Influence Of Additive On Microstructure Of Alumina Powder

There are many kinds of microstructure for alumina. And the microstructure of powders will determine the applications of the ultimate productions directly. So particle shape control has aroused increasingly extensive attention.In this dissertation powders of alumina were synthesized by the hydrolysis of aluminum isopropoxide and hydrothermal treatment. During the preparing process AlF3, acetic acid and carbamide were respectively introduced as additives. The effects of additive concentration, heat-treated temperature, kind of alumina precursor, hydrothermal temperature, hydrothermal time and way of additive introduced on the phase transformation and microstructure were investigated systemically by XRD, TG, TEM and SEM.The results indicate that adding AlF3 can enhance the kinetic rate of the phase transformation for gamma to alpha alumina and reduce the transformation temperature of alpha phase to 900℃. And no significant change of phase has been found after increasing the calcination temperature up to 1200℃.α-Al2O3 passes through the morphology transformation of irregular platelet to flat hexangular platelet with increasing AlF3 concentration at the certain hydrothermal conditions; then the morphology ofα-Al2O3 passes through the transformation of polyhedron to hexangular platelet to vermiform morphology with increasing hydrothermal temperature.It is shown that the effect of acetic acid as additive on transformation temperature of alpha phase is quite feeble. Theα-Al2O3 particles prepared are seriously hard aggregated. The quantity of particles joined into combination is amplified with increasing acetic acid concentration. And there is the same trend with increasing hydrothermal temperature.Carbamide introduced as additive has the influence on the size ofα-Al2O3 particles. The sizes of particles are amplified with increasing carbamide concentration and reducing hydrothermal temperature.And the mechanism of influence for varied factors on the microstructure of alumina powders was analyzed and discussed in detail on the base of experimental results.