The Y2O3-La2O3 additive-coated
Si3N4 powders of about 1.5 μm in size were prepared
by the sol-gel method. X-ray diffraction, X-ray photoelectron spectroscopy,
differential thermal analysis, thermogravimetric analysis, electron
microscopies, and particle size analysis were used to study the coating on
the Si3N4 particles. The results show that properties
of the bulk Si3N4 powder are not affected by using the
sol-gel coating and the powders are homogeneously coated by a thin layer of
the Y2O3-La2O3 additives. The
structure of the Y2O3-La2O3
coating layer is amorphous or microcrystalline with a submicron thickness.
The coated powders are then more sinterable, and the mechanical properties
of the ceramics prepared from such powders are improved.