Structural studies on boroaluminosilicate glasses

Two series of boroaluminosilicate glasses having varying mole ratios of B₂O₃/Na₂O (series 1) and B₂O₃/SiO₂ (series II) were prepared by conventional melt-quench method. Based on ²⁹Si and ¹¹B MAS NMR studies, it has been established that for series I glasses up to 15 mol% B₂O₃ content, Na₂O preferentially interacts with B₂O₃ structural units resulting in the conversion of BO₃ to BO₄ structural units. Above 15 mol% B₂O₃ for series I glasses and for all the investigated compositions of the series II glasses, silicon structural units are unaffected whereas boron exist in both trigonal and tetrahedral configurations. Variation of microhardness values of these glasses as a function of composition has been explained based on the change in the relative concentration of BO₄ and BO₃ structural units. These glasses in the powder form can act as efficient room temperature ion exchangers for metal ions like Cu²⁺. It is seen that the ion exchange does not affect the boron and silicon structural units as revealed by IR studies.