The Preparation And Characterization Of Ultrafine ?-Al₂o₃

In this paper,ultrafine ?-Al₂O₃ ceramic powders were prepared by alkoxide hydrolysis method,using two-step hydrolysis and one-step hydrolysis with the addition of HNO₃,respectively.The morphology,phase transition and phase transition temperature of the as-prepared ?-Al₂O₃ were explored systematically.The effects of surfactants on dispersity of ?-Al₂O₃ were also investigated.The main contents and results are as follows:1.During the two-step hydrolysis experiments,the preparation parameters,including the aluminium isopropoxide concentration,hydrolysis temperature,the volume of isopropanol and water,affecting the morphology of ?-Al₂O₃ were investigated and discussed systematically.The warm-like ?-Al₂O₃ particles with a narrow size distribution and good uniformity were obtained by the hydrolysis temperature of 80 °C,0.1 M aluminum isopropoxide concentration,nAIP:nC3H8O = 1:4,nAIP:nH2O = 1:5.After the calcination of 1200 °C,the ?-Al₂O₃ powers were obtained.The phase transition process is as follows: ?-AlOOH ? ?-Al₂O₃ ? ?-Al₂O₃ ? ?-Al₂O₃ ? ?-Al₂O₃?2.Adding HNO₃ as catalyst,stable ?-AlOOH sol was obtained by one-step hydrolysis method.The compact precursors accomplished ? phase transformation at 1100 °C.The phase transformation process is as follows: ?-AlOOH ? ?-Al₂O₃ ? ?-Al₂O₃.Except for ?-Al₂O₃,no other transition phases of Al₂O₃ occured.However,the ?-Al₂O₃ powder was severely agglomerated.Without adding HNO₃,the loose precursors with high specific surface area were obtained.The calcination temperature of the alpha phase transformation was 1200 °C.Besides,there are ? and ? phases formed in the transformation process.3.Adding proper amount of PVP as surfactant in the one-step hydrolysis experiments,the structure of ?-Al₂O₃ powder was changed from dense structure into porous structure,but the dispersity was not improved.When proper amount of CTAB was added,wormlike ?-Al₂O₃ with uniform paricle size and good dispersion were obtained.In the view of phase transition process,the adding of PVP made ?-Al₂O₃ formed,but CTAB had no effect on it.4.The precursor prepared by the two-step hydrolysis method was porous network structure.By adding proper amount of CTAB,the size of ?-Al₂O₃ decreased.If the amount of CTAB is excess,the dispersity of ?-Al₂O₃ became worse.Furthermore,CTAB can promote a phase transition of Al₂O₃.