Improving the microstructure of Si3N4–TiN composites using various PEIs to disperse raw TiO2 powder

An in situ synthesis route was developed for the preparation of dense and homogenous Si3N4–TiN (5 vol% TiN) composites, with TiN grains formed from TiO2 and AlN. The dispersion of TiN grains in the Si3N4 matrix using various polyethyleneimines (PEIs) as dispersing agents for raw TiO2 powder was investigated by scanning electron microscopy (SEM). We found that the microstructure of Si3N4–TiN composites was improved with the aid of PEI to disperse TiO2 particles in the mixture. It was critical to disperse original TiO2 particles with the appropriate dispersant before the sintering process, because the size of TiN grains in the Si3N4–TiN composites was strongly dependent on the size of TiO2 particles. PEI molecules modified the surface of TiO2 particles and protected the TiO2 particles in the slurry from aggregations. It was a practical and useful way to obtain the Si3N4–TiN composites with homogeneous microstructures without the alteration of the preparation procedure.