Precipitation of SnO2 nano-crystallites from Na2O/B2O3/SnO2/(Al2O3) glasses

The system Na2O/B2O3/SnO2/(Al2O3) exhibits a fairly large glass forming range, samples with up to 10 mol% SnO2 could be prepared. The glasses were thermally treated at temperatures in the range from 580 to 820 °C. From glasses with large [Na2O]/[B2O3]-ratios, Na2SnO3 crystallized, while [Na2O]/[B2O3]-ratios ⩽ 1.125 resulted in the precipitation of SnO2. In an intermediate [Na2O]/[B2O3]-range, Na2Sn2O5 crystallized. The crystals had mainly needle-like morphology with lengths of up to some micrometers and thicknesses in the range of 20-80 nm. The glassy matrix phase and some additionally crystallized phases, such as NaBO2 or Na2Al2B2O7 could be dissolved in diluted acetic acid. Using this procedure, the SnO2 crystals were obtained as residual insoluble phase.