Ali Shahverdi

Synthesis of single-walled carbon nanotubes using induction thermal plasma technology with different catalysts: thermodynamic and experimental studies

The effects of the type and quantity of three catalyst mixtures (i.e. Ni-Y2O3, Ni-Co-Y2O3, and Ni-Mo-Y2O3) on single-walled carbon nanotubes (SWCNT) synthesis by induction thermal plasma process have been examined in order to evaluate their individual influences on SWCNT production. Thermodynamic calculations, in gas and particularly in liquid solution phases, have also been performed to better understand the effects of the catalysts on the production of SWCNT. Characterization of the synthesized SWCNT by different techniques including Raman spectroscopy, high resolution scanning electron microscopy (HRSEM) imaging and thermogravimetric analysis (TGA) clearly indicated that the best quality of SWCNT was achieved using Ni-Co-Y2O3 catalyst mixture in the feedstock.

CFD Simulation of Single-walled Carbon Nanotube Growth in an RF Induction Thermal Plasma Process

A Radio Frequency (RF) inductively coupled plasma technique is a new and promising synthesis method of Single-Walled Carbon Nanotubes (SWCNTs) at large scales, for industrial and commercial applications. With this method, a mixture of carbon black and metal catalysts is directly vaporized by a plasma jet, generated from an induction plasma torch. Subsequently, inside a reactor chamber, and under a controlled temperature gradient, carbon-metal clusters are formed and become the potential sites for the nucleation and growth of SWCNTs. In this process, the local plasma properties and the thermo-fluid field in the system affect the yield rate of SWCNTs, thus it is important to find an appropriate operating condition, which maximizes the yield rate. Numerical modeling in conjunction with experimental studies can help investigate the contribution of the thermo-fluid field and process parameters in the formation of catalyst nanoparticles and carbon nanotubes in the induction thermal plasma system. The goal of this work is to perform CFD simulations of the RF thermal plasma process in the synthesis of SWCNT in order to numerically study the thermo-flow fields inside the synthesis system. The effect of thermal conductivity of the reaction chamber’s graphite liners were also investigated on the flow and the temperature fields in the system. The thermal conductivity of the graphite liners was measured at different temperatures and implemented into the CFD code. The comparison between our current simulations with our previous results indicates that the thermal conductivity profile of the graphite liners imposes variations on the flow and the temperature fields inside the reaction chamber.

In situ removal of amorphous carbon from single-walled carbon nanotubes synthesized by induction thermal plasma

In this work, a simple, efficient and cost-effective in situ purification method has been developed based on gas-phase oxidation, in an effort to increase purity of single-walled carbon nanotubes (SWNT) in the course of SWNT synthesis by induction thermal plasmas. This newly developed purification method has the following advantages compared with the conventional off-line gas-phase oxidation techniques; 1) residual heat carried by plasma gases from the reactor can be utilized as a heat source for the thermal oxidation reaction; 2) oxidizing reactants can pass through the SWNT soot collected on the surface of metallic filters, resulting in more uniform and effective etch of amorphous carbons; 3) this one-step process is basically continuous and easy to be scaled up. In the purification experiments, for the thermal oxidation of the SWNT soot, pre-heated oxygen is injected into the collection chamber during the SWNT synthesis with three different oxygen flow rates of 5, 7.5 and 10 vol% 02, and then subsequent changes in the SWNT soot are analyzed by various material characterization techniques, such as thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results clearly show that the major by-product of amorphous carbons can be successfully eliminated by this method and the purity of the SWNT has been increased approximately from 35 wt% to 60 wt% due to preferential removal of amorphous carbons. The parametric study on the effect of the flow rate also suggests that the most effective flow rate of the oxidizing gas is around 10 vol%. However, the diameter distribution of the SWNT samples has been narrowed during the in situ thermal oxidation process because of a significant loss of thin nanotubes.