The Preparation And Formation Mechanism Of Flaky Alumina

The flaky α-Al₂O₃ powder as an important ceramic material,has unique chemical,electrical and mechanical properties.It belongs to corundum structure,with high mechanical strength and hardness,low electrical conductivity,good thermal conductivity,and chemical inertness and other characteristics.In addition to the excellent properties of ordinary alumina materials,the flaky α-Al₂O₃ powder has a special sheetlike two-dimensional structure,and its surface activity is moderate,the adhesion is better,the reflection ability and shielding effect of light are higher.The flaky α-Al₂O₃ powder materials have a wide range of application in the field of cosmetics,pearlescent pigments,refractory materials and toughened ceramics and so on.Finally,the growth mechanism of alumina was studied,and the mechanism of the formation of flaky alumina was explored.The controlling of the morphology of flaky α-Al₂O₃ powders is essential,asmultimorphological α-Al₂O₃ platelets are needed in various applications.In this study,a large aspect ratio flaky alumina material was prepared by sol-gel method and molten salt method,which used aluminum sulfate as raw material,sodium sulfate and potassium sulfate as molten salt,and a series of liquid and solid phase reaction were conducted.In order to form the alumina material with large particle size and thin thickness,this paper through optical microscopy,X-ray diffraction,scanning electron microscopy,comprehensive thermal analysis and infrared spectroscopy,detected the effects of different alumina salt raw materials on the morphology of the flaky α-Al₂O₃,explored the effects of the technological parameters in the process of sol-gel and molten salt,including the reaction end point pH,reaction temperature,aging time and sintering temperature on the final product,and attentively studied the influence of different aluminum salt materials and additives including titanium dioxide,zinc sulfate,stannous sulfate on morphology and aspect ration of flaky alumina.The results show that the flaky alumina of large size and uniform distribution can be obtained by using alumina sulfate.When the molar ratio of aluminum sulfate to molten salt is 1:4,the prepared alumina surface is smooth and shiny.In the sol-gel process,as the extension of aging time,the larger and narrower distribution of the particle size of flaky alumina are formed.When the calcination temperature is 1000 1200 oC,the final product is α-Al₂O₃ crystal,but the aspect ratio reached the maximum at 1100 oC.With the increase of sintering temperature,the crystal size increases hardly with thickness dramatic increases,resulting in a decrease in the aspect ratio.In addition,the selection of suitable additives has a significant effect on the anisotropic growth of alumina crystals,and was reduced the amount of finely divided crystals,so that the particle size distribution would be more uniform.When 2 wt% zinc sulfate and 0.4 wt% stannous sulfate were added to prepare the flaky alumina powders,the particle size was 25 μm to40 μm,the thickness was 200 nm to 300 nm,and the aspect ratio was more than 100.Combined with grain-growth discontinuity,it was proposed that the growth of alumina was underlied by oriented-aggregetion mechanism.