Brown coal derived carbonaceous gels. Part 2. Drying mechanisms and shrinkage

Abstract

Carbonaceous gels have been shown to form rapidly from colloidal dispersions of brown coal and produce a resilient network structure. Upon drying, these gels form hard glassy structures under the capillary stresses of contraction. The evolution of this increasingly less compliant microstructure was followed by yield stress and modulus measurements as drying proceeded. Moisture and shrinkage profiles were determined and a drying model suggested based upon ceramic counterparts. An approximate solution to a differential equation which relates the strain rate due to shrinkage, the pressure driving the drying liquid flow, and the pressure gradient to the microstructure via the permeability was examined over the initial 2 h drying period and shown to represent the solids concentration at the surface but not the gradient of the concentration profiles.