Selective Corrosion Preparation and Sintering of Disperse α‐Al 2 O 3 Nanoparticles

Disperse fine equiaxed α‐Al 2 O 3 nanoparticles with a mean particle size of 9 nm and a narrow size distribution of 2–27 nm were synthesized using α‐Fe 2 O 3 as seeds and isolation via homogeneous precipitation‐calcination‐selective corrosion processing. The presence of α‐Fe 2 O 3 acting as seeds and isolation phase can reduce the formation temperature to 700°C and prevent agglomeration and growth of α‐Al 2 O 3 nanoparticles, resulting in disperse fine equiaxed α‐Al 2 O 3 nanoparticles. These α‐Al 2 O 3 nanoparticles were pressed into green compacts at 500 MPa and sintered first by normal sintering to study their sintering behavior and finally by two‐step sintering (heated to 1175°C without hold and decreased to 1025°C with a 20 h hold in air) to obtain nanocrystalline α‐Al 2 O 3 ceramics. The two‐step sintered bodies are nanocrystalline α‐Al 2 O 3 with an average grain size of 55 nm and a relative density of 99.6%. The almost fully dense nanocrystalline α‐Al 2 O 3 ceramic with finest grains achieved so far by pressureless sintering reveals that these α‐Al 2 O 3 nanoparticles have an excellent sintering activity.