Controlled Synthesis And Application Of Ultrafine Alumina Powder

Ultrafine alumina has excellent physical and chemical properties such as high temperature resistance,strong insulation performance,corrosion resistance,high thermal conductivity,EUV resistance,large specific surface area,high strength,etc.,it is widely used in ceramics,medicine,microelectronics,military industry,electrical machinery,petrochemical and other industries.With the rapid development of these industries,the demand for ultra-fine alumina powder in the material market is increasing,which will promote the further growth of the demand and production of ultra-fine alumina,and bring huge economic benefits.Therefore,ultrafine alumina powder occupies an important position in the field of materials.In this paper,the preparation of random ultrafine alumina powder and spherical alumina and flaky alumina are studied;the spherical alumina and flaky alumina are filled into nitrile rubber to study its thermal conductivity.SEM,thermal conductivity instrument and other testing instruments are used to characterize and analyze the products.The main contents of the study are as follows:（1）Using industrial-grade alumina as the raw material,ultrafine alumina powder was prepared with a planetary ball mill,and the best process conditions were finally determined by examining the influence of the factors such as ball-to-material ratio,ball mill speed,ball milling time and grinding aid on the powder.The ball-to-powder ratio was 3:1,the grinding speed was20r/s,and added 10m L grinding aid to grind for 4h.Finally,the ultrafine alumina power with small particle size and narrow particle distribution was prepared.（2）The sol-gel method combined with spray drying technology was used to prepare spherical alumina with aluminum nitrate and concentrated ammonia as raw materials.The effects of factors such as aluminum source concentration,solution pH,the time of adding ammonia water and aging time on the powder were investigated,and the best process conditions were determined.The most suitable aluminum source concentration is 0.1mol/L.At this concentration,the spherical alumina matrix has a more uniform growth space;when pH=9,it can provide the most suitable growth environment for the spherical alumina particles;We extend the dropping time of ammonia water to 4h,which delay the reaction rate and provide a uniform growth space and sufficient growth time for the particles matrix;after standing and aging for16h,the intermediate products were washed with deionized water multiple times by vacuum suction filter to remove the soluble salt.Then,the intermediate is added with appropriate amount of deionized water to be ultrasonically dispersed into a suspension.finally the rapid separation of solid and liquid was achieved by spray drying technology,and the products were calcined in a box-type resistance furnace at 900℃for 2 hours to prepare ultrafine spherical alumina powder with high ball formation rate,uniform particle size distribution and smooth surface.（3）Flake alumina was synthesized by the molten salt method using Al₂（SO₄）₃,Na₂SO₄,K₂SO₄ and anhydrous Na₂CO₃ as the main raw materials,and the product was characterized by SEM,laser particle size distribution analyzer etc.The effects of factors such as molten salt ratio,drying method and time,crystal growth space,metal ion additives and other factors on the powder morphology were investigated to determine the optimal process conditions.The best molten salt ratio is 1:1:1;drying in a drying box is better than spray drying;8h should be given for sufficient drying;Add 10ml of deionized water to give the crystal a suitable space for growth,so as to prepare flaky alumina with a 99.49%purity and a narrow particle size distribution and uniform particle size;The addition of metal ions increases the particle size of the powder.The addition of Zn²⁺ions has a promoting effect,while the addition of Ti⁴⁺and Mn²⁺has a suppressive effect.（4）Prepared nitrile-based thermally conductive composite materials through the process of mixing,primary vulcanization,secondary vulcanization and using Al₂O₃,BN,SiC as thermally conductive filler,nitrile rubber as matrix,and with an appropriate amount of cross-linking agent.Characterized the products with SEM and thermal conductivity tester,etc.The effects of powder type,powder filling ratio,vulcanization times,powder particle size and powder particle size distribution on the thermal conductivity of nitrile rubber were explored.Experiments show that the three inorganic non-metals can improve the thermal conductivity of nitrile rubber,but due to the difference in particle size and morphology,the gap between the three is not large;the increase in powder loading,the decrease in particle size,and the narrowing of particle size distribution and spherical morphology are beneficial to improve the thermal conductivity of the composite material;nitrile rubber has poor heat resistance and is not suitable for secondary vulcanization.