Study On Three Processes For Preparing Spherical Alumina Powder

Due to its unique properties such as small particle size,high sphericity,and good dispersion,spherical alumina has a huge demand in the alumina market.Therefore,the preparation of spherical alumina powder with excellent performance has also become a domestic and international research hotspots of aluminum powder research scholars.In this paper,three different methods of alkoxide hydrolysis method,homogeneous precipitation method and hydrothermal method were used to prepare alumina powder with spherical morphology.The effect of different conditions on the microscopic morphology of the powder was explored.Scanning electron microscope(SEM),particle size analysis,X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),thermogravimetry(TG-DSC)and other characterization methods to characterize the micro-morphology and phase structure of the product,At the same time,the formation mechanism of the spherical alumina precursor formed by various methods was analyzed.The specific research contents are as follows:(1)Using aluminum sec-butoxide(ASB)as the raw material,an appropriate alcohol solution was selected as the solvent,and the alumina precursor was synthesized by alkoxide hydrolysis,the influence of its technological parameters on the formed product and the mechanism of ball formation were studied,and the discussion The effect of different calcination temperatures on the product morphology and size in the calcination process is discussed.The study found that products with spherical morphology could not be synthesized in a single alcohol solution.The addition of hydrophilic acetonitrile effectively slowed the rate of hydrolysis and polycondensation and was conducive to the formation of spherical morphology.The best process obtained through investigation is:a mixed solution of acetonitrile and n-butanol with a volume ratio of 6:4 as a solvent,c(ASB)=0.005 mol/L,n(ASB):n(H2O)=1:3,ultrasonic Aging for 25 minutes.During the hydrolysis polycondensation reaction,a precursor with a narrow particle size distribution range,good spheroidization,uniform distribution and a particle size of about 357 nm was synthesized by the mechanism of oil-in-water emulsion.After high-temperature calcination,the precursors were sequentially converted from amorphous to?-Al2O3 and then to?-Al2O3,which eventually produced chemically stable spherical?-Al₂O₃ with an average particle size of about 564 nm.(2)Using aluminum nitrate(Al(NO3)3)and sodium sulfate(Na2SO4)as raw materials,adding a precipitant,a homogeneous precipitation method was used to synthesize an alumina precursor,and the influence of different process conditions of the precursor and ball formation were studied Mechanism,and discussed the calcination method,investigated the effect of different calcination temperature on product morphology and size.The study found that changes in the concentration of aluminum nitrate have a great influence on the resulting product.The concentration increases,the product spheroidity decreases,and the problem of agglomeration is serious.Therefore,only products with good morphology can be synthesized under lower concentration conditions,which is also a synthesis The main reason for the low product yield.After investigation,the best process conditions were obtained:urea as precipitant,c[Al(NO3)3]=0.010 mol/L,c[Al(NO3)3]/c[Na2SO4]=0.5,c[Al(NO3)3]/c[CON2H4]=1:16,aged 1h.In the process of thermal decomposition synthesis reaction,under the guidance of self-organizing growth mechanism,Al4SO4(OH)10·5H2O precursor with good spherical morphology,high yield and particle size of about 713 nm was finally obtained.After high-temperature calcination,the precursors were sequentially converted from amorphous Al₄SO₄(OH)₁₀·5H₂O into amorphous 3Al₂O₃·4SO₃ and then into?-Al₂O₃,finally obtaining a spherical surface with a porous surface and an average particle size of about 948 nm?-Al₂O₃.(3)Using aluminum sulfate(Al2(SO4)3)as the raw material,sodium hydroxide(Na OH)as the precipitant,and a mixed solution of deionized water and absolute ethanol as the solvent,an alumina precursor was synthesized by hydrothermal method.The effects of different process conditions and the mechanism of ball formation were studied,and the effects of different calcination temperatures on product morphology and size in the calcination process were discussed.The study found that the different volume ratio of hydroalcohol determines the formation of spherical morphology.Only when the volume ratio of hydroalcohol is 2:4 will the spherical morphology appear.The best process conditions were obtained through investigation:n(Al2SO4)/n(Na OH)=1:3,V(H2O):V(C2H5OH)=2:4,hydrothermal time 6 h,hydrothermal temperature 180?,select rapid Way to heat up.In the process of hydrothermal reaction,guided by the polymerization mechanism,a sodalite Na Al3(SO4)2(OH)6 precursor with an average particle size of about 776 nm,uniform dispersion,and spherical morphology was finally obtained.After high-temperature calcination,the precursors were sequentially converted from Na Al3(SO4)2(OH)6 to Na Al(SO4)2,and then to Na2Al22O34,and finally the content of??-Al₂O₃ was 65.4%,the content of?-Al₂O₃ was 34.6%,and the spherical shape The appearance disappeared,irregular mass appeared,and the average particle size was about 1414nm.