Characterization and control of selective corrosion of α,β′-brass by acoustic emission

Acoustic emission (AE) associated with electrochemical measurements (electrochemical impedance spectroscopy and polarization curves) are used to study the selective corrosion of alpha,beta'-brass in an ammonia buffer solution. AE reveals, in this work, three different populations of events during the corrosion of this alloy. The corrosion process was found to proceed via oxygen reduction following a diffusion-controlled mechanism and selective dissolution of alpha,beta'-brass was controlled by the zinc atoms diffusion through oxide film. The diffusion coefficient obtained for zinc in alpha,beta'-brass following Cottrell law is of the order of 9.28 x 10(-12) cm(2)/s. An equivalent circuit modelling the reactions taking place at the electrode/electrolyte interface was suggested. The analysis by X-ray diffraction of residual stresses, before and after corrosion, showed that the dezincification of metal produces two types of residual stresses: macro and microstresses. Their evolution correlates perfectly with the measured acoustic activity. These stresses are then the sources of AE. This shows the important potential of AE in the detection and the control of selective corrosion phenomena. (C) 2003 Elsevier Science Ltd. All rights reserved.