Preparation Of Al₂O₃-2SiO₂ Powders By Sol-Gel Method And Study On Its Application

As an important series of clayey materials,the metakaolinite has wild potential applications,such as catalysts,adsorbents,and inorganic membrane separators.Usually,these materials posses surface permeability,large specific area,and low density,highly mechanical and thermal stability.Thus the metakaolinite with excellent performance have recently aroused interest in materials science research.Surveys have shown that the performance of metakaolinite depends heavily on the chemical composition.Usually,the nature metakaolinite is fabricated by calcinations process with Kaolin(Al₂O₃-2SiO₂·2H₂O)in 600-900℃.However,the type of metakaolinite is not pure and the Al/Si mole ratio is not fixed because the forming age and site of Kaolin mine are different.For this purpose,this work designs the sol-gel method for synthesizing the amorphous phase Al₂O₃-2SiO₂ powders with tetraethoxysilane(TEOS)and aluminum nitrate (ANN)as the starting material that Si/Al mol ratio of 1 and validates its alkali-activity.DTS,TEM,SEM,BET and some other experiment methods were employed to study the effect of processing parameters,such as quantities of water and ethanol,hydrolysis temperature,aging time and drying methods,on the size,specific surface area and structure of nanometer powders.In order to examine the alkali-activity of the powder, alkali-polycondensed tests and hydrothermal reactions were performed.The mechanism of its alkali-activity was investigated according to the MAS-NMR analysis.The results showed that the optimum processing parameters for preparing low agglomeration Al₂O₃-2SiO₂ nanometer powders are as follows:the mole ratio of water and ethanol to TEOS are 0:1 and 12:1 respectively,solution hydrolysis temperature is 40℃,aging time is 36 h and the drying way is azeotropic distillation with microwave drying.The powders possess uniform size,laminar structure and monodispersity.The average particle diameters of the powders were in the range of 60～80 nm and the largest BET specific surface area were up to 669.27 m²/g.The synthetic powder that has alkali-activity and its polymerized reaction mechanism and microstructure are similar to that of nature metakaolin.Alkali activated cementitious material with high compressive strength of 24Mpa and NaA zeolite with the calcium exchange capacity of 366 mg CaCO₃/g can be obtained.