Physicochemical studies of glucose, gellan gum, and hydroxypropyl cellulose—Inhibition of cast iron corrosion
Introduction
Cast iron is an indispensable material that is used to produce variety of objects found in day-to-day life due to its ductility, toughness and strength. Acid solutions are widely used in several industries for different purposes, for example, acid cleaning, acid pickling, descaling and oil wet cleaning and so on (Lagrenee et al., 2002, Li et al., 2008). Metals and alloys, in general, tend to deteriorate under corrosive environments. The employment of inhibitors is one of the best-known methods to suppress the corrosion rate. The inhibitors containing electronegative functional groups such as sulphur, phosphorous, nitrogen, oxygen and aromatic rings have shown excellent corrosion retarding properties.
Polymers are one of the important types of corrosion inhibitors that have high affinity toward the metal surfaces (Kesavan, Gopiraman, & Sulochana, 2012). Carbohydrates are the most abundant renewable materials in natural resources. The derivatives of carbohydrates are very useful biomaterials for several applications (Klemm, Schmauder, & Heinze, 2002). However, very few natural and semi-synthetic carbohydrates were studied for the subject of corrosion inhibition. For example, carboxymethyl cellulose (Bayol et al., 2008, Solomon et al., 2010, Umoren et al., 2010), guar gum (Abdallah, 2004), Arabic gum (Umoren, Ogbobe, Igwe, & Ebenso, 2008), and starch (Bello et al., 2010, Mobin et al., 2011) were examined for corrosion inhibition of steels in different acid medium. Exudate gum (Umoren, Obotl, Ebenso, & Okafor, 2008) was also reported as a corrosion inhibitor for aluminum in an acid medium.
In view of material properties, inexpensiveness, and potential environmental benefits, in this study, gellan gum and hydroxypropyl cellulose were evaluated against the acid corrosion of cast iron. It is much interesting to compare the efficacy of a monosaccharide with polysaccharides. Therefore, glucose was also examined for corrosion inhibition. The inhibitors were evaluated by means of weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The addition of halide ions alongside with inhibitors increases the inhibition potential of the inhibitor with decreasing the amount of the inhibitor required. Therefore, the effect of KI addition to the corrosion-inhibition system was also studied. In order to understand the adsorption mechanism of the inhibitors, the inhibitors adsorbed on the steel surface were analyzed by Fourier transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WAXD) and the morphological changes on the iron specimens were observed under scanning electron microscopy (SEM) and the results were presented in the following sections.
Section snippets
Materials and methods
Corrosion tests were performed using cast iron consisting of the following composition (wt%) C, 6.09; Al, 1.13; Mn, 0.78 and the remainder being Fe. The cast iron specimens were cut into dimensions of 1 cm × 1 cm × 0.02 cm and the surface was abraded with a series of emery papers from grades 600, 800, 1000, and 1200. The specimens were washed with double distilled water, degreased with acetone and then dried at room temperature. The electrolyte solution, 1 M HCl, was prepared from analytical grade HCl
Effect of inhibitor concentration
The values of IE%, surface coverage (θ), and standard deviation (σ) were given in Table 1. The IE% was found to increase along with the increment of the inhibitors’ concentration by suppressing the corrosion rate. The inhibitors A, B, and C showed IE% of 70%, 81%, and 90% respectively. Among the studied inhibitors, hydroxypropyl cellulose (C) exhibited higher IE%, which is attributed to its molecular structure. The propylene oxide units in the side chain of C may extend its interaction with the
Conclusion
All investigated carbohydrate inhibitors act as effective cast iron corrosion inhibitor in 1 M HCl solution and the inhibition efficiency follows the order C > B > A at room temperature with little differences in their efficiency values in all methods employed. The inhibitor C exhibited higher IE% at 298 K, where as at elevated temperatures inhibitor B was found to be efficient due to chemisorption mechanism. The addition of KI showed antagonism toward the IE% at lower concentration of KI and
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