Structural role of RO and Al2O3 in borate glasses using an ultrasonic technique

The ternary alkaline earth aluminoborate glasses RO-Al2O3-B2O3, where R = Mg, Ca, Sr, have been prepared by the normal quenching method. Ultrasonic velocities and attenuation were measured in these glasses using the pulse-echo technique to explore the structural role of RO and Al2O3 in these glasses. From the measured densities and velocities, various parameters such as elastic moduli, microhardness and Poisson's ratio have been determined. Results obtained are discussed in terms of the field strength of the interstitial cation, molar ratio (Al2O3/RO), fraction of four coordinated boron atoms, number of network bonds per unit volume, average cross-link density and fractal bond connectivity of the network. It was found that the network connectivity of these glasses increases in the order Mg > Ca > Sr. Makishima and Mackenzie theory has been applied to correlate the experimental and theoretical data and good correlation was observed. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.