Effect of Sintering Aids Synthesized via Combustion of Aluminum Nitrates on Properties of Al₂O₃–3YSZ Ceramics

We have studied the effect of α-Al₂O₃ powders added as sintering aids (15 wt %) on the hardness and porosity of Al₂O₃–3YSZ ceramics. The alumina powders were synthesized via combustion of aluminum nitrates or by solution combustion synthesis (SCS) with the use of glycine and urea as organic reducing agents. The use of aggregates of submicron alumina particles that remained intact after SCS was shown to prevent preparation of high-density ceramics. After sintering at 1550°C, the relative density of the ceramics was 75 to 85% on account of considerable closed porosity. The microhardness of the ceramics ranged from 1 to 11.1 MPa and correlated with the variations in their density and porosity. A reference sample, containing pure-grade alumina additions, had the highest relative density, 98%, without closed porosity.