Preparation And Characterization Of Fine-grained α-Al₂O₃Powders With High-purity

In this paper, fine-grained a-alumina powders with high-purity were synthesized using boehmite or ammonium alumina carbonate hydroxide (AACH) as precursors after the calcinations process. The obtained precursors and final α-Al2O3powders were characterized in detail by XRD, SEM, TEM, TG-DSC, and particle size distribution analysis. The effect of experiment parameters, process technology and calcinations process on the properties of precursor samples and final α-Al2O3powder was investigated. The relationship between the preparation parameters and the microstructures of the materials are established, which might provide a theoretical basis for the synthesis of precursors and α-Al2O3with good performance.1. Preparation of fine-grained a-alumina powders with high-purity from boehmite with seeding additionFine-grained a-alumina powder was prepared from boehmite sol with pseudo-boehmite as seed. The effect of the seed on the formation temperature and the particulate properties of α-Al2O3was investigated using XRD, SEM, TEM, TG-DSC and particle size distribution analysis. TG-DSC and XRD results showed that the phase transformation from prepared boehmite to α-Al2O3begins to occur at-1250℃with vermicular agglomerated particles obtained, but the phase transition for as-prepared pseudo-boehmite could take place at～1150℃. When a small amount of pseudo-boehmite were added into boehmite sol, during calcinations α-Al2O3particles formed in situ from pseudo-boehmite at lower temperature can play a role as seed nucleation, which then induce the phase transformation from boehmite precursor to α-Al2O3and obviously lowered the tranformation temperature. The experimental results showed that the obtained α-Al2O3powders had an average particle size of-250nm with high purity, good dispersity and narrow particle size distribution. With the increasing of the seed amount, no remarkable change was observed in the average particle size of α-Al2O3particles, but the particle size distribution became narrower.2. Preparation of fine-grained a-alumina powders with high-purity by thermal decomposition of AACHFine-grained α-alumina powder was prepared by thermal decomposition of ammonium aluminum carbonate hydroxide (AACH), a new precursor obtained via the precipitation reaction between ammonium aluminum sulphate (NH4Al(SO4)2) and ammonium hydrogen carbonate (NH4HCO3). The precursor and the calcined product were characterized by XRD, SEM, TEM, TG-DSC and particle size distribution analysis. The effect of experiment parameters, process technology and mechanical milling pre-treatment on the properties of precursor and final α-Al2O3product was investigated. The results showed that less-agglomerated, well-discrete and cuboid-like AACH precursor can be successfully synthesized in the optimal technical condition; AACH sample with different particle size was obtained by varying the titration rate of the raw material solutions; mechanical milling AACH precursor drastically lowered the a-alumina transition temperature and spherical-like α-Al2O3particles with less-agglomerated rather than vermicular agglomerated particles were obtained at lower calcination temperature; α-Al2O3powder with controllable diameter was finally successfully synthesized by calcining different-sized AACH precursor.