Effect of CNT quantity and sintering temperature on electrical and mechanical properties of CNT-dispersed Si3N4 ceramics

Electrically conductive carbon nanotube (CNT)-dispersed ceramics with high strength were fabricated by varying the CNT quantity and the firing temperature. We investigated the effect of these factors on density, electrical conductivity, bending strength, and microstructure of the developed ceramics. The relative density of the CNT dispersed Si3N4 ceramics was higher than 90% except for the sample containing less than 1 wt % of CNTs and fired at a temperature of 1800°C. It was confirmed that CNTs exist in the samples with a higher density. The pullout length of CNTs on the fracture surface in samples fired at higher temperatures was shorter because of the degradation of the CNTs. By TEM observation, CNTs were found to exist in the grain boundary in the Si3N4 ceramics, and their diameter was found to be almost the same as that of raw CNTs. Electrical conductivity appeared in the samples by adding CNTs more than 1 wt % though the sample by adding 0.5 wt % CNTs was insulator. The electrical conductivities of the samples increased with an increase in the firing temperature, which was explained by the grain growth of β-Si3N4. The bending strength of the samples with 1 wt % of CNTs was as high as that of samples without CNTs. Thus, CNT-dispersed Si3N4 ceramics having both electrical conductivity and a higher bending strength were obtained by controlling the CNT quantity and the firing temperature.