The influence of lignosulphonate on the properties of single and mixed Si3N4 and ZrO2 suspensions

Lignosulphonate (LS), was evaluated as a dispersing agent for single and mixed powder slips, containing Si3N4 and ZrO2 powders, respectively. The surface charge was investigated by measuring the electrophoretic mobility in dilute powder dispersions. The slip stability was determined by visual observations of the settling of the powder and the fluidity of the slip was monitored by measuring the viscosity. It was evident that the different powder dispersions were most successfully stabilized by a high charge induced at high pH-values. However, in order to produce a sufficient fluidity of the slip, a dispersing agent had to be introduced. The optimal concentration range of LS at pH=10 was found to be 0·2wt%. The stabilizing mechanism in alkaline dispersions seems to be electrostatic depletion stabilization. The flow properties were finally tested by recording the viscosity for a mixed (composite) powder containing 68·4wt% Si3N4 and 31·6wt% ZrO2 at a total solids content of 29-37vol%.