Effect of external electromagnetic field and bias voltage on the vapor growth, morphology and properties of carbon micro coils

Carbon microcoils were obtained by the Ni-catalyzed pyrolysis of acetylene at 770 degrees C using thiophene as an impurity with and without an externa l electromagnetic (EM) field and by applying or not applying a bias: voltag e to the substrate. The effects of the external EM field and bias voltage o n the growth rate, morphology and some properties of the carbon microtoils were examined, It was observed that the external EM field accelerated the d ecomposition of acetylene resulting in a coil yield of 1.3-1.7 times higher than that without the external EM held. The application of the bias voltag e also resulted in an increase of the coil yield; the yield linearly increa sed with increasing bias voltage. The coil yield obtained with a DC bias of 600 V and an AC bias of 2000 V with an applied external EM field was 1.9 a nd 2.1 times higher than that without the EM field and bias voltage, respec tively. The very regularly-coiled carbon fibers with Bat fiber cross-sectio ns and irregularly-coiled carbon fibers with circular fiber cross-sections were obtained with the Ehl field and without the EM field irrespective of t he bias voltage, respectively. (C) 2000 Elsevier Science Ltd. All rights re served.