Room-Temperature Freeze Casting for Ceramics with Nonaqueous Sublimable Vehicles in the Naphthalene–Camphor Eutectic System

Freeze casting for Al2O3 was accomplished at room temperature with nonaqueous sublimable vehicles in the naphthalene– camphor eutectic system with a eutectic temperature of 31°C. A fully dense sintered body (>99.5% of theoretical density (T.D.)) was obtained with a eutectic composition vehicle, whereas at most 90% T.D. was obtained with an off-eutectic (i.e., hypoor hypereutectic) composition vehicle due to formation of large uniquely shaped voids. Microstructural observation suggested that growing pro-eutectic crystals rejected the suspended Al2O3 particles to form large voids during the solidification process. At the eutectic composition, formation of fine lamellar microstructure in a solidified vehicle is considered to inhibit particle rejection resulting in large voids.