Containerless high energy X-ray diffraction measurements have been performed on molten Al2O3-SiO2 as a function of composition. The data show a strong distortion of the SiO4 tetrahedral units and a breakdown of intermediate range order as alumina is added. For silica-rich compositions, the X-ray pair distribution functions are consistent with the presence of 4-fold oxygen triclusters predicted by molecular dynamics simulations, where these liquids exhibit relatively high viscosities compared to other binary silicates. For higher alumina content liquids, the average cation-oxygen coordination number gradually increases with increasing Al2O3 content, but the pair distribution functions change very little with composition, suggesting the increased presence of disordered AlOn (n = 4,5,6) polyhedra are associated with low viscosity melts. A comparison of the liquid and glassy X-ray pair distributions functions at the alumina-rich mullite composition indicate a significant distortion of the polyhedra in the melt, suggesting structural changes are temperature dependent.
- SIO2-AL2O3 GLASSES