A comparison of the colloidal stabilization of aqueous titanium carbide suspensions using anionic and cationic dispersants

The aqueous colloidal stability of titanium carbide (TiC) suspensions has been assessed using both anionic and cationic dispersants. The zeta potential of TiC suspensions, both without and with polyelectrolyte addition, is examined as a function of pH and the relative responses of the polyelectrolytes are compared. Without a dispersant, the TiC powder used shows an isoelectric point at similar to pH 2.6. The use of an anionic polyelectrolyte, an ammonium salt of polymethacrylate (PMA-NH4) does not significantly alter the isoelectric point. Conversely, the addition of a cationic dispersant, polyethylenimine (PEI) with a molecular weight of either 1800 or 10,000, significantly alters the isoelectric point. The theological behaviour of the TiC suspensions was examined using a concentric cylinder geometry. In each case a shear thinning response is observed, and a transition to shear thickening is seen on all the PMA-NH4 trials, and some, but not all, of the PEI experiments at high shear rates (similar to 600 s(-1)). The PMA-NH4 was found to produce optimum slip stability at lower concentrations, (similar to 0.02 wt.%) versus the PEI, which obtained the same slip stability at concentrations of similar to 0.30 wt.%. However, increasing the PMA-NH4 concentration does not provide increased stability; above this point it begins to degrade the slip properties through increasing viscosity. Conversely, the PEI does not exhibit a plateau and subsequent drop off of the slip stability with increasing concentration for the dispersant range studied. For TiC, both polyelectrolytes appear to be suitable dispersants for processing at their respective regions of the pH scale. The PMA-NH4 provides sufficient stability at similar to pH 8.5, and the PEI provides essentially equal stability in the pH 4.5 region for the concentrations examined. (C) 2010 Elsevier Ltd. All rights reserved.