Dispersion Properties of Silicon Nitride Powder Coated with Yttrium and Aluminium Precursors.

A coated silicon nitride (Si3N4) powder with yttria and alumina precursors as sintering additives was prepared by a heterogeneous precipitation method. The rheological and electrophoretic properties of the suspensions obtained from the coated (CO) powder were investigated and compared with those of pure Si3N4 powder and of the mechanically mixed (MM) powders of Al2O3, Si3N4, and Y2O3. The results showed that the CO powder calcined at 500 degreesC exhibited improved dispersion properties compared with the pure Si3N4 powders. The CO powder possessed the surface character of Al2O3 and Y2O3 particles, that made it easier to process in aqueous media, yielding a higher solid loading than the pure Si3N4 powder. These improvements were attributed to a change in the resultant interaction forces between particles from attractive (pure Si3N4, and MM powders) to repulsive in the case of the CO powder. A homogeneous distribution of sintering additives in the Si3N4 matrix was obtained. Copyright 1998 Academic Press.