High purity carbon nanotubes are synthesized by methane decomposition using an arc-jet plasma of high temperature (5000-20000 K). Since the arc-jet plasma process is continuous and easily scalable, it is a promising technique for the large-scale commercial production of carbon nanotubes. In this experimental work, the arc-jet plasma is generated by a dc non-transferred plasma torch, in which a mixture of argon and hydrogen is used as a plasma forming gas and nickel powder as a metal precursor.Morphology, crystallization degree and purity of the carbon nanotubes in the soot produced under various processing conditions are evaluated by using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. From the results of these material analyses, we have found that multi-walled carbon nanotubes of high purity were produced in the optimal operating condition. In addition, the thermal plasma characteristics for the carbon nanotubes growth are discussed from numerical simulation result of the arc-jet plasma.

We present a method of producing carbon nanotubes by means of the thermal plasma decomposition of methane (CH 4 ) in an arc-jet plasma of high temperature (5000-20000 K). Carbon nanotubes are produced under a floating condition by introducing CH 4 and a mixture of Ni-Y powders into the arc-jet plasma flame generated by a non-transferred plasma torch. Material evaluations of the synthesized product by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) reveals that the growth rate of carbon nanotubes is very high ,and that the produced carbon nanotubes mainly have a multi-walled structure even though the single-walled and coiled structures are rarely found. Since this process is continuously operable and easily scalable, it is expected to be a promising technique for large-scale commercial production of carbon nanotubes.

Radio frequency (RF) thermal plasma treatment is studied for the size reduction and the spheroidization of coarse glass particles to change them into submicrometer-sized powders of spherical shape. Such ultra-fine spherical powders are the key ingredients of a sintering aid to achieve efficient package and high performance in ceramic electronic applications. The coarse glass powders injected into the high-temperature RF thermal plasma undergo rapid heating, melting, and evaporation, followed by quenching, and then condense to very fine spherical powders. In the thermal plasma treatment with high RF powers of 18-23 kW at a powder feeding rate of 3 g/min, the scanning electron microscopy images and the particle size distribution graphs obtained from the treated glass powders indicate that most glass powders with initial average diameters of around 2 lm are reformed into spherical ones with sizes of below 500 nm. It is also observed in a 4 MHz RF thermal plasma reactor that the maximum size of particles decreases down to 200 nm when the reactor is operated under conditions of reduced pressure, low powder feeding rate, and high RF power. The compositions of glass powders before and after the plasma treatment are compared by using the wet and the inductively coupled plasma-optical emission spectroscopy analyses. Negligible composition changes appear within a range of o2 wt% during the RF thermal plasma process, which demonstrates the successful preparation of submicrometer-sized glass powders in spherical shape applicable to the advanced ceramic electronic devices.

The photoplethysmography (PPG) signal measured from a mobile healthcare device contains various motion artifacts occurring from a patient's movements. Recently, to reject the motion artifacts, the method of using an acceleration sensor was suggested, but such sensors are very expensive. Therefore, this study deals with a novel sensor device to replace the acceleration sensor, and evaluated the performance of the proposed sensor experimentally. In the results of the experiments, it is shown that the proposed sensor device can reconstruct the PPG signal despite the occurrence of motion artifacts, and also that the variation rate in heart rate analysis was 1.22%. According to the experimental results, the proposed method can be applied to design a low-cost device.

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