VIBRATIONAL STUDY OF THE ROLE OF TRIVALENT IONS IN SODIUM TRISILICATE GLASS

The structure of glasses in the system Na2O . xR2O3 . (3 - 2x)SiO2 (R = Al, B) has been studied by employing Raman and infrared reflectance spectroscopies. These particular glass compositions were chosen for elucidating the role of aluminum and boron substitution on glass structure and properties while keeping the Na/(Si + R) ratio fixed. In the presence of aluminum, the equilibrium 2Q3 double-line arrow pointing left and right Q4 + Q2 shifts to the left. The role of boron was found to be the opposite, since it induces the destruction of the Q3 species and the creation of the highly charged Q2 and Q1 species, as well as the fully polymerized Q4 silicate units. The combined far-infrared and XPS results on the same glasses suggest that the average charge density of sites populated by sodium ions is smaller in aluminosilicate than in borosilicate glasses.