Fully sintered alumina with a higher Vickers hardness prepared using a gel-casting process

The dispersant (commercial ammonium polyacrylate), sintering additive (Mg²⁺), and chelating agent (EDTA) effects on the Zeta potential and rheological behavior of alumina slurry with high solid content were investigated. The alumina ceramic green microstructures and sintered microstructures prepared using slurries with different additives using the gel-casting process were also studied. It was observed that the dispersion deteriorated after adding Mg²⁺. Slurry simultaneously added with dispersant and EDTA-chelated Mg²⁺ produced higher absolute Zeta potential value and low viscosity due to EDTA chelating with Mg²⁺. The sample added with dispersant and EDTA-chelated Mg²⁺ exhibited a uniform green microstructure, high relative sintered density (99.5% theoretical density), and a nearly pore-free microstructure with an average grain size of about 1.5 μm. For the first time to our knowledge, the maximum Vickers hardness (22 GPa) was obtained for alumina simultaneously added with Mg²⁺ and EDTA, pressureless sintered at 1500°C in air.