Drying is an important step in many ceramic processes for which a solvent is involved. Drying results in a body shrinkage which could lead to stresses and then potential defects such as warping or cracks. Information on the evaporation rate is then required in order to adjust drying conditions of the surrounding air, to avoid defects and to optimise drying cycle for energy savings. Beyond the classical description found in the literature which consists of a Constant Rate Period (CRP) followed by one or two Falling Rate Periods (FRP), ceramic green bodies often exhibit a more complex behaviour. We have examined the drying rate in relation with the ceramic nature, the powder characteristics (grain size and specific surface area) and the presence of organic additives which are frequently used in ceramic processing (glycerol and polypropylene glycol).
Green bodies were subjected to convective drying in a climatic chamber where mass and surface temperature were monitored. The shrinkage was also evaluated. Evaporation rate was deduced from the mass variation with time and the dimensional changes which reduce the area exposed to drying.  
Even though the classical behaviour of a CRP followed by 2 FRP is found for alumina and kaolin green bodies prepared with water, the CRP can continue even after the end of the major shrinkage and this depends on the powder characteristics. The addition of glycerol or polypropylene glycol has a strong influence by decreasing the drying rate and a CRP can no longer be identified. The mechanisms involved in this reduction are examined especially by an experimental determination of the distribution of the two solvents in the green body during the drying.
This information is relevant for the development of ceramic formulations for innovative processes.