Influence of oxygen concentration, fuel composition, and strain rate on synthesis of carbon nanomaterials

Hou, Shuhn-Shyurng; Huang, Weicheng

doi:10.1007/s11051-015-2879-7

Cited by 8 publications

(3 citation statements)

References 40 publications

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“…One of the control parameters in diffusion flame synthesis is the inlet oxygen concentration. Previous flame synthesis experiments showed that an increase in inlet oxygen concentration improves CNT growth [15,16]. A previous study pointed out that an increase in oxygen concentration provides more combustion and thus larger high temperature region [11].…”

Section: Introductionmentioning

confidence: 97%

The Influences of Oxygen Concentration and External Heating on Carbon Nanotube Growth in Diffusion Flame

Zainal

Yasin

et al. 2021

CFDL

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Tight control of the carbon nanotube (CNT) synthesis process in flames remains a challenge due to the highly non-uniform gradient of flame thermochemical properties. The present study aims to establish a baseline model for flame-enhanced chemical vapor deposition (FECVD) synthesis of CNT and to analyze the CNT growth region at varying flame and furnace conditions. The numerical model comprises a computational fluid dynamics (CFD) simulation that is coupled with the CNT growth rate model to simulate the flow field within the furnace and the CNT growth respectively. Validation of the flame shape, flame length, and temperature profile are carried with a reasonable comparison to experimental measurements. A parametric study on the effects of furnace heating capacity and oxidizer concentration is conducted. The results of the CNT growth rate model reveal that there is a positive correlation between the heater power and CNT length. Supplying a higher concentration oxidizer at a fixed furnace power is predicted to result in further improvement in CNT length and high yield region. Flame structure analysis showed that with the heater turned on at 750 W (corresponding to heat flux of 21,713W/m2), the growth region expands twofold when oxygen concentration is increased from 19% to 24%. However, the growth region shrinks when the oxygen concentration is further increased to 27% which indicates depletion of carbon source for CNT growth due to excess oxygen. The finding of this research could guide and optimize the experiment of the flame-assisted CNT production in the future.

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Section: Introductionmentioning

confidence: 97%

The Influences of Oxygen Concentration and External Heating on Carbon Nanotube Growth in Diffusion Flame

Zainal

Yasin

et al. 2021

CFDL

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“…Therefore, flame synthesis shows a more promising potential for inexpensive, rapid, mass production of CNMs than other synthesis methods. In recent years, great effort has been devoted to studying the synthesis of CNMs in flames [ 10 , 11 , 12 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

Effects of Acoustic Modulation and Mixed Fuel on Flame Synthesis of Carbon Nanomaterials in an Atmospheric Environment

Sari

Hou

et al. 2016

Materials

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In this study, methane–ethylene jet diffusion flames modulated by acoustic excitation in an atmospheric environment were used to investigate the effects of acoustic excitation frequency and mixed fuel on nanomaterial formation. Acoustic output power was maintained at a constant value of 10 W, while the acoustic excitation frequency was varied (f = 0–90 Hz). The results show that the flame could not be stabilized on the port when the ethylene volume concentration (ΩE) was less than 40% at f = 10 Hz, or when ΩE = 0% (i.e., pure methane) at f = 90 Hz. The reason for this is that the flame had a low intensity and was extinguished by the entrained air due to acoustic modulation. Without acoustic excitation (f = 0 Hz), the flame was comprised of a single-layer structure for all values of ΩE, and almost no carbon nanomaterials were synthesized. However, with acoustic excitation, a double-layer flame structure was generated for frequencies close to both the natural flickering frequency and the acoustically resonant frequency. This double-layer flame structure provided a favorable flame environment for the fabrication of carbon nanomaterials. Consequently, the synthesis of carbon nano-onions was significantly enhanced by acoustic excitation near both the natural flickering frequency and the acoustically resonant frequency. At f = 20 Hz (near the natural flickering frequency) for 0% ≤ ΩE ≤ 100%, a quantity of carbon nano-onions (CNOs) piled like bunches of grapes was obtained as a result of improved mixing of the fuel with ambient air. High-density CNOs were also produced at f = 70 Hz (close to the acoustically resonant frequency) for 40% ≤ ΩE ≤ 100%. Furthermore, carbon nanotubes (CNTs) were synthesized only at 80 Hz for ΩE = 0%. The suitable temperature range for the synthesis of CNTs was slightly higher than that for the formation of CNOs (about 600 °C for CNTs; 510–600 °C for CNOs).

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“…Fuel type strongly influences the heat source (flame temperature) and carbon source (precursor), which are critical parameters for CNS growth. For the synthesis of CNSs, most studies have employed gaseous fuel, such as methane [15], propane [19], ethylene [20], and acetylene [16]. The effects of gaseous fuel type on the formation mechanism were studied by Camacho and Choudhuri [19].…”

Section: Introductionmentioning

confidence: 99%

Ethanol flame synthesis of carbon nanotubes in deficient oxygen environments

Lin

2016

Nanotechnology

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In this study, carbon nanotubes (CNTs) were synthesized using ethanol diffusion flames in a stagnation-flow system composed of an upper oxidizer duct and a lower liquid pool. In the experiments, a gaseous mixture of oxygen and nitrogen flowed from the upper oxidizer duct, and then impinged onto the vertically aligned ethanol pool to generate a planar and steady diffusion flame in a deficient oxygen environment. A nascent nickel mesh was used as the catalytic metal substrate to collect deposited materials. The effect of low oxygen concentration on the formation of CNTs was explored. The oxygen concentration significantly influenced the flame environment and thus the synthesized carbon products. Lowering the oxygen concentration increased the yield, diameter, and uniformity of CNTs. The optimal operating conditions for CNT synthesis were an oxygen concentration in the range of 15%-19%, a flame temperature in the range of 460 °C-870 °C, and a sampling position of 0.5-1 mm below the upper edge of the blue flame front. It is noteworthy that the concentration gradient of C2 species and CO governed the CNT growth directly. CNTs were successfully fabricated in regions with uniform C2 species and CO distributions.

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Influence of oxygen concentration, fuel composition, and strain rate on synthesis of carbon nanomaterials

Cited by 8 publications

References 40 publications

The Influences of Oxygen Concentration and External Heating on Carbon Nanotube Growth in Diffusion Flame

The Influences of Oxygen Concentration and External Heating on Carbon Nanotube Growth in Diffusion Flame

Effects of Acoustic Modulation and Mixed Fuel on Flame Synthesis of Carbon Nanomaterials in an Atmospheric Environment

Ethanol flame synthesis of carbon nanotubes in deficient oxygen environments

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