TAPE CASTING OF FINE ALUMINA-ZIRCONIA POWDERS FOR COMPOSITE FABRICATION

Ceramic films, containing Al2O3 with up to 40 vol% ZrO2, have been fab ricated using the tape casting process. Finer powders (average mean di ameter of 250-300 nm) than have generally been reported for tape casti ng were used in this study. The optimum formulation for tape casting i s affected substantially by decreasing particle size. For example, the amount of dispersant needed is increased. Moreover, the amount of pla sticizer/binder must be increased so as to maintain the solids content in the dried tapes below a critical level (about 55 vol% in this case ), which decreases with particle size. Rheological studies on the effe ctiveness of menhaden fish oil and phosphate ester as dispersants show that phosphate ester can be used in lower concentrations, for the pre paration of higher solids loading slurries, and was therefore selected for further study. The amount of dispersant required to obtain minimu m slurry viscosity was found to be primarily dependent upon the effect ive particle surface area, defined as that available to the dispersant molecules. In the case of particles composed of agglomerated crystall ites (such as the ZrO2 powder used here), this may be considerably les s than that measured by nitrogen absorption. Moreover, the porous inte rnal structure of such powders is filled with solvent, which increases the effective solids loading of the slurry, and thus its viscosity. P article morphology also influences the packing efficiency; i.e., the g reen density decreases as ZrO2 is added.