Investigation On Preparation And Properties Of Porous ZrO₂-mullite Ceramics

With the rapid development of material science and the increasing attention to the eco-friendly and energy conservation,a higher requirement has been presented for the performance of porous materials.Among many porous ceramic materials,porous mullite ceramics have been widely studied for various applications like hot gas filters,thermal insulation materials,waste water filters and catalyst supports due to high melting temperature,low density,excellent chemical inertness,low thermal conductivity and excellent creep resistance.However,a higher porosity of porous ceramic leads to a relatively lower mechanical strength.Hence,it has attracted much concern for researchers that how to eco-friendly prepare porous mullite ceramics with both high strength and porosity.In order to overcome this problem,the second phase or mullite fibers have been introduced into the porous mullite ceramic matrix,which is one of the most effective methods to prepare high performance porous mullite ceramics with both porosity and high strength.Therefore,in this study,the porous mullite ceramics were selected as research object,and it aimed to prepare porous mullite ceramics with both porosity and high strength as well as achieve the double purpose of eco-friendly and energy conservation.In this study,the natural mineral zircon and bauxite were used as raw materials,a certain proportion of starch and graphite powders as pore forming agent,porous ZrO2-mullite ceramics have been fabricated by using pore-forming agent method.The effects of different amounts of pore forming agent and sintering temperature on properties of porous ZrO2-mullite ceramics have been investigated.ZrO2-mullite-bonded porous fibrous mullite ceramics have been fabricated by using mullite fibers as matrix,zircon and bauxite as binder utilizing TBA based gel-casting method.A novel and eco-friendly aqueous gel-casting process has been successfully developed to fabricate ZrO2-mullite-bonded porous fibrous mullite ceramics by using mullite fibers as matrix,ρ-Al2O3 as binder.The effects of different amounts of mullite fiber on sintering behaviors,porosity,phase composition,microstructure,pore distribution,compressive strength and thermal conductivity of porous ZrO2-mullite-bonded porous fibrous mullite ceramics have been investigated.In addition,the effects of Y2O3 on the properties of ZrO2-mullite-bonded porous fibrous mullite ceramics have been studued.The main conclusions are as follows:(1)Porous ZrO2-mullite ceramics have been fabricated by using pore-forming agent method.With increasing the amount of pore-forming agent,the apparent porosity increased and the compressive strength of porous ceramics decreased.Zircon finally completely decomposed at 1600℃.The main phase composition for the porous ceramics was ZrO2 and mullite.(2)A narrow range of pore size distribution of ZrO2-mullite-bonded porous fibrous mullite ceramics have been fabricated by utilizing TBA based gel-casting method,as the amount of fibers increased,the apparent porosity increased,the linear shrinkage,bulk density,compressive strength and thermal conductivity decreased.Porous ceramics have been fabricated with porosity in the range of 68.1-84.3%,compressive strength from 0.54-6.32MPa,thermal conductivity of 0.244-0.566W(m·K)-1 and a small average pore size distribution around 5pm.(3)A novel and eco-friendly aqueous gel-casting process has been successfully developed to fabricate ZrO2-mullite-bonded porous fibrous mullite ceramics.As the amount of fibers increased,the apparent porosity increased,the linear shrinkage,bulk density,compressive strength and thermal conductivity decreased.Porous ceramics with porosity in the range of 47.3-55.6%,compressive strength from 10.4-14.4MPa,thermal conductivity of 0.752-0.854W(m·K)-1 and a small average pore size distribution around 3.8-5.0μm have been fabricated.There are little effects on porous ceramics performances when adding fiber content ratio is 1:3.(4)After adding Y2O3,the apparent porosity of porous ceramics decreased while compressive strength increased.