Studies On Effects Of Additives And Substrate On Zirconia Ultrafiltration Membrane Prepared By Sol-Gel Method

With the solution to the crucial technique in the preparation of ceramic ultrafiltration membrane by means of Sol-Gel method as the groud work, this paper studies the concrete preparation of zirconia ultrafiltration membrane so as to provide necessary technique foundations for the realization of the industrialization of ceramic ultrafiltration membrane.Suspension stability is the primary factor to prepare integrated membrane without defect. With stable zirconium sol prepared by Zr(NO₃)₄·5H₂O as raw materials, this paper studies in details the effects of the types and doses of organic binders and Drying Control Chemical Additives (DCCA) upon the stability of the suspension. Meanwhile, the effect of stability of suspension and crystal phase stabilizer upon the process of membrane is explored as well. It shows that PVA and neutral DCCA such as glycerol are most suitable for zirconium sol system selected in this paper. It also indicates that sol is not absorbed by the support and the surface of membrane is homogeneous throughout by controlling the amount of PVA with 2³%. Membrane is crack-free by adding neutral DCCA. Yttrium nitrate(Y:Zr=0.08:0.92) could avoid membrane defect caused by crystal phase transformation.Substrate has a distinct effect on membrane preparation by Sol-Gel method. In this paper, the effect of substrate micro-structure on membrane micro-structure and material property matching problem between substrate and membrane are discussed at length in order to choose suitable substrate for suspension. EDX analysis is introduced to observe suspension absorbed into substrates with different pore diameter. It shows that the smaller the substrate pore diameter, the easier the fact that membrane could form on it. Membrane mass loss rate under the same ultrasound power and ultrasound time is raised to represent material property matching problem. It shows membrane mass loss rate is the least on zirconia substrate. However, after dip-coating for 5 times on three different substrates, large pore size defects still exists.Influences of the dip-coating time, dry conditions and sintering program are investigated systemically. It is found the thickness of the top layer increases linearly with the square root of the dip-coating time after coating for 1 time. It is suitable to control dip-coating time at 60s. With the increase of coating frequency, membrane thickness also increases and then goes to a constant gradually. After coats for 5 times (600℃ for 2h), membrane almost reaches intergrity. Pure water flux is about 100 L·m^-2·h^-1 and rejection rate of 500000D dextran and 70000D dextran are 80% and 20% respectively. Membranecrack is avoided effectively by introducing humidity during dry process. Pore diameter increases with the increase of the sintering temperature , which leads to a decrease in rejection rate. Pore diameter distribution is measured between 40nm and 50nm by mercury porosimetry. Surface and cross-sectional SEM of zirconia ultrafiltration membrane show that membrane surface is smooth and the top membrane thickness is about lum.