Effect of LiAl5O8 additions on the sintering and optical transparency of LiAlON

LiAl5O8 (zeta alumina) was reaction sintered with α-Al2O3 and AlN to produce γ-LiAlON. Zeta alumina transforms from a primitive to a face-centered cubic structure above 1290 °C with a lattice parameter similar to γ-AlON. Weight loss measurements combined with XRD suggest solubility of Li in the spinel structure at elevated temperatures. The Vickers hardness, at a 1-kg load, of the pressureless sintered LiAlON was 16.5 ± 0.5 GPa, independent of the grain size or amount of zeta alumina added, for LiAl5O8 additions ranging between 0 and 16 wt.%. In-line transmission in the visible and near-IR regions increased with increasing grain size, most likely due to pore coalescence.