Behaviour of open-cell cordierite foams under compression

Abstract

Cordierite foams were produced using the polymer foam replication method. The effects of both the structure of the polymeric foam template and the slurry's solid loads on the compressive strength and the sintered structure of the ceramic foam were evaluated in order to achieve the optimal manufacturing conditions. The compressive strengths of cordierite foams were measured at room temperature. Polyurethane (PU) foams were used as templates. Aqueous ceramic suspensions were prepared with solids weight fraction ranging from 50 to 65%. The effects of both the PU density and the solids volume fraction on porosity and strength of the developed cordierite foams were evaluated. The cordierite foams produced are of semiclosed-cell type. Some impregnation difficulties were experienced with increasing of the PU density. The compressive strength of the cordierite foams increased (from 0.1 to 2 MPa) with increasing solids volume fraction. These data are in agreement with the predictions of the model developed by Gibson and Ashby. However, the exponent of the model was half of the measured one (≈3) over the range of relative densities investigated (80–90%). Such discrepancy might be related to several factors such as the morphological differences in the structural unit of the developed foams with respect to a cubic open-cell foam or to the mixture of both open and closed cells or to the presence of non-periodic cells. In addition, it was found that the compressive strengths depended on the cell size for foams of similar relative densities and generally decreased with increasing of the cell size, which deviates from the theoretical predictions. When the starting polymeric substrate contained a higher fraction of closed cell windows, however, the ceramic material present on the cellular structure was not only distributed on the struts but also filled the cell walls. This contributed to an increase of the relative density of the cordierite foams and consequently to higher compressive strengths.