RHEOLOGICAL PROPERTY AND STRESS DEVELOPMENT DURING DRYING OF TAPE-CAST CERAMIC LAYERS

Rheological property and stress development of tape-cast ceramic layer s derived from nonaqueous alumina (Al2O3)poly(vinyl butyral) (PVB) sus pensions mere observed during drying. Casting suspensions exhibited st rong shear-thinning behavior, with a low shear Newtonian plateau appar ent viscosity >10(2) Pa . s. The apparent suspension viscosity display ed a power-law dependence on the Al2O3 volume fraction during the init ial stage of drying (less than or equal to 30% solvent loss), Stress d evelopment, measured by a cantilever deflection method, and parallel w eight loss measurements mere performed during the drying of tape-cast layers and pure binder coatings, Maximum drying stresses (sigma(max)) of 1.37-0.77 MPa were observed for plasticized tapes cast at gap heigh ts of 150-400 mu m. In contrast, nonplasticized tapes of similar thick ness displayed a more gradual stress increase, with sigma(max) values approximately an order of magnitude higher than their plasticized coun terparts, The stress histories of the corresponding binder coatings we re quite similar to the tape-cast layers, albeit slightly lower sigma( max) values were observed, Stresses decayed beyond sigma(max) with a l ogarithmic time dependence to an almost constant value of 0.2-0.4 MPa for the plasticized tapes, Based on these observations, process method ologies have been offered to minimize stress development and retention in tape-cast ceramic layers.