| This paper focuses on the preparation of coal-based carbon nanotubes (CNTs) and carbon microballs. The CNTs were prepared by DC arc discharge of coal-based rods in water, while the ball-like carbons were made by DC arc discharge of coal-based rods in different gases. The products were characterized using scanning electron microscope (SEM), transmission electron microscope (TEM) , X-ray diffraction technique (XRD), X-ray energy dispersive spectroscopy (EDS) and IR spectroscopy, at the same time, the optical emission spectroscopy (OES) was adopted for in situ diagnosis of active species involved in the arcing process. On basis of the experimental results, the formation mechanism of coal-based CNTs as well as the formation mechanism of ball-like carbons are proposed and discussed in terms of the process parameters and coal properties.The results show that it is possible to produce CNTs with high quality and low cost by arc discharge of coal-based carob rods in water. The OES analysis revealed that in addition to C1 and C2, some other active species also get involved in the formation reactions in the arc plasma. It leads one to believe that the formation of CNTs in water medium may proceed via a scheme that is different from the conventional arc discharge in gaseous medium, in which some large active fragments released from coal-based carbon rods may play an important role in the growth process of CNTs.A novel ball-like carbon material with diameter in micrometer range was successfully prepared, for the first time, from coal-based carbon rods by dc arc discharge method. It has been found that the ball-like material mainly consists of carbon with a high degree of graphitization. These novel micro-sized carbons have a diverse morphology, such as chain-like or plate-like carbons. It is found that adding acetylene into the buffer gas in the arc system can help promote the formation of these ball-like carbons which also depends, to some degree, on the surface properties of the anode. |
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