Abstract
An investigation was conducted to improve the corrosion inhibition efficiency of molybdate-based inhibitors for mild steel which is the main construction material of cooling water systems, using nitroethane as an organic compound beside zinc. In this study a new molybdate-based inhibitor was introduced with the composition of 60 ppm molybdate, 20 ppm nitrite, 20 ppm nitroethane, and 10 ppm zinc. Inhibition efficiency of molybdate alone and with nitrite, nitroethane, and zinc on the uniform corrosion of mild steel in stimulated cooling water (SCW) was assessed by electrochemical techniques such as potentiodynamic polarization and electrochemical impedance (AC impedance) measurements. Weight loss measurements were made with coupon testing specimens in the room temperature for 48 h. Studies of electron microscopy, including scanning electron microscopy (SEM) photograph and X-ray energy dispersive spectrometry (EDS) microanalysis, were used. The results obtained from the polarization and AC impedance curves were in agreement with those from the corrosion weight loss results. The results indicate that the new inhibitor is as effective as molybdate alone, though at one-ninth of the concentration range of molybdate, which is economically favorable.
Highlights
The protection of cooling water systems as well as heat supply water has become one of the great important issues in the world economy
The presence of aggressive ions such as chloride (Cl−) and sulfate (SO4−2) anions reduces the efficiency of MoO42−, so higher concentrations are necessary for corrosion inhibition [6, 7], which is not economically favorable
The presence of corrosion inhibitor could be more clearly investigated by means of surface analysis techniques
Summary
The protection of cooling water systems as well as heat supply water has become one of the great important issues in the world economy. The best method to improve inhibitive capability is using inhibitors in combination with others [8,9,10,11] As it has been observed previously, organic inhibitors usually designated as a film forming protect the metal by forming a hydrophobic film on the metal surface. Jefferies and Bucher recently studied the addition of zinc as cathodic inhibitor to improve the corrosion inhibition behavior of molybdatebased inhibitors [13]. As a result, it is worth investigating the corrosion inhibition of mild steel in stimulated cooling water (SCW) by using new developed inhibitor containing molybdate, nitrite, nitroethane, and zinc
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