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.