Preparation Of Nano-sized α-Al₂O₃ Powder And Its Dispersion In Water

In this research, ammonium aluminum carbonate hydroxide (AACH), the precursor of α -AL₂O₃, was synthesized by precipitation method using NH₄AL(SO₄)₂ and NH₄HCO₃ as raw materials. The research firstly showed that the α -AL₂O₃ powder obtained by directly calcining the AACH at 1150℃ owned a bad microstructure. Then, we utilized the additives of α -AL₂O₃ powder seeding, alumina sol seeding, TiO₂-sol , ammonium nitrate , and high-energy ball milling on the precursors to investigate these factors' influences on the α transformation temperature, the microstructure of as-received nano-sized α -AL₂O₃ powders and transformation sequences. This research indicated all these factors can reduce the α transformation temperature, but the range of reduction and the influence on the microstructure of powders were not identical. Among these factors, alumina sol seeding was the most effective. AJS20, the precursor contained 20wt% alunina sol seeding, was calcined at around 1000℃ to get free-aggregation nano-sized a -AlaOs powders with a median particle size of 70nm. And, calcining AJS2, the precursor contained 2wt% alumina sol seeding, at HOO'C , we get a -AlaOs nano-sized powders with a particle size of lOOnm and good dispersion by TEM . This paper also gives the proper mechanisms of these factors' influences on the transformation to alpha phase.In addition to, the dispersion state of nano-sized a -A^Os powder in water was characterized by analyzing the particle size distribution and calculating the average size. We also used this method to search the best dispersion agents. The result shows that PAA is the best dispersion agent for the a -AhOs powder at basic system.