MEASUREMENT OF PASSIVE FILM EFFECTS ON SCRATCHED ELECTRODE BEHAVIOR

There has been controversy recently regarding the interpretation of measurements from scratched electrodes. In work, a discussion of the various effects of ohmic drop on bared surface measurements is presented. Experiments were conducted in which the interaction between the surrounding filmed surface and the bared surface was studied. The experimental variables investigated were the ratio of the filmed to bare areas (A(f)/A(b)) and the solution conductivity. The results indicate that a large ohmic drop in the solution can cause the surrounding filmed surface to affect the measurement. In all cases, the effect is a decrease in the peak current measured. In some cases, the ohmic drop can also cause a spreading of the current transient. These results show that the use of as small a bared area as possible is the most effective means to reduce the errors associated with ohmic drop. The implications of these effects on bared surface measurements are discussed, as are techniques to minimize them.