Preparation And Characterization Of Monodisperse Nano Alumina Powder

In recent years,with the continuous development of nanotechnology,more and more nanomaterials have come to people’s attention.As one of special functional materials of nanometer alumina oxide is a kind of high melting point,high strength,high hardness,heat resistance,wear resistance,corrosion resistance and a series of excellent properties,the nanometer alumina has been widely applied in biological catalysis,military aviation and battery of new energy and other fields,is one of the important raw materials for optical single crystal and fine ceramics.Nowadays,there are more and more methods to develop and prepare nano alumina powder,among which the precipitation method in wet chemical method has obvious advantages such as low raw material cost,simple equipment,high purity,small particle size,narrow distribution range of powder size and good control of particle size composition.However,there is a serious problem of powder agglomeration in the preparation process.Agglomeration is an urgent problem in the preparation of nanometer ultrafine powders.The effects of different environments on powder agglomeration and the mechanism of flocculant and traditional dispersant in the preparation of nano alumina powder by precipitation and low temperature combustion were investigated.In this paper,using aluminum nitrate(Al(NO3)3·9H2O)and ammonium bicarbonate(NH4HCO3)as raw materials,ultrasonic fields were introduced into the precipitation reaction system to prepare precursors and target powders under different drying methods,reaction temperatures,types and amounts of surfactants.Using aluminum nitrate and mannitol as raw materials in the low-temperature combustion system,target powders with different molar ratios,reaction temperatures,pH values and different proportions of flocculant and traditional dispersant were also prepared.Their morphology and agglomeration were observed by scanning electron microscope(SEM).Combined with thermogravimetric analysis(tg-dsc)and X-ray diffraction(XRD)to analyze the composition of the powder,the particle size range of the powder was obtained with the aid of the laser particle size meter.The following experimental results were:Precipitation reaction system:(1)In the experiment,Al(NO3)3·9H2O was used as the aluminum source,NH4HCO3 was used as the precipitator,and the ratio of the amount of substances was 1:8.It was found that the agglomeration phenomenon of the target powder prepared by normal drying oven was more serious than that by freeze drying.(2)The presence or absence of ultrasonic wave has a certain effect on the agglomeration of target powder.When ultrasonic wave is introduced into the system,the SEM scanning results of the target powder show a small agglomeration phenomenon and a complete spherical powder.(3)The reaction temperature has a certain effect on the hard agglomeration of powder.When the temperature of the water bath is 25℃,the agglomeration of powder is not obvious.When the temperature rises,the agglomeration of powder is more obvious,and the particle size distribution is narrower.(4)The addition of surfactant PEG6000 was set as the gradient of 3%,4%,5%,6%and 7%of the total mass of the reactants.The investigation showed that the agglomeration of powder was significantly inhibited when the surfactant was 6%of the total mass.(5)When the molar ratio of sodium citrate to aluminum nitrate was 0.3:1,nano alumina powders with finer particle size and better dispersion could be obtained.A further addition of 6%PEG6000 can make the powder easier to disperse and the particle size distribution narrower.Low temperature combustion reaction system:(1)With aluminum nitrate as oxidant and mannitol as burner,the system pH=4 was roasted in muffle furnace at 1100℃ for 4h.he particle size distribution of the target powder is more uniform under the condition of 1:1.5,and the powder after calcining has better dispersion and sphericity.(2)The effects of calcination temperature on the crystal transformation of alumina were investigated,and temperature gradiences of 800℃,900℃,1000℃ and 1100℃ were set.The results showed that the crystal began to change as the temperature increased.Finally,at 1000℃,the crystal gradually changed from γ-Al2O3 to α-Al2O3.(3)The pH value of the system is regulated by ammonia,and the α-Al2O3 powders calcined at 1100℃ at different pH values have different characteristics.The results show that the agglomeration of powder is improved obviously when the pH value is 4.(4)The addition of surfactant PEG6000 and flocculant citric acid had a little influence on the agglomeration and particle size distribution of powder.The results showed that when the surfactant PEG6000 was used as 6%of the total mass of the reactants and the ratio of citric acid to aluminum nitrate was 0.3:1,the hard agglomeration of the obtained powder was significantly inhibited.