In this article, we experimentally studied the effect of acetone impurities on the induction time and soot yield during the self-decomposition of acetylene behind shock waves. The results of the ...experiments showed that variation of the acetone impurity in the range 0.5–3.0%, characteristic of technical acetylene, does not have a significant effect on the pyrolysis kinetics and soot yield, while the addition of acetone to acetylene in a ratio 1 : 3 increases it only slightly. At the same time, the results of modeling using modern kinetic mechanisms predict in the presence of acetone additives a significant acceleration of pyrolysis and increase in the yield of polyaromatic compounds and soot particles in acetylene. This result indicates the need for further improvement of kinetic schemes for a successful description of the kinetics of self-decomposition of acetylene and soot formation. The results should be taken into account when developing promising energy cycles based on the energy of acetylene self-decomposition, as well as when analyzing the risks of spontaneous explosions in technological processes associated with its use.
This paper presents a concept of dispersion of liquid iron nanoparticles synthesized during the pyrolysis of iron pentacarbonyl behind incident shock waves, which makes it possible to explain the ...anomalous drop in the optical density of the condensed phase recorded by the laser-extinction method when passing through the front of the reflected shock wave.
In the present study the carbon-encapsulated iron nanoparticles were synthesized by shock waves pyrolysis of the Fe(CO)5 vapor in the mixture with C2H2 or C6H6 diluted by argon. The iron ...nanoparticles were formed behind incident shock waves at the temperatures of 600–1200 K. The pyrolysis of hydrocarbons behind the reflected shock waves at the temperatures of 1100–2500 K resulted in carbon shell formation over iron nanoparticles. The mean particle sizes measured by transmission electron microscopy were found to be 3.5–5 nm and 7–10 nm for the samples formed in the mixtures with presence of acetylene and benzene correspondingly. The extinction measurements of condensed phase growth and laser-induced incandescence measurements of particle sizes were used as in-situ diagnostics. The dependences of particle volume fraction and final particle size on temperature of pyrolysis and kind of hydrocarbon are presented and discussed.
•Carbon encapsulated iron nanoparticles were synthesized in wide temperature range.•The carbon cover formed at temperatures lower than that of soot formation.•The temperature influences particle structure and aggregation.•The type of hydrocarbons is a key parameter of particle formation.
In this paper, the dependence of the sublimation temperature of soot particles synthesized during the combustion of various hydrocarbons, depending on their size and structure, is obtained. The ...experimental approach is based on the analysis of the thermal radiation of particles heated to the sublimation temperature by a nanosecond laser pulse. The sublimation temperature of soot particles was measured using the two-color pyrometry method. In this paper, it is proposed to use the average size of primary particles to compare data in different flames. It is established, that the sublimation temperature of soot particles depends mainly on the stage of their formation, which is characterized by an increase in average size. It is shown, that with an increase in the average particle size from 12 to 23 nm, their sublimation temperature increases significantly from 2700 to 4500 K. This reflects a significant difference in the thermodynamic and optical properties of the so-called “young” and “mature” soot particles, which must be taken into account when developing methods of soot diagnostics and in the thermo-physical analysis of combustion and pyrolysis processes with the formation of soot.
The influence of small additions (0.3-2 ppm) of iron or carbon nanoparticles on ignition delay times in stoichiometric mixture of 20% (methane + oxygen) diluted in argon was investigated. The ...experiments were performed in 50 mm diameter shock tube behind reflected shock waves. The nanoparticles were synthesized in pyrolysis of 0.5-1% Fe(CO)5 and 1-2% of C6H6 diluted in argon in the experiment before the ignition test. The residual nanoparticles were pulled into the flow behind incident and reflected shock wave from the shock tube walls and their volume fraction was measured by laser light extinction at the wavelength 633 nm. Additions of 0.3-2 ppm of iron nanoparticles to stoichiometric methane-oxygen mixture resulted in twofold decrease of ignition delays at temperatures below 1400 K relatively to calculated and experimental data for the mixture without nanoparticle addition. At additions of 0.4-1 ppm of carbon nanoparticles to stoichiometric methane-oxygen mixture a weak decrease of ignition delay relatively to the calculated data for the mixture without additives of carbon nanoparticles was observed.
The data on the optical band gap and dispersion coefficient of soot particles as functions of their primary size are presented. Optical properties of particles are obtained by interpretating the data ...on the spectral absorbance measured by the laser extinction method at wavelengths of 405–850 nm. Premixed flame is used as a reactor for synthesizing soot particles. It is shown that as the soot primary particle size increases from 11 to 20 nm, the optical band gap decreases from 0.8 to 0.02–0.05 eV, and the dispersion coefficient decreases from 1.8 to 1. The cause of changes in optical properties is soot particle growth from the so-called “young” to “mature” ones accompanied by changes in their structure, i.e., an increase in their degree of graphitization. The internal structure of particles during their growth approaches to the graphite structure. It is found that an additional parameter affecting changes in optical properties is the type of fuel used in the synthesis of soot particles.
In this study the laser-induced incandescence (LII) diagnostics has been applied for sizing of carbon-encapsulated iron nanoparticles (CEINs). The carbon covered iron nanoparticles were synthesized ...by shock waves pyrolysis of the mixtures of Fe(CO)5 with C2H2 or C6H6 diluted with argon. Iron nanoparticles were formed in the shock tube behind incident shock waves at the temperatures of 700-1000 K. The pyrolysis of hydrocarbons behind reflected shock waves at the temperatures of 1400-2000 K resulted in formation of carbon shell over iron nanoparticles. At the end of the CEINs formation process, particles were heated by one pulse of Nd:YAG laser operated at wavelength 1064 nm with fluences varied in the range 70- 800 mJ/cm2 to collect LII signals. The LII model, which had been used previously for iron and carbon nanoparticles separately, was updated for carbon-encapsulated iron nanoparticles. Additionally, the nanoparticle samples were investigated by a transmission electron microscope (TEM). The iron core size and carbon shell thickness were measured by statistical treatment of microphotographs. The comparison of TEM and LII particle sizing results is discussed.
The effect of the size and structure of soot particles synthesized during combustion in a flat premixed flame of hydrocarbons and during pyrolysis behind shock waves on their optical properties is ...analyzed. Experiments are conducted to measure the optical properties and structure of soot particles in a propylene–air flame and during the pyrolysis of mixtures of 3% of acetylene, 5% of ethylene, and 2% of propylene in argon behind shock waves in an shock tube. The function of the refractive index of soot particles and its change in the visible and near-IR spectral ranges are obtained using the laser-induced incandescence method. The mean soot particle sizes and parameters of the internal structure of soot particles are measured using transmission electron microscopy. Based on the analysis of the results obtained in this study and those available in the literature, it is found that, as the size of soot particles increases, the refractive index function for them at a wavelength of 1064 nm increases by a factor of 2.5 (from 0.2 to 0.5) and depends on the synthesis conditions and type of hydrocarbon. The ratio of the refractive index at a wavelength of 1064 nm to its value at 532 nm with an increase in the average particle size increases slightly or remains approximately constant (in the range of 0.8 to 1.15) for most soot particles or increases more significantly (from 1.1 to 1.5) in the case of acetylene soot. The observed significant changes in the optical properties are correlated to a decrease in the average distance between parallel graphene planes in the structure of growing soot particles and an increase in the number of adjacent parallel planes. These structural changes characterize the graphitization process of soot particles as they grow.
A setup for measuring natural-radioactivity backgrounds and ultralow concentrations of the isotope
14
C in samples of a liquid organic scintillator was created at the low-background laboratory of the ...Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) at a depth of 4900 mwe. The concentration of the radiocarbon
14C
in a sample of a scintillator based on domestically produced linear alkylbenzene was measured, and it was found that
14
C/
12
C (3.3 ± 0.5) × 10
−17
.
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