Improved efficiency of carbon nanotube yarn formation using gas discharge breakdown

抄録

1. Introduction

We found CNT filament formation phenomenon induced by gas discharge breakdown.[1] In this phenomenon, the gas discharge breakdown generated between electrodes, which was covered with carbon nanotube (CNT) film, created a lot of dust-like CNT bundles and these CNT bundles formed long CNT bundles by effect of an electric field. This phenomenon is promising for a simple and high efficiency CNT spinning method. Using this phenomenon, we have successfully formed CNT yarns by spinning these filaments.[2] However, the CNT yarns formed this method is short (typically <15 mm), and formation of longer CNT yarns is necessary. This requires further enhancement of the CNT filament formation by gas discharge breakdown. To this end, we used a collection electrode that consists of both cone-shaped and wire-shaped electrodes to improve the collection efficiency of CNT filaments, instead of the conventional electrode that consisted of cones electrode or wire electrode only. Furthermore, we increased the amount of the CNTs attached on the cathode to increase the formation efficiency of the dust-like CNTs that was required for the efficient CNT filament formation. We examined the effect of these improvements on the filament formation efficiency by the gas discharge breakdown.

2. Experimental

CNTs grown by thermal chemical vapor deposition were formed into a mat-shaped sheet and it was pressed onto a stainless-steel plate (cathode). At this time, the amount of the CNTs attached to the cathode increased three times as much as that of conventional procedure. A tungsten wire (0.15 mm in diameter) was used as the anode, which was fixed parallel to the cathode [Fig. 1(a)]. A wire-shaped auxiliary electrode was placed at the side of the anode, with the tip of the wire facing the anode. In addition, a collection electrode for CNT filaments was placed above these electrodes. A wire was placed both sides of the cone-shaped electrode so that the axes of the cone and the wires were parallel. The discharge chamber in which the electrodes were placed was evacuated and Ar gas was introduced to 6.2 kPa. Bias voltages of +50 V and +100 V were then applied to the collection and auxiliary electrode, respectively. A discharge breakdown was generated by applying a DC voltage of -800 V between the cathode and anode to produce CNT filaments. The CNT filaments were collected by a collection electrode to form filament bundles.

3. Results and discussion

The formation of the CNT yarn using the experimental setup described above was carried out by the following procedure. First, the gas discharge breakdown was generated to create dust-like CNTs from the CNT mats on the cathode. The dust-like CNTs floating around the electrodes were collected by the collection electrode, forming the CNT filaments as shown in Fig.1(b). During the formation of the filaments, the collection electrode was moved upward to form a CNT filament bundle. Then the CNT filament bundle was twisted by rotating the collection electrode [Fig.1(c)]. This process was repeated again to elongate the CNT yarn. Finally, the long CNT yarn was obtained as shown in Fig. 1(d). The length of the yarn was 35 mm, which was longer than in the previous study.[2] It is considered that formation of further longer CNT yarns is possible by further repetition of the process described above.

Acknowledgment

This study was supported by JSPS KAKENHI Grant Number 22K04872.

References

[1] H. Sato et. al., Vacuum 198, 110877 (2022).

[2] H. Hayama et al., Jpn. J. Appl. Phys., 62, SA1010 (2023).