Effect of controlled capillary force variation on particle alignment and mechanical strength in slip-cast bimodal alumina.

This study investigates how small, controlled variations in mould capillary force influence the microstructure and mechanical reliability of slip-cast bimodal alumina. Capillary pressure was systematically adjusted by varying the plaster-to-water (P/W) ratio of Plaster of Paris (PoP) moulds within a narrow range around the manufacturer's specification. The resulting changes in pore structure and wettability were quantified to calculate effective capillary stresses, which were then correlated with particle alignment and surface-dependent mechanical performance. Bimodal alumina containing large, platy particles was used to statistically track capillary-induced alignment during casting, while three-point bend testing assessed the strength and reliability of sintered bars loaded on the PoP-contact surface. Results show that capillary pressure varies nonlinearly with P/W ratio and that even <15% changes in capillary stress cause measurable differences in particle orientation, grain symmetry, and Weibull modulus. The most uniform microstructure and highest reliability occurred under intermediate capillary conditions that balanced infiltration and shear. These findings reveal that slip casting is highly sensitive to minor fluctuations in processing-induced capillary force. Quantifying this sensitivity provides new insight into the dynamic mould–slurry interface and establishes a framework for improving the reproducibility and defect control of colloidal ceramic forming.