Study On Nano-sized α-Al₂O₃ Prepared In Integrated High-gravity And Microwave Field

The nanometerα-Al2O3 powder, one of the important structural and functional ceramic material, has excellent properities such as good wear resistance, high temperature stability and good corrosion resistance, high resistivity, high heat conductivity, high surface activity and high light absorption. It has considerable potential for a wide range of applications including fine ceramics, composite material, flourescent material, wet sensitivity materials, electronic ceramics, high strength materials and catalysts etc.The key to preparation of nano-sizedα-Al2O3 lies in controling of it crystal shape, size distribution and dispersion. Theα-Al2O3 powders are usually prepared by heat treatment of precursor of aluminum hydroxide and transition sluminum compounds. However, the formation of nano-sizedα-Al2O3 is exceedingly difficult.Therefore, it is necessary to research and develop of a new process route for preparing nano-sizedα-Al2O3. The new process route should have characteristics of high prodiction, low energy consumption, low pollution and particle size controllable.This paper presents a route of synthesizing nano-sizedα-Al2O3 by integration high-gravity field and microwave field. Taking advantage of Strengthening micromixing and transmision process in super-gravity field, and combining with the actual situation in a aluminum mill, Using NaAlO2 and CO2 as starting materials and dispersed by PEG400, we prepared nano pseudo-boehmite by carbonation in rotating bed with helix channels(RBHC), and a series of post-processing. This is the most desirable process route with high production efficiency, low pollution, and the granularity of product controllable. Thesis mainly explore process conditions of preparing nanometer pseudoboehmite by using high-gravity, Examines the influence of temperature, NaAlO2 solution concentration, high-gravity level, G/L on crystal shape, crystallinity and grain size of pseudoboehmite, obtained the optimum process of carbonization reaction in preparing pseudoboehmite:low temperature(<30℃), low NaAlO2 solution concentration (0.1-0.4 mol/L), high-gravity level(>1000 rpm), Appropriate G/L ratio(1.0-1.5); Aging treatment of products by combining water thermal aging and Alcohol aging, using dilute ammonium nitrate solution wash the filter cake, and adopting microwave dry the products with dry processing. Therefore, abtain the nano-pseudoboehmite with high dispersity and stable crystal. Make use of microwave field characteristics of Zero gradient evenly heating and uniform temperature controlled, calcined pseudoboehmite intoα-Al2O3 by microwave calcinations method,with the microwave frequency of 2.45 GHz. We have investigated the influence of different calcining methods and heating mode in microwave on the crystal ofα-Al2O3. The product was characterized by XRD, TEM and SEM etc. The results show that using this new process route to prepare nano-sizedα-Al2O3 with high crystallinity、distinct lines of crystal and complete crystal form calcined by microwave method has a particle size of 10-20 nm and narrow diameter distribution.