Effect Of Oxide Addition On Structure And Properties Of Mullite Porous Ceramics

Mullite is an engineering application material with low coefficient of thermal expansion,low volume density,excellent high temperature strength and high thermal shock resistance.Due to the special forming conditions of high temperature and low pressure,mullite can rarely be formed naturally,but it is one of the most important phases used in traditional and advanced ceramics.Using its good physical and chemical properties,combined with the manufacturing process of porous ceramics,high temperature application engineering materials with excellent properties can be produced.Such as refractories,high temperature gas/melt filtration,high temperature catalyst carrier and so on.Porous mullite ceramics with high porosity and good mechanical properties were prepared by foaming method using kaolin and alumina as main raw materials and sodium polyoxyethylene ether sulfate as foaming agent.The effects of three different oxides（Mg O/Ti O₂/Y₂O₃）,their content and sintering process on the microstructure and properties of mullite porous ceramics were studied.Through systematic research,the main results of this paper are as follows:（1）Sintering at 1450℃for 2 hours produced mullite porous ceramic with porosity up to 80%and compressive strength of 5 MPa.Increasing sintering temperature,porosity decreases and compressive strength increases.Prolonging the sintering time promoted the formation of mullite phase in sintering reaction.Among the mullite porous ceramics fabricated by sintering at 1600℃for 2 hours,the porosity was 72.15%,the compressive strength was 12.18 MPa,and the pore size distribution was uniform mainly centered between 0.1-0.2 mm and 0.2-0.3 mm.（2）The addition of Mg O is helpful to the formation of acicular and prismatic mullite phase with good mechanical properties,increase the amount of mullite phase in the sample,increase the degree of densification,decrease the porosity and increase the compressive strength.When the Mg O content was 6%,the porous mullite ceramics were sintered at1450℃for 2 hours,the porosity of the prepared mullite porous ceramics was 64.32%,the mullite phase content was 68.55%,and the compressive strength 13.12MPa.The mullite porous ceramics prepared by sintering at 1500℃for 2 hours,the mullite phase content is80.23%,the porosity is 61.9%,the compressive strength is 21.9MPa,and the uniform pore size distribution is mainly concentrated in 0.1-0.2mm.（3）With the addition of Ti O₂,it is helpful to the transformation and formation of mullite phase,increase the amount of mullite phase in the sample,increase the densification degree of the sample,decrease the porosity and increase the compressive strength.When the Ti O₂content is 6%,the mullite porous ceramics are sintered at 1450℃for 2 hours,the porosity of the prepared mullite porous ceramics is 65.44%,the mullite phase content is 61.29%,and the compressive strength 16.78MPa.The mullite porous ceramics prepared by sintering at 1600℃for 2 hours have the best comprehensive properties.The mullite phase content is more than 95%,the porosity is 60%,the compressive strength is 32.29Mpa,and the pore size distribution is uniform,mainly concentrated in the range of 0.1-0.2mm.（4）The addition of Y₂O₃is helpful to the transformation and formation of mullite phase,and the effect decreases with the increase of the amount of Y₂O₃.The amount of mullite phase in the sample increases,the densification degree of the sample increases,the porosity decreases and the compressive strength increases.When the Y₂O₃content was 6%,the porous mullite ceramics were sintered at 1450℃for 2 hours,the porosity of the prepared mullite porous ceramics was 64.27%,the mullite phase content was 63.66%,and the compressive strength 16.42MPa.The comprehensive properties of mullite porous ceramics prepared by sintering at 1500℃for 2 hours are the best,with mullite phase content of 61.27%,porosity of 64.38%,compressive strength of 18.67MMa and uniform pore size distribution between 0.1-0.3mm.