Drying characteristics of ceramic precursors

All ceramics tend to shrink during drying and unless this is controlled, it may lead to crack development within the green body. Controlled drying is thus a crucial stage when processing ceramic monoliths. It is, therefore, particularly pertinent to determine the kinetics of drying industrially relevant ceramic precursors and thus the rate controlling mechanisms. Experimental drying data, including relative length shrinkage and sample core temperature profiles, for clay SB75, boehmite PURAL SB I and lead zirconate titanate (PZT) are presented over a range of drying conditions. These data are explained in terms of the rate controlling drying mechanisms during the different periods of drying. It has been verified by heat transfer calculations that drying during,the constant-rate period is compatible with free evaporation from the saturated specimen surface. It has been deduced that capillary flow is the dominant mechanism of drying for both the clay and boehmite paste systems, with diffusion being the rate controlling drying mechanism during the final stages of drying. The drying characteristics of the PZT system suggest that the rate controlling drying mechanism is diffusion throughout the drying process.