Microstructure Control And Thermal Shock Performance Of Porous Alumina Ceramics

Alumina ceramics have excellent high temperature resistance,corrosion resistance and chemical stability.They are widely used in high temperature engineering fields such as molten metal filters and high temperature gas purification filters.Ceramic materials are inevitably affected by thermal shock in high temperature applications,and the poor thermal shock properties of ceramic materials may cause catastrophic damage in the use process.Therefore,it is of great significance to improve the thermal shock properties of ceramic materials.In this context,gelcasting-pore forming method was used to introduce pores into alumina ceramics,and the mechanical properties and thermal shock properties of materials were improved by adjusting the microstructure of ceramic materials.Firstly,the effects of different dispersant types,pH,dispersant content,milling time and solid content on the viscosity of ceramic slurry were studied.When the calgon was used as dispersant,pH was 13,dispersant content was0.6 % and ball milling time was 5 h,the best ceramic slurry was prepared.After that,porous alumina ceramics with porosity of 30 %-70 % were prepared by adjusting solid content(30 vol%-50 vol%)and starch pore-forming agent addition(0 vol%-62 vol%).The effects of solid content and pore-forming agent addition on the porosity of porous alumina ceramics were analyzed in detail.Porous alumina ceramics with the same pore size of 4,10,30 and 62 ?m were prepared by controlling the particle size of cross-linked polyethylene microspheres.In addition,pore shapes of porous alumina ceramics prepared by different pore-forming agents were studied.Elliptical pore shapes were obtained by yeast pore-forming agents,pore shapes of various shapes were obtained by carbon powder pore-forming agents,spherical pore shapes were obtained by cross-linked polyethylene microsphere pore-forming agents,and rod-shaped pore shapes were obtained by rod-shaped microcrystal pore-forming agents.The effects of porosity on mechanical properties and thermal shock properties of porous alumina ceramics were studied.The compressive strength,flexural strength,fracture toughness and modulus of elasticity of porous alumina ceramics decrease with the increase of porosity,and the decay rate of compressive strength and modulus of elasticity decrease with the increase of porosity.Consistent with the increase of critical crack size with the increase of porosity,the residual strength retention rate of porous alumina ceramics increases with the increase of porosity,which represents that the thermal shock damage resistance gradually increases with the increase of porosity.The critical temperature difference of porous alumina ceramics increases first and then decreases with the increase of porosity,which indicates that the thermal shock fracture resistance increases first and then decreases with the increase of porosity.When the porosity was 55 %,the porous alumina ceramics had better thermal shock damage resistance and thermal shock fracture resistance.The linear shrinkage,flexural strength and modulus of elasticity are almost unchanged with the increase of pore size in the range of 4-30 ?m,while the fracture toughness increases slightly with the increase of pore size.The critical crack size,residual strength retention rate and critical temperature difference increase with the increase of pore size,which represents that the thermal shock damage resistance and thermal shock fracture resistance increase with the increase of pore size at the same time.When the pore size reached 62 ?m,the flexural strength,fracture toughness and modulus of elasticity increase sharply and the thermal shock damage resistance and thermal shock fracture resistance decrease simultaneously due to the change of the microstructure of the material.