D > E > B > A. These extracts behave as mixed inhibitors, i.e., they affect both the cathodic and anodic processes. The activation energy of corrosion was calculated in absence and in presence of extracts. It was found that the presence of extracts in 1.0 M HCl solutions increases the values of activation energy of corrosion in that order of their inhibition efficiency. The inhibiting effect of these extracts results from their adsorption on the electrode surface via the adsorption centers of the compounds present in the extracts. The adsorption of these extracts onto the surface of muntz follows Frumkin,s isotherm. The atomic absorption spectroscopic measurements showed that the presence of these extracts greatly inhibits the preferential dissolution of zinc from the alloy and the occurrence of simultaneous dissolution of both zinc and copper.]]>
S.S. Mahmoud*
Chemistry Department, University College of Girls for Arts, Science and Education, Ain Shams University, Heliopolis, Cairo, Egypt
Received 14 de October 2005; accepted 25 July 2006
Abstract
This work presents the results of corrosion inhibition of muntz alloy (63% Cu, » 37% Zn) in 1.0 M HCl by water extracts of some naturally occurring plants. These are: outer brown skin of onion (A), onion bulb (B), the cloves of garlic bulb (C), orange peels (D), and henna leaves (E). The techniques of measurements for the determination of the amount of each zinc and copper dissolved from the alloy in the aggressive solution were: weight-loss, galvanostatic polarization, linear polarization and atomic absorption spectroscopy. From these measurements the values of surface coverage, q, and inhibition efficiency were calculated. It was found that the investigated extracts have high inhibition efficiency on the corrosion of muntz alloy in 1.0 M HCl. Their inhibition efficiency decreases according to the order: C > D > E > B > A. These extracts behave as mixed inhibitors, i.e., they affect both the cathodic and anodic processes. The activation energy of corrosion was calculated in absence and in presence of extracts. It was found that the presence of extracts in 1.0 M HCl solutions increases the values of activation energy of corrosion in that order of their inhibition efficiency. The inhibiting effect of these extracts results from their adsorption on the electrode surface via the adsorption centers of the compounds present in the extracts. The adsorption of these extracts onto the surface of muntz follows Frumkin,s isotherm. The atomic absorption spectroscopic measurements showed that the presence of these extracts greatly inhibits the preferential dissolution of zinc from the alloy and the occurrence of simultaneous dissolution of both zinc and copper.
Keywords: muntz alloy, inhibitors, water extracts, natural products.
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*Corresponding author. E-mail address: drsohairr@hotmail.com
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