The paper presents results of investigation of growth of carbon fibers in low-current electrical discharges. The method is based on hydrocarbon pyrolysis in electrically generated plasma in oxygen-free atmosphere. Various types of corona discharges of both polarities were tested with regard to their applications to carbon fiber synthesis.

The discharge was generated between a stainless steel needle, and a plate made of a nickel alloy, spaced at 15 mm. The experiments were carried out in argon atmosphere in normal temperature and pressure. Cyclohexane or n-hexane were used as the carbon feedstock gases. The voltage of the discharges was changed in the range from 2 kV to 30 kV to obtain a stable low-current arc discharge. The current of the arc discharge was varied from 1 to 6 mA. The changes in morphology of the carbon fiber surface was observed under a SEM Hitachi S3400N.

Fig. 1.

It was noticed during the experiments that carbon fibres were built at the tip of the discharge needle electrode as an effect of plasma pyrolysis. The length of synthesised carbon fibers varied in the range from 0.5 to 13 mm after a constant time of syntheses of 30 s, and their diameter was from about 20 to 100 mm. With the current increasing up to about 2 mA, the growth rate increased (Fig.1). For larger currents the growth rate started to decrease, and next, for the current >3 mA, increased slowly again. For small currents (<2 mA), the structure of the fiber was homogeneous and the surface was smooth. For larger currents (>3 mA), the fiber consisted of two different co-axial structures: a central core and an external porous shell. An example of carbon fiber synthesised in the discharge is shown in Fig.2.

Fig. 2.

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