Fabrication And Compressive Strength Of Porous Alumina By Freeze-casting Using Binary Solvent Systems As Template

Freeze casting method is a new preparation technology of porous ceramic by using the principle for forming pores with direct sublimation after solvent crystallization.And the porous ceramics were fabricated by freeze casting has the advantages of good mechanical properties in a particular direction,and porosity,pore direction and size is controllable.At present,many studies focus on changing the crystallization behavior of solvent by adding different additives in the solvent for obtaining different shapes of pores.However,these additives can not be removed directly by freeze drying.They need subsequent calcinations or special treatment.The residual pore will damage the performance of porous ceramics.In order to solve this problem,the porous ceramics were fabricated by directional freezing casting method using tertiary butyl alcohol（TBA）/water binary soluble solvent which can removed directly by freeze drying as the liquid medium,and the influence of pore morphology and strength of porous ceramics with different concentrations of tertiary butyl alcohol was discussed.At the same time,the annealing process was applied in the freezing process to optimizating mechanical property of porous ceramics.In addition,fabrication of porous ceramic by directional freezing casting method using diphenyl methane/water binary insoluble solvent as the liquid medium was investigated,the pore morphologies of porous ceramics were observed and the properties of porous ceramics were measured.The following results were obtained:（1）Mixture solvents of water and tert-butyl alcohol has been used as the liquid medium to prepare Al₂O₃porous ceramics by freeze drying method.When the tert-butyl alcohol concentration increased from 0%to 100%,the morphology of porous ceramics holes constantly changed from lamellae to snowflake,dendritic,needle-like,and hexagonal.The compressive strength of the porous ceramics were in 3.5MPa～59.2MPa.When the concentration of tert-butyl alcohol was 100%,the 59.2MPa highest compressive strength of porous ceramics was obtained;（2）Porous ceramics with water-based ceramics slurries were fabricated by annealing and freeze casting method.When the annealing temperature from-25℃,-15℃to-5℃,the pore morphology of the porous ceramics changed from finer river lamellae to the circular hole.Porous ceramics with TBA/water-based ceramics slurries were fabricated by annealing and freeze casting method.The morphology of porous ceramics with 30%TBA concentration ceramics slurries was dense and uniform small holes.The compressive strength of porous ceramics using 30%TBA solvent with annealing process was increased by nearly 3.6 times than the compressive of porous ceramics using 30%TBA solvent without annealing process;（3）Fabrication of porous ceramic by directional freezing casting method using diphenyl methane/water binary insoluble solvent as the liquid medium was investigated,the double hole type of porous ceramics with a large pore size of a lamellar hole and a small pore size of a circular hole was obtained.When the diphenyl methane content was 25%,the largest specific surface area of porous ceramic was 566m²/mg,which is increased by nearly 20%than the specific surface area of porous ceramic used pure water as the solvent.