001 Elsevier S cience B.V. All rights reserved.