Lowering the synthesis temperature of α‐Al₂O₃ by increasing the content of pentacoordinate aluminum in the precursors

Abstract α‐Al 2 O 3 , commonly known as corundum, plays a significant role in various industrial applications. Typically, the synthesis of α‐Al 2 O 3 requires elevated temperatures exceeding 1200°C, which results in reduced specific surface area and increased particle size due to high‐temperature calcination. In this study, α‐Al 2 O 3 powder was primarily investigated. The precursor was prepared by non‐hydrolytic sol‐gel (NHSG) method, employing alcohols and other nonaqueous oxygen donors in nucleophilic substitution reactions with AlCl 3 . The precursor was then processed by mechanochemical method, leading to the attainment of α‐Al 2 O 3 at temperatures below 800°C. The resultant α‐Al 2 O 3 was in the form of thin flakes, with significantly increased specific surface areas up to 27.9 m 2 /g. Upon characterizing the precursors post‐ball milling, a large amount of pentacoordinate aluminum was observed. The pentacoordinate aluminum has activated the alumina lattice and increased the phase transition rate, a key factor in the low temperature preparation of α‐Al 2 O 3 . This innovative approach not only simplifies the preparation process but also enables the production of high‐purity, large specific surface area lamellar α‐Al 2 O 3 at lower temperatures, paving the way for more efficient and cost‐effective industrial processes.