A novel process to high-strength and controlled-shrinkage Al₂O₃ foams with open-cell by Al powder hollowing technology

Ceramic foams with open-cell structures have attracted extensive attention due to their unique structure and superior properties. But these materials often exhibit the weakness of high sintered shrinkage and low strength at high porosity levels. In this work, novel ceramic foams with open-cell structures have been obtained using Al powder by combining direct foaming and gelation freezing (DF-GF). The foams are assembled by hollow Al2O3 particles resulting from the Kirkendall effect, in which expanded particles overcome the shrinkage of sintering. The influence of sintering temperature on the microstructure and properties of foams are investigated. The Al2O3 foams show near-zero-shrinkage at 1773 K after undergoing the process of first expansion and then shrinkage. Compared to other conventional open-cell foam, this foam displays relatively high compressive strength of 0.35-2.19 MPa at high porosity levels of 89.45%-94.45%, attributed to hierarchical pore structure and reaction bonding between Al and O-2. This method from pore structure design provides a novel route for the preparation of controlled shrinkage and high-compressive strength alumina foam with open-cell toward potential application.