Porous ceramics with near‐zero shrinkage and low thermal conductivity from hazardous secondary aluminum dross

Abstract Herein, a simple, versatile, and low‐cost approach has been proposed to realize the green utilization of secondary aluminum dross, the hazardous solid waste, namely directly sintering dry‐pressed green bodies from secondary aluminum dross to fabricate porous ceramics according to high‐temperature foaming process spontaneously without adding spare foaming agents. Aluminum nitride (AlN) in secondary aluminum dross was employed to realize high‐temperature foaming due to its oxidation, which makes traditional AlN and salts removal process needless. Moreover, near‐zero shrinkage or even expansion during sintering of porous ceramics have occurred because in‐situ foaming process together with the oxidation of Al particles well offset the sintering shrinkage. After sintering at 1400°C for 2 h, porous ceramics composed of α‐Al 2 O 3 and spinel phases with open porosity of 37.91%, sintering expansion rate of 1.13%, flexural strength of 45.67 MPa, and thermal conductivity of 0.97 W/(m·K) have been prepared. Cenospheres as pore‐forming agents have been added to further improve the porosity, and alumina‐based porous ceramics with open porosity of 28.39%–43.20% and flexural strength of 15.80–52.48 MPa have been obtained. This effective solution for recycling secondary aluminum dross could supply high‐performance porous ceramics, which is expected to be applied in the fields of light‐weight structural components and thermal insulations.