On the Amorphisation Trajectory of Carbon Nanotubes
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On the Amorphisation Trajectory of Carbon Nanotubes
Saveria Santangelo1 and Candida Milone2 1
Dipartimento di Ingegneria Civile, dell’Energia, dell’Ambiente e dei Materiali (DICEAM)
Università “Mediterranea”, Loc. Feo di Vito, 89122 Reggio Calabria, Italy. 2
Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale (DIECII)
Università di Messina, Viale Ferdinando Stagno d’Alcontres 31, 98166 Messina, Italy.
ABSTRACT A very simple model for the kinetics of oxidation of carbon Nanotubes (NTs) is proposed which is able to reproduce the main features of their measured kinetic thermal oxidation profiles. Based on this model the resistance to oxidation of NTs is found to decrease with increasing defect density and amorphous phases, i.e. sp3 bonding component. This finding supports the validity of assumptions previously made to explain the correlation between results of Raman Spectroscopy (RS) and Kinetic Thermal Analysis (KTA) on NTs via a three-stage model, inspired to that proposed by Ferrari and Robertson for other nanocarbons. INTRODUCTION Despite of the increasing popularity of other forms of carbon, NTs continue to attract much attention for their great commercial potential in a large variety of nanotechnology applications [1]. RS is widely utilized for the fast and non-destructive characterization of all forms of carbon [2,3]. It allows easily identifying its allotropes and evaluating effects of disorder/ defects that are of great interest in all fields where localization matters. Very recently, by systematically investigating a wide set of NTs with different specifics (size, morphology, crystalline quality and purity degree), we demonstrated [4] the existence of a correlation between strength of C bonding, as measured by the G-band position (ωG) in Raman spectra, and oxidative resistance of the samples, as monitored by the maximum oxidation-rate temperature (TM) in kinetic thermal profiles. In order to get a deeper insight into the problem, here we elementarily model the NT oxidation process. CONSIDERED SAMPLES All the samples considered, listed in Table I, were object of previous studies focused on various aspects of their behavior [4í6]. Samples include Heat Treated (HT) at moderate temperature (1273í1773 K), as well as as-grown NTs. The latter sample typology comprises
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Table I. Main properties of the considered samples: metallic impurity content (xM), amorphous fraction (ξAC) and oxidative resistance (TM) of the samples as assessed by TG and KTA, and defect density and strength of C bonding, as monitored by D/G intensity ratio (ID/IG) and position of the G-band (ωG) in Raman spectra. Sample Ref xM ID/IG TM ξAC Code (wt%) (wt%) (K) AR1 4 0.3 0.0 811.7 0.41 AR2 5 3.3 0.0 815.3 1.41 AR3 5 6.7 0.0 843.7 1.18 AR4 5 4.1 0.0 823.8 2.20 AR5 5 3.7 0.0 839.0 1.40 HQG 5 0.0 0.0 1054.9 0.11 LQG 5 0.0 0.0 1038.1 0.47 AAC 4 2.7 100.0 756.5 0.48 AF1 5 17.8 0.0 812.1 1.30 AF2 5 3.5 0.0 827.2 1.78 AF3 5 7.3 0.0 831.0 1.49 AF4 5 15.2 0.0 825.6 1.61 AF5 5 11.2 0.0 831.1 1.43 AF6 5 4.2 0.0 843.5 0.86 AF7
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