The Study On The Preparation Technology Of Mullite Porous Ceramics Without Organic Additive

Porous ceramics composed by mullite whiskers feature good mechanical properties and thermal shock stability,but only a few literatures report the processing of acicular mullite and the works usually used low-cost rare materials or complex setups.This thesis aims to explore eco-friendly methods to prepare mullite porous ceramics using low-cost materials,which may save energy and realize industrialized production.Firstly,inorganic cementitious material was used to fabricate porous mullite in this study.ρ-Al2O3 and diatom frustules were selected as the main raw materials,AIF3 and MoO3 were used as additives.The water hardening characteristic of ρ-Al2O3 was used to solidify ceramic slurry.Then porous mullite ceramics were fabricated by sintering the green body at high temperatures.This method is an environment-friendly process without emission of organics.The effects of temperature on phase composition,microstructure,linear shrinking rate,open porosity,and compressive were studied by XRD,SEM and so on.The results show that porous mullite ceramics are made of mullite whiskers,and the porosity can be up to 82.3%when sintered temperature is 1500 ℃.Secondly,silica fume was used for the first time as Si precursor for synthesis of porous mullite ceramics with fibrous pore morphology.The SiO2 from silica fume has small particle size and high reaction activity.The porous mullite ceramics were prepared by mould pressing method without using any porogen and binder.The open porosity is 49%and near zero sintering shrinkage is observed for this porous mullite.The porous ceramics have flexural strength of 27.7 MPa at the porosity of 49%when sintering temperature is 1600 ℃ and holding time is 3 hours.Thirdly,diatom frustules were used as Si precursor for synthesizing porous mullite ceramics with fibrous pore morphology by mould pressing method without using any oxide additives,porogen and binder.The original circular pores of diatom frustules provide the space for the growth of mullite whiskers.The porous ceramics show flexural strength of 15.86 MPa at the porosity of 59.3%when sintering temperature is 1600 ℃ and holding time is 3 hours.