Acoustic Emission From Corroding Electrodes Available to Purchase

Acoustic emission measurements have been performed on unstressed Al alloys which were freely corroding or coupled to Cu, 4130 steel, Cd or Zn in 3.5% NaCl. The rate of acoustic emission is in qualitative agreement with the observed corrosion rates. The acoustic emission is probably a result of hydrogen bubble evolution in the acidified pits. The rate of acoustic emission of 4130 steel in HCl also follows the corrosion behavior, decreasing significantly with addition of organic corrosion inhibitor. Stainless steel Type 304 was studied freely corroding or at applied constant anodic or cathodic currents. The highest rates of acoustic emission were determined at cathodic currents; when an anodic current was applied, the acoustic emission rate was higher than for a freely corroding sample and showed wide fluctuations which continued for some time when anodic polarization was discontinued. For localized corrosion of Al alloys and stainless steel, the acoustic emission process seems to reflect the statistical nature of the pitting process.