Development of low-current plasma process with ultrasonic cavitations for synthesizing metal-filled carbon nanocapsules in organic solutions

Nanoparticles of metal carbides (Fe₃C, χ-Fe_2.5C, Co₃C, TiC) wrapped in mutilayered graphitic sheets, called as carbon nanocapsules (CNCs), were synthesized by a new method in which low-current plasma discharge was generated even in insulating organic solutions such as benzene and ethanol due to an ultrasonic irradiation. In this process, ultrasonic horn was utilized not only for ultrasonic irradiation but also for cathode electrode. Anode electrode materials such as iron, cobalt and titanium were optionally selected. In this study, ultrasonic cavitation bubbles were induced between the gap of cathode and anode electrodes in the organic solutions. Consequently, an electric plasma discharge could be generated in liquid organics at power as low as around 45-165 W (DC 30-55 V, 1.5-5 A). The structure, morphology and phases of CNCs were characterized by high-resolution transmission electron microscopy and X-ray diffraction. The magnetic properties (saturation magnetization, coercivity) of the CNCs samples were measured by a vibrating sample magnetometer at room temperature.