Interfacial and Rheological Characteristics of Maghemite Aqueous Suspensions

The interfacial properties and rheological behavior of the maghemite/water system have been investigated in this work. It has been determined that the real pzc and iep values of maghemite immersed in aqueous solution, containing KNO3 as electrolyte, are very close to 6.6. It has also been shown that the triple-layer site-binding model likely describes the electrical double layer of the maghemite/water system. The parameters obtained from this model indicate that the mechanism responsible for charging involves complexation reactions and that the interfacial properties of aqueous suspensions containing maghemite are very similar to those containing magnetite. Finally, rheological characterization of three maghemite samples with different average particle size showed that the maximum yield stress, at a fixed solid concentration, decreases as the sample particle size decreases. This anomalous behavior is originated by the apparition of relaxation superparamagnetic phenomena as a consequence of the decrease in the sample particle size. Copyright 1998 Academic Press.