Grain Size And Morphology Control Of Alumina Powder

Alumina powder is widely used in ceramics,surface coatings,medicine,optical materials,composite materials and other fields,because of its high strength,high hardness,wear resistance,high temperature resistance and high resistivity.Due to large specific surface area of small particles and surface energy,alumina powder is easy to form agglomeration during preparation,impacting the product's strength and density and limiting the application of alumina powder,which has aroused widespread concern of researchers.In this paper,alumina precursors and alumina powders were prepared by direct precipitation using aluminum nitrate and ammonia as raw materials.XRD,SEM and laser particle size analyzer were used to study the effects of pH value,preparation temperature,Al3+ concentration,ultrasonic treatment,stirring time,and the dispersants on the particle size and morphology of alumina precursor and alumina powder.The conclusions are as following:(1)The pH value has certain influence on the crystalline phases and particle size of alumina precursor.When pH<7,the precursor is amorphous;7?pH?8,precursor is convered to?-AlOOH;8<pH<9,the precursor has both the ?-AlOOH phase and a-Al(OH)3 phase;When pH ?9,precursor is converted into a-Al(OH)3.The particle size of alumina precursor firstly increases and then decreases with the increase of pH value.When pH=8,the particle size of the precursor is the largest.(2)Preparation temperature,Al3+ concentration,ultrasonic treatment and mixing time have influence on the particle size of Alumina precursor.With the increase of the preparation temperature,the particle size of alumina precursor increases obviously;With the increase of Al3+concentration,the particle size of alumina precursor firstly decreases and then increases;ultrasonic treatment can inhibit the particle size of alumina precursor to increase;The particle size of alumina precursor decreases with the increase of mixing time.(3)The degree of polymerization of PEG has a great influence on the particle size and morphology of alumina particles.As the degree of polymerization increases,the particle size of alumina powder decreases and the granule morphology changes from bulk to small.The effects of PEG20000,PEG2000,and PEG400 decrease sequentially.(4)The types and amounts of dispersant have some influence on the particle size and morphology of alumina powder.Under the experimental conditions,the optimum addition of different dispersants's amount and particle size of the powder are as follows:adding 1.0wt%PEG20000,the median diameter size is 7.61?m;adding 1.0wt%PVP,the median diameter size is 9.90 ?m,particles being well dispersed sphere;adding 1.Owt%(NaPO3)6,the median particle size is 10.64 ?m,particles being sphere;adding 0.3 wt%PVA,median particle the diameter size is 11.31 ?m.