Preparation of α-Al2O3 by low-temperature calcining γ-Al2O3 with α-phase seed in-situ obtained by ball milling

Due to the high activation energy barrier and the sporadic nature of nucleation, the temperature required for the transition from cubic dense & gamma;-Al2O3 to tripartite & alpha;-Al2O3 is as high as 1100-1200 degrees C. In this work, a two-step strategy was employed to reduce the phase transformation temperature, and prepare & alpha;-Al2O3 particles with good dispersion. As the first step, 10 nm sheet & gamma;-Al2O3 was obtained by ammonium aluminum carbonate (AACH) decomposition, which was more favorable to the crystal transformation in the next ball-milling processing. In the second step, & gamma;-Al2O3 powder with partial & alpha;-Al2O3 produced in situ by ball-milling & gamma;-Al2O3 was calcined, and & alpha;-Al2O3 nanoparticles were obtained at just 850 degrees C. The content of the & alpha;-Al2O3 is determined by the Rietveld Refine method. The relationship between ball-milling time and & alpha;-Al2O3 content was clarified, and the effect of & alpha;-Al2O3 content on the transformation temperature and morphology of & gamma;-Al2O3 was discussed. The results showed that the & alpha;-Al2O3 content rises with the increase of ball milling time, and spherical & alpha;-Al2O3 nanoparticles can be obtained when the & alpha;-Al2O3 content is 5 %. The addition of & alpha;-Al2O3 seeds reduces the phase transition temperature but agglomeration exists. Our proposed two-step low-temperature calcination strategy is an important method for the preparation of alumina nanoparticles