Transparent polycrystalline nanoceramics consisting of triclinic Al2SiO5 kyanite and Al2O3 corundum

Transparent polycrystalline nanoceramics consisting of triclinic Al2SiO5 kyanite (91.4 vol%) and Al2O3 corundum (8.6 vol%) were fabricated at 10 GPa and 1200-1400 degrees C. These materials were obtained by direct conversion from Al2O3-SiO2 glasses fabricated using the aerodynamic levitation technique. The material obtained at 10 GPa and 1200 degrees C shows the highest optical transparency with a real in-line transmission value of 78% at a wavelength of 645 nm and a sample-thickness of 0.8 mm. This sample shows equigranular texture with an average grain size of 34 +/- 13 nm. The optical transparency increases with decreasing mean grain size of the constituent phases. The relationship between real in-line transmission and grain size is well explained by a grain-boundary scattering model based on a classical theory.