Alumina ceramic foams with an open hierarchical pore structure prepared by oxidation hollowing of aluminum

Abstract The application of high‐porosity open‐cell alumina ceramic foams has been hindered due to their significant sintering shrinkage and low strength. In this study, alumina ceramic foams with open‐cell and hierarchical structures were fabricated by utilizing spherical aluminum powder as raw material and polyurethane sponge as a template. Based on the Kirkendall effect, the near‐net size fabrication of alumina ceramic foams was realized through the expansion generated by the oxidation hollowing of sphere aluminum powder, and the mechanical properties of ceramic foams were optimized by constructing micrometer alumina hollow spheres. The oxidation hollowing mechanism of sphere aluminum powder was investigated using X‐ray diffraction, Raman spectroscopy, and scanning electron microscope, the possible reaction process is Al → γ‐Al 2 O 3 → θ‐Al 2 O 3 → α‐Al 2 O 3 . Cracks induced by sintering shrinkage caused a sharp decline in the mechanical properties of ceramic foams when the sintering temperature exceeded 1100°C. By adjusting impregnation times of foam slurry, alumina foams with a bulk density of 0.23–0.48 g/cm 3 , total porosity of 94.3%–87.8%, compressive strength of 0.79–1.35 MPa, and sintering expansion of 0.76%–1.40% were prepared at 1100°C. This study provided a feasible strategy and theoretical basis for optimizing the mechanical properties of open‐cell alumina ceramic foams.