Fabrication of Highly Textured Fine‐Grained α‐Alumina by Templated Grain Growth of Nanoscale Precursors

0001] textured alumina ceramics with a fine grain size were fabricated between 1400°C and 1600°C via templated grain growth (TGG) using fine alumina platelets (~0.6 and ~3 μm diameter) aligned by tape casting in either a 50 nm α‐Al₂O₃ matrix powder, or in a seeded boehmite sol. The 3 μm templates could be readily aligned by tape casting in both matrices (orientation parameters r = 0.27 and 0.18, respectively), whereas 0.6 μm diameter templates were well aligned in the seeded boehmite sol only (r = 0.29). Improved alignment in boehmite sols is attributed to inorganic gelation, resulting in a strongly pseudo‐plastic rheology that preserves template alignment against the influence of Brownian motion. The in situ formation of fine α‐Al₂O₃ matrix after transformation in the seeded boehmite system results in a higher driving force for TGG and improves texture development. The combination of 3 μm templates with a seeded boehmite matrix results in extremely high texture qualities (texture fraction f = 0.97–0.99, r = 0.17) while maintaining a relatively fine grain size (5–10 μm in diameter and 1.5–3 μm in thickness). Although undoped samples can be fully textured at 1600°C, adding as little as ~0.25 wt% CaO/SiO₂ dopant improves TGG kinetics and yields full texture at 1400°C.