Pore Structure Control And Compressive Of Lamellar Al₂O₃ Porous Ceramics

Alumina(Al2O3)porous ceramic has the characteristics of low cost,large specific surface area,high temperature resistance and corrosion resistance,and has wide application value in the fields of filtration and separation,biological tissue engineering,catalyst support.The freeze-casting method is a common method for preparing porous ceramics,which has the characteristics of flexible and simple process and controllable pore structure.Existing studies describe the influence of freeze-casting process on pore structure,and analyze the relationship between pore structure and mechanical properties.There are bridge structures in the porous ceramics prepared by freeze-casting technology,and the formation mechanism of these bridge structures and their mechanism of action on mechanical properties are not yet clear.In this paper,the freeze-casting method was used to prepare Al2O3 porous ceramics.The effect of solid content and freezing temperature on the pore structure was studied.The dimensionless physical quantity(M)was used to characterize the pore morphology of Al2O3 porous ceramics and the formation mechanism of the bridge structure was revealed.The effect of the pore structure on the mechanical properties of compression was studied.The mechanism of the bridge structure on the mechanical properties of Al2O3 porous ceramics was studied by a combination of finite element simulation and experiment.The results showed that:(1)Al2O3 porous ceramic exhibits a gradient pore structure from the bottom to the top,followed by dense area,transition area and lamellra pore area.The pore structure changes from cell to dendrite and then to lamellar.There is a deflection angle along the freezing direction of the tunnel.As the height increases,the deflection angle gradually disappears,and the tunnel is parallel to the freezing direction(2)When the solid content is increased from 20vol.%to 30vol.%,The pore diameter of the lamellar pore area of Al2O3 porous ceramic is reduced from 35.49?m to 25.33?m,and the porosity is reduced from 54%to 41%,the linear shrinkage rate is 15%It fell to 11.2%.When the freezing temperature is reduced from-20? to-40?,the pore diameter is reduced from 33.74 to 19.55?m,the thickness of the pore wall is reduced from 161.32?m to 76.53?m,and the structure wavelength is reduced from 195.06?m to 96.08?m(3)The formation mechanism and control method of the bridge structure were analyzed When the freezing temperature was reduced from-20? to-40?,the bridge density increased from 1.25×10-5 ?m-2 to 5.44×10-5 ?m-2.When the solid content is increased from 20vol.%To 30vol.%,The bridge density decreases from 2.98×10-5 ?m-2 to 1.02×10-5?m-2.The dimensionless physical quantity(M)is used to describe the pore morphology.When the value of M increases,the bridge density decreases.The formation mechanism of the pore structure is expounded.(4)The Al2O3 porous ceramic undergoes three stages of elastic deformation,plastic deformation and densification from deformation to fracture.The stress-strain curve has the characteristics of the porous material when it is compressed in one direction.The deformation of Al2O3 porous ceramics takes the form of Euler buckling.When the porosity is reduced from 57.5%to 45.4%,the compressive strength is increased from 3.7MPa to 8.6MPa.The relationship between relative density and compressive strength conforms to Gibson-Ashby model.When the structure wavelength is increased from 71.67?m to 117.39?m,its compressive strength increases from 5.3MPa to 11.2MPa.When the M value was reduced from 7.16 to 5.29,the compressive strength increased from 6.3MPa to 10.5MPa.When the relative density increased from 42.5%to 60.6%,the elastic modulus increased from 94.3MPa to 495.2MPa,and the two also conformed to the Gibson-Ashby model.(5)The finite element simulation results show that:during the process of reducing the M value from 10 to 5,the maximum dangerous point stress value and strain value of the model decrease accordingly,and the compressive strength of the Al2O3 porous ceramic model is improved.The results of uniaxial compression experiments show that as the value of M decreases,the compressive strength of Al2O3 porous ceramics increases,and the simulation results are consistent with the experimental results.