Sol gel synthesis and spark plasma sintering of lanthana-doped alumina glass

Amorphous materials of eutectic composition in the La2O3-Al2O3 system were prepared from powders synthesized by the sol-gel method and then flame sprayed to form amorphous transparent beads similar to 10-150 mu m in diameter. These were subsequently consolidated by the spark plasma sintering (SPS) method. The final density of sintered samples showed a dependence on temperature and the applied pressure. The transmittance increased with temperature up to 860 degrees C, then decreased with further increase in temperature, as a consequence of crystallization. The measured glass transition and crystallization temperatures, T-g and T-x, are 845 and 905 degrees C, respectively. Crystallization below T-x is likely the consequence of the applied electric field during sintering. The highest observed transmittance in the red-end of the visible region (650 nm) was determined to be about 40%. The transmittance of sintered amorphous samples in the IR region was between about 50% and 60% with a significant broad absorption band at about 2.9 mu m. The occurrence of this band is attributed to the stretching of the O-H bond of residual OH species in the samples. (C) 2012 Elsevier B.V. All rights reserved.