Sintering and thermal properties of multiwalled carbon nanotube-BaTiO3 composites

Densified multiwalled carbon nanotube (MWNT)-BaTiO3 composites were successfully fabricated through a spark plasma sintering (SPS) method. The influences of sintering temperature, annealing time, and the content of carbon nanotubes on the densification of composites were studied in detail. The morphology of fracture surface was observed using field emission scanning electron microscope (FE-SEM). Through analyzing the temperature dependent shrinkage rate, we found that the incorporation of carbon nanotubes can effectively accelerate the densification process of MWNT -BaTiO3 composites. Excellent electrical and thermal conductivity of MWNTs were proposed to account for this unexpected sintering behavior. Thermal properties of MWNT-BaTiO3 composites, including specific heat capacity, thermal diffusivity, and thermal conductivity, were also principally investigated. The experimental results show that the thermal diffusivity and thermal conductivity both unusually decreased although the specific heat capacity increased after adding CNTs into composites. It was suggested that the interfacial thermal barrier between CNTs and the BaTiO3 matrix plays a crucial role in determining the thermal conductivity of bulk composites. A simplified effective medium approximation formulation was used to simulate and predict the thermal conductivity of the MWNT-BaTiO3 composite, but only fitted well with the measured values for low CNTs content (2.45 vol%). The reason for this deviation was proposed and needs further work to make it clear thoroughly.