Preparation Of Ultrafine Alumina From Industrial Sodium Aluminate Solution Under Ultrasonic Fiel

With the increasing demand for high performance ceramics,the traditional alumina materials can not meet the market demand.As a new functional material,ultrafine alumina is widely used in new materials.At present,the main production processes of ultrafine alumina in China are mechanical crushing,chemical precipitation,liquid phase and gas phase.However,in the actual production process,due to the lack of high purity and purity,different particle size and uneven particle size distribution,the yield of ultrafine alumina is low,the particle size distribution is wide,the product purity is poor and the particle shape is irregular,which can not meet the market demand.Therefore,the research and development of high-efficiency and high-purity ultra-fine alumina is currently the focus of research at home and abroad.Based on the advantages of the thermal decomposition of ammonium aluminium carbonate and the characteristics of ultrasonic technology,the technology of preparing ultrafine alumina is studied in this paper.In this paper,high purity Aluminum hydroxide was prepared from industrial sodium aluminate solution after impurity removal and decomposition.The high purity Aluminum hydroxide was prepared by acid Aluminum hydroxide,the precursor aluminum ammonium carbonate（ACCH）was prepared by ultrasonic-assisted chemical precipitation,and finally,the crystal seeds were added to the ACCH to reduce the phase transition temperature,thus reducing the hard agglomeration caused by sintering.In the process of impurity removal from industrial sodium aluminate solution,adding CaO 10g/L,MgO 5g/L,reaction temperature 105°C,Reaction Time 2h,the desilication rate can reach 66.4%,adding sodium oxalate 10g/L,reaction time 60min,under the action of ultrasonic wave,the iron removal rate can reach 95%.By response surface method,the remarkable degree of decomposition is as follows:seed coefficient>decomposition time>decomposition temperature.Compared with the decomposition products under ultrasonic field and non-ultrasonic field,the decomposition products under ultrasonic field have higher crystallinity,more uniform particles,better dispersion and higher purity.ACCH precursor was prepared by ultrasonic-assisted chemical precipitation method after acid dissolution of the prepared Aluminum hydroxide.It was found that ultrasonic pretreatment was beneficial to the dissolution of Aluminum hydroxide.The optimal solution conditions were as follows:120°C,37%HCL concentration,2 h,20rpm,3.25:1 liquid-solid ratio,the solubility was 93.18%.During the preparation of the precursor,the reaction conditions were as follows:the concentration of Al Cl₃ was0.2 mol/l,the concentration of NH₄HCO₃ was 2 mol/L,the ultrasonic intensity was240 w,the dropping speed was 16 ml/min,the dispersant was PEG-4000,the addition amount was 16%,after washing with anhydrous ethanol and drying in vacuum,the spherical precursor ACCH with good crystallization,complete crystal development and good dispersity was prepared.The median particle size was 6.797μm.The results show that the agglomeration between particles is opened and the precursor particles with good dispersion and high crystallinity can be obtained due to the shock wave and micro-jet produced by ultrasound during the precipitation process.Finally,the precursor ACCH was mixed with seedα-Al₂O₃and the TG-DSC diagram showed that the addition of seedα-Al₂O₃could effectively reduce the transition temperature of transition alumina to steady-Al₂O₃,therefore,theα-Al₂O₃particles with seedα-Al₂O₃ as precursor have better dispersion after calcination.At the calcination temperature of 1200°C and holding time of 2h,the ultrafine alumina with average particle size of 159.1 nm can be obtained,and the purity of the product can reach 3N grade.