Sintering effects on the porous characteristics of functionally gradient ceramic membrane structures

A method to drain cast porous ceramics has been conceived and established, where samples were shown to have a functionally gradient cross-section with a continuously increasing mean particle size between the two principal sur faces. Ceramic discs approximately 45 mm in diameter, and 3.3 mm thick were cast b y sedimentation. These green bodies were dried prior to sintering. Maximum sintering temperature and the length of the sintering soak time were varied for samples made from suspensions of both 5 and 10 volume percent solids. Mercury porosimetry was used to obtain the porosity and pore size distribut ion in each sample. Additionally, a number of atomic force microscopy (AFM) measurements were made on some samples in order to correlate bulk porous p roperties with those on the outside surfaces. The results showed that as the sintering temperature increased, the densifi cation of the bodies proceeded more rapidly. In general, the longer the sin tering soak time, the denser the samples became as well. For the samples pr epared at the lower temperatures however, the porosity showed less of a soa k time dependence. The green body had a clustered and asymmetric microstruc ture, which contributed to differing degrees of localized densification and coarsening effects depending on the sintering temperature. Densification e ffects were more pronounced with the samples made from the more concentrate d suspenisions. There was an inverse correlation between the bulk and surface pore dimensio ns, attributable to the different size scales of particles in the two regio ns. The much finer surface layer particles were able to undergo some amount of densification while surface diffusion sintering mechanisms were primari ly at work elsewhere in the structure.