A SURFACE STUDY ON ADSORPTION OF LIGNOSULFONATE ON MIXED SI3N4-Y2O3 POWDER DISPERSIONS

In the colloidal processing of high performance ceramics, knowledge of the interfacial properties is of crucial importance. Studies have accordingly been made of the surface composition and the dispersion behavior of a silicon nitride-yttrium oxide-lignosulphonate system, prior to sintering. The effect of pH on the adsorption of yttria (Y2O3) and lignosulphonate (LS) on the silicon nitride (Si3N4) powder surface is reported. The samples were studied by particle size measurements, SEM, X-ray photoelectron spectroscopy (ESCA) and carbon analyses. The ESCA annlyzing techniques used were (I) relative surface atomic concentrations (ACs) and (2) evaluation of the substrate coverage derived from the Tougaard background analysis. It was found that the particle size distribution of the Si3N4-Y2O3 system to be strongly dependent on the pH and concentration of the lignosulphonate added in the dispersion. The ESCA results confir med that lignosulphonate adsorbed both on the silicon nitride and yttrium oxide particles. It was also found that at pH 7 the relative amount of yttria was increased at the surface with increasing amount of lignosulphonate added in the dispersion.