Alumina/YAG 20 vol% composites prepared by the dawsonite thermal decomposition

The co-precipitation of alumina/YAG precursor from the aqueous solution of aluminum and yttrium nitrates with ammonium carbonate results in ammonium dawsonite (NH4Al(OH)2CO3) with yttrium built into its structure. The decomposition of dawsonite at elevated temperatures leads to the formation of γ-Al2O3. The δ- and θ-Al2O3 modifications appear at higher and higher temperatures. A full transformation to α-Al2O3 and YAG occurs at the temperatures higher than 1230 °C. The starting powder for sintering experiments was prepared using the co-precipitated precursor calcination at 600 °C. Seeding of such a powder with 5 wt% α-Al2O3 proved to be necessary in order to receive the dense composite material at 1500 °C. Such a material shows much lower wear susceptibility as compared to the dense pure alumina polycrystal. The unseeded powder led to the high porosity samples and showed symptoms of a discontinuous grain growth.