Structural characterization of Si3N4–carbon nanotube interfaces by transmission electron microscopy

Silicon nitride based ceramics with carbon nanotubes (CNTs) were prepared by various milling techniques and hot isostating pressing. For better homogeneity ultrasonic agitation of CNT-powder mixtures were also used in the case of ball milling. The grain boundaries and ceramic/CNT interfaces play an important role in resulting properties of ceramic composites. This is based on some new evidence obtained from transmission (TEM) and high resolution (HREM) electron microscopy studies on Si3N4/CNT composites. In the case of ball milling and after sintering the average size of β-Si3N4 grains was ∼1 μm and the pore size was ∼500 nm. In comparison, in the case of attritor milling smaller grain sizes ∼300 nm and pore size ∼250 nm resulted after sintering. The CNTs have been found to be located mainly into porosities and particularly, embedded in intergranular places. The TEM investigations showed that CNTs located in porosities resulted in similar orientations in the case of both milling processes.