Acoustic Emission During Corrosion

The corrosion of commercially pure copper, commercially pure aluminum and mild steel in 10% FeCl3 solution was studied with respect to corrosion rate and rate of acoustic emission. Corrosion rates were established by weight loss measurements and acoustic emission was monitored using a transducer with a resonant frequency of 175 kHz and amplifications of 90 dB. The parameters recorded were the root mean square of the ampliture (RMS) and total counts. Corrosion rates for all three metals were very similar, in the range 0.01–0.02 g cm−2 h−1, but acoustic emission behavior was quite different. Corrosion of aluminum resulted in a very high rate of acoustic emission starting immediately upon immersion of the specimen in the FeCl3 solution whereas corrosion of copper resulted in no acoustic emission. Steel emitted no acoustic signals upon immersion but began to emit about 3h after immersion. The acoustic emission during corrosion is attributed to the evolution of hydrogen and the different emission behavior of the three metals is explained using Pourbaix diagrams.