Preparation,Characterization And Performance Simulation Of Spherical Alumina

The application of alumina in many fields is intimately correlated with the shapes and sizes of its powder.Among them,spherical alumina is widely applied in various fields due to its particles characterized by the uniform size,smooth surface,low abrasion and long service life.In the field of ceramics,it is conducive to improving the sintering performance and compressive strength of ceramic materials,with prominently better than alumina of other shapes.In the field of polishing,its spherical shape plays a decisive role in enhancing the surface finish of workpiece.In the field of catalysts,its advantages of low particle abrasion and long service life benefit the reduction of production costs greatly.Therefore,a large number of studies,in recent years,have focused on the preparation of alumina characterized by the regular morphology,controllable particle size,high chemical purity and high rate of spheroidization.The paper first focused on the influencing factors of the preparation of spherical alumina powder,and then explored the influence of various molding methods on the structure and properties of spherical alumina particles.Finally,the crystalline change of alumina during calcination was simulated.The spherical alumina was characterized by SEM,XRD,TG-DTA and nitrogen adsorption.The main research contents and conclusions were as follows:（1）Using aluminum nitrate as raw material and ammonia as precipitant,spherical alumina powders were prepared by the combination of sol-gel and spray drying methods.The effects of the aluminum salt concentration,the sort of dispersant,the sort of solvent,the titrating and mixing speed of precipitant,the p H of the solution,the reaction temperature and the aging time on spherical alumina powders were investigated.It was found that spherical alumina precursors with good dispersion were more easily produced when the concentration of aluminum nitrate solution was 0.1～0.2mol/L.The addition of PEG-400 inhibited the transformation from amorphous aluminum hydroxide to aluminum hydroxide.The product was best dispersed at the titrating speed of 0.5m L/min and mixing speed of 1500r/min.The calcination temperature had no significant effect on the morphology of the products.（2）Using alumina sols as raw materials,spherical alumina particles were prepared by the oil-ammonia column molding method and the rotational molding method,respectively.The effects of the height ratio of oil column and ammonia,the aging time,the drying temperature and the calcination temperature on the product properties were investigated using the oil-ammonia column forming method.And the effects of the rotation temperature,the aging time,the drying temperature and the calcination temperature on the product properties were investigated using the rotational molding method.It was found that the maximum specific surface area of the product obtained using the rotational molding method was 220m²/g and the maximum pore volume was 0.64cm³/g.The product performance was better than that obtained by oil-ammonia column molding.（3）In order to study the effect of different calcination temperatures on alumina crystallization,the alumina precursors were calcinated at different temperatures.Then the analysis of the XRD patterns of the products revealed the crystallographic transformation process of alumina,namely:Al（OH）₃→Al O（OH）→γ-Al₂O₃→δ-Al₂O₃→θ-Al₂O₃→α-Al₂O₃.Using the CASTEP module of Materials Studio 2019 software to calculate the total energy,energy band structure,density of states,Mulliken atomic population and Mulliken bond population for different crystalline alumina types.And verified the order of crystalline transformation of alumina during calcination.By analyzing the mechanical,thermodynamic and optical properties ofγ-Al₂O₃,θ-Al₂O₃ andα-Al₂O₃,we found that the anisotropy:α-Al₂O₃<γ-Al₂O₃<θ-Al₂O₃;Debye temperature:α-Al₂O₃>γ-Al₂O₃>θ-Al₂O₃;photosensitivity:α-Al₂O₃>γ-Al₂O₃>θ-Al₂O₃.