Reactor flush time correction in relaxation experiments

The present paper deals with the analysis of experimental data from conductivity relaxation experiments. It is shown that evaluation of the chemical diffusion and surface transfer coefficients for oxygen by use of this technique is possible only if accurate data for the conductivity transient can be measured at short times, i.e., immediately after the step change in the surrounding oxygen partial pressure. The flushing behavior of the reactor volume may, however, significantly influence the early stage of the relaxation process. Large errors in the transport parameters are obtained from fitting the relaxation data to the theoretical equations if this phenomenon is not properly recognized. Equations are presented which describe, the transient conductivity taking into account the finite flush time of the reactor. The regimes of surface- and diffusion-controlled kinetics are discussed quantitatively. (C) 2001 The Electrochemical Society. All rights reserved.