Modeling of liquid desiccant drying method for gelcast ceramic parts

Gelcasting is a promising new technology for manufacturing of advanced structural ceramic components. The process involves drying of the “green” gelcast part before densification. Conventional methods in drying green gelcast part, using dry air or gas with a specific condition of humidity and temperature usually are confronted with many difficulties. Non uniform and differential drying in various regions due to the solvent gradient induces structural and residual stresses, that cause defects such as cracking, warping, bending and the other malformations, which make the part useless. Liquid desiccant drying method, as a novel method, has been used for drying green gelcast ceramic parts in the purpose of increasing the drying rate and removing the defects due to the release of residual stresses. In this study, the kinetics of one-dimensional drying of green gelcast ceramic parts through this method is described by a Fickian model, which accounts for the movement of the gel surface. For a constant mutual diffusion coefficient, D m, the fractional approach to equilibrium, F, is only a function of dimensionless time τ 0 ∗ , and the equilibrium volume ratio, Φ. By using simple method experimental values of D m which account for the movement of the gel boundary are obtained. Experimental data for alumina gelcast cylinders having diameters of 7 and 9 mm are well fitted by the model, and the amount of ceramic loading was 5, 10, 20, 30 and 35% by volume, respectively. Various concentrations of aqueous solution of PEG1000 were used as liquid desiccants.