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Microstructural characterization of copper corrosion

in aqueous and soil environments

A.Srivastava,R.Balasubramaniam *

Department of Materials and Metallurgical Engineering,Indian Institute of Technology,Kanpur 208016,India

Received 22March 2005;received in revised form 12April 2005;accepted 15April 2005

Abstract

Scanning electron microscopy has been used to investigate the surface films on pure copper after exposure to different aqueous and soil environments,containing chloride,sulfide and ammonium salts.The morphology of the films formed on copper surface in aqueous and soil environments was different for the same amount of pollutants.The surface films formed in soil environments were not homogenous in contrast to the films formed in aqueous environments.The damaging effect of chloride ions and the benign role of sulfide ions were revealed in both the environments.Local compositional analysis confirmed that the surface films formed on copper consisted predominantly of copper and oxygen.D 2005Elsevier Inc.All rights reserved.

Keywords:Copper;Corrosion;Soil;Surface film;Characterization

1.Introduction

When one considers the existence of human beings on this planet,one of the earliest metals intelligently used for practical applications is copper [1].Copper is one of the most frequently encountered metals in our society.Copper eventually forms a thin layer of cor-rosion,generally brownish-green or greenish-blue in color.This layer is called patina [2].Once the patina is established it tends to be extremely stable and become a permanent part of the copper object.Changes in

patina,which can occur under some conditions,may be detrimental for the base metal.Copper corrosion products are known to have a protective effect against corrosion.However,a different behavior could be obtained in presence of pollutants (chloride,sulfide,etc.).This can be due to corrosion products morphol-ogy and degree of crystallization,rather than their phase composition [3].

Cuprite (Cu 2O)is known to play a decisive role in the protectiveness of corrosion layers on copper [3].In aqueous media,hydrated oxides of copper have also been reported to form over underlying Cu 2O film [4].A low degree of hydration has been found to give much better stability than that of fully hydrated metal oxide in flowing conditions.North et al.[5]found that

1044-5803/$-see front matter D 2005Elsevier Inc.All rights reserved.doi:10.1016/j.matchar.2005.04.004

*Corresponding author.

E-mail address:bala@iitk.ac.in (R.Balasubramaniam).

Materials Characterization 55(2005)127–

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