Deposition of colloidal sintering-aid particles on silicon nitride

The deposition of alumina (Al2O3) and yttria (Y2O3) particles on silicon nitride (Si3N4) by electrostatic and electrosteric interactions was studied using acoustophoretic measurements. The characteristics of Si3N4, Al2O3' and Y2O3 powders in an aqueous environment were studied by measuring the electrokinetic sonic amplitude (ESA), and appropriate conditions for deposition by adsorption were identified. The deposition of Al2O3' Y2O3, and Y(NO3)3 on Si3N4 particles was conducted at different pH values where these chemically dissimilar particles exhibit electrical charges of opposite sign. The deposition studies indicated that the particle size has a strong effect on the amount of coating on Si3N4 particles. The presence of polyacrylic acid as an electrosteric stabilizer for Si3N4 had no measurable effect on Al2O3 adsorption. The shift of the isoelectric point of Si3N4 with Al2O3 showed that the total quantity of Al2O3 adsorbed on Si3N4 reached a maximum at approximately 75% coverage of the total surface area of Si3N4. Bremsstrahlungexcited Auger electron spectroscopy (AES) results showed that the as-received Si3N4 powder has a native oxide film of 8.9 Å. The presence and relative differences in the surface composition of coated particles were established using X-ray photoelectron spectroscopy (XPS).