Toughness of Si3N4 ceramics obtained by precipitating sintering aids as hydroxides

Sintering aids were added to silicon nitride slurries through hydroxide precipitation from aluminum and yttrium nitrate solutions and subsequent calcination. Spray-dried powder and sintered products were characterized by light optical and electron microscopy. esult of the homogeneous dispersion of the sintering aids, sintered density of the system approached the theoretical value even when the total amount of sintering aids was as low as 5%. Mechanical properties of the sintered product, however, were not significantly improved over samples obtained with traditional methods; this was probably due to the presence of hard agglomerates and/or to a microstructure which contained long, unattached grains of β-silicon nitride.