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Abstract
The aim of this work is to investigate and characterize the photo-ignition process of dry multi-walled carbon nanotubes (MWCNTs) mixed with ferrocene (FeCp2) powder, using an LED (light-emitting diode) as the light source, a combination that has never been used, to the best of our knowledge. The ignition process was improved by adding a lipophilic porphyrin (H2Pp) in powder to the MWCNTs/FeCp2 mixtures—thus, a lower ignition threshold was obtained. The ignition tests were carried out by employing a continuous emission and a pulsed white LED in two test campaigns. In the first, two MWCNT typologies, high purity (HP) and industrial grade (IG), were used without porphyrin, obtaining, for both, similar ignition thresholds. Furthermore, comparing ignition thresholds obtained with the LED source with those previously obtained with a Xenon (Xe) lamp, a significant reduction was observed. In the second test campaign, ignition tests were carried out by means of a properly driven and controlled pulsed XHP70 LED source. The minimum ignition energy (MIE) of IG-MWCNTs/FeCp2 samples was determined by varying the duration of the light pulse. Experimental results show that ignition is obtained with a pulse duration of 110 ms and a MIE density of 266 mJ/cm2. The significant reduction of the MIE value (10–40%), observed when H2Pp in powder form was added to the MWCNTs/FeCp2 mixtures, was ascribed to the improved photoexcitation and charge transfer properties of the lipophilic porphyrin molecules.
Highlights
Carbon nanotubes (CNTs), since their discovery, have attracted the attention of researchers and companies for their mechanical, electrical, thermal, and optical unconventional properties, and for their particular dimensions and chemical structure
2.5 ms ForSince carrying out ignition tests,emits the high purity (HP)-multi-walled carbon nanotubes (MWCNTs)/FeCp nanoparticle was the first to be the LED
HP-MWCNTs/FeCp with a 1:3 weight; frames are temporally spaced at 200 ms
Summary
Carbon nanotubes (CNTs), since their discovery, have attracted the attention of researchers and companies for their mechanical, electrical, thermal, and optical unconventional properties, and for their particular dimensions and chemical structure. The CNTs photo-ignition process was observed, accidentally, by exposing single-walled carbon nanotubes (SWCNTs) to the light pulse of an ordinary camera [1]. The structural changes observed in the post-ignited samples in Ajayan et al [2] suggested that the ignition was due to a local temperature increase (higher than 1500 ◦ C) sufficient to initiate the carbon oxidation. The local thermal increase is due to the high efficiency of CNTs in absorbing light radiation, because of their black color and their higher thermal conductivity with respect to the metallic nanoparticles. Smits et al highlighted the importance of a metallic catalyzer, contained in SWCNTs, for the photo-ignition process [3]; when exposing samples of high-purity, as-produced
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