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 mi xed powder slips, containing Si3N4 and ZrO2 powders, respectively. The surf ace charge was investigated by measuring the electrophoretic mobility in di lute powder dispersions. The slip stability was determined by visual observ ations of the settling of the powder and the fluidity of the slip was monit ored by measuring the viscosity. It was evident that the different powder d ispersions were most successfully stabilized by a high charge induced at hi gh pH-values. However, in order to produce a sufficient fluidity of the sli p, 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 alka line dispersions seems to be electrostatic depletion stabilization. The flo w properties were finally tested by recording the viscosity for a mixed (co mposite) powder containing 68.4wt% Si3N4 and 31.6 wt% ZrO2 at a total solid s content of 29-37 vol%. (C) 1998 Elsevier Science Limited All rights reser ved.