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In this study, the ferrocene weight was increased from 0.1 to 0.2 g to demonstrate the growth of MWCNTs on Si/SiO2/Al2O3 substrate. Ethylene was used as carbon precursor for CNTs nucleation. The as-grown multiwalled carbon nanotubes (MWCNTs) were investigated for the effect of ferrocene weight on yield and crystallinity of nanotubes. TEM, Raman and TGA studies revealed that an increase in ferrocene weight to a certain limit significantly improves the diameter, crystallinity, alignment and %yield of the product. However, above 0.15 g of ferrocene, few nanotubes were having surface defects and some black spots were also evident in TEM images. The lowest inner-shell spacing and ID/IG ratio were evident for 0.15 g ferrocene catalyst which was an indication of relatively pure CNTs growth. Raman spectra also confirmed the highly crystalline and relatively pure CNTs structures with ID/IG ratio of 0.851 for 0.15 g ferrocene. TGA data also revealed the formation of pure MWCNTs especially for 0.15 g ferrocene with oxidation temperature of 620°C. [ABSTRACT FROM AUTHOR]

To date, focus of the research activities in nanoscience was to control the chemical vapor deposition (CVD) growth of carbon nanotubes (CNTs) by changing the precursor pressure and process temperature. The effect of the precursor flow rate and process time on CNTs growth parameters has been overlooked in past studies and therefore is very little known. This study was focused on the optimization of the ethylene flow rate and CVD process time for CNTs growth over Fe2O3/Al2O3catalyst in a fluidized bed chemical vapor deposition (FBCVD) reactor, operating at atmospheric pressure. Argon and hydrogen were considered as the carrier and supporting gases, respectively. Transmission electron microscope (TEM) and Scanning Electron Microscopy (SEM) were used to investigate the surface morphology, nanostructures, purity and yield of the grown CNTs. In-depth analysis revealed an increase in tube length, yield and the carbon concentration with ethylene flow rate in the range of 50–110 sccm. However, an inverse relationship between flow rate and tube diameter distribution was predicted in the given work. The most favorable results were obtained at an ethylene flow rate of 100 sccm and a CVD process time of 60 minutes. The dense and homogeneous growth of relatively pure nanotubes of increased tube length and narrow diameter distribution, in the range of 20–25 nm, was observed at optimized flow rate and process time. [ABSTRACT FROM PUBLISHER]

This study aimed at investigating the effect of the fluidized bed chemical vapor deposition (FBCVD) process parameters on growth mechanism, morphology and purity of the multiwalled carbon nanotubes (MWCNTs). Nanotubes were produced in a vertical FBCVD reactor by catalytic decomposition of ethylene over Al 2 O 3 supported nano-iron catalyst buds at different flow rates. FESEM, TEM, Raman spectroscopy and TGA thermograms were used to elaborate the growth parameters of the as grown MWCNTs. As the growth process was driven by the process temperatures well below the iron-carbon eutectic temperature (1147 °C), the appearance of graphite platelets from the crystallographic faces of the catalyst particles suggested a solid form of the catalyst during CNT nucleation. A vapor-solid-solid (VSS) growth mechanism was predicted for nucleation of MWCNTs with very low activation energy. The nanotubes grown at optimized temperature and ethylene flow rate posed high graphitic symmetry, purity, narrow diameter distribution and shorter inter-layer spacing. In Raman and TGA analyses, small I D /I G ratio and residual mass revealed negligible ratios of structural defects and amorphous carbon in the product. However, several structural defects and impurity elements were spotted in the nanotubes grown under unoptimized process parameters. [ABSTRACT FROM AUTHOR]

This study investigated the effect of process temperature and activation energy on chemical vapor deposition growth of multi-walled carbon nanotubes (MWCNTs). A vertically fluidized bed reactor was used to grow MWCNTs by catalytic decomposition of ethylene over FeO/AlO at the cost of very low activation energy of 19.516 kJ/mole. FESEM, TEM, and Raman spectroscopy were used to characterize the growth parameters of MWCNTs in the temperature range of 873.15 K to 1273.15 K (600 °C to 1000 °C). SAED patterns were taken to investigate the crystallinity of the grown structures. The experimental results revealed that MWCNTs grown at the optimum process temperature of 1073.15 K (800 °C) exhibited hexagonal crystal structures, narrow diameter distribution and shorter inter-layer spacing. However, the inner and outer walls of most of MWCNTs grown at the temperatures above and below the optimum were non-uniform and defective. The higher process temperatures promoted the agglomeration of the catalyst particles and decomposition of the carbon precursor, which in return increased the tube diameter, surface defects and amorphous carbon content in the product. The intensity ratio plots also predicted low crystallinity in MWCNTs grown at unoptimized process temperatures. The highest I/ I ratio of 1.43 was determined at 1073.15 K (800 °C), which reflects high pct yield, purity and crystalline growth of MWCNTs. [ABSTRACT FROM AUTHOR]

Large scale production of impurity-free carbon nanotubes is a current challenge. For the bulk production of carbon nanotubes, the selection of an appropriate catalyst is also an important task. In this study, an aluminum oxide/iron nitrate catalyst was prepared by using a co-precipitation method. The surface morphology and composition of the catalyst were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results were compared with a commercially available ferrocene catalyst. Multiwalled carbon nanotubes were grown by catalytic decomposition of ethylene over the catalyst via floating catalytic chemical vapor deposition. The yield of nanotubes increased with an increase in the mass of aluminum oxide/iron nitrate but remained unchanged with an increase in ferrocene mass. The yield of carbon nanotubes remained between 68% and 93%, which was much higher than obtained with only ferrocene (4%). In case of ferrocene, rather affecting the product yield, the catalyst mass affected the diameter of the nanotubes. The tube diameters were between 20 nm and 34 nm for aluminum oxide/iron nitrate and between 39 nm and 71 nm for ferrocene. [ABSTRACT FROM AUTHOR]

Controllable synthesis of quality carbon nanotubes is a precondition for their broad applications. The objective of the work was to study the effect of catalyst concentration on the quality, diameter, length, alignment and crystallinity of the grown multiwalled carbon nanotubes (MWCNTs). To meet the stated objective, MWCNTs were successfully synthesized by using floating catalytic chemical vapor deposition technique. The ferrocene concentration was varied from 0.1 to 0.2 g and MWCNTs were synthesized with ethylene as a carbon precursor at reaction temperature of 850°C. The grown MWCNTs were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The obtained data revealed that an increase in concentration of the ferrocene significantly affects the diameter, crystallinity and growth of nanotubes, however, negligible effect on the CNTs forest length was noticed. The dense, uniform and meadow like patterns of grown CNTs were observed for 0.15 g ferrocene. The average diameter of the grown CNTs was ranged from 32-75 nm. Above 0.15 g ferrocene, some of the grown CNTs were found defective and few black spots were also appeared in TEM images. [ABSTRACT FROM AUTHOR]