Obtaining of Hydrotalcite-based Ceramic Monoliths through Extrusion The investigation of the effect of additives on the rheological behaviour of the ceramic pastes

based on microcrystalline hydrotalcite (M II 1-x M III x (OH) 2 ) x+ A n-x/n mH 2 O, used for the preparation of monoliths with circular section through extrusion. The experimental studies regarding the rheological behaviour of hydrotalcite pastes lubricated with stearin shows that these materials have viscoplastic behaviour. Two rheological models are proposed (Bingham-Schwedoff and Herschel-Bulkley) for the correlation of experimental data and for the determination of rheological parameters (n and k). It is shown that Herschel- Bulkley model is more appropriate than Bingham-Schwedoff model to describe these ceramic mixtures and that stearin has a lubricating role, improving the flowing parameters. By using the bifactorial analysis of variance it was also investigated, from the statistical point of view, the influence of the studied factors (the content of the plasticizer agent and the shear rate . γ ).