Near-electrode layers at “Hot” electrodes

Abstract

References [1, 2] present a definite approach to the problem of theoretically describing the near-electrode layers for a change of potential at “hot” electrodes located in a weakly-ionized gas stream. There it was assumed that the degree of gas ionization near the electrode and its temperature are such that the Debye length computed from parameter values near the surface of the electrode is smaller than the mean free path of the charged particles (d ≲ ℓ). In this case, the problem of the near-electrode layer is separate from the problem of the distribution of quantities in the gas stream and its solution is used to formulate the boundary condition. Moreover, in solving the problem of the near-electrode layer, we can assume collision-free motion of the charged particles throughout this layer.

In the indicated references the near-electrode layer problem was not solved. The quantities necessary for formulating the corresponding boundary conditions were assigned on the basis of physical considerations.

In this article, some of the assumptions of [1, 2] are refined on the basis of the solution of model problems and a more detailed analysis of the effects in question. It is shown, in particular, that the theory is inadequate for describing near-electrode layers at electrodes made from a material that is a poor neutralizer for ions.

On the basis of an analysis of solutions of model problems of the near-electrode layer for both “ion-absorbing” and “ion-reflecting” surfaces, an attempt is made to construct a semi-empirical theory of the near-electrode layer. For certain cases, experimental data are compared with calculated data and, in particular, the experimental constants needed to construct the theory are determined.

Although the experimental and calculated data seem to agree, one should remember that the amount of data is still insufficient to make a final decision on the quality of the proposed theory. It is necessary to perform special carefully organized experiments to study near-electrode layers under different conditions. On the basis of an analysis of such experiments the experimental constants of the theory must be determined and then substituted in the calculation formulas. The results of such experiments may considerably modify our ideas about the phenomena taking place in near-electrode layers and may possibly require improvements in the theory.