Elsevier

Carbohydrate Polymers

Volume 95, Issue 1, 5 June 2013, Pages 288-294
Carbohydrate Polymers

Physicochemical studies of glucose, gellan gum, and hydroxypropyl cellulose—Inhibition of cast iron corrosion

https://doi.org/10.1016/j.carbpol.2013.02.069Get rights and content

Highlights

  • Gellan gum, hydroxypropyl cellulose are effective against acid corrosion of cast iron.

  • Hydroxypropyl cellulose showed high inhibition efficiency (IE%) at 298 ± 1 K.

  • At elevated temperatures, gellan gum exhibits greater inhibition efficiency.

  • Addition of KI showed both synergism and antagonism towards IE%.

  • Adsorption of the inhibitors on metal surface is mainly through physical interactions.

Abstract

Glucose, gellan gum, and hydroxypropyl cellulose were studied against the acid corrosion of cast iron by means of weight loss, potentiodynamic polarization, and AC impedance spectroscopy techniques. The inhibition efficiency was found to increase with increasing concentration of the inhibitors. The effect of immersion time and temperature were also studied. The addition of potassium iodide to the corrosion-inhibition system showed both antagonism and synergism toward inhibition efficiency. Polarization studies revealed the mixed-type inhibiting nature of the carbohydrates. The adsorption of inhibitors on the cast iron surface obeys Langmuir adsorption isotherm model, both in presence and absence of KI. Physical interaction between the inhibitor molecules and the iron surface was suggested by the thermochemical parameters, rather than chemical interaction.

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

References (23)

Cited by (117)

View all citing articles on Scopus
View full text