Development of CNT/Si3N4 composites with improved mechanical and electrical properties

Silicon nitride based composites with different amount (1, 3 or 5 wt%) of carbon nanotubes have been prepared by using hot isostatic pressing. Composites with 1, 5 or 10 wt% carbon black and graphite have been manufactured, in comparison. Optimisation of the manufacturing processes has been performed, providing intact carbon nanotubes during high temperature sintering. In the case of 1 or 3 wt% carbon nanotube addition, the increase of gas pressure during sintering resulted in an increase of bending strength. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements. Scanning electron microscopy showed that carbon nanotubes have a good contact to the surface of silicon nitride grains. The electrical properties of silicon nitride matrices with carbon addition may change essentially.