BROWN-COAL DERIVED CARBONACEOUS GELS .2. DRYING MECHANISMS AND SHRINKAGE

Carbonaceous gels have been shown to form rapidly from colloidal dispe rsions of brown coal and produce a resilient network structure. Upon d rying, these gels form hard glassy structures under the capillary stre sses 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 a nd a drying model suggested based upon ceramic counterparts. An approx imate solution to a differential equation which relates the strain rat e due to shrinkage, the pressure driving the drying liquid flow, and t he pressure gradient to the microstructure via the permeability was ex amined over the initial 2 h drying period and shown to represent the s olids concentration at the surface but not the gradient of the concent ration profiles.