| Ceramic membranes are widely used in the field of chemical,food,medicine and environmental protection due to their excellent properties.The commercialized ceramic membranes usually have the multilayer asymmetric structure,i.e.,several transition layers and a top layer with a separation function prepared on the porous support.The porous support provides ceramic membranes with the strength and has an obvious effect on the preparation of the top layer,which is the key factor to prepare the ceramics membranes with the excellent properties.At present,the problems to be solved are that the too wide pore size distribution of the ceramic membrane support,and the contradiction of the porosity to the strength(i.e.the support body has low porosity but high strength,and vice versa),which related with the poor sintering activity,the irregular shape of the domestic alumina powder.However,it is impossible to use the foreign coarse spherical alumina powder as raw material to prepare ceramic membrane because its price is 40 times of domestic alumina powder under the background of the high preparation cost of ceramic membrane itself.In the present work,ceramic microfiltration membrane supports were prepared using the domestic alumina powder as raw materials.The obtained supports were characterized by SEM,Mercury Intrusion Porosimetry,Laser particle size analyzer and universal material testing machine.The effect of the design of the alumina particle gradation,the innovated adding technical method which makes the small sintering aid distributes uniformly with alumina powders and the kind and content of pore former on the performance of the ceramic membrane supports were studied.The ceramic membrane supports with high bending strength,high porosity and sharp and controllable pore size distribution were obtained.Based on those preparation conditions,19-channels ceramic microfiltration membrane supports were prepared by extrusion method in a pilot scale.The conclusions can be drawn as follow:(1)The design of particle size gradation is the basement and keypoint to obtain the ceramic membrane supports with high bending strength,high porosity and sharp and controllable pore size distribution.It is found that the particle size of the coarse alumina particles has the decisive effect on the pore size of the support if the coarse alumina particle is the major in the raw material,which is also the major factor to adjust the pore size of the supports;The medium-grained particle has the important effect on the bending strength of the support;The fine particles can be used to adjust the porosity and the pore size distribution of the support in some degree.The results show that if the mass ratio of coarse particle W50(d50=37?m)is in the range of 60 wt%-80 wt%,the bending strength of the support decreases with the decrease of the mass ratio of the medium-grained particle W10(<d50=8.2?m).However,the porosity of the support has the opposite change.When the coarse alumina particle is the major(the mass ratio is 80wt%),the medium and fine particles have less effect on the formation of the bone of the porous support.The porosity and the pore size distribution of the support changes slightly with the mass ratio of the medium and fine particles.However,the bending strength of the support decreases with the decrease of the content of W10(d50=8.2p,m);When the mass ratio of coarse alumina particles is in the range of 70wt%? 60wt%,the bending strength of the supports decreases with the increase of the content of fine particles.However,the porosity increase slight and the pore size distribution of the support changes wide.The ceramic membrane supported with the bending strength of>45MPa can be obtained after calcined at 1650? for 2h with the mass ratio of coarse particles(d5o=37?m):medium particle(d50=8.2?m):fine particle(d50=1.6?m)=70:24:6.(2)The sintering aid TiO2 could not mix uniformly with the coarse alumina particles by mechanical mixing and in-situ deposition,which has less sintering-aid action on the sintering of coarse grains.By in-situ hydrolysis,0.4wt%nano Ti02 could mix uniformly with coarse alumina particles and has the good sintering-aid action.The sintering temperature of the support can be decrease obviously and the support also has the high bending strength by this method.(3)Based on the technology of the particle size gradation and the addition of nano TiO2,the support can own both the high bending strength and the high porosity using 5wt%starch as pore former.(4)19-channels ceramic membrane supports are prepared by extrusion method in a pilot scale.The obtained supports sintered at 1650? for 2h has the porosity of>40%,the bending strength of>80MPa,the sharp and controllable pore size distribution and the good acid/alkali corrosion-resistance. |
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