Papers by Author: Siang Piao Chai

Abstract: Magnetite (Fe₃O₄) nanoparticles were synthesized in aqueous solutions without any surfactants. The Fe₃O₄ nanoparticles are nearly spherical and have an average diameter of 10.33nm and a narrow size distribution. Bundles of single-walled carbon nanotube (SWCNT) were synthesized using these Fe₃O₄ nanoparticles supported by MgO. Transmission electron microscopy (TEM) images show that tremendous amount of bundles SWCNT with uniform diameters were produced. The average diameter of bundles SWCNT is 1.22nm. Raman spectrum shows that well graphitized SWCNTs were formed based on the low ratio of I_D/I_G. Fe₃O₄ nanoparticles could be an effective active metal to synthesize large quantity bundles of SWCNT.

Abstract: Fe₃O₄ was used to synthesize narrow diameter of carbon nanotubes (CNTs). The effect of concentration of Fe₃O₄ on the diameters of carbon nanotubes (CNTs) synthesized by methane decomposition at 1000°C was investigated. We used conventional impregnation method to prepare Fe₃O₄/MgO catalysts. The results show that the concentration of Fe₃O₄ greatly affects the diameter distributions of produced CNTs. The CNTs formed by Fe₃O₄/MgO catalysts, with the mole ratio set at 0.25:9.75 and 1:9 had diameter of 3.23 ± 1.71 and 49.04 ± 33.62nm, respectively, showing that a decrease in concentration of Fe₃O₄ yields smaller diameter and narrower diameter distribution. A growth model explaining tip-growth and base-growth mechanism is proposed for understanding formation of CNTs.

Abstract: The effect of calcination temperature for Fe₂O₃/MgO catalysts on the formation of carbon nanotubes (CNTs) was examined. CNTs were synthesized over Fe₂O₃/MgO catalysts calcined at different temperatures by catalytic decomposition of methane at 1000°C. The synthesized CNTs were investigated by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results show that the effect of calcination temperatures greatly governed the diameter and the quality of the SWCNTs formed. The catalysts calcined at 500, 600 and 700°C produced CNTswith the diameters of 1.53, 1.95 and 2.97nm, respectively. Generally, an increase in the calcination temperature increases the average diameter and decreases the quality of the CNTs produced.