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

Abstract

Abstractα‐Al2O3, commonly known as corundum, plays a significant role in various industrial applications. Typically, the synthesis of α‐Al2O3 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‐Al2O3 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 AlCl3. The precursor was then processed by mechanochemical method, leading to the attainment of α‐Al2O3 at temperatures below 800°C. The resultant α‐Al2O3 was in the form of thin flakes, with significantly increased specific surface areas up to 27.9 m2/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‐Al2O3. This innovative approach not only simplifies the preparation process but also enables the production of high‐purity, large specific surface area lamellar α‐Al2O3 at lower temperatures, paving the way for more efficient and cost‐effective industrial processes.