Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol–gel route under seeding

Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol–gel route using polyhydroxoaluminum (PHA) and RECl3 solutions under α-alumina (∼ 75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900 °C under 5 mass% α-alumina seeding, consisted of ∼ 80-nm α-alumina particles and γ-alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 μm could be obtained at 1400 °C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 μm at 1400 °C.