A. V. Eremin

Size measurement of carbon and iron nanoparticles by laser induced incadescence

Application of the laser-induced incandescence method for instant size measurements of nanoparticles is considered. Laser heating and subsequent cooling processes of carbon and iron nanoparticles suspended in a gas medium are simulated. The process of laser energy absorption by nanoparticles in Releigh limit is thoroughly analyzed, taking into account time and spatial energy distribution in the laser beam, as well as the cooling of nanoparticles, by collisions with ambient gas molecules of in the free-molecular regime and in the course of evaporation. On the basis of this model, software has been created for analyzing and interpreting the heat radiation signals of laser-heated nanoparticles (laser-induced incandescence) obtained in experiments, as well as for determining their sizes. Using the developed approach, data on the sizes of carbon nanoparticles formed in the course of C2H2 pyrolysis, as well as the time profiles of iron nanoparticles produced in the course of laser photolysis of Fe(CO)5, are obtained and are in good agreement with transmission electron microscopy data.

Ignition of multicomponent hydrocarbon/air mixtures behind shock waves

Experimental and numerical investigations are performed of the temperature dependences of delays in the ignition, behind shock waves, of multicomponent mixtures simulating the products of steam conversion of methane. Experimental investigations are performed in the temperature range from 930 to 1880 K at pressures from 2.5 to 9 atm. It is demonstrated that ignition delays in mixtures of air with products of 50 and 100% steam conversion of methane may be described using the results of numerical calculations based on the known kinetic schemes of methane combustion. At the same time, a considerable (by a factor of two–three) reduction of delays in the ignition of methane/air mixtures during addition of steam is observed and discussed, which is not described by the known kinetic schemes. The obtained results may be used in developing hypersonic scramjet engines.

A new model for carbon nanoparticle formation in the pyrolysis process behind shock waves

A new conceptual model for carbon nanoparticle formation in shock waves that is based on recent data of the temperature dependence for finite sizes of resulting particles and an abrupt increase in their refractive index during the change in particle sizes from 5 to 15 nm. The model is based on the two following physically distinct assumptions. First, the volumetric fraction of condensed carbon remains constant from complete decomposition temperatures for the initial carbon-containing molecules (1600–2000 K) up to evaporation temperature for carbon nanoparticles (3000–3500 K). Second, the surface growth rate for particles is determined by the rate of collisions between vapor molecules and particles. The proposed model allows an explanation of all observed regularities of the carbon nanoparticle growth, including a decrease in finite sizes of particles at a rise in temperature and a corresponding decrease in the time of particle formation.

Investigation of the kinetics of carbon nanoparticle charging in shock-heated plasma

The experimental results and a computer simulation of charging of carbon nanoparticles formed in the process of pyrolysis of the carbon suboxide C3O2 behind shock waves are presented. It is shown that the time necessary for the onset of an equilibrium distribution of charges in the gas-nanoparticle system at pressures of 15–30 bar decreases from 400 to 40 μs with a temperature rise from 2000 to 3600 K. The equilibrium concentration of free electrons in the presence of nanoparticles in the mixture is much lower than that in the same gas without particles. Step ionization of sodium and a subsequent recombination of free electrons and sodium ions on the nanoparticle surface are considered in order to analyze the kinetics of nanoparticle charging.

Dissociation of CO2 molecules in a wide temperature range

Expressions are derived for the dissociation rate constants of molecules of carbon dioxide in the temperature range from 300 to 40000 K under both thermally equilibrium and nonequilibrium conditions. Under nonequilibrium conditions, the rate constants are represented as a two-temperature dependence (on the gas temperatureT and on the unified temperature Tvof all vibrational modes of CO2) and as a one-temperature dependence in which averaged vibrational nonequilibrium is included

The effect of chlorine atoms on the charging kinetics of carbon nanoparticles forming in shock-heated plasma

This work continues the study on the charging kinetics of soot during the formation of carbon nanoparticles in hydrogen-free systems upon the pyrolysis of carbon-containing materials behind shock waves. The experimental results and results of computer simulation of electrical charging of the carbon nanoparticles formed during the pyrolysis of CCl4 behind the shock waves are given. It is shown that the natural impurity of sodium atoms amounting to 1012–1013 cm−3 are the main source of free electrons. It is established that the time required for relaxation of the charge distribution in the gas-nanoparticle system at 15–30 bar decreases from 400 to 100 μs in a 0.5% CCl4 + Ar mixture with increasing the equilibrium temperature from 2000 to 3600 K and from 350 to 50 μs in a 5% CCl4 + Ar mixture with increasing the equilibrium temperature from 1500 to 2500 K. The equilibrium concentration of free electrons in the presence of the nanoparticles in the system decreases by one to two orders of magnitude compared to that in the system without nanoparticles. The presence of chlorine atoms in the mixture leads to a considerable decrease in the concentration of electrons in the gas-nanoparticle system and to a decrease in the concentration of charged nanoparticles. The electron kinetics in the mixtures under consideration is characterized by a high (as compared with sodium) concentration of chlorine atoms having a larger electron affinity.

Formation of detonation wave upon condensation of supersaturated carbon vapor

The results are given of observation of a fundamentally novel phenomenon, namely, the formation of detonation wave of condensation. Experiments are performed behind shock waves in mixture containing 10–30% carbon suboxide C3O2 in argon. The release of the energy of condensation of highly supersaturated carbon vapor formed upon instantaneous thermal decomposition of carbon suboxide C3O2 → C + 2CO behind the wave front leads to the amplification of shock wave and its transition to the detonation mode.

Energy gain of the detonation pyrolysis of acetylene

In this paper we investigated experimentally the formation of a detonation wave as a result of energy release during pyrolysis of acetylene behind the shock wave. The kinetics and thermodynamics of the physical and chemical processes are analyzed; it is shown that the main heat release, which determines a positive integral energy balance of the detonation pyrolysis of acetylene, occurs at the stage of formation and growth of condensed carbon nanoparticles. Based on these results, the principles of a new clean energy cycle are stated, enabling the obtaining of thermal and kinetic energy without use of oxygen or formation of carbon dioxide. We propose construction of a power plant based on the detonation pyrolysis of acetylene.

Anomalous behavior of optical density of iron nanoparticles heated behind shock waves

Nonmonotonous variation of the optical properties of iron nanoparticles with a temperature increase during heating behind reflected shock waves is discovered. Iron nanoparticles, within 12 nm in size, were formed at 0.5–1% Fe(CO)5 pyrolysis in argon behind the incident shock waves. Using a laser extinction method, a variation of the volume fraction of the condensed phase was registered at the main wavelength of 633 nm and, in several experiments, at the additional wavelengths of 405, 520, and 850 nm. At the second heating of the produced nanoparticles behind the reflected shock waves within the temperature range 800–1500 K, the function of the complex refractive index, E(m), decreased at all the wavelengths. Within the temperature range of 1500–2250 K, it increased with the temperature increase behind the reflected shock wave almost up to the values that we observed behind the incident shock wave. At the temperatures above 2250 K, due to the essential evaporation of the iron nanoparticle material, the optical properties were not measured. The iron nanoparticle E(m) variations within the temperature range 800–2250 K are possibly related to their structure variations.