Coupled thermal analysis of carbon layers deposited on alumina nanofibres

Солодовниченко, В. С.; Симунин, М. М.; Лебедев, Д. В.; Voronin, A. I.; Emelianov, Aleksei V.; Mikhlin, Yu. L.; Парфенов, В. А.; Ryzhkov, Ilya I.

doi:10.1016/j.tca.2019.02.012

Cited by 17 publications

(7 citation statements)

References 45 publications

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“…In the stationary state, the production/consumption of species in chemical reactions is balanced by the transport of reactants and reaction products by convection and diffusion. The described system corresponds to the commercial CVD furnace OTF-1500X-UL-3 and vaporization system LVD-F1 (MTI Corp., USA), which were previously used by the authors for depositing carbon layers on nanoporous membranes [33][34][35][36]. However, the results obtained below could in principle be applied for any other tube furnace.…”

Section: The Cvd Reactormentioning

confidence: 99%

“…The heat transfer coefficient in the boundary condition of the tube wall is taken as 5 W/m 2 K [44], while its emissivity is set to 0.45 [46]. The substrate diameter is 40 mm and the thickness is 0.4 mm, see [33,34] for more details.…”

Section: Boundary Segment Momentum Transfer Equations Energy Transfer Equation Species Transfer Equationsmentioning

confidence: 99%

“…The latter represent an array of aligned cylindrical nanopores with controlled diameter [31], and can be employed for chemically selective molecular transport and separation of complex molecular mixtures [32]. The ethanol CVD is also a promising technique for growing carbon layers on alumina nanofiber membranes (previously obtained using propane in [33,34]). The conductive carbon layer introduces new mechanisms of ion transport through nanopores due to polarization effects [35].…”

Section: Introductionmentioning

confidence: 99%

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Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Минаков

Симунин

Ryzhkov

2019

International Journal of Heat and Mass Transfer

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Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900°C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates.

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Section: The Cvd Reactormentioning

confidence: 99%

Section: Boundary Segment Momentum Transfer Equations Energy Transfer Equation Species Transfer Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Минаков

Симунин

Ryzhkov

2019

International Journal of Heat and Mass Transfer

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“…Later, this company developed a similar technology for manufacturing aerogels based on aluminum silicate Al 2 O 3 •SiO 2 (so-called mullite). The recently developed CVD technology of carbon deposition on the surface of nafen/mullite nanofibers makes it possible to fabricate conducting aerogel samples [6][7][8]. As a result of such graphenization, a shell of several graphene layers with a large number of defects forms on the surface of aerogel nanofibers.…”

Section: Introductionmentioning

confidence: 99%

Activated hopping transport in nematic conducting aerogel at low temperatures

Tsebro,

Nikolaev,

Lugansky

et al. 2022

Preprint

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The transport properties of nematic aerogels, which consist of highly oriented Al2O3•SiO2 nanofibers coated with a graphene shell with a large number of defects, are studied. The temperature dependences of the electrical resistivity in the range of 9-40 K strictly follow the formula derived to describe the variable range hopping (VRH) conductivity, in which exponent α changes from 0.4 to 0.9 when the number of layers in the graphene shell decreases from 4-6 to 1-2. The dependence of α on the shell thickness can be explained by a simultaneous change in the dimensionality of hopping transport and the character of the energy dependence of the density of localized states near the Fermi level. The fact that α approaches unity at the minimum graphene shell thickness indicates a gradual transition from VRH transport to nearest neighbor hopping (NNH) transport. The magnetoresistance measured at T = 4.2 K is negative, increases significantly with decreasing graphene shell thickness, and is approximated by a formula for the case of weak localization with a good accuracy. The phase coherence lengths are in a reasonable relation with the graphene grain sizes. The conducting aerogels under study complement the well-known set of materials that exhibit hopping electron transport at low temperatures, which is characteristic of media with strong carrier localization, and also a negative magnetoresistance, which usually manifests itself under weak localization conditions.

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“…), которые более удобны для тестирования образцов и упрощают процедуры отмывок системы при её многократном применении. В качестве матрицы для фиксации МНА интерес могут представлять нановолокна оксида алюминия (НВОА), позволяющие получать сетчатые конструкции, которые обладают структурной стабильностью в водных средах [11,12].…”

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Fabrication of a composite based on aluminum oxide nanofibers and nanodiamonds to construct phenol detection systems

Ронжин

Posokhina

Mikhlina

et al. 2019

Доклады Академии наук

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A composite based on aluminum oxide nanofibers (AONF) and modified nanodiamonds (MND) synthesized by explosion technique was made by mixing aqueous suspensions of components at a 5:1 weight ratio and incubating the mixture for 15 minutes at 32 C. It is assumed that the formation of a composite is provided by the difference in the zeta-potentials of the components - negative for MND and positive for AONF. Vacuum filtration of the mixture through a fluoroplastic filter (pore diameter of 0.6 m) formed discs with a diameter of 40 mm with subsequent heat treatment at 300 C to impart structural stability to the composite. Using scanning electron microscopy (SEM), it was revealed that the resulting composite has a network structure in which the MND particles are distributed over the AONF surface. It was established that MND incorporated into the composite catalyze the azo coupling reaction (phenol - 4-aminoantipyrine - H2O2) with the formation of a colored product (quinoneimine). The applicability of the composite for the multiple detection of phenol in aqueous samples is demonstrated.

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Coupled thermal analysis of carbon layers deposited on alumina nanofibres

Cited by 17 publications

References 45 publications

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Activated hopping transport in nematic conducting aerogel at low temperatures

Fabrication of a composite based on aluminum oxide nanofibers and nanodiamonds to construct phenol detection systems

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