Synthesis and Phase Transition Mechanism of Monodisperse Cubic Porous α‐Al ₂ O ₃

ABSTRACT

To address the bottleneck issues of irregular morphology and severe agglomeration in conventional α‐Al ₂ O ₃ powders, this study employed an alcohol‐water synergistic hydrothermal synthesis (under optimal conditions of a 1:1 alcohol–water volume ratio, 200°C, and 11 h) to successfully prepare monodisperse cubic precursors. The complete crystallographic transition pathway and mechanisms during the thermodynamic evolution of the precursor—encompassing dehydration, desulfurization, amorphous network collapse, and the final evolution into α‐Al ₂ O ₃ —were systematically elucidated. Multiscale characterization reveals that the calcined α‐Al ₂ O ₃ successfully retains the microscale cubic morphology of its precursor, maintaining excellent monodispersity without experiencing melting or severe agglomeration during the high‐temperature phase transition. Concurrently, driven by the volatilization and decomposition of lattice water and sulfate groups, alongside atomic rearrangement during the phase transition, the outward release of gaseous sulfur compounds acts as an in‐situ pore‐former. This process reconstructs a highly interconnected, sponge‐like porous framework within the particles, thereby increasing the specific surface area to 6.41 m ² /g. By integrating classical thermodynamic and kinetic models, this study provides profound insights into the burst nucleation and anisotropic growth mechanisms of the cubic precursors, as well as the synergistic effects of the high‐temperature phase transition and gas evolution in reconstructing the porous α‐Al ₂ O ₃ network. This research provides a prospective theoretical foundation and technical pathway for the large‐scale preparation of uniform, monodisperse α‐Al ₂ O ₃ powders.