Fabrication and microstructural characterization of the novel optical ceramic consisting of α-Al2O3@amorphous alumina nanocomposite core/shell structure

In this study, α-Al2O3@amorphous alumina nanocomposite core-shell structure was synthesized from AlCl3 and the commercial α-Al2O3 nanoparticles as the starting materials via a wet chemical route. The results indicated that the shell material mainly comprised of ammonium chloride and boehmite phases. Boehmite was transformed to the amorphous and γ-Al2O3 phases after the calcination process and the shell material was completely converted to γ-Al2O3 at 1000 °C. However, for the α-Al2O3@amorphous alumina core-shell nanoparticles were completely converted to α-Al2O3 at 1000 °C. It can be concluded that α-Al2O3 core particles, as the seed crystalline, help to transforming of γ-Al2O3 phase as the shell material directly without forming transitional phases to α-Al2O3. The optical polycrystalline alumina was fabricated using spark plasma sintering of α-Al2O3@amorphous alumina core-shell nanocomposite. The body sintered has a final density of ∼99.8% and the in-line transmittance value is ∼80% within the IR range.