(246b) Development of Slurry Characterization Method for Tape Casting

Tape casting process is widely used to produce ceramic substrate, multilayer structure capacitor, solid electrolytes, solid oxide fuel cell, etc. However, cracking often occurs in the green tape during drying. In this paper, slurries were evaluated by the constant rate filtration and stress relaxation test in order to predict and prevent the crack formation. Slurries were prepared from alumina powder with an average particle size of 0.48µm and distilled water by ball-milling for 2h. The solid concentration was 45vol%. A solution of hydrochloric acid was used to adjust of the pH values of slurries in order to control the degree of flocculation. The prepared slurries were tape cast on a polypropylene film. A gap of 0.5mm under the blade and a casting rate of 145mm/min were selected for all the casting tests. The green sheets obtained from this experiment had 200mm width and 400mm length. The cast tapes were dried at room temperature for 15h. After drying the density and number of cracks were measured. The constant rate filtration and stress relaxation test was conducted by using an acrylic cylinder with a diameter of 35mm. The prepared slurry was pored into this cylinder until 13mm height and then filtered by a constant rate of 0.14mm/min. After filtration the formed cake was compressed until the stress reached at 1MPa and then the strain of the cake was kept constant. The time change of the pressure and cake height were measured. It was found that the stress relaxation rate has a good correlation with the number of cracks in the green sheet, therefore, the constant rate filtration and stress relaxation test should be applied to optimize the slurry conditions for tape casting.