Phase Transformation of Transition-Alumina upon Hastened Sintering

The potential uses of hastened spark plasma sintering (SPS) for the fabrication of metastable Al₂O₃ porous supports with ultra-filtering applications as well as for the sintering of transition aluminas are investigated. Submicron-sized transition aluminas were prepared by reacting AlCl₃·6H₂O with NH₄OH, and calcining at 1173K for 1h. SPS runs on these powders were carried out within 1∼3min, applying 40 MPa from 1223 to 1883 K. To some extent it is possible to retain both the metastability and fine nature (1-2μm) of precursors. Transition-Al₂O₃ filters with a variety of porosity are fabricated by this route. Polymorphism proceeds according to: γ δ θ → γ δ θ α → δ θ α → θ α → α and is practically finished near to 1513 K. Massive α-Al₂O₃ transformation occurs exceeding 1313 K. Specimens of virtually full density are obtained at 1883 K.