Microstructure And Properties Of Porous Al₂O₃-ZrO₂ Ceramics Fabricated By Freezing Casting Method

Energy and environmental issues are very serious nowadays; porous ceramic material attracts more and more attention and rapidly becomes one of the focuses as a new kind of green environmental protection material for special applications such as infiltration, separation, dispersion, thermal insulation, sound absorption, adsorption and catalysis in recent years.This paper reviewed the research achivements at home and abroad, and fabricated highly porous Al O -ZrO ceramics with a cylindrical shape by freezing casting method with different solid contents, using camphene as the solvent. In this study, the density, porosity and shrinkage of the green bodies and the final porous ceramics were calculated by the parameters derived from direct measurement. DTA-TGA 2 3 2thermal analysis method was applied to determine the sintering parameters. The relationship between various parameters and final microstructure/properties were also studied. The compressive strength of porous ceramics was tested using a universal material testing machine. The pore size and its distribution and specific surface area were measured by mercury intrusion method using different solid content of the porous ceramic products. Scanning electron microscope was used to observe the pore morphology within the porous ceramic products. In addition, the study also had successfully fabricated the production of the salt/porous ceramic preform composite (NaCl/Al_2O3-ZrO₂) heat storage material at 1000℃according to the spontaneous infiltration mechanism, the influence of the different infiltration conditions on the heat storage composite material were also studied, and the pore morphology of the heat storage composite was observed by scanning electron microscopy after infiltration.The results showed that the addition of 3wt% Texaphor963 in the slurry could improve the strength of green bodies and make handle easy, but excessive Texaphor963 was disadvantageous to the curing process and reducing the strength. The loss of volatile camphene within the green body increased exponentially with the dying time. The DTA-TGA curves showed that the thermal decomposition of camphene appeared at 299℃, and thermal decomposition temperature for Texaphor963 was about at 370℃. When the solidcontent varied from 10vol% to 20vol%, the density increased from 0.6g/cm3 to 1.6g/cm³, porosity decreased from 87% to 67%, shrinkage of diameter varied from 3.8mm to 0.45mm, compressive strength increased from 0.83 MPa to 22MPa. The compressive strength changed exponentially with the porosity and density of the law. Mercury instrusion testing results showed that porous ceramics contained two sizes of pores, corresponding to the primary and secondary dendritic arms of camphene crystals and the stacking of ceramic particles. SEM results not only confirmed the mercury intrusion testing results, but also showed that the pores within the porous ceramic body presented a graded variation trend. All of the pores aligned along the direction of the freezing gradient. Lower freezing temperature was conducive to the formation of smaller pore size.Infiltration of NaCl within the pore channels of porous Al O -ZrO ceramic showed that the majority of pores were filled with NaCl after infiltration, a lower solid content and a longer infiltration time were helpful to improve the infiltration rate of the porous ceramics. The phase of the NaCl/Al_2O3-ZrO₂ composite did not change after infiltration process. Thermal diffusivity and thermal conductivity decreased as the temperature, but specific heat with increased in the 100⁵00℃range.