Abstract
This work aims to investigate and characterize the photo-ignition phenomenon of MWCNT/ferrocene mixtures by using a continuous wave (CW) xenon (Xe) light source, in order to find the power ignition threshold by employing a different type of light source as was used in previous research (i.e., pulsed Xe lamp). The experimental photo-ignition tests were carried out by varying the weight ratio of the used mixtures, luminous power, and wavelength range of the incident Xe light by using selective optical filters. For a better explanation of the photo-induced ignition process, the absorption spectra of MWCNT/ferrocene mixtures and ferrocene only were obtained. The experimental results show that the luminous power (related to the entire spectrum of the Xe lamp) needed to trigger the ignition of MWCNT/ferrocene mixtures decreases with increasing metal nanoparticles content according to previously published results when using a different type of light source (i.e., pulsed vs CW Xe light source). Furthermore, less light power is required to trigger photo-ignition when moving towards the ultraviolet (UV) region. This is in agreement with the measured absorption spectra, which present higher absorption values in the UV–vis region for both MWCNT/ferrocene mixtures and ferrocene only diluted in toluene. Finally, a chemo-physical interpretation of the ignition phenomenon is proposed whereby ferrocene photo-excitation, due to photon absorption, produces ferrocene itself in its excited form and is thus capable of promoting electron transfer to MWCNTs. In this way, the resulting radical species, FeCp2+∙ and MWCNT−, easily react with oxygen giving rise to the ignition of MWCNT/ferrocene samples.
Highlights
The results reported in [4] for SWCNTs have been confirmed for multiwall carbon nanotubes (MWCNTs) in [5]
The minimum power thresholds necessary to trigger the ignition of the MWCNT/ferrocene mixtures will be reported for different mixture weight ratios and using the entire lamp spectrum
The luminous power thresholds for triggering ignition were found for different mixture weight ratios varying the parameters of the continuous wave (CW) Xe light incident on the sample such as the luminous power and the wavelength range
Summary
The authors conjectured that the ignition and combustion occur when there is a local increase in temperature sufficient to initiate the oxidation of carbon. Their interpretation was that SWCNTs lend themselves to this photo-effect due to their black color, which allows better absorbing of the visible flash light and transmits the resulting thermal energy to the Fe nanoparticles. The local transient high temperature inside the nanotubes must be at least ≈1500 °C in order for a structural reconstruction process to take place This results in a permanent change in the SWCNT structure to a non-tubular structure, rather than merely elastically deforming.
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