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

Abstract

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 O2. 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.

Hierarchical porous MgAl2O4 ceramic in situ structured by hollow particles: Low‐shrinkage and high‐strength

“…The primary reason for this phenomenon is attributed to the formation of a hollow structure in Al powder during the oxidation process, which results in a volume expansion that counteracts the sintering shrinkage. Sometimes the expansion generated is greater than the shrinkage, such as our previous studies 9 that have reported negative shrinkage (expansion) in samples sintered at 1400°C. But in this work, due to the inclusion of a solid‐state reaction within the system, the resulting sample will not undergo expansion.…”

“…5,6 One recent effective approach involves utilizing the Kirkendall effect for the production of hollow particles. 7 Prior research 8,9 has demonstrated that the differential diffusion rate between metal Al and oxygen can be leveraged to create pores through vacancy migration, thereby enriching the internal pore structure of the material. In addition, the expansion of particles can offset sintering shrinkage.…”