Study On The Preparation Process Of Alumina Aerogel Based On Pseudo-boehmite

In this paper,γ-AlOOH aerogel was prepared from pseudo-boehmite by powder dispersion method and sol-gel process at atmospheric pressure.After heat treatment,Al2O3aerogel was prepared.In this paper,the peptisation properties and mechanism of pseudo-boehmite and the factors affecting the preparation ofγ-AlOOH sol were studied.The gelation process ofγ-AlOOH sol and the thermal behavior of alumina aerogel were investigated.In this paper,the pseudo-boehmite and its peptisation properties were studied.The pseudo-boehmite contains three kinds of water and the total amount is 31.92%.The adsorption water combined with van der force is 16.34%and the interlayer water with hydrogen bond is 3.75%and the crystal water with Al-OH is 11.83%.Pseudo-boehmite structure can be expressed asγ-AlOOH·0.31H2O··1.38H2O.Interlayer water determines the peptisation properties of pseudo-boehmite and adsorption water has no effect on the peptisation properties of pseudo-boehmite.The peptisation process of pseudo-boehmite can be divided into four stages,the dismembering stage of pseudo-boehmite particles,the stage of sol formation,the stage of sol stabilization and the stage of initial instability of sol.The crystal structure of pseudo-boehmite was not changed during peptization process.The results also show that pseudo-boehmite can be peptize in water,DMF and formamide,andγ-AlOOH sol with uniform particle size distribution can be obtained in water and DMF.Theγ-AlOOH sol with particle size is 36.91nm and Zeta potential is 36.91mV were prepared when water was used as solvent,the solid content was 15%,the ratio of acid to aluminum was 0.06,the amount of DMF was 15%,the peptisation time was 120min,the peptisation tempreture was 40℃.The solid content can be increased to 50%when DMF is used as solvent,and the particle size and its distribution have no change.The pseudo-boehmite can be completely peptized when the ratio of acid to aluminum is 0.09 and the particle size ofγ-AlOOH non-aqueous sol is 18.05 nm,Zeta potential is 47.52 mV.The effects of the content with solid and TEOS and propylene oxide on the gelation process ofγ-AlOOH sol were also studied.The gelation time ofγ-AlOOH sol decreased with the increase of conten with the addition of solid and TEOS and propylene oxide.The effects of different displacement solutions on the drying process ofγ-AlOOH wet gel were also investigated.When the substitution solution was 20%ethyl orthosilicate ethanol solution and ethanol solution of 50%acetonitrile and ethanol solution,the cracking degree was the least in the drying process.The heat treatment process of Al₂O₃ aerogels at different temperatures was studied in this paper.The specific surface area of aerogels after heat treatment at 200℃,500℃,800℃,1000℃and 1150℃was 352.43m²/g,323.89m²/g,280.78m²/g,197.43m²/g and 49.15m²/g.The aerogels were completely densified at 1250℃and the specific surface area was reduced to 5.17m²/g.Al₂O₃ aerogels have resistance to high temperature sintering and phase transition.The presence of SiO₂ inhibits the sintering and phase transition of Al₂O₃ aerogels and increases the phase transition temperature.The crystalline phase is mainlyγ-Al₂O₃ andθ-Al₂O₃ at 1150 C heat treatment.SEM photos show that the pores in Al₂O₃ aerogel are mesoporous and the pore size and particle sizedistribution are uniform,particle size about 30nm.