The rheological properties of aqueous dispersions of the Al-Mg mixed metal hydroxide (MMH) that form solid-like structures have been investigated. Special emphasis has been laid on the phenomenon of thixotropy. Structural recovery at rest after steady shear is considered a fundamental thixotropic process and has been characterized by steady shear and small amplitude oscillatory shear measurements, With increasing MMH concentration, the behavior changes from predominately viscous to a solid-like response. The magnitude of the storage modulus, G', increases strongly and becomes less dependent on frequency with increasing MMH concentration. After cessation of steady shear complex viscosity increases monotonically with time and even after 3 h no equilibrium viscosity value is reached, while shear stress under steady rate of 10 s^-1 approach equilibrium value only after about 10 min. The recovery of MMH suspension after cessation of steady shear is strongly affected by pre-shear history and rebuliding time. The greater the intensity of preshearing, the lower the values of the elastic moduli after preshearing has ceased; The longer the rebuliding time, the larger the values of the elastic moduli. These results are similar to those obtained for clay dispersions of different ionic strength and clay concentration. Similarities in particle size and shape, though oppositely charged, and rheology between the two systems provide indirect evidence of similar rebuilding mechanism, so it is assumed that, for positively charged MMH suspension, long-range electrostatic double layers forces lead to the formation of a solid-like structure.

Key words: ALUMINIUM COMPOUNDS, MAGNESIUM COMPOUNDS, MAGNESIUM HYDROXIDE, ALUMINIUM HYDROXIDE, MIXING, METALLIC HYDROXIDES, COLLOID, RHEOLOGY, SUSPENSION, THIXOTROPY