Structural Analysis of Na₂O-B₂O₃ Melts by Pulsed Neutron Total Scattering Method and Molecular Dynamics Simulation

Abstract

In order to obtain direct information on the structure of sodium borate melts which are of use in metallurgical processes, pulsed neutron total scattering measurements have been carried out on 10mol%Na₂O- and 30mol%Na₂O-B₂O₃ melts at 1073 K, in addition to the previous measurement on pure B₂O₃ melt. Molecular dynamics (MD) calculations have also been made on pure B₂O₃ and 30mol%Na₂O-B₂O₃ melts at 1073 K.
With increase in Na₂O content, the first peak of RDF(r), representing B-O correlation, spread asymmetrically to larger r side, and the coordination number of O atoms around a reference B atom n_B-O increased from 3.0 to 3.5, showing variation of B-O correlation. This increase in n_B-O could be explained by the simple assumption that two BO₃ triangle structure units are converted to two BO₄ tetrahedron structure units with the addition of one Na₂O molecule in the same way as in Na₂O-B₂O₃ glasses. These n_B-O values also agreed well with those obtained by MD calculations, which showed the clear evidence of the appearance of BO₄ units that the distribution of O-B-O bond angle spread from 120° to smaller angle side for 30mol%Na₂O-B₂O₃.
From these results, it is safely concluded that a part of BO₃ triangle structure units converted to BO₄ tetrahedron structure units with the addition of Na₂O up to 30 mol% to B₂O₃ melt in the same way as in Na₂O-B₂O₃ glasses.