High-strength α-Al₂O₃ porous ceramics from hydratable alumina via cold sintering process

High-strength α-Al₂O₃ porous ceramics are highly valuable for applications in aerospace, chemical catalysis, and related fields due to their exceptional mechanical properties and chemical stability. However, their development has been hindered by performance degradation and high energy consumption associated with traditional high-temperature sintering methods. While the cold sintering process (CSP) can effectively address these challenges, research on fabricating phase-pure α-Al₂O₃ via CSP remains limited. In this work, α-Al₂O₃ porous ceramics were prepared from hydratable alumina by CSP without sintering aids and post-processing. The hydration characteristics of ρ-Al₂O₃ were exploited to optimize the distribution of the transient liquid phase within the system, and the existence of vapor pressure was detected. The influence of CSP parameters on the phase composition, microstructure, and mechanical properties of the samples were systematically investigated. The obtained porous ceramics exhibited a porosity of 42.3%‒34.4%, an average pore size of 463.6 nm, a compressive strength of 89.4‒140.2 MPa, a thermal conductivity ranging from 12.7 to 2.2 W/(m·K) from room temperature to 1200°C, and withstood sintering temperatures up to 1300°C. The study elucidated the nucleation of boehmite and its phase transformation to α-Al₂O₃ within the hydrothermal framework, a mechanism supported by direct experimental evidence of the vapor pressure generated in situ. This finding offers significant scientific implications for advancing CSP in the fabrication of α-Al₂O₃ porous ceramics.