A Comparison of the Mass and Resistance Change Techniques for Investigating Thin Film Corrosion Kinetics

Abstract

In situ quartz crystal oscillator microbalance (QCM) and electrical resistance change (RC) measurements were carried out simultaneously on identically prepared Permalloy films in order to establish the sensitivity and reproducibility of each technique for investigating atmospheric corrosion. Both techniques were found to be highly sensitive to thickness changes (better than 1A) resulting from corrosion in a high humidity atmosphere containing trace quantities of acid-forming, gaseous pollutants. However, the QCM results were found to be an order of magnitude more reproducible than the RC data. Moreover, it was established from the QCM findings that the average mass increase due to corrosion was quite closely proportional to the square root of exposure time in the test chamber. Thus complex thin film corrosion kinetics can be determined with considerable accuracy provided reasonable experimental procedures are employed. The results of both measurements were compared also in an isochronal plot where it was found that the resistance change was proportional to the square of the mass increase arising from the formation of corrosion-products. The origin of this relationship was investigated by carrying out simulated corrosion studies involving punching out holes in an aluminized Mylar structure while determining the effects of material loss on electrical resistance. © 1977, The Electrochemical Society, Inc. All rights reserved.