Preparation And Properties Of Mullite Ceramic Filter Materials

Porous ceramics have excellent properties such as low density,high strength,high melting point,creep resistance,strong electrical insulation,strong seismic performance and good acid and alkali resistance.They are widely used in filtration,chemical,metallurgy,high temperature,catalysis and environmental protection.And many other fields.The common porous ceramics mainly include Al₂O₃,Si₃N₄,etc.,because of the high raw material price and high sintering temperature,the production cost is high,which limits its promotion and application.The main chemical composition of high-aluminum fly ash is Al₂O₃ and SiO₂,and contains impurities such as Na₂O,K₂O,MgO,CaO,etc.Because it contains more mullite crystals,it can be used to prepare mullite porous ceramics.In addition,the use of high alumina fly ash to prepare porous ceramic filter material can not only eliminate the environmental pollution caused by fly ash storage,but also save resources and cost,and has significant economic and environmental benefits.Firstly,the process,microstructure and properties of mullite porous ceramics were prepared by using 70.01 wt%desiliconized high alumina fly ash,10 wt%kaolinite,24 wt%alumina,and spherical graphite.Influencing factors;then,mullite porous ceramics with 30 wt%spherical graphite and 1400? for 2 h were used as supports.The mullite film was prepared by solid particle sintering and sol-gel method respectively.Stone ceramic filter material,and its microstructure and properties were studied.The results show that the mullite ceramic support obtained by sintering at1150? for 2 h consists of mullite,a small amount of corundum and quartz.When the sintering temperature rises above 1350?,the quartz disappears.The sample is mainly composed of mullite and contains a small amount of corundum;prolonged holding time has little effect on the phase composition.The addition of 30 wt%spherical graphite had no effect on the phase composition of the mullite ceramic support,but the bulk density and flexural strength decreased more,and the apparent porosity,water absorption and permeation flux were significantly improved.With the increase of spherical graphite addition,the apparent porosity and water absorption of mullite ceramic support gradually increase,the bulk density and flexural strength decrease gradually,the large pore content increases,the pore connectivity becomes better,and the permeation The amount gradually increases.When 30 wt%spherical graphite was added,the apparent porosity and water absorption of the mullite ceramic support gradually decreased with the increase of the firing temperature and the holding time,and the bulk density and flexural strength increased gradually.The permeate flux increases with increasing temperature at lower sintering temperature,and decreases slightly after 1350?.However,as the holding time increases,the permeate flux of mullite ceramic support decreases.Compared with calcium carbonate,starch and flake graphite,the comprehensive performance of mullite ceramic support is better when spherical graphite is used as the pore former.The mullite ceramic support prepared by adding 30 wt%spherical graphite and sintered at 1400? for 2 h has the best comprehensive performance,and the flexural strength and permeation flux are 8 MPa and 3.64 mL·cm^-2·min^-1,respectively.Has good acid and alkali corrosion resistance.When the mullite ceramic membrane is prepared by solid particle suspension slurry prepared from high alumina fly ash,kaolinite and alumina,the integrity and micro-structure of the membrane occur as the solid content and coating times of the slurry increase.Change the penetration flux is gradually reduced.The solid content of the slurry was 10 wt%,coated twice,and sintered at 1400? for 2 h,the permeation flux of the membrane reached 3.49 mL·cm^-2·min^-1.The viscosity of the sol prepared by using tetraethyl orthosilicate and aluminum isopropoxide as a raw material gradually decreases as the solid content increases.When ammonia is used to adjust the pH of the sol to be alkaline,its film forming performance is poor;the sol can be obtained by using a hydrochloric acid-adjusted sol;when the pH is adjusted to 2 by nitric acid,a transparent,uniform and stable sol can be obtained.After gelation,calcination at above 1100? can be completely converted into mullite,which is suitable for preparing mullite ceramic membrane.With the increase of the number of sol coating,sintering temperature and holding time,the continuity and coverage of the film layer are gradually increased,and the permeation flux is gradually reduced.When the coating is applied three times,sintered at 1400?,and kept for 2 h,more film appears.The cracks;the mullite film obtained by coating twice,sintered at 1300? for 1 h,has good integrity and uniform structure,and the permeation flux is 3.41 mL·cm^-2·min^-1,and the comprehensive performance is good.