Preparation Of High Purity Aluminum Oxide Powder For LED Substrate Materials

With the development of science and technology and social progress,one of the important lighting paraphernalia LED has been applied widely and increasingly.Sapphire which used widest for LED substrate material,the essential component is high pure and superfine alumina.High pure and superfine alumina is a special type function material with excellent physical and chemical properties such as high melting point,high heat-resistance,high corrosion-resistance,good electrical insulation,high-thermodynamic stability and high-chemical durability,etc,and has been used in the fields of ceramics,machinery,chemical,electron,biomedicine and optics,aero-space,and so on.The preparation methods of high purity and superfine alumina are many and for the purpose of increasing Al₂O₃ purity and reducing Al₂O₃ production cost,in this paper combined with the latest research methods all over the world we give a new preparation method of high pure and superfine alumina.?-Al₂O₃ powders were prepared by using electrolytic aluminum and sodium hydroxide as the main raw material in this paper.Aluminum is dissolved in NaOH solution and then into the gas CO₂ for carbonation precipitation,subtractive process and get the final product high-purity ?-Al₂O₃ by precursor calcining.The principle flow chart includes key steps of comminution,alkaline bath,desilication,carbonation precipitation,sodium removal,and calcine.In this paper we also studied and explored the CaO desilication mechanism and CO₂ carbonate decomposition mechanism.Though single factor experiment,we explored and examined the scope of the best parameters of each process stage systematically,studied the influence of multiple conditions on production purification effect and it is concluded that the optimal experimental conditions are as follows:phase of alkaline bath,the concentration of NaOH is 112.4g/L,55?,reaction time is 5h and liquid-solid ratio is 20:1;phase of desilication,CaO addition is 8g/L,reaction time is 2h and reaction temperature is 80??85?;phase of carbonation precipitation,reaction temperature is 50??55?,CO₂ ventilation rate is 15L/h?20L/h,precipitation time 20min and CO₂ purity quotient is 5%;phase of sodium removal,pre-calcine temperature is about 580?,dilute hydrochloric acid concentration is 15g/L,reaction time 30min and temperature 40??45 ?,liquid-solid ratio is 12.5:l,in order to improve the effect of sodium removal we need to add ultrasonic;phase of calcine,calcine temperature is 1450?,heating rate is 10K/min,and then heat preservation 30min.Phase change reaction of precursor is?Bayerite Al?OH?3 and Gibbsite Al?OH?3??amorphous Al₂O₃ ? ?-Al₂O₃ ? ?-Al₂O₃??-Al₂O₃.Purity,morphology,size and others features of each stage product have been analyzed by XRD,TG-DSC,SEM,ICP-OES,etc.Study result indicated that the approximately spherical high-pure micron-?-Al₂O₃ powder with purity of 99.9959%,average particle size of 22.3 ?m.