Formation of metal oxide nanoparticles in combustion of titanium and aluminum droplets

Карасев, В. Е.; Onishchuk, A. A.; Khromova, S. A.; Глотов, О. Г.; Зарко, В. Е.; Pilyugina, E. A.; Tsai, Chuen-Tinn

doi:10.1007/s10573-006-0098-3

Cited by 18 publications

(13 citation statements)

References 12 publications

(29 reference statements)

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“…The results for single magnesium particles [47] predict that the dependence of the average size of the MgO particles is the same as the experimental dependence for the gas suspensions of particles: d ox ∼ d 1/3 10 p 1/3 [8,10]. For the aluminum combustion products, the calculated estimates and experimental dependence of the size of initial globules of Al 2 O 3 on the aluminum particle radius d ox ∼ log d 10 are in good agreement between each other [7]. In aluminum combustion models, in a steady formulation for single particles [46] and in an unsteady formulation for a monodispersed gas suspension [9], it was assumed that the combustion is controlled by the kinetics of surface reactions of aluminum with oxygen with the formation of intermediate suboxide Al 2 O and that the product of such gas-phase combustion is formed as a result of chemical condensation.…”

Section: Formation Of a Condensed Phase During The Combustion Of Metasupporting

confidence: 57%

“…In experiments with single particles [6,7], where the initial particle size could be varied in a much wider range, such a dependence in aluminum combustion was found (though it was poorly manifested): as the aluminum particle diameter increased in the range d 10 = 4-40 μm, the average diameter of the Al 2 O 3 particles changed from d ox = 17 nm to 68 nm. The diameter of titanium oxide particle does not depend on the initial size of the titanium particle [7]. A weak dependence d ox ∼ (d 10 ) 1/3 is also observed during combustion of magnesium particles (d 10 = 2.0-80.0 μm) [8].…”

Section: Formation Of a Condensed Phase During The Combustion Of Metamentioning

confidence: 98%

“…These models, both older [46,47] and newer [6,7] ones, are based on the assumption of homogeneous nucleation of combustion products (MgO and Al 2 O 3 ) when the rate of nucleation is much higher than the rate of diffusion combustion of metal particles. The results for single magnesium particles [47] predict that the dependence of the average size of the MgO particles is the same as the experimental dependence for the gas suspensions of particles: d ox ∼ d 1/3 10 p 1/3 [8,10].…”

Section: Formation Of a Condensed Phase During The Combustion Of Metamentioning

confidence: 99%

“…Obviously, such methods may include varying the particle size of fuel [6][7][8], the concentration of fuel and oxidizer [2,9], the total pressure [10,11], and the electric influence on combustion and phase formation in a dispersed system [2]. This paper is devoted to generalization of the main results of the experimental and theoretical studies conducted at the ICUT OMNU to solve the problems described above.…”

Section: Introductionmentioning

confidence: 99%

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Gas-disperse synthesis of metal oxide particles

Zolotko

Poletaev

Vovchuk

2015

Combust Explos Shock Waves

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The main results of years of research of metal dust flames aimed at the development of the scientific basis for the method of gas-disperse synthesis of metal oxide nanopowders are discussed. Methods of burning metal dust in oxide-containing media, the key problems of gas-disperse synthesis, and possible ways to solve these problems are considered. The ways of controlling the disperse composition of vapor-phase and gas-phase combustion products of metal particles by variation of the macroparameters of the dust flame and ionization of condensed and gaseous phases in the combustion zone with the help of adding easily ionized atoms to the fuel are analyzed. It is shown that an adequate description of condensation in a flame is impossible without consideration for the influence of electrophysical processes on nucleation and coagulation in the flame. It is established that ionization of the condensed phase is the most significant factor during coagulation of nano-oxide particles in a dust flame. This allows expecting that the influence on particle ionization may turn out to be an effective method of controlling the dispersion of the target products of gas-disperse synthesis.

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Section: Formation Of a Condensed Phase During The Combustion Of Metasupporting

confidence: 57%

Section: Formation Of a Condensed Phase During The Combustion Of Metamentioning

confidence: 98%

Section: Formation Of a Condensed Phase During The Combustion Of Metamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Gas-disperse synthesis of metal oxide particles

Zolotko

Poletaev

Vovchuk

2015

Combust Explos Shock Waves

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“…In the first stage (nucleation) nuclei of a new phase are formed. This occurs by homogeneous [4][5][6], heterogeneous [7,8] or chemical [9] nucleation of gas-phase or vapor-phase combustion products of the metal particles. The second stage (coagulation) involves the rapid growth of the particles due to a sharp increase in the probability of particle collisions.…”

Section: Introductionmentioning

confidence: 99%

Formation of condensed combustion products in metal dust flames: Nucleation stage

Poletaev

2015

Combust Explos Shock Waves

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The nucleation of the ionized combustion products of small (d 10 ≈ 5 μm) particles of Al, Mg, Zr, Fe, and Ti under laminar dust flame conditions at atmospheric pressure is considered in an isothermal approximation. It is shown that under conditions close to the experimental ones, the condensation of the products of gas-phase combustion of these metals is "rapid." Description of the "rapid" nucleation regime requires a nonstationary approach and knowledge of the kinetics of nucleation of the condensed phase and does not need a detailed analysis of the influence of environmental parameters on the free energy of formation of small nuclei. It is shown that the characteristic nucleation time of the gas-phase combustion products of metal particles is several orders of magnitude smaller than the residence time of the products in the combustion zone of the flame dust. This allows coagulation to be considered as the basic process which determines the degree of dispersion of primary particles of the metal combustion products.

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Minimum explosible concentrations of mist and dust clouds

Britton¹,

Harrison

2018

Process Safety Progress

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When hot vapor condenses the nucleation particles initially formed coalesce rapidly and exothermically. Most of the heat of coalescence is released in less than a millisecond while droplets are less than 100 nm diameter. Consequently, the heat is released close to the source of the vapor and has no effect on dispersion. Coagulation rate is governed by an inverse square law with respect to number density; calculations showed that a vapor cloud initially within its flammable range should produce droplets smaller than 10 µm after a minute of coalescence. Such micronized droplets completely vaporize in flame preheat zones and behave as premixed vapors rather than as individual droplets; this characteristic is not due to the increased surface energy accompanying subdivision into micronized droplets but to short evaporation times in the thick preheat zones of limit flames. Droplet growth time is a nonlinear function of cloud mass concentration and if the latter exceeds about 10 times the minimum explosible concentration (MEC), droplets quickly grow to above 20–40 µm. These larger droplets tend to burn individually and the estimation of MEC becomes complicated, although rain‐out of large droplets might hasten dispersal to below the MEC. With the assumption that micronized crystalline organic materials behave similarly to liquid droplets, we derive “intrinsic” MEC values for both hydrocarbons and a series of CHOx fuels having increasing O:C ratios. In each case, the MEC attains a constant “terminal value” as carbon number is increased. Terminal MEC values are 40 g m−3 for CH (hydrocarbons), 50 g m−3 for CHO (aldehydes, ethers, etc.), 60 g m−3 for CHOO (esters), 67 g m−3 (polyethylene glycols), and 103 g m−3 (carbohydrates). MEC values for CHO and CHOO decrease rapidly with increased carbon number since additional hydrocarbon units dilute the functional oxygen group. For polyethylene glycols and carbohydrates, the MEC is less dependent on carbon number since oxygen is contained in a repeating group. Although scission and/or decomposition replace simple evaporation as carbon number increases, flash pyrolysis data for polyethylene in air show that the products of decomposition can have little effect on MEC. Nevertheless, owing to experimental deficiencies published MEC values for polyethylene are as low as 10–30 g m−3. Of the many factors affecting MEC tests, we focus on the effects of gravity and flame radiation. Radiation not only affects MEC but also the burning rates of metal dusts such as titanium; such tests should be carried out on an adequately large scale. © 2017 American Institute of Chemical Engineers Process Process Saf Prog 37:4–17, 2018

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Formation of metal oxide nanoparticles in combustion of titanium and aluminum droplets

Cited by 18 publications

References 12 publications

Gas-disperse synthesis of metal oxide particles

Gas-disperse synthesis of metal oxide particles

Formation of condensed combustion products in metal dust flames: Nucleation stage

Minimum explosible concentrations of mist and dust clouds

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