Carbon nanotubes as ceramic matrix reinforcements

Multiwall carbon nanotube reinforced silicon nitride composites have been realised by hot isostatic pressing. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes in composites and to avoid damage during high temperature (1700 degrees C) and high nitrogen gas pressure (20 MPa) processing. As shown by scanning and transmission electron microscopy carbon nanotubes have good adherence to the silicon nitride grains, as observed for low and high pressure processing as well. Moreover, carbon nanotubes have been found to be located not only at grain boundary surfaces, but may be incorporated directly into silicon nitride grains. Composites with higher strengths can be obtained by increasing the nitrogen gas pressure.