Catalytic chemical vapor deposition synthesis of single- and double-walled carbon nanotubes from α-(Al1−Fe )2O3 powders and self-supported foams

Integral low-energy electron Mössbauer spectroscopic studies of the surfaces of carbon nanotube-nanocomposite powders

“…Four components were found to be required to obtain adequate fits for these spectra: (a) an outer sextet characteristic of α-Fe, (b) an inner sextet that could be attributed to Fe 3 C, (c) an Fe 3+ doublet due to iron ions present in the lattice of the α-Al 2 O 3, and (d) a singlet that corresponds to a γ -Fe phase, which may possibly be alloyed to carbon (γ -Fe-C). Basically, the emission spectra exhibit the same shape as that of the transmission spectra as reported by de Resende et al and also the hyperfine parameters (Table 1) do not significantly differ from those derived from the latter [3]. The relative spectral areas RA of the respective Fe phases as obtained from the transmission and emission spectra are listed in Table 2.…”

“…The synthesis of the CNTs-Fe-Al 2 O 3 and CNTs-Fe-MgAl 2 O 4 and their characterization by X-ray diffraction, transmission Mössbauer spectroscopy, transmission-and scanning electron microscopy are described in detail elsewhere [3,4]. Briefly, the CNTs-Fe-Al 2 O 3 nanocomposite powders were prepared by a catalytic chemical vapor deposition (CCVD) route involving the reduction of α-( Mössbauer spectra at room temperature were collected with a spectrometer operating in constant acceleration mode with triangular reference signal.…”

“…In this contribution ILEEMS results will be presented for different selected CNTs-nanocomposite systems. These nanocomposite systems were synthesized and characterized by several techniques earlier [3,4]. It is intended to demonstrate that the characteristics of the top surface layers of these systems are The values of isomer shifts are with reference to metallic iron B hf,m hyperfine field at maximum of the distribution (T ), 2ε Q quadrupole shifts (mm/s), E Q,m quadrupole splitting (mm/s),δ isomer shifts (mm/s) a Fixed parameters Results for transmission spectra are from reference [3] very often significantly different as compared to what is observed for the bulk by transmission Mössbauer spectroscopy.…”

Insights into carbon nanotube growth using an automated gravimetric apparatus

“…XPS of the reduced catalyst also failed to detect hercynite by the small $0.1 eV Fe +2 and Fe +3 shifts in Fe 2p 3/2 , or the larger 1.3 eV Al 2p shift (Al 2 O 3 : 75.8 eV; FeAl 2 O 4 : 74.5 eV) [89]. Hercynite detection in the literature by Mö ssbauer spectroscopy [90] has proven similarly inconclusive. These findings do not, however, exclude oxide retention or hercynite formation because species may not be present on the Al 2 O 3 surface, or the crystallite size and dispersion are below detection thresholds.…”

Evaluation of iron-containing carbon nanotubes by near edge X-ray absorption technique

“…Nonetheless, iron-containing phases filling CNTs are known to be inherent to this production process (Antunes et al, 2011;Dillon et al, 2012;Nagata et al, 2013). Researchers have acquired CNTs filled with α-iron, γ-iron and iron carbides (Antunes et al, 2011;Resende et al, 2009;Longbottom et al, 2007). and the literature indicates that depending on the synthesis method and precursor materials, CNTs can be filled with different nanoparticles (Gao et al, 2004;Liu and Wehmschulte, 2005).…”