Particle in flame

Yagi, S. Kunii, D. "Studies on Combuston of Carbon Particles in Flames and Fulidized Beds" 5th Symposium (Int l) on Combustion, 1955, 231-244. 

Chemiluminescent processes occur in most combustion reactions, giving flames many of their characteristic colors. However, hot solid carbon particles in flames emit (usually yellow) thermal radiation in an equilibrium radiative process which therefore is not chemiluminescence,... 

Ionization Associated with Solid Particles in Flames... 

Ionization associated with the presence of solid particles in flames is small and easily obscured by gaseous ionization of volatile impurities. It can be demonstrated experimentally in certain systems and can be shown to depend on the particle size, number density, and work function as predicted by the theory of Smith or Soo and Dimick. Salts such as the alkali halides volatilize slowly and mix by diffusion. Residual inhomogeneities in ion distribution give the appearance of particulate ionization. 

Experimental studies on the ionization associated with particles in flames show that while such ionization occmrs to a measurable extent, it is frequently associated with and even masked by ionization derived from gaseous material. The volatilization of such material can be a slow process and the dispersion of the vapor by diffusion even slower, so that each particle is marked by a meteor trail of ionized gas. Even when the particle has volatilized completely, such a trail may give the appearance of particulate matter. One result of this microscopic inhomogeneity is that estimates of the evaporation of droplets which assume a uniform distribution of vapor can be grossly in error. 

Product quality and application characteristics of nanoscaled solids depend strongly on size distribution and morphology, so that the degree of aggregation defined by the size and number of primary particles. In flame reactors, within a few milliseconds during the early stages of the synthesis process, chemical reaction of the precursor... 

Ulrich, G.D., Riehl, J.W., 1982. Aggregation and growth of submicron oxide particles in flames. J. CoUoid Interface Sci. 87 (1), 257-265. 

Miquel FP, Katz JFJF. Formation and characterization of nanostructured V-P-O particles in flames a new route for the formation of catalysts. J Mater Res 1994 9 746-... 

Yagi S, Kunii D. Studies on combustion of carbon particles in flames and fluidized beds. Proc. 5th Int. Symp., Combustion. Van Nostrand Reinhold, New York, 1955, pp 231-244. 

Whereas many of these technologies are not really new, they have never had the regulatory and economic justification for their use in metallizing. Each of these general methods has many variants. Some may be directed to waste treatment, some to recycle, and some to reclaim. An example is filtration, used to prevent release to air of zinc particles from flame spraying, microfiltration of cleaners to extend hfe, in combination with chemical precipitation to remove metal particles from wastewater, and many other uses. 

Any refractory material that does not decompose or vaporize can be used for melt spraying. Particles do not coalesce within the spray. The temperature of the particles and the extent to which they melt depend on the flame temperature, which can be controlled by the fueLoxidizer ratio or electrical input, gas flow rate, residence time of the particle in the heat zone, the particle-size distribution of the powders, and the melting point and thermal conductivity of the particle. Quenching rates are very high, and the time required for the molten particle to soHdify after impingement is typically to... 

Humphry Davy showed carbon particles are the source of luminosity in flames (lamp black). 

Vei y small solid fuel particles such as sawdust, agricultural grains, or coal dust can sustain flames when they are suspended in air. In fact, very serious fires have occurred in grain storage towers and coal mines because of the flammability of suspended dusts. The combustion of the individual particles follows the usual pattern of solid particle burning— devolatization and char burning. The combustion of the whole cloud of particles is similar to spray combustion and its characteristics depend on the nature of the fuel, size of the particles, and the number of particles in a given volume. 

Heat transfer in the furnace is mainly by radiation, from the incandescent particles in the flame and from hot radiating gases such as carbon dioxide and water vapor. The detailed theoretical prediction of overall radiation exchange is complicated by a number of factors such as carbon particle and dust distributions, and temperature variations in three-dimensional mixing. This is overcome by the use of simplified mathematical models or empirical relationships in various fields of application. 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

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