Particle thermionic emission charging

Millikan s experiment did not prove, of course, that (he charge on the cathode ray. beta ray, photoelectric, or Zeeman particle was e. But if we call all such particles electrons, and assume that they have e/m = 1.76 x Hi" coulombs/kg. and e = 1.60 x 10" coulomb (and hence m =9.1 x 10 " kg), we find that they fit very well into Bohr s theory of the hydrogen atom and successive, more comprehensive atomic theories, into Richardson s equations for thermionic emission, into Fermi s theory of beta decay, and so on. In other words, a whole web of modem theory and experiment defines the electron. The best current value of e = (1.60206 0.00003) x 10 g coulomb. 

One of the important characteristics of gas-solid multiphase flows is concerned with the electrostatic effect. Particles can be charged by surface contact in a collision, by corona charging and scattering in an ionized gas, by thermionic emission in a high-temperature environment, and by other charging mechanisms such as colloidal propulsion... 

The phenomena of the electrification of solids are complex. In gas-solid flows, surface contact by collisions, ion collection, and thermionic emission are known to be the major modes of particle electrification. Details of these three charging modes are introduced in the discussion that follows. 

When solid particles are exposed to a high-temperature environment, typically for T > 1,000 K, charging by thermal electrification becomes important. The electrons inside the solid can acquire the energy from the high-temperature field and be freed by overcoming the energy barrier or the work function. By losing electrons in such a thermionic emission process, the particles are thermally electrified. 

It is noted that the rate of electrification is not constant. Once the tendency is established for an electron to escape from the solid particle by thermionic emission, the charge buildup occurs on the particle, which then attempts to recapture the to-be-freed electron by the attracting Coulomb force. Therefore, the equilibrium of thermal electrification of solid particles in a finite space is possible. Details on the equilibrium and the rate of electrification concerning the thermionic emission are available in Soo (1990). 

As he continued to study filaments in vacuum and different gas environments, he began to study the emission of charged particles from hot filaments (thermionic emission). He was one of the first scientists to work with plasmas and was the first to call these ionized gases by that name, because they reminded him of blood plasma. Langmuir and Tonks discovered electron density waves in plasmas that are now known as Langmuir waves. 

Flame charging occurs when particles are formed in or pass through a flame. At the high temperature of the flame, direct ionization of gas molecules creates high concentrations of positive and negative ions and thermionic emissions of electrons... 

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