Evaluation of Chromate as Dezincification Inhibitor for α-brass (Cu/Zn : 64/36) in 3% Chloride Buffer Solutions

H. H. Rehan*, N.A. Al-Moubarak, H.A. Al-Rafai

Chemistry Department, College of Education for Girls, Malaz, Riyadh 11417, P.O. Box 27104, Kingdom of Saudi Arabia

Received 20 September 2002; accepted in revised form 5 December 2002

Abstract

The inhibition behavior of chromate ions towards corrosion and dezincification of α-brass (Cu/Zn: 64/36) in acetate buffer solutions (pH 2.4, 7.0 and 8.5) containing 3% sodium chloride was studied. Weight loss and solution analysis were used for a long period (four weeks) and electrochemical polarization for a short period (one hour). Chromate accelerated corrosion and dezincification at pH 2.4 by acting as depolarizer but chromate suppressed efficiently the corrosion and dezincification at pH 8.5. At pH 7.0 the corrosion and dezincification suppressed in the presence of chromate but the inhibition action started to deteriorate at chromate concentration less than 0.005 mol/L. The inhibition effect is attributed to adsorption of chromate ions on the corroding surface and improvement of the passivity. Chromate led to an increase in the concentration of copper species in solution due to the formation of the more soluble CuCrO₄ than Cu₂O, which contributed to the apparent suppression of dezincification.

Keywords: a-brass, corrosion inhibition, dezincification, chromate.

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*Corresponding author: on leave from Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt. E-mail address: hyman_rehan@yahoo.com.