Processing of functionally gradient ceramic membrane substrates for enhanced porosity

A method to cast functionally gradient porous ceramics was conceived and established. A previous initial study had established viability of the technique: samples were shown to have a functionally gradient cross section with a continuously increasing mean particle size from top to bottom. This article reports on a modified two-level factorial experimental design that was undertaken to determine the interdependent effects of pH, polyelectrolyte additive concentration, sintering temperature, and powder blend on the sintered microstructure. Ceramic disks appr. 45 mm in diameter and 3.3 mm thick were cast by sedimentation. The green bodies were dried prior to sintering. For each point in the experimental space, mercury porosimetry was used to obtain the porosity and pore-size distribution in the solid sample. From metastable suspensions, it was possible to form functionally gradient porous structures. Porosimetric data obtained in this study corroborated pervious observations. Structures were produced with a wide pore-size range and high porosity (up to 0.68). These structures, formed from a one-step process, could be used as-is for ultrafiltration applications, but they also had a sufficiently fine top layer for facilitating subsequent thin-coating operations.NRC publication: Ye