Development of a Freeze-Drying Process for Wet Gelcast Bodies

Abstract

Wet gelcast body contains the same amount of water as the starting slurry, which has to be eliminated by a subsequent drying step. But in an indirect solid freeform fabrication (ISFF) process, the wet gelcast body is surrounded by an integral sacrificial mold, and drying cracks may be formed due to mold constrains. In the paper, freeze-drying was first introduced to deal with the wet gelcast body for preventing the cracking by minimizing drying shrinkage. First, the contents of non-freezing, freezing bound and free water in polyacrylamide gel (PAG) were evaluated by differential scanning calorimetry(DSC). Secondly, the prefreezing temperature and time were determined by an electrical resistance method. The change rule of the freeze-drying shrinkage with the prefreezing temperature was discovered. Finally, complex-shaped ceramic parts were fabricated to verify the feasibility and effectiveness of the freeze-drying process.