SIMULATION OF GELATION OF SOLS BY LIQUID REMOVAL USING A CLUSTER-CLUSTER AGGREGATION MODEL

This paper reports the application of a cluster-cluster aggregation mo del for the simulation of the gelation process by removal of the liqui d medium from a particulate sol. Gelation by removal of the liquid med ium is relevant in the production of fine powders by drying of soi dro plets, manufacture of ceramic membranes by capillary absorption of wat er from a sol by a porous substrate, production of gels by evaporation etc. Simulations including liquid removal are seen to result in clust ers with structures very different from those with no removal of the l iquid medium. The model has been used to determine the effect of proce ssing variables like sol concentration, pH, and evaporation rates of t he liquid and of the acid on the structure of the gels produced. The s imulations show that two phenomena, namely surface crowding and bulk g elation, are operative and the gel structure is the resultant of these competing phenomena. The process exhibits different kinetics dependin g on which phenomenon is dominant. (C) 1997 Acta Metallurgica Inc.