High-surface-area corundum by mechanochemically induced phase transformation of boehmite

In its nanoparticulate form, corundum (α-Al₂O₃) could lead to several applications. However, its production into nanoparticles (NPs) is greatly hampered by the high activation energy barrier for its formation from cubic close-packed oxides and the sporadic nature of its nucleation. We report a simple synthesis of nanometer-sized α-Al₂O₃ (particle diameter ~13 nm, surface areas ~140 m² g^-1) by the mechanochemical dehydration of boehmite (γ-AlOOH) at room temperature. This transformation is accompanied by severe microstructural rearrangements and might involve the formation of rare mineral phases, diaspore and tohdite, as intermediates. Thermodynamic calculations indicate that this transformation is driven by the shift in stability from boehmite to α-Al₂O₃ caused by milling impacts on the surface energy. Structural water in boehmite plays a crucial role in generating and stabilizing α-Al₂O₃ NPs.