Effect of high alumina cement on permeability and structure properties of ZrO2 composites

Porous ZrO2 based ceramics are widely used for filtration/separation processes due to the good chemical and thermal stability. For these applications it is desirable that the material have a controlled porous structure in order to obtain good permeability. In this study Ca stabilized ZrO2 composites were developed from a starting mixture of pure ZrO2 containing different mole proportions of calcium aluminate cement. Ceramics disks were uniaxially pressed and subsequently sintered at 1300–1450 °C. The influence of process parameters such as chemical compositions and sintering temperature on textural characteristics (volume fraction of pores, pore size distribution) and permeability was followed by apparent density measurements, Hg porosimetry and N2 permeation, respectively. Sintered microstructure was examined by scanning electron microscopy SEM. The XRD analysis showed that m-ZrO2 transformed to tetragonal and/or cubic ZrO2, these phases probably coexisted at relatively low CaO addition. For 30 mol% addition, amount of the cubic Ca0.15Zr0.85O1.85 phase appreciably increased. At 50 mol% CaO, CA2 was the major phase of the composite with minor CaZrO3 formation whereas relative content c-ZrO2 is slightly reduced.The composites had 30–40 vol% porosity with typical pore radius of 1–1.3 μm and the corresponding Darcian permeability k1 values varied between 2 and 4 × 10−14 m2, such structure parameters slightly increased for high cement addition. The k1 of ceramics produced from 50 mol% CaO composition remained nearly constant up to 1450 °C due to similar densification degree. The experimental permeability dependence on pore structure parameters as well as the comparison with the value estimated by Ergun's equation are showed.