Prediction and measurement of corrosion inhibition of mild steel by imidazolines in brine solutions
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I. INTRODUCTION
CORROSION is a very common phenomenon that has wide ranging effects in industrial, municipal, and private settings. The economic costs of corrosion in the United States alone have been estimated at $137.9 billion per year (1998) for direct costs, and the cost extrapolated to the U.S. economy is $275.7 billion per year (1998).[1] Surfactants are well known as corrosion inhibitors.[2,3] It has been reported[4] that imidazoline surfactants are well used in the field of oil well and oil pipeline protection. Since the primary action of corrosion inhibition is determined by the adsorption of the surfactant functional group onto the metal surface,[5] adsorption is critical to corrosion inhibition. The effectiveness of surfactant adsorption is mainly determined by surfactant concentration, surfactant functional group, alkyl hydrocarbon chain length, environment, etc.[6,7] When the surfactant concentration is below the surface aggregation concentration, which is usually named as critical micelle concentration (CMC) in the field of surface technology, individual surfactant molecules tend to adsorb on exposed interfaces to inhibit corrosion and reduce surface tension; above the CMC, additional surfactant molecules lead to the formation of mutilayer coverage or micelles. Thus, when the additional surfactant is added beyond the CMC, it will not inhibit corrosion directly and the surface tension will not change significantly. The effects of these properties on surfactants’ behavior and their associated relationships with surfactant adsorption and corrosion inhibition will be presented later. This article is devoted to the analysis and prediction of mild steel corrosion inhibition by imidazoline surfactants in brine solutions. II. EXPERIMENTAL PROCEDURES
0.1 mg. The plate was first cleaned by deionized water and heated to an orange color using a Bunsen burner to ensure organic debris removal between tests; then, it was suspended in air. Afterward, a solution with surfactant was placed in a very clean glass dish, which was raised by means of a small screw jack until contact between the plate and solution was made. By measuring the force exerted by solution on the plate suspended at the solution line, the surface tension was determined. The maximum force exerted by the solution at the plate/solution interface was used as the surface tension. Corrosion inhibition tests[15] were conducted using a typical three-electrode arrangement. A mild steel rod (AISI 1018) of approximate composition C 0.1 to 0.15 pct, Si 0.10 to 0.30 pct, Mn 0.3 to 0.6 pct, P 0.05 pct, and S 0.05 pct was used as working the rotating disc electrode (RDE), which was mounted in a TEFLON-sealed and epoxy precoated holder and rotated at 1000 RPM (the rotation was controlled by an AFMSRX rotator, Cypress Systems, KS). A platinum counter electrode was used along with a standard calomel reference electrode in this threeelectrode configuration. All tests were performed using a 750 mL glass vessel that was maintained at 31 °C controlled by isot
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