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

Abstract

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 Si 3 N 4 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 Si 3 N 4 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 ¢-Si 3 N 4 . The bending strength of the samples with 1 wt % of CNTs was as high as that of samples without CNTs. Thus, CNT-dispersed Si 3 N 4 ceramics having both electrical conductivity and a higher bending strength were obtained by controlling the CNT quantity and the firing temperature.

Development of CNT-Si₃N₄ Composites with High Strength and Electrical Conductivity by Adding HfO₂

“…They were above 90% after GPS and above 93% after HIP. As shown in this figure, the relative density decreased with an increase in the quantity of CNTs; this is similar to the tendency of the relative density observed in the previous research on CNT-dispersed Si 3 N 4 ceramics [10][11][12]. The reason for the degradation of the density was that the CNTs hampered the densification of Si 3 N 4 by forming gases after reacting with Si 3 N 4 or SiO 2 .…”

“…The tuberous particles observed to project from the fracture surface are CNTs. Many CNTs remained in the sintered body, which had the same microstructure as the CNT-dispersed Si 3 N 4 ceramics developed in our previous research [10][11][12]. The CNTs dispersed well and existed randomly; thus, the formation of electrical conduction paths could be expected.…”

“…In a previous study on CNT-dispearsed Si 3 N 4 ceramics, many researchers applied various sintering processes like spark plasma sintering and hot pressing to obtain dense ceramics. [7][8][9] Dense CNT-dispersed Si 3 N 4 ceramics was fabricated using TiO 2 as a sintering aid in our previous study, [10][11][12] [16][17] Therefore, it is expected that as an additive, HfO 2 makes it possible for CNT-dispersed Si 3 N 4 ceramics to be densified using gas-pressure sintering at temperatures lower than those used with other sintering aids.…”

Surface modification of carbon nanofibers with SiC by heating different SiO vapor sources in argon atmosphere

“…37)43) The mechanisms of CNTs and graphene formation on SiC substrate were explained by the research group of Kusunoki. 37)40) The fine fibers and branch-like tubes formed in this study might not be SiC but carbon because an amount of the formed SiC decreased in the specimen heated with Si/SiO 2 powder at 1800°C, that is, the formed SiC was reacted with O 2 (g) and CO (g) to form carbon though the reactions (13) and (14). When CNFs were heated with SiO 2 and Si/SiO 2 powders at 1600 and 1800°C in this study, SiC particles were formed on the surface of CNFs.…”

Development of CNT-dispersed Si3N4Ceramics by Adding Lower Temperature Sintering Aids

“…In a previous study on CNT-dispearsed Si 3 N 4 ceramics, many researchers applied various sintering processes like spark plasma sintering and hot pressing to obtain dense ceramics. [7][8][9][10] Dense CNT-dispersed Si 3 N 4 ceramics was fabricated using TiO 2 as a sintering aid in our previous study, [11][12][13] because TiO 2 improves densification of Si 3 N 4 . 14) In this study, we focused on simultaneous addition of HfO 2 and TiO 2 as a sintering aid because it promotes the densification of Si 3 N 4 on account of the reaction between HfO 2 , Y 2 O 3 , and Si 2 O 3 at around 1600°C to generate a liquid phase.…”