THE USE OF STARCH FOR THE PREPARATION OF POROUS CORDIERITE CERAMICS BY SLIP CASTING PROCESSES

Native starch is a popular pore-forming agent for the preparation of ceramics with controlled porosity and pore size. In this contribution basic information is provided for the preparation of porous cordierite ceramics via traditional slip casting with starch and so-called "starch consolidation casting". Results of a comparative study are reported using different types of raw materials and different types of native starches (potato, corn, tapioca). The chemical composition (measured via X-ray fluorescence analysis) and particle size distribution (measured via laser diffraction) of the raw materials and the rheological behavior of the suspensions (measured via rotational viscometry) are compared. Values of bulk density and estimated porosity are given as well as selected elastic properties (measured via impulse excitation) of the porous ceramics made with native starch as a processing auxiliary. Key points concerning chemical composition, particle size, rheology and elastic constants are discussed. The apparent viscosity of suspensions prepared in this work (with total solids volume fractions in the range 26-43 %) is below 200 mPas, which is at the lower limit of ceramics suspensions for casting. For porous cordierite ceramics with a porosity of 42-51 % the Young's modulus is approx. 23-39 GPa, the shear modulus approx. 9-16 GPa and the Poisson ratio approx. 0.257. The results indicate that the porosity dependence of the Young's modulus is reasonably well predicted by an exponential relation, irrespective of the starch type used.