Preparation And Characterization Of Composite Ceramic Membranes With Inorganic Precursors

In this project, single-component sols of Al2O3, SiO2and ZrO2were prepared bysol-gel process using aluminium nitrate、tetraethoxy silicone and zirconyl chloride asprecursors. Besides, based on single sols, composite membranes of Al2O3-SiO2,SiO2-ZrO2and Al2O3-SiO2-ZrO2were prepared. The optimal preparation parametersand influencing factors for composite membranes were discussed. Thermal stability,microstructure and the chemical compound of composite membrane werecharacterized by means of TG-DTG、XRD、IR、AFM and BET etc.Al2O3sols were prepared by the sol-gel method using low-cost inorganicaluminium nitrate as precursor. The effects of the way and sequence of mixing the rawmaterials, peptizator, hydrolysis temperature, concentration of raw materials andaging conditions on the quality of sol were investigated and the optimized technologyof the preparation of Al2O3sols were obtained:1mol/L aluminum nitrate in80°Cwater bath under high speed stirring, adjusting the pH value of a2mol/L NH3·H2Osolution to9.2by a slow adding rate to get stable AlOOH precipitation. Adding acertain amount of peptizer (HNO3) to completely dissolve the precipitate and stirred atreflux for1h, aging for more than4h in a water bath at80°C. Stable, colorless andtransparent Al2O3sol can be preparedUsing Al2O3, SiO2and ZrO2single sols, composite sols of Al2O3-SiO2,SiO2-ZrO2and Al2O3-SiO2-ZrO2were prepared. The effects of chemical composition,hydrolysis reaction temperature, stirring time, DMF addition on the quality of solwere investigated. The optimal parameters was listed as follows: Al2O3:SiO2(mol/mol)=1:2, SiO2:ZrO2(mol/mol)=2:0.5, Al2O3:SiO2:ZrO2(mol/mol/mol)=1:2:0.5,Adding30%(volume fraction) DMF. In a water bath at40℃was stirred for30min.The effect of heat treatment process to status of gel had been discussed. Theoptimal heat treatment parameters were listed as follows: Drying under normalpressure, keeping relative humidity70%under60℃, the temperature increase at0.5℃/min in the temperature range from normal temperature to600℃,and keep2hat600℃. At the faster of the mass loss time slow heating and proper insulation.When drop to normal temperature, the good performance of the membrane was obtained.TG-DTG, IR and XRD analysis showed that this method obtained compositemembrane that mainly exist in γ-Al2O3、m-ZrO2and amorphous SiO2and constitutedby the SiO2network skeleton. It maintains the characteristics of nano-porouscomposite membrane. With increasing aluminum content, Al3+more and more intothe SiO2structure, and destruction of the Si-O-Si network structure and the formationof Si-O-Al bond. Adding Al2O3and ZrO2improves the thermal stability of thecomposite membrane.BET and AFM analysis showed that Al2O3-SiO2membrane specific surface areawas634.21m2/g, the average pore radius was18.06nm; SiO2-ZrO2membranespecific surface area was444.52m2/g, the average pore radius was16.94nm;Al2O3-SiO2-ZrO2membrane specific surface area was197.80m2/g, the average poreradius was11.81nm. Al2O3-SiO2and SiO2-ZrO2membranes are mesoporousmaterials which has a high specific surface area and a narrow pore size distribution.Al2O3-SiO2-ZrO2film is relatively low specific surface area, in addition to containingmesoporous structure there is still a microporous structure.