Chemical additives for pressure tape casting

Suspensions of ceramic raw material and different deflocculant polyelectrolytes were prepared with a solid content of about 78% in industrial water. The rheological behavior of these suspensions was tested by evaluation of the shear dependence in a 4-step cycle and by a modified off-on procedure that reproduced the typical times involved in tape casting. The best deflocculants were found to be Na hexametaphosphate and polyacrylate, but their capability differed a little from mixtures of hexametaphosphate and Na disilicate or from ternary mixtures. The deflocculants made the suspensions slightly dilatant, had a low viscosity and yield stress values close to zero, that permitted an easy degasification of the suspensions. The additives, alone or in mixture, had adequate characteristics for use in pressure tape casting.