ABSTRACT

In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the number of the fiinge evolutions durhlg the corrosion test of a pure copper, 99% Cu, and an aluminium brass, 76% Cu+22% Ni+2%A1, in natural seawater. In other words, the anodic dissolution behaviors (corrosion) of the pure copper and the aluminium brass were determined by holographic interferometry, an electromagnetic method. So, the abrupt rate change of the number of the fi~ge evolutions during corrosion tests of the both copper alloys is called electrochemical emission spectroscopy. The corrosion process of both copper alloys was carried out in the seawater at room temperature. The electrochemical-emission spectra of both copper alloys in seawater represent a detailed picture of the rate change of the anodic dissolution of both copper alloys throughout the corrosion processes. Furthermore, the optical interferometry data of the both copper alloys were compared to data obtained from the common methods of electrochemical techniques of corrosion measurements, namely, the linear polarization method, and the Electrochemical Impedance (El) spectroscopy. The comparison indicates that there is a good agreement between the data of the electrochemical-emission spectra of both copper alloys with data of the electrochemical techniques in seawater. In both techniques of the electrochemical-emission spectroscopy and the electrochemical techniques, the corrosion behavior of the pure copper was observed higher than that of the aluminium brass. Consequently, holographic interferometric is found very useful for monitoring the anodic dissolution behaviors of metals, in which the number of the fringe evolutions of both copper alloys can be determined in situ.

INTRODUCTION

In recent works conducted by the author [1-16] an optical transducer was developed for materials testing and evaluation of different electrochemical phenomena. The optical transducer was developed based on incorporating methods of holographic interferometry for measuring microscopic deformations and electrochemical techniques for determining electrochemical parameters of samples in aqueous solutions. In addition, the optical transducer was applied not only as an electrometer for measuring different electrochemical parameters but also, the optical transducer was applied as a 3D- interferometric microscope for detecting different micro-alterations at a metal surface in aqueous solution, at a microscopic scale. Initially, the optical transducer was used to determine the mechanochemical behaviors of metals in aqueous solution, i.e., stress corrosion cracking, corrosion fatigue, and hydrogen embrittlement ~vs~. Determinations of the mechanochemical behaviors of metals in aqueous solutions, was based on detecting micro-deformations and measuring the corresponding current density by the optical transducer. Further more, the optical transducer was applied as an optical corrosion-meter t6-8~ for measuring cathodic deposit and anodic dissolution layers of metals in aqueous solutions. Also, the optical corrosion-meter was utilized to determine the cathodic and anodic current densities which correspond to the cathodic deposit and anodic dissolution layers, respectively. The cathodic and anodic current densities were measured electromagnetically by the optical transducer, rather than electronically by one of the classical methods, i.e, an Ammeter, of measuring the flow of the electronic current in a conductor. In addition, the optical transducer was applied to measure uniform corrosion and localized corrosion on metal surfaces and on substrates covered by organic coatings or under crevice assemblies [8-14]. The optical transducer

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