Seeding of the Reaction-Bonded Aluminum Oxide Process

The effect of the initial α-Al₂O₃ particle size in the reaction-bonded aluminum oxide (RBAO) process on the phase transformation of aluminum-derived γ-Al₂O₃ to α-Al₂O₃, and subsequently densification, was investigated. It has been demonstrated that if the initial α-Al₂O₃ particles are fine (～0.2 μm, i.e., 2.9 × 10¹⁴γ-Al₂O₃ particles/cm³), then they seed the phase transformation. The fine α-Al₂O₃ decreases the transformation temperature to ～962°C and results in a finer microstructure. The smaller particle size of the seeded RBAO decreases the sintering temperature to as low as ～1135°C. The results confirm that seeding can be utilized to improve phase transformations and densification and subsequently to tailor final microstructures in RBAO-derived ceramics.