Rheological characterisation of electrosterically dispersed alumina suspensions during in situ coagulation

A near-net shape route for the production of advanced ceramic components has been developed that uses carboxylic acid derivatives as coagulants to achieve the destabilization of electrosterically dispersed high solids content ceramic suspensions via pH modification driving the suspension towards its IEP. In the present work, the effect of the time-dependent in situ hydrolysis of the coagulant, D-gulonic-c-lactone, on the progressive destabilization of the precursor suspension to form highly viscous pastes has been characterized rheologically. The macroscopically determined dynamic storage and loss modulii, G0 and G00, obtained during oscillatory investigations have been found to be sensitive rheological parameters that describe the structural changes occurring at a microscopic level within the material. The progression of coagulation has been found to be critically dependent on the coagulant concentration and suspension temperature. Increasing either of these variables greatly accelerates the extent and rate of coagulation. Furthermore, with judicious control over them, coagulation characteristics approaching idealized behavior can be obtained.