Surface charge and viscosity of mixed Si3N4-Y2O3 suspensions containing lignosulphonate

We have studied the surface charge and the dispersion behavior of silicon nitride-yttrium oxide-lignosulfonate powder dispersions, prior to sintering. In our previous study we reported on the effect of pH on the adsorption of yttria (Y2O3) and lignosulfonate (LS) on the surface of silicon nitride (Si3N4) powder. The adsorption was studied by particle size measurements, scanning electron microscopy, X-ray photoelectron spectroscopy (ESCA) and carbon analyses. In this study, we report the results from the electrophoretic mobility and surface charge determinations and viscosity measurements of the slip. The viscosity measurements were performed as a function of the LS concentration added in the dispersion. This was done in order to determine the optimum concentration of lignosulfonate added in the dispersion, i.e. the concentration which would result in the lowest viscosity for the highest possible dry content of the slip. The surface charge was determined via potentiometric titrations and by measuring the electrophoretic mobility.