Kinetics of capillary extraction of organic vehicle from ceramic bodies. Part II: Partitioning between porous media

Abstract

Abstract An attempt was made to quantify the one-dimensional flow of molten wax from a ceramic body into a powder bed using permeability data deduced in Part I. The flow curve may be divided into three stages: (i) a transient stage of very rapid flow; (ii) a stable stage during which the majority of the wax is extracted, which is parabolic with time and is characterized by a sorption constant as for wax extraction from an unlimited supply; (iii) a reduced velocity stage in which the residual wax in the body approaches the pendular configuration (in which isolated liquid lenses exist at particle junctions). It was found that the residual wax in the body remained uniformly distributed during extraction and its saturation decayed. On the other hand, wax flow into the powder bed approximated to a one-dimensional column of fixed saturation. The absence of a permeability-saturation relationship for diverse powders is one of the main obstructions to a general theory of capillary extraction of binder, and this limited the agreement between measured and calculated sorption constants.