Electro-exchange in the system of the condensed dispersed phase and a heated titanium particle

Abstract

The results of studies of titanium particles with diameters from 10 to 100 microns heated above the melting point in air are presented. A diagram and photographs of an experimental facility are shown. It consists of a generator of heated titanium particles, a temperature measurement unit, which includes a photoelectric temperature sensor for moving particles, an electric charge measurement unit, consisting of vertical flat parallel charged metal plates, and a unit for measuring particle velocity. It has been experimentally established that around such particles when they move in air a condensed dispersed phase – c-phase – consisting of titanium oxides nanoparticles is formed. The results of electron microscopy studies of the condensed dispersed phase has shown that the particle size of the condensed dispersed phase lies in the range of 5 - 100 nm and depends on the initial conditions. Theoretical calculations that determine the electro-exchange in the system of a heated spherical particle and the condensed dispersed phase surrounding it has shown the agreement with the experimental data within the measurement error, and the particle charge was on the order of hundreds of thousands – a million of electron charges. A theoretical study of the kinetics of thermionic charging of titanium particles has shown that the accumulation time of 95% of the equilibrium particle charge at temperatures of 3000–2200 K was 14 ns – 33 μs, respectively. At the temperature of 2000 K, the accumulation time of 85% of the equilibrium charge was 240 μs. At the temperature of 1400 K, the accumulation time of 91% of the equilibrium charge of the same particle was 610 μs. Estimates have shown that during a charge relaxation time for a titanium particle at temperatures greater than 1400 K the time of charging practically does not change. This allows us to consider the process of thermionic charging of particles under these conditions as quasistationary. The results can be used in studies of the processes of electro-exchange in aerodispersive systems at high temperatures. The developed model of thermionic charging of particles allows its further use to simulate the behavior of the c-phase around heated particles, as well as for other purposes. The obtained results show a satisfactory agreement between the experimental and calculated values of the charge.