Preparation and Reaction Kinetics of Carbon Nanotubes/Aluminum Composite Powders Using Polymer Pyrolysis Method

doi:10.3724/SP.J.1077.2014.13494

Abstract

Abstract:

The method of polymer pyrolysis chemical vapor deposition (PP-CVD) was used to in situ grow carbon nanotubes (CNTs) on the micro and nano sized flake like aluminum powder substrates. The vapor species were in situ produced by pyrolysis of polyethylene glycol (PEG) including the carbon sources, which was the main difference between the PP-CVD and conventional CVD methods, while the catalyst nanoparticles were produced by the reaction between citric acid (CA) and cobalt nitrate (Co(NO₃)₂) on aluminum powder surfaces. The reaction mechanism of PP-CVD was studied with the analysis of experiments and reaction kinetics modeling, revealing the influence of the vapor species produced by pyrolysis of PEG and CA and surface vapor-solid reactions on catalyst nanoparticles on CNT growth rates. The CNTs growth rates increases with the increase of reaction temperature and initial partial pressure of CO, which is influenced by the content of PEG and CA, and decreases with the increase of catalyst density and initial partial pressure of H₂. The variation trends of the simulated CNTs average length with reaction temperature and time are consistent with the experimental results. Thus, this work provides new theoretical basis to the further optimization of fabricating CNTs/aluminum composite powders.

Key words: carbon nanotubes, aluminum, composites, in situ, polymer pyrolysis chemical vapor deposition, reaction kinetics

CLC Number:

TB331

XU Run, LI Xin-Da, LI Zhi-Qiang, ZHAO Ren-Yu, FAN Gen-Lian, XIONG Ding-Bang, TANG Jie, XU Yong, ZHANG Di. Preparation and Reaction Kinetics of Carbon Nanotubes/Aluminum Composite Powders Using Polymer Pyrolysis Method[J]. Journal of Inorganic Materials, 2014, 29(7): 687-694.

Figures/Tables 10

Fig. 1 Schematic drawing of CNTs grown by PP-CVD (a) The temperature and pressure monitoring system; (b) The closed batch reactor; (c) Al nanoflakes with Co nanoparticles and CNTs as grown; (d) The gas-solid reaction pathway and tip growth mode of CNTs. The dashed arrows represent collision of gaseous species and the solid arrows represent surface diffusion of carbon atoms around the Co nanoparticle

Table 1 Nomenclature of the symbols used in the modeling

Symbols	Definition
Cp	Encapsulating carbon
(S)	Surface species
C(S)	Active carbon atom
	The forward (f ) reaction rate constant of the i th reaction
	The reverse (r) reaction rate constant of the i th reaction
A	The Arrhenius pre-exponential factor
	The Arrhenius temperature coefficient
E_i	The activation energy of the i th reaction
R	The universal gas constant
	The change in the Gibbs free energy of formation as a result of the reaction
	The net stoichiometric coefficient for species j in i th reaction
q_i	The rate of progress of the i th reaction
R_j	The net rate of production of species j
C_j	The volumetric concentration of species j
V_deposited	The volume of deposited carbon atoms
	The volume of encapsulating carbon
V_C	The volume of a carbon atom
	The density of Co nanoparticles
	CNTs growth rate
d	The diameter of Co nanoparticles
N_A	Avogadro constant
Do	The surface diffusion coefficient of carbon atoms

Fig. 2 Flow diagram of modeling process

Table 2 Composition of the PEG-CA-Co(II) pyrolysis gases in the batch reactor

The initial pressure /(1.013×10⁵, Pa)	The initial partial pressure /(1.013×10⁵, Pa)
The initial pressure /(1.013×10⁵, Pa)	CH₄	CO	CO₂	H₂O	H₂
22	1.61	6.24	6.18	5.65	1.53

Table 3 The ratio of Co nanoparticle surface area to the projected area of carbon source gas molecules

Species	CH₄	CO	CO₂
Projected area^a	2.43×10^-2	2.01×10^-2	3.45×10^-2
Ratio^b	3656	4388	2531
Active site density ^c	1.72×10^-9	2.06×10^-9	1.19×10^-9

Fig. 3 Morphologies of CNTs at different scales (a) SEM image of the Al flake substrates; (b) SEM image of the CNTs; (c) TEM image of the CNTs; (d) HRTEM image of the CNTs and SEAD pattern of catalyst particle

Fig.4 Effects of different vatiables in the modeling on the CNT growth rates in 60 min (a) Partial pressure of CO; (b) Partial pressure of H2; (c) Co nanoparticles density; (c) Reaction temperature

Fig. 5 Mole fraction of gaseous species in the batch reactor versus the growth time at 873 K

Fig.6 SEM images with length and normalized frequency statistic (inset) of the CNTs after grown at 873 K for (a) 0 min, (b) 30 min and (c) 60 min. (d) Raman spectra of the CNT/Al composite powders The lengths of CNTs were measured on the corresponding SEM images randomly, and 120 CNTs were counted at each reaction time

Fig. 7 Mean length of CNTs grown at 873 K vs growth time

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