STRUCTURAL-ANALYSIS OF NA2O-B2O3 MELTS BY PULSED NEUTRON TOTAL SCATTERING METHOD AND MOLECULAR-DYNAMICS SIMULATION

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 1 073 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 1 073 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-degrees to smaller anlge side for 30mol%Na2O-B2O3. From these results, it is safely concluded that a part of BO3 triangle structure units is converted to BO4 tetrahedron structure units with the addition of Na2O up to 30mol% to B2O3 melt in the same way as in Na2O-B2O3 glasses.