Low-Temperature Fabrication of Plate-like α-Al2O3 with Less NH4F Additive

Abstract

Fluorinated compounds are effective mineralization agents for the fabrication of plate-like α-Al2O3. However, in the preparation of plate-like α-Al2O3, it is still an extremely challenging task to reduce the content of fluoride while ensuring a low synthesis temperature. Herein, oxalic acid and NH4F are proposed for the first time as additives in the preparation of plate-like α-Al2O3. The results showed that plate-like α-Al2O3 can be synthesized at a low temperature of 850 °C with the synergistic effect of oxalic acid and 1 wt.% NH4F. Additionally, the synergistic effect of oxalic acid and NH4F not only can reduce the conversion temperature of α-Al2O3 but also can change the phase transition sequence.

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

“…These "seeds" serve to increase nucleation sites, thereby reducing the formation temperature of α-Al 2 O 3 , allowing the synthesis of α-Al 2 O 3 at approximately 850 • C. Additionally, several additives, especially fluorides like AlF 3 , Zn 2 F, and NH 4 F have demonstrated efficacy in lowering the calcination temperature of α-Al 2 O 3 . [16][17][18] The reduction of the transformation temperature was mainly attributed to the formation of intermediate compound of AlOF, which was considered to accelerate the mass transportation from transition alumina to α-Al 2 O 3 . This method allows the synthesis of α-Al 2 O 3 at approximately 900 • C. The molten salt method stands out as another widely employed technique for temperature reduction.…”