Synthesis of Pyrolytic Carbon Composites Using Ethanol As Precursor

Abstract

Chemical vapor infiltration and deposition of carbon fiber bundles are applied to synthesize pyrolytic carbon composites using the oxygen-containing precursor ethanol. The influence of the temperature (1373 and 1423 K) and pressure (1−7 Pa) on the microstructure and the deposition rate of pyrolytic carbon are experimentally studied. Higher partial pressures of ethanol are demonstrated to favor the growth of highly ordered graphene-like pyrocarbon, whereas lower partial pressures help to suppress the carbon texture transition. The gas-phase composition and reaction kinetics are numerically analyzed on the basis of a reacting flow model with a detailed reaction mechanism. Methane and C2 species are shown to be the dominant intermediate species of ethanol pyrolysis. According to the simulation, a large amount of CH3 radicals is produced, which explains the fact that the pyrolytic carbon from ethanol exhibits a texture similar to the one produced with CH4 as precursor.

Mesoporous alumina infiltrated with a very thin and complete carbon layer

“…Models of CVI in porous carbons via multi-step CVI/CVD are based on the idea that complicated radical reactions in gas phase lead to the formation of small linear molecules C 2 eC 4 , aromatic benzene-like C 6 species and polycyclic aromatic (С 6 ) n hydrocarbons [21e23, 36,37] as well as to chemisorption of molecules/particles from gas phase onto the active sites of the matrix surface. During the synthesis of CCA750-41*, gas phase could exhibit an optimum ratio of aromatic to small linear hydrocarbons, which was necessary for the deposition of a high textured carbon layer according to Dong et al [36].…”

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

“…Apart from hydrocarbons, ethanol can be considered as an attractive alternative precursor for pyrolytic carbon formation. The presence of hydroxyl group in ethanol weakens the C-H bond, which may result in an increased reactivity in comparison with C 2 hydrocarbons [15]. The experimental studies of ethanol pyrolysis were reported in [16][17][18], and the major observed products were hydrogen, water, carbon monoxide, ethylene, methane, acetaldehyde, and formaldehyde.…”

“…The pyrolysis experiments in the presence of radical trappers (toluene) were performed in [18] in order to determine the rate constant of ethanol decomposition reaction into ethylene and water. The synthesis of pyrolytic carbon composites using ethanol as a precursor was reported in [15,21]. It was found that ethanol exhibits much higher deposition rate in comparison with methane.…”

An interpretation of the hydrogen inhibiting effect on chemical vapor deposition of pyrocarbon

“…Such products are often prepared by densification of a fibrous preform with a pyrolytic matrix of carbon through a chemical vapor infiltration or deposition process (CVI/CVD). This process consists in the deposition of a matrix of pyrocarbon on a substrate surface by thermal decomposition of gaseous hydrocarbons such as methane or propane [1][2][3][4][5], unsaturated species (ethylene, acetylene…) [6][7] or organic species [8] at high temperature and low pressure. The CVD/CVI of pyrocarbon from pyrolysis of a hydrocarbon precursor is a complex phenomenon which is still an object of scientific research despite it has been widely studied for several decades.…”

“…Indeed, during the last few years, a significant number of experimental and modeling studies has been carried out in order to elucidate the chemistry of pyrocarbon deposition and to establish the most important parameters involved in the formation of pyrocarbon, as temperature, pressure, residence time or the ratio of the carbon fibers area and the volume of the gas phase (A/V) [1][2][3][4][5][6][7][8][9][10].…”