Flame Synthesis Of Carbon Nanotubes Research Articles

Flame-synthesis of carbon nanotubes on silicon substrates and their field emission properties

We reported the flame-synthesis of patterned multiwalled carbon nanotubes (CNTs) on silicon substrate by a shadow mask and their field emission properties. It was found that CNTs with tangled and curved morphology were preferentially grown around the cracked edges of Ni dot pattern. A crack-induced catalyst-activation growth mechanism was proposed. The patterned CNTs fabricated by such a simple flame-synthesis method exhibited good field emission characteristics with uniform emission patterns and reproducible and stable emission behaviors, although the CNTs possessed many defective graphite layers and showed relatively higher turn-on and threshold field than other reported CNTs grown by chemical vapor deposition. Our results demonstrated that such a low-cost and scaleable CNT pattern fabrication process can be expected to have favorable applications in field emission devices.

Flame synthesis of carbon nanotubes with high density on stainless steel mesh

Multi-walled carbon nanotubes grew directly on wires of stainless steel mesh in controllable methane diffusion flames. The formation and morphology of carbon nanotubes were dependent on gas composition of the flames. On pre-etched mesh wires with HCl, high density of carbon nanotubes were synthesized with uniform outer diameters of 60 nm and large inner diameters of 50 nm. With the high yield of carbon nanotubes, less carbon impurities were formed in the process. A mechanistic model was proposed in detail to suggest the formation of catalyst directly on bulk surface and explain the whole process of carbon nanotubes growth in this study.

A detailed model for the flame synthesis of carbon nanotubes and nanofibers

Many experimental investigations of CNT/CNF flame synthesis have been recently reported. However, there are as yet no comprehensive models regarding their formation, growth or structure. Herein, a CNT/CNF growth rate model is proposed that is applicable for any method of CNT/CNF production (although our particular interest lies in flame synthesis in ethylene/air flames). While it is usual for most existing models to consider only a single carbon-carrying gas that contributes towards carbon deposition, our extended model can consider a complex hydrocarbon mixture that can mimic a flame environment. The model shows that before carbon nucleation is initiated, the surface density of carbon atoms increases as they are added through diffusion from the leading face of the catalyst nanoparticle. Over time, the diffusion potential decreases due to a reduction in the carbon atom concentration gradient. However, with the onset of nucleation and growth, diffusion is reinstated as the major driving potential for carbon atom transport through the nanoparticle. Steady carbon deposition and filament growth occurs once there is a stable carbon cluster size due to nucleation. The results support our hypothesis that flame synthesis can be a much faster and higher throughput process than CVD. The CNT/CNF growth rate decreases with increasing height above the burner. Decreasing temperature at higher locations leads to slower catalyst deactivation, but the CO concentration, which is the major contributor to carbon deposition, also decreases with increasing height above the burner. One of the major findings in this work is the contribution of CO to CNT formation by flame synthesis. The concentration of hydrocarbons in the vicinity of the toroidal zone near, which most of the CNT growth is observed, is negligible compared to CO concentration. Our results provide a basis to conduct future multiscale simulations of CNT/CNF growth.

Flame nanotube synthesis in moderate electric fields: From alignment and growth rate effects to structural variations and branching phenomena

The flame synthesis of carbon nanotubes (CNTs) coupled with application of moderate electric fields is studied experimentally as a means to control CNTs growth rates and morphology. The nanotubes are grown on a conductive metal-based catalytic probe positioned at the fuel side of the opposed flow oxy-flame. The probe was connected to an external voltage source to generate radial electric fields on its surface. At low applied voltages (from 0.3 to 2 V), the effect of the electric field on alignment and growth rate enhancement revealed the generation of vertically aligned carbon nanotube (VACNT) arrays with uniform distribution of CNT diameters. Further increases of the applied voltage resulted in structural modifications of the generated nanotubes. In particular, helically coiled CNTs were observed at applied voltages of ∼3 V. At higher voltages the arrays contained multi-walled CNTs with fascinating modified morphologies such as Y, T, and multi-junction patterns. Analysis of the samples generated at applied voltage of 5 V showed the presence of particle sprouting and early CNT junctions in the form of small bumps extruding from the outer surface of the CNTs. Analysis of material samples synthesized at 12 and 25 V showed the presence of fully branched CNT structures.

Flame synthesis of carbon nanotubes in a wall stagnation flow

We have investigated the flame synthesis of carbon nanotubes (CNTs) using a wall stagnation flow burner, in which a rich ethylene/air premixed gas diluted by nitrogen was used as a reactant gas. A trumpet-shaped flame was formed only on the boundary between the reactant flow and the atmospheric air, so that the wall surface was exposed to the unburned reactant gas. Multi-walled CNTs with tidily parallel and straight layers were synthesized on the stagnation wall, which was covered by Ni metal. This flame synthesis technique is very unique, and it may have potential for utilization in mass production.

The chemistry of premixed flame synthesis of carbon nanotubes using supported catalysts

A premixed flame is used to create the reactive environment for carbon nanotube (CNT) synthesis using stainless steel mesh supporting Co as catalyst. The CNT relative growth density, morphology, and internal structure are interpreted in terms of the chemical composition of the flame gases. Different flame gas compositions are produced by varying the fuel/air equivalence ratio, . For> 1.62, carbon deposition occurs too rapidly relative to reactive etching of surface carbon by species such as H2, CO2, and H2O. For