Drying of gelcast ceramic parts via the liquid desiccant method

Conventional methods in drying ceramic parts, using dry air or gas with particular conditions of humidity and temperature, is usually confronted with many difficulties. Non-uniform and differential drying in various regions due to the solvent gradient, induces structural and residual stresses which cause defects, such as cracking, warpage, bending and the other malformations, which make the articles useless. These malformations can be minimised or eliminated by using the liquid desiccant drying method due to the release of residual stresses. In this work, gelcast green parts have been brought in contact with an appropriate liquid desiccant with the purpose of withdrawing above 30 wt.% solvent in a reasonable period of time, i.e. 3 h. The effects of factors such as loading level of ceramic powders, liquid desiccant concentration and its gradient, effective thickness and geometry of parts and type of liquid desiccant solution (aqueous or non-aqueous), on the drying rate were studied. Lower solid content in the gel, higher liquid desiccant concentration and lower effective thickness of parts, increase the drying rate. Decrease of aspect ratio in cylindrical parts changes the diffusion mechanism from radial to longitudinal direction. Drying of parts in aqueous solution of PEG 1000 is more homogeneous than the non-aqueous one, but drying rate of parts in non-aqueous solution of PEG1000 is greater than the aqueous one. (C) 2003 Elsevier Ltd. All rights reserved.