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It is crucial to understand the behavior of the optical properties of soot in the visible and near-IR spectral range to calculate the magnitude of their emission and absorption. Such information also helps in the development of diagnostic methods for soot. We measured the absolute value of the refractive index functions of soot nanoparticles E ( m , 1064 ) at a wavelength of 1064 nm, as well as the ratio of the refractive index functions at laser wavelengths of 532 nm and 1064 nm in a premixed ethylene/air flame using laser-induced incandescence. E ( m , 1064 ) increased with the flame height from 0.29 to 0.43. Depending on the height above the burner, the ratio of E ( m , 1064 )/ E ( m , 532 ) increased from 0.88 to 1. These changes in the optical properties are attributed to differences in the soot structure, such as the different sizes of graphene planes, which increased from 0.96 to 1.24 nm as the height above the burner increased from 10 to 20 mm. The presented data provide comprehensive information about the optical properties of soot in a premixed ethylene/air flame according to the height above a burner and make it possible to compare measurements of the soot optical properties in various target flames.

Acetylene black is a special type of carbon black, obtained from the thermal decomposition of acetylene. Acetylene flames enable the investigation of the soot optical properties. A reliable knowledge of the optical properties of acetylene soot is necessary for interpreting the optical measurements in flames and the development of acetylene black applications in industry. However, a wide variation in the optical properties of soot is observed in different formation conditions. The main factors affecting soot formation in flames are fuel composition, equivalence ratio, and reaction time connected with the height above a burner. In this study, we measured the absolute value of the refractive index function of acetylene soot E(m,1064) at a wavelength of 1064 nm, as well as the ratio of the refractive index functions E(m,1064) / E(m,532) at laser wavelengths of 532 nm and 1064 nm in a premixed acetylene/air flame using laser-induced incandescence. The soot structure was studied using high-resolution electron microscopy. The obtained results showed that E(m,1064) increased from 0.19 to 0.53 and that the ratio of E(m,1064) / E(m,532) increased from 1.12 to 1.55 according to the height above a burner. These changes in the optical properties are attributed to differences in soot structure, such as different distances between graphene planes inside soot crystallites, which decreased from 0.43 to 0.36 nm as the height above the burner increased from 5 to 20 mm. It was concluded that the optical properties and structure of acetylene soot differ from those formed in other hydrocarbon flames.

AbstractThis 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 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.

Low background segmented liquid scintillator detector, doped with an indium as a target for solar neutrino registration, can be used for measuring total solar neutrino spectrum including neutrinos. A detector consisting of small modules filled with liquid scintillator in the volume of 1–2 L is considered. Silicon matrices are used for light collection. The background of indium beta-activity is suppressed by triple coincidences. The detector of such a type can measure Be neutrino flux with high accuracy and independently check the measurement performed by the Borexino Collaboration.

AbstractThe 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.

AbstractThe 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.

AbstractEvaporation of iron nanoparticles in carbon shells under pulsed laser irradiation is analyzed. Iron–carbon nanoparticles are synthesized in a shock tube reactor with the aid of pyrolysis of the 0.25% Fe(CO)5 + 0.25% C6H6 mixture in argon. Laser radiation is used for additional heating to temperatures that exceed the evaporation threshold of the iron core of nanoparticles. Time profiles of the thermal radiation of laser-heated nanoparticles are measured. The two-color pyrometry is used to determine the evaporation temperature of nanoparticles, and the laser extinction makes it possible to monitor the loss of volume fraction of the condensed phase upon evaporation. Approximation of experimental signals of laser-heated nanoparticles using model curves is employed to determine effective enthalpy of evaporation of iron–carbon nanoparticles. It is shown that the iron core of nanoparticles is evaporated through the carbon shell and the energy spent by such a process is approximately twice greater than the evaporation enthalpy of bulk iron with free surface.

The energy resolution is calculated for a neodymium-containing liquid organic scintillation detector (Nd-OS) with a volume of several liters to search for neutrinoless double beta decay of 150 Nd as a function of the neodymium concentration up to 5 g/L. The results are presented in detailed tables and graphs.

A new experimental approach to the analysis of thermodynamic properties of amorphous carbon nanoparticles synthesized via hydrocarbon pyrolysis behind shock waves is discussed. The proposed approach is based on the analysis of thermal radiation of nanoparticles heated by a laser pulse. The sublimation temperature of the carbon nanoparticles might be determined by the two-colour pyrometry; their sizes, by laserinduced incandescence; and the volume fraction of the sublimated substance, by the laser extinction method. The sublimation temperature depends on both the particle size and the temperature conditions of their formation. The value of surface energy for amorphous carbon nanoparticles was estimated.