Polymeric precursors to Si3N4 were mixed with
Si3N4 powder, in various combinations, to form
coatings in Si3N4 and to control microstructure of
Si3N4. The microstructure of polymer-derived
ceramic and preceramic materials was examined by transmission electron
microscopy (TEM) after heat treatment at 900°C and 1200°C and sintering at
1650°C. The observed micro-structure suggests that the
polymer-derived-material properties will approach those of conventionally
formed Si3N4. With proper viscosity control, gaps
between α-Si3N4 powder particles as narrow as 5 to 10
nm are filled by the polymer-derived-material, ensuring full wetting of the
α-Si3N4. Voids as large as 0.3 μm between
(α-Si3N4 particles are filled by the ceramic
precursor, reducing the size of pores formed during subsequent sintering
processes. Intimate bonding between the amorphous, polymer-derived-material
and the crystalline Si3N4 grains is observed after
heat treatments or sintering, a necessary condition for achieving
high-quality properties similar to conventional material. Acicular grains of
α-Si3N4 formed from the equiaxed
β-Si3N4 powder/PCMS mixture upon sintering are also
observed.