Fabrication of cellular cordierite foams

Cordierite foams were fabricated by the polymer foam replication process, where a polyurethane (PU) template is infiltrated with slurries containing appropriate binders and ceramic particles, followed by the removal of excess slurry, burning out of the polymer to leave a ceramic replica of the polyurethane and finally high temperature sintering. Two PU foam grades of the same density (0.021 g(.)cm(-3)) were used as templates. The structure of the sintered foams was evaluated through density measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Rheological studies showed that optimum dispersion and stabilisation conditions were achieved for aqueous slurries containing 40-vol% of solids, 2-wt% of bentonite and 0.8-wt% of dispersant. Differential thermal analysis (DTA) was used to optimise the burnout of the polymer. Upon heating, decomposition of the polymer occurs, resulting in vaporisation as well as formation of a melt around 300degreesC. Cracks were observed by SEM on the struts' surfaces of the fabricated foams. The struts had an angular cross-section and cracks were seen along the cell edges and the cell walls. The density of the sintered foams was typically 20% of the struts density. The volumetric shrinkage was approximately 30% and the linear shrinkage appeared fairly isotropic.