Thermal Properties of Continuously Spun Carbon Nanotube Fibres Phys

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Thermal properties of continuously spun carbon nanotube fibres

Abstract

As indicated by theory and experimental measurements individual carbon nanotubes (CNTs) have very high values of thermal conductivity. One of the challenges is to achieve high thermal conductivity in macroscopic assemblies of CNTs such as fibres, films and composites, paving the way to a wide range of applications. CNT fibres have tremendous potential in succeeding as the future materials for a variety of applications when properties at the nanoscale are translated to their macroscopic assemblies. In this paper we report the measurements of thermal conductivity of continuously spun CNT fibres and its dependence on temperature. Thermal conductivity measurements were performed using in-house built temperature sensing microscope probe. Specific thermal conductivity of CNT fibres showed an order of magnitude advantage over the traditional materials used for heat dissipation.

Introduction

Exceptional thermal properties of carbon based materials are very attractive due to the benefits associated with the material low density. The best in the family are graphene (with thermal conductivity measured between 1500 and 2000   W/mK [1], [2], [3]), diamond (with thermal conductivity up to 2200   W/mK [4]) and special carbon fibre T1300 (with thermal conductivity up to 1300   W/mK [5]). However these materials are expensive due to their multistage and time consuming production. It has been demonstrated experimentally that individual single-wall CNTs, which also belong to the carbon family, reach extremely high thermal conductivity of around 3500   W/mK [6]. Due to their high performance and the relative ease of formation of CNT macroscopic assemblies such as fibres and films they naturally attracted massive interest of the community and industry.

Thermal conductivity depends on many properties of a material, particularly its microstructure and composition. For instance, pure crystalline substances exhibit very different thermal conductivities along different crystal axes, due to differences in phonon coupling along a given crystal axis. Moreover, thermal conductivity value of a particular material should be reported along with the temperature, at which it was measured because it has a non-linear dependence on temperature.

There are various possibilities to measure thermal conductivity, each of them suitable for a limited range of materials, depending on the thermal properties and the medium temperature. Also most of the methods are suitable for bulk materials (like the steady-state and transient techniques). It is however challenging to measure thermal properties of fibres made of different materials. In this paper a Veeco explorer AFM thermal probe setup adapted for work in high vacuum was built in-house and used for the thermal conductivity measurements. It has been calibrated with different fibres of common materials before applied to the measurements of CNTs.

Section snippets

Materials

CNT fibres used in this work were directly spun from the CVD reactor according to already published procedure [7]. The synthesis temperature was 1300   °C and the feedstock was ethanol/ferrocene/thiophene. A typical scanning electron microscope (SEM) image of the macroscopic fibre is shown in Fig. 1.

Methods

The CNT fibre was wedged mechanically (using a micromanipulator) between the arms of a Veeco Thermal Probe, shown in Fig. 2A, which consists of an Ag Wollaston wire (75   mm in diameter) etched at the tip

Results

The experimental setup demonstrated in this paper was first tested using aluminium wire, representing a single solid few micron diameter fibre, of known thermal conductivity value reported by the manufacturer 195   W/mK [8] at room temperature.

The maximum heat steps height (max ΔQ) was measured at different probe's temperatures and a summary of the measurements is shown in Table 1.

The calculated thermal conductivity value of the Al wire is 198.1±18   W/mK. There is no correlation between the thermal

Conclusions

In this work a Veeco explorer AFM thermal probe setup was used to measure thermal conductivity of fibres made of different materials with different thermal properties and fibre structure. After careful calibration of the system macroscopic CNT fibres were measured at different probe temperature. It was found that around room temperature the thermal conductivity value was the highest 1255±317   W/mK and then decreased with increasing the probe temperature. By taking into the account the density of

Acknowledgements

K. Koziol thanks the Royal Society (RG68715) for financial support.

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Source: https://www.sciencedirect.com/science/article/abs/pii/S1386947716310153