Thermal Conductivity Of Multi-walled Carbon Nanotubes Research Articles

Residual impact resistance behavior of concrete containing carbon nanotubes after exposure to high temperatures

Multi-walled carbon nanotubes (MWCNTs) have not only high strength and toughness, but also good thermal stability and thermal conductivity. By investigating the failure patterns and fractal index (i.e., impact crushing fractal dimension Df) of MWCNTs reinforced concrete (MC), this paper explored the effect of MWCNTs on impact resistance of concrete after exposure to high temperature. Results showed that after exposure to high temperature, Df increased with the increase of strain rate and temperature. However, compared with plain concrete (PC), MC had relatively few fragments, low Df value, enormous energy consumption, and high residual dynamic compressive strength. The variation of Df essentially depends on the development of cracks and compactness of concrete. It is precisely because the strengthening and thermal conductivity of MWCNTs on the matrix, which effectively alleviated the thermal cracking and impact crushing, thus improving the thermal resistance and impact resistance of concrete. Moreover, the pore fractal dimension (Dp) of concrete after exposure to high temperatures were also investigated and compared with Df. The results noted that the change trend of Dp and Df of MC and PC were completely opposite. The Dp of MC was larger than that of PC, but its Df was smaller than that of PC.

Investigation on the thermal conductivity and rheological properties of multiwalled carbon nanotube (MWCNT)—dowtherm a nanofluids

ABSTRACTIn the present work, the thermal conductivity and viscosity studies of multiwalled carbon nanotubes (MWCNTs)—Dowtherm A (eutectic mixture of biphenyl (C12H10) and diphenyl oxide (C12H10O)) nanofluids—are presented considering the influence of particle weight percentage (0.001–0.005 wt%) and temperature ranging from 303 K to 323 K. As-received MWCNTs are characterized using x-ray diffraction (XRD), FT-Raman spectroscopy, thermogravimetric analysis, and transmission electron microscopy (TEM). The suspensions consist of MWCNTs dispersed in Dowtherm A and they are stabilized by sonication. The result shows that the thermal conductivity of MWCNT–Dowtherm A nanofluids depends strongly on particle concentration and temperature which increases linearly with both the weight percentage of nanoparticles and also with that of temperature. It is also observed that the viscosity of nanofluids increases with the increase in concentration of nanoparticle and decreases with the rise in temperature. Stabilization mechanisms of dispersions are analyzed by UV-visible (Vis) spectrophotometry measurement to quantitatively characterize the colloidal stability of the MWCNT dispersions.

Effect of grinding speed changes on dispersibility of the treated multi-walled carbon nanotubes in aqueous solution and its thermal characteristics

For the purpose of increasing the dispersibility and thermal conductivity of fluid containing nanoparticles, raw multi-walled carbon nanotubes (MWCNTs) were treated by strong acids. The purified structures were dispersed into aqueous solution by using wet grinding conditions at various rotation speeds (300–600rpm) merged with ultrasonication. The particle size analyzer reveals that the agglomerated size of ground particles at rotation speed of 300rpm was 39.811μm. Nevertheless, the agglomerated size of particles significantly decreased to 11.482μm after grinding at rotation speed of 600rpm. The maximum absorbance (4.0 abs at wavelength of 300nm) and highest thermal conductivity (0.6074W/mk at 30°C) of the suspension corresponds to the grinding speed of 600rpm assisted by ultrasonication dispersion. From the overall results, grinding method with high rotation speed plays can be significantly increased both the dispersibility and thermal conductivity of MWCNTs in aqueous solution.

Thermal boundary resistance and thermal conductivity of multiwalled carbon nanotubes

Thermal boundary resistance (Kapitza resistance) and thermal conductivity of multiwalled carbon nanotubes (MWCNTs) are calculated assuming the properties of graphite in the temperature range of $10--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. By including the thermal boundary resistance between the MWCNT and the measuring device, calculated thermal conductivity of MWCNT is in very good agreement with the experimental data of Kim et al. [Phys. Rev. Lett. 87, 215502 (2001)], showing that the thermal behavior of MWCNTs is similar to graphite. Thermal conductivity of MWCNT as measured by Kim et al. is smaller than the thermal conductivity of graphite fibers and pyrolytic graphite at low temperatures due to thermal boundary resistance. The intrinsic mean free path of phonons in MWCNTs in the temperature range of $10--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is found to be similar to the mean free path in graphite fibers. Finally, it is shown that the thermal boundary resistance could be one of the main reasons that the thermal conductivity of MWCNT bundles as measured by Kim et al. is lower than the thermal conductivity of a single MWCNT.