Abstract: The rheology of aqueous Al Mg MMH(mixed metal hydroxide) dispersions and electrophoretic mobility of MMHcolloidal particles were studied by rheological and electrokinetic measurements as a function of MMHconcentration, pHof dispersion and NaCl concentration. It was found that the suspensions are Newtonian at low MMHconcentrations, while increasing MMHconcentration gives rise to the suspensions with a yielding type of behavior. However, a transition from Newtonian to non-Newtonian flow curves may occur at relatively low MMHconcentration(2%) when suspensions was formulated near the isoelectric point(pH_iep) for MMHor with NaCl being added to MMHsuspensions below pH_iep. It appears that the rheology of MMHdispersions is closely correlated to the MMHconcentration and the surface charge of MMHparticle. When the recovery experiments with a relatively high vigorous stirring and at a low shear rate were performed on inherent MMHsuspensions consisting of positively charged platelike particles, the evolution of the gel structure is very slow, similar to the result for aqueous Laponite system consisting of negatively charged platelike particles. This result suggests that it is also the long range electrostatic double layer forces that lead to the formation of a repulsive gel in MMHsuspensions, similar to aqueous Laponite system at a high pH.

Key words: Mixed metal hydroxide, Thixotropy, Rheology, Suspension