Study On Preparation Of Porous Mullite Lightweight Material From Fly Ash And Its Performance

Porous mullite lightweight materials are widely used in thermal insulation materials,catalyst carriers,gas-liquid filtration and separation materials because of its excellent performance.However,porous mullite lightweight materials prepared by traditional methods have shortcomings such as low porosity,large pores,and large shrinkage,resulting in poor mechanical properties of porous mullite lightweight material and restricting their application fields.In response to the above problems,in present paper,porous mullite lightweight materials were prepared by microemulsion template method and particle stabilization method combined with reaction sintering using fly ash and bauxite as raw materials,Al F₃·3H₂O as additives.The effects of surfactant content,oil content,additive content and sintering temperature on the linear shrinkage,bulk density,microstructure,normal temperature mechanical properties and thermal conductivity of porous mullite lightweight materials were investigated.The research results showed that:(1)Porous mullite lightweight materials were prepared by microemulsion template method using fly ash and bauxite as raw materials,polyoxyethylene sorbitan monooleate(Tween 80)as surfactant,isooctane as the oil phase,ethylene glycol glycidyl ether as the binder and tetraethylenepentamine as curing agent.When the volume ratio of Tween 80 to water is 2:50 and the volume ratio of isooctane to water is 1.6:1,the prepared porous mullite lightweight materials with a porosity of 71.5%and a pore diameter of 260?m have the compressive strength and the flexural strength is as high as 33.3 MPa and 15.9 MPa respectively.(2)Porous mullite lightweight materials were prepared by particle stabilization method combined with reaction sintering,dodecyl trimethyl ammonium chloride(DTAC)as cationic surfactant.As the content of surfactant DTAC increased from 0.04 wt%to 0.28wt%,the porosity of as-prepared porous mullite lightweight materials decreased from78.5%to 67.4%,and the average pore size decreased from 500?m to 280?m.The flexural strength and the compressive strength respectively increased from 12.5 MPa and 18.7 MPa to 21.0 MPa and 29.0 MPa,and its thermal conductivity increased from 0.057 W/(m·?)to0.082 W/(m·?).(3)The whisker-reinforced porous mullite lightweight materials were prepared by the particle stabilization method combined with reaction sintering using Al F₃·3H₂O as an additive.When the content of Al F₃·3H₂O is 9 wt%,the average length of mullite whiskers in the prepared porous mullite lightweight material samples with a porosity of 72.3%via sintering at 1400?/2 h reaches the maximum of about 19.2?m,and the flexural strength and compressive strength of the samples are respectively 17.8 MPa and 31.0 MPa,which are higher than those(the flexural strength of 9.5 MPa and compressive strength of 17 MPa)of the porous samples prepared without Al F₃·3H₂O.