Preparation And Properties Of A New Alumina Ceramic Membrane

Membrane has attracted more and more attention because of its selectively permeable and semi-permeable properties and the ability to separate two phases.With the gradual improvement of the demand for water treatment technology in the world,the innovation and application of membrane separation technology become more and more important.At present,the inorganic ceramic membrane is mainly made of alumina（Al₂O₃）material.The alumina ceramic membrane has the advantages of simple operation,high separation accuracy and environmental protection.Compared with other membrane materials such as organic membrane,the mechanical strength is higher and the chemical stability is better.However,the alumina ceramic membrane still has the problems of poor membrane integrity and complicated preparation path,which to some extent inhibits the large-scale application of alumina ceramic membrane in related fields such as separation and filtration.In order to improve the separation and filtration performance of alumina ceramic membrane,the sol-gel method was used to prepare the sol,which was coated on the alumina support body by impregnation method,and then the membrane was made by high temperature sintering.The effects of p H value,hydrothermal temperature,impregnation time,sol ratio and sintering temperature on the filtration properties of Al₂O₃ceramic membrane and Al₂O₃-SiO₂,Al₂O₃-SiO₂-TiO₂ composite ceramic membrane were studied.The main research results are as follows:1.The study on the preparation of Al₂O₃ ceramic membrane by sol-gel method was carried out,and the influence of p H value,hydrothermal temperature,impregnation time,sol ratio,sintering temperature and other factors on the crystal phase and filtration performance of Al₂O₃ ceramic membrane was discussed.It was found that the particle size of boehmite sol increased with the increase of hydrolysis temperature in the preparation of alumina ceramic membrane in a certain range of hydrolysis temperature,but the phenomenon of colloidal agglomeration would occur when the temperature was too high,and the best hydrolysis temperature was 80℃.When after add acid p H>3,the appearance of the sol with a white opaque,quiet place for a period of time will produce obvious stratification,namely that sol is not stable and precipitation incomplete glue solution,p H<3,the appearance of the sol is not much change,but when it happens to let stand for 12h gel phenomenon,its viscosity increases,not suitable for late coated membrane;When the p H value of the sol is controlled at about 3,the sol has good fluidity and can still exist stably after standing for a period of time,and there is no white precipitation and no stratification phenomenon.At this time,the properties of the sol prepared are more ideal.Within a certain soaking time range,the thickness of alumina ceramic film on the support will increase with the increase of soaking time,and the film thickness has no significant change after soaking 60s.With the increase of PVA content,the thickness of ceramic film gradually increases,and the surface becomes denser.In a certain range of heat treatment temperature,the porosity of ceramic membrane increases with the increase of heat treatment temperature,but if the heat treatment temperature is too high,the porosity of ceramic membrane will decrease.It was found that the best conditions were hydrolysis at 80℃,gel solution p H at 3.0,support soaking for 60s,heat treatment at 500℃,and the thickness of the prepared ceramic film was about 2.11μm.2.Al₂O₃-SiO₂ composite ceramic membrane was prepared by sol-gel method.The effects of p H value,hydrothermal temperature,impregnation time,sol ratio,sintering temperature and other factors on the crystal phase and filtration performance of Al₂O₃-SiO₂ composite ceramic membrane were discussed.The results show that when preparing Al₂O₃-SiO₂ composite ceramic membrane,the sintering temperature is the same,and the support is impregnated with the composite sol once,the penetration flux of composite ceramic membrane is higher than that of impregnated twice.With the increase of sintering temperature,the permeability flux of ceramic membrane decreases when the support is impregnated in sol for the same number of times.The permeation flux of the composite ceramic membrane prepared by sintering at 1300℃and sintering for different times did not change significantly in the interval of 0.5-1h,which was 3.42m L·cm^-2·min^-1.When the holding time was from 1 to 2.5h,the permeability of the membrane decreased significantly,and decreased to 2.50m L·cm^-2·min^-1 at 2.5h.When the support is impregnated for one time,sintering at 1400℃and sintering for different times,the penetration flux of the ceramic membrane sintered for 1h is higher than that of the ceramic membrane sintered for 2h.When the support is impregnated twice,the penetration flux of the ceramic film sintered for 1h is lower than that of the ceramic film impregnated once,which is 3.28m L·cm^-2·min^-1,and the permeability is poor.When the sintering time is 2h,the permeation flux of the membrane decreases.With the increase of impregnation time,the thickness of ceramic films prepared at 15s,45s,60s and 90s increased gradually.The thickness of ceramic films increased faster in the range of15s-45s,but was slower in the range of 45s-60s,and there was no significant change in the thickness of 60s-90s.The ceramic films sintered at 1000℃have diffraction peaks of corundum and quartz besides mullite peaks.With the increase of temperature,the peaks of corundum and quartz disappeared after 1100℃,and only the diffraction peaks of mullite were observed.When the ratio of Al/Si sol is 4:1,the product is mullite,while when the ratio is 2:1,3:1 and 1:4,no mullite is found.Therefore,it can be known that only when the ratio of Al/Si sol is 4:1,the mullite ceramic film can be produced.Through research,it is found that the optimal conditions of impregnation twice,impregnation time 60S,sintering 1h at 1300℃,the ratio of aluminum sol and silicon sol is 4:1,the thickness of the prepared Al₂O₃-SiO₂ composite ceramic film is 1.82μm,the measured pore size of the film is 1.2nm,the porosity is 21.1%,and the permeability flux is 3.32m L·cm^-2·min^-1.3.Al₂O₃-SiO₂-TiO₂ composite ceramic membrane was prepared by sol-gel method,and the effects of p H value,hydrothermal temperature,impregnation time,sol ratio,sintering temperature and other factors on the crystal phase and filtration performance of Al₂O₃-SiO₂-TiO₂ composite ceramic membrane were discussed.When preparing Al₂O₃-SiO₂-TiO₂ composite ceramic membrane,when the sintering temperature is the same,the support is impregnated with the composite sol once,and the thinner ceramic membrane and the higher permeability flux are obtained.With the increase of sintering temperature,the permeability flux of ceramic membrane decreases when the support is impregnated in sol for the same number of times.The permeation flux of the composite ceramic membrane prepared by sintering at 1400℃and sintering for different times did not change significantly in the range of 1-1.5h,which was 3.34m L·cm^-2·min^-1.When the holding time was 1.5-2.5h,the permeability of the membrane decreased significantly,and decreased to 2.41m L·cm^-2·min^-1at 2.5h.When the support is impregnated for one time and sintered at 1400℃for different times,the penetration flux of the ceramic membrane sintered for 1.5h is higher than that sintered for 2.0h.When the support is impregnated twice,the permeability flux of the ceramic membrane sintered for 1.5h is lower than that of the ceramic membrane impregnated once,which is 3.32m L·cm^-2·min^-1,and the permeability performance is poor.When the sintering time is 2.0h,the permeability flux of the membrane decreases.With the increase of impregnation time,the thickness of ceramic films prepared at 30s,45s,60s and 90s gradually increases,and the curve increases more slowly at 60s-90s than at 45s-60s.The ceramic film was prepared under the conditions of dipping 60s,dipping twice and sintering at 1400℃.When the ratio of aluminum sol,silicon sol and titanium sol was 4:1:1,the thickness of the ceramic film was 3.26μm,the pore size of the film was 1.1nm,the porosity was 20.23%,and the permeability flux was 3.12m L·cm^-2·min^-1.When the ratio of aluminum sol,silicon sol and titanium sol is 1:4:1,the thickness of the ceramic film is 4.35μm,the pore size of the film is 2.3nm,the porosity is 25.38%,and the permeability flux is 3.49m L·cm^-2·min^-1.When the ratio of aluminum sol,silicon sol and titanium sol is 1:1:4,the thickness of the ceramic film is 4.56μm,the pore size of the film is 3.9nm,the porosity is 30.25%,and the permeability flux is 3.87m L·cm^-2·min^-1.Through the study,it was found that the optimal conditions were impregnation twice,impregnation time 60s,sintering at 1400℃for 1.5h,the ratio of aluminum sol,silicon sol and titanium sol was 4:1:1.The film thickness of the prepared Al₂O₃-SiO₂-TiO₂ composite ceramic film was 3.26μm,the pore diameter of the film was 1.1nm,the porosity was 20.23%,and the permeability flux was3.12m L·cm^-2·min^-1.