Study On The Microstructure And Properties Of Al₂O₃ And ZrO₂/Al₂O₃ Porous Ceramics Prepared By Gel-foaming

In this paper,Al₂O₃ porous ceramics and ZrO₂/Al₂O₃ porous ceramics were fabricated by gel-foaming and pressureless sintering method with Al₂O₃ powder and ZrO₂ powder as raw materials,sodium alginate as a gel system and sodium dodecyl sulfonate as foaming agent.The viscosity of the slurry was studied by a rotational viscometer.The foaming and foam stability of the surfactant were studied by using the Waring Blender stirring method.The curing mechanism of the sodium alginate gel system was analyzed by infrared spectrometer.The microstructure of Al2O3 porous ceramic and ZrO2/Al2O3 porous ceramic green bodies and sintered bodies were observed by scanning electron microscopy.The phase composition of the porous ceramic sintered bodies were analyzed by X-ray diffractometer.The mechanical properties of the porous ceramic green bodies and the sintered body were tested by a universal testing machine.The effects of dispersant content,pH value,solid phase content,foaming agent content and ZrO₂ content on slurry properties,structure and properties of the green body and the sintered body were investigated,as well as the influence of different sintering temperatures on the mechanical properties and microstructure of ZrO2/Al2O3 porous ceramics.The experimental results show that ceramic particles and foam were held in the three-dimensional network formed by the reaction between sodium alginate and free calcium ions,and the slurry are consolidated simultaneously when Al₂O₃ porous ceramic and ZrO₂/Al₂O₃ porous ceramic were prepared with sodium alginate as organic monomer.The addition of MgO+TiO₂ sintering aid enabled liquid phase sintering of the porous ceramic.The mechanical properties of the materials was improved when TiO₂ forms a solid solution with Al₂O₃,promoting the sintering process,and MgO and Al₂O₃ formed magnesium aluminum spinel?MgAl₂O₄?,inhibiting the abnormal growth of crystal grains and promoting densification of the hole support improves.The foaming performance and foam stability of the slurry increased first and then decreased with the increase of the foaming agent content.The viscosity which has an effect on foaming and foam stability of foaming agent,microstructure and mechanical properties of porous ceramic increased with the increase of solid content,decreased with the increase of pH value,decreased first and then increased with the increase of dispersant content.The microstructure of Al₂O₃ porous ceramics was uniform,and there were a large number of through-holes.The porosity increased first and then decreased with the increase of solid phase content and foaming agent content,and the compressive strength decreased first and then increased.The Al₂O₃ porous ceramic sintered body had a uniformly open pore structure.The strength of the porous ceramic was ensured while the pore support structure was uniform and compact.When the solid phase content is 25 vol.%,the foaming agent content is 3.0 wt.%,the dispersant content is 0.4 wt.%,and the pH is 12,the porosity of the Al₂O₃ porous ceramic is the largest.In the preparation of ZrO₂/Al₂O₃ porous ceramics,as the ZrO₂ content increased,the viscosity of the slurry increased,the porosity of the green body decreased,the compressive strength increased,and the shrinkage rate of the sintered body decreased.As the sintering temperature increased,the shrinkage of the ceramic increased and the porosity decreased significantly.When the solid phase content is 25 vol.%,the ZrO₂content is 15 wt.%,and the sintering temperature is 1350°C,the porosity and strength of the ZrO₂/Al₂O₃ porous ceramics reach an optimum value.Compared with Al₂O₃porous ceramics,the porosity of ZrO₂/Al₂O₃ porous ceramics is reduced,but the compressive strength and thermal shock resistance are significantly improved.