Comparative synthesis of Al2O3 via three wet-chemical methods: Implications for sintering behavior and microstructural evolution

Wet-chemical method (WCM) provides a versatile and potentially scalable route for preparing alumina (Al 2 O 3 ) powder under relatively mild processing conditions. However, a comparative analysis of the structural evolution, phase transformation, and sintering behavior across different WCM-derived precursors remains lacking. In this study, three WCMs—direct precipitation (DP-Al 2 O 3 ), gas-bubbling-assisted precipitation (GB-Al 2 O 3 ), and sol-gel synthesis (SG-Al 2 O 3 )—were adopted to prepare Al 2 O 3 precursor powders. Their thermal evolution was then compared, focusing on temperature-dependent phase transformations, particle coarsening, and particle morphology evolution. Sintering behavior was likewise assessed under identical thermal profiles. Among the as-synthesized precursors, GB-Al 2 O 3 exhibits the smallest agglomerate size. Both DP-Al 2 O 3 and GB-Al 2 O 3 remain amorphous after calcination at 600 °C, whereas SG-Al 2 O 3 retains residual boehmite alongside amorphous Al 2 O 3 . Phase evolution pathways diverge: DP-Al 2 O 3 and SG-Al 2 O 3 follow the conventional γ-Al 2 O 3 →θ-Al 2 O 3 →α-Al 2 O 3 sequence, while GB-Al 2 O 3 undergo a direct γ- to α-phase transition, bypassing the θ-phase. The SG-Al 2 O 3 displays the lower densification onset temperature than DP-Al 2 O 3 and GB-Al 2 O 3 . All three ceramics exhibit heterogeneous densification, resulting in microstructural inhomogeneity featuring coexisting porous and locally densified domains. These results provide actionable guidance for rationally selecting and optimizing WCMs to tailor the particle size, morphology, and phase composition of Al 2 O 3 particles.