A-phase aluminum oxide has characteristics such as high melting point,high strength,thermal stability,and wear resistance,and is widely used in ceramics,thermal/refractory materials,grinding materials,and other fields.
　　With Aluminium hydroxide as raw material.The pre treated raw materials were calcined at different temperatures,and the calcined powder was treated to prepare submicron alumina.The chemical composition and microstructure were characterized using XRD,SEM,and particle size analyzer.The results indicate that:1)pretreatment of raw materials can significantly reduce the content of Na2O in the raw materials,thereby improving the conversion rate of alumina powder phase a after calcination and reducing its Na2O content.2)The optimal calcination temperature is 1250℃.The a-AI2O3 prepared at this temperature has high conversion rate and good activity.After grinding,the particle size can reach sub micron level.

　　As AI2O3 is an ionic bond compound,its particle diffusion coefficient is low,and the sintering temperature of pure aluminum oxide is high,which leads to grain growth,difficult to eliminate pores,and reduced Strength of materials properties.In addition,different powder preparation methods,due to their own characteristics and different raw materials,lead to large differences in impurity content,particle size,and microscopic morphology of the powder,thus affecting the sintering and microstructure of aluminum oxide to varying degrees.Therefore,ultrafine submicron sized,non agglomerated,and well dispersed submicron alumina powders occupy a place in materials for obtaining fine-grained structures,and the mechanical properties of the materials will also be improved accordingly.
　　Briefly summarize the preparation method:pretreat Aluminium hydroxide,calcine the treated Aluminium hydroxide at 1200℃~1430℃,and obtain submicron aluminum oxide powder after post-treatment.Summary in one sentence:One is the pre processing,and the other is the post processing(both of which are at the lower level of the pre processing,and I will try to clarify them separately).The most suitable preparation and calcination temperature is 1250℃.

　　As shown in Table 1;The pre-treatment of raw materials can significantly reduce the Na2O content in the raw materials.As the Na2O content in the raw materials decreases,the Na2O content in the prepared a-AI2O3 also significantly decreases,and the conversion rate of the a-phase is also significantly improved.Supplementary note:At the calcination temperature for producing a-AI2O3,the Na2O carried by it can be generatedβ-Al 2O 3,when the Na2O content in alumina powder is higher,βPhase alumina will rapidly crystallize,resulting in a decrease in the content of phase alumina and a lower conversion rate of a-AI2O3.
　　Under the action of high temperature,Aluminium hydroxide undergoes the removal of attached water,Water of crystallization,and crystal transformation.As the temperature increases,the conversion rate becomes faster and faster,the conversion rate of phase A gradually increases,the crystallization tends to improve,and the specific surface area decreases.Reasonable control of calcination temperature is the main process for obtaining qualified a-AI2O3:(as shown in the following figure)

　　(The alumina powder calcined at 1200~C contains transition phase 0,with a conversion rate of 53.6%.As the temperature increases,there are more and more a-A1203.When the temperature reaches 1250℃,the sample only contains a phase,with a conversion rate of 95%.).
　　Preparation of alumina coarse powder for post-processing:using ball milling(tank ball milling/planetary ball milling)processing technology to gradually reduce the particle size of the powder,as proven by practice;The average particle size obtained by ball milling for 8H is the thinnest,and controlling the original crystal size is crucial for producing submicron sized alumina.
　　In summary:1)Different impurity contents in raw materials will directly affect the phase transformation of alumina after calcination.
　　2)On the premise of using Aluminium hydroxide as the raw material,the calcination temperature is 1250℃,which has better sintering activity/higher a-phase transformation.
　　3)The ball milling time is controlled at 8H,and the particle size of the powder is the smallest,followed by an increase.