Slip Casting of Alumina: Additives and Rheological Optimization for High-Performance Ceramics

Slip casting method of making traditional ceramic has a long history, and it is considered high in green density, low in shrinkage, and efficient in densification. Its use has however been restricted in engineering ceramics, including alumina because of its wide use in hot pressing, a high-cost and geometrically constraining technique. An improvement in an accessible fabrication path will be beneficial to alumina which has an excellent thermomechanical situation. This paper examines slip casting which is then considered as a low-cost and large-capacity alternative for creating dense and homogenous alumina ceramics. Some of the processing parameters such as pH, viscosity, deflocculation, and solid loading were determined as key parameters which were optimized to enhance rheological behavior and final mechanical properties. Response surface regression and ANOVA were used to estimate the effect of polyacrylic acid (PAA), silica ([Formula: see text] and polyvinyl alcohol (PVA) on critical responses including slurry viscosity, pH, green density, sintered density, and homogeneity. The best additive levels were selected as PAA (0.4–0.45 wt.%), [Formula: see text] (0.5–0.6 wt.%) and PVA (0.85–0.9 wt.%). The validation tests at these levels showed positive results: viscosity of the slurry of 193–204 mPa⋅s, stable pH of 8.4–8.5, green density over 63% and sintered density greater than 95%, and homogeneity levels of 4–5. The alumina ceramics gave high values of hardness of up to 1640 Vickers pyramid number (HV). It was however noted that the strength can be restrained by iron inclusions that may be injected during processing. These results show that slip casting is a viable and effective process in making high-performance alumina ceramics when administered accurately slurry chemistry and rheology.