Development and characterization of micro-coil carbon fibers by a microwave CVD system

Abstract

Nano-and micro-coiled carbon fibers find applications in electronic devices, electromagnetic absorbers and filters. Smart devices can be conceived using tunable films on these fibers and tunable host materials. A new method of producing helical carbon fibers with dimensions in the order of less than a micrometer has been developed using microwaves. The microwave CVD system presented here eliminates the use of the toxic impurity gas, which is required in the conventional method. Both methods involve gas phase reactions over a substrate seeded with an appropriate catalyst. Micro-coiled carbon fiber (MCCF) was grown by the catalytic pyrolysis of acetylene on a silicon carbide substrate on which nickel metal powder was dispersed as a catalyst. Various factors, for example flow rate of the gas, particle size of the catalyst, effect of reaction temperature and time, were studied in order to understand the growth of the microwave synthesis of MCCF. MCCFs were also synthesized by a conventional method in the presence of thiophene as an impurity gas so that a comparison can be made with the materials obtained by the microwave system. The morphology of the final products were investigated by scanning electron microscopy. The carbon products obtained by traditional and microwave methods were investigated with the help of x-ray diffraction. The effect of various reaction conditions on the morphological development of a MCCF were examined in detail. Furthermore, a brief study was made on the microwave absorbing property of the MCCF.

<title>Carbon and ceramic microcoils for MEMS by microwave CVD</title>

“…In order to get the optimal reaction condition for the growth of carbon microcoils, a series of experiments have been done to check the effect of reaction temperature, reaction time, flow rate and the size of Ni particle. The results were shown in our previous paper [7].…”

“…Furthermore, the helical structure makes microcoils as potential candidates for effective fillers in EM shielding and absorber materials. Varadan, et. al reported about 15 dB of reflection reduction from carbon microcoils in a free space measurement [7].…”

Large-scale microwave CVD system for synthesis of carbon nanotubes

“…of SPIE Vol. 5055 211 nanostructures by microwave CVD just like their micro coil counterparts as presented by Varadan et.al [31]. Figure 8 shows helical nanotubes obtained by the microwave CVD method presented above.…”

“…This method has been successfully adopted for the fabrication of long (in the order of several centimeters) micro- [31] and nano- [32] coiled carbon fibers. These materials are observed to have large surface area with excellent mechanical, electrical and electronic properties.…”

Homeland security monitoring sensors and early warning relay and diagnostic system

“…Large quantity production of MWCNT has been reported by the Varadan's group [11]. MWCNTs were grown on Silicon carbide substrate using Microwave assisted Chemical Vapor Deposition (CVD).…”