Delayed Coarsening of Submicron‐Grained Transparent Alumina Ceramic

Submicron grain size Al 2 O 3 has been considered to be an important transparent ceramic for windows, domes and nozzles for semiconductor etching machines. This study emphasized on density, pore size distribution, and sintering activity of Al 2 O 3 green bodies formed by pressure filtration (PF) and spontaneous coagulation casting (SCC), using 180 nm particles as starting materials. The results reveal that de‐binded PF bodies possess higher relative density (65%), smaller pores size (∼39.6 nm) and narrower pore size distribution compared to SCC bodies, all of which contributed to a lower densification activation energy of 1.63 eV. For further hot isostatic press (HIP) sintering, the PF body was pre‐sintered to 96% relative density at 1210°C, while the SCC body needed 1250°C to reach the same density. After 1250°C HIP treatment, the average grain size, in‐line transmittance, and flexural strength of the PF ceramics reached 0.46 µm, 55.4%, and 829 MPa, respectively. In contrast, those of SCC ceramics were 0.54 µm, 51.6%, and 696 MPa, respectively. These findings demonstrate that high‐density green bodies possess a low activation energy for densification. They could be sintered at lower temperatures. Thus, grain growth was constrained, and superior mechanical and optical performance were obtained. It is therefore concluded that optimizing forming techniques to enhance green body with high density and narrow pore size distribution is an effective strategy for fabricating high‐performance transparent alumina ceramics and other ceramics at lower temperatures.