Corrosion inhibition, hydrogen evolution and antibacterial properties of newly synthesized organic inhibitors on 316L stainless steel alloy in acid medium

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Abstract

Electrochemical corrosion behavior and hydrogen evolution reaction of 316L stainless steel has been investigated, in 0.5 M sulfuric acid solution containing four novel organic inhibitors as derivatives from one family, using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and surface examination via scanning electron microscope (SEM) technique. The effect of corrosion inhibitors on the hydrogen evolution reaction was related to the chemical composition, concentration and structure of the inhibitor. The inhibition efficiency, for active centers of the four used compounds, was found to increase in the order: –Cl < –Br < –CH3 < –OCH3. The corrosion rate and hydrogen evolution using the compound with methoxy group as a novel compound was found to increase with either increasing temperature or decreasing its concentration as observed by polarization technique and confirmed by EIS measurements. The compound with methoxy group (newly synthesized) has very good inhibition efficiency (IE) in 0.5 M sulfuric acid (98.3% for 1.0 mM concentration). EIS results were confirmed by surface examination. Also, antibacterial activity of these organic inhibitors was studied. The results showed that the highest inhibition efficiency was observed for the compound that posses the highest antibacterial activity.

Introduction

‘Stainless steel’ covers a wide range of steel types and grades for corrosion or oxidation resistant applications. The main requirement for stainless steels is that they should be corrosion resistant for a specified application or environment. The selection of a particular “type” and “grade” of stainless steel must initially meet the corrosion resistance requirements [1]. Additional mechanical or physical properties may also need to be considered to achieve the overall service performance requirements. 316L stainless steel alloy (similar to 304 with Mo added to increase opposition to various forms of deterioration), offers the most resistance to corrosion in numerous standard services. The lower carbon ‘variants’ (316L) were established as alternatives to the ‘standards’ (316) carbon range grade to overcome the risk of intercystalline corrosion (weld decay), which was identified as a problem in the early days of the application of these steels [1]. Applications include cooking utensils, textiles, food processing equipments, exterior architecture, equipments for the chemical industry, truck tailors, and kitchen sinks [2]. Corrosion is a process contributing to economic losses and pollution of our environment. Thus the use of organic inhibitors is one of the most practical methods to protect metals and alloys against corrosion, especially in acid media [3]. The inhibition of corrosion for iron in acid solution by organic inhibitors has been studied in considerable detail [3], [4]. Among alternative corrosion inhibitors, organic products containing one or more polar functions (with N, O and S atoms) have been shown to be quite efficient in preventing corrosion, in addition to heterocyclic compounds containing polar groups and π-electrons [5]. The inhibiting action of these organic compounds is usually attributed to interactions with metallic surfaces by adsorption. Considering the inhibition for corrosion of 316L stainless steel alloy, the effective inhibitors should suppress both corrosion and hydrogen evolution. The sources of hydrogen are water decomposition and reaction of water with the metal [6]. The requirement for effective inhibition of hydrogen uptake is to inhibit the hydrogen evolution, to promote the hydrogen gas recombination and to inhibit the hydrogen entry [7]. The number of adsorption active centers, the charge density, the mode of adsorption, and the projected area of the organic inhibitor could affect the inhibitor efficiency, and also the influence of the molecular area and molecular weight [8] of the organic molecule. Recently a number of studies have been focusing on the relationship between the structural properties of the organic inhibitor molecules and their inhibitory effects, in order to appraise the organic compounds as inhibitors and to design novel inhibitors for vested purpose.

This work aims to find a good corrosion inhibitor for 316L stainless steel in acid medium that makes that alloy to be used in chemical industry and to examine the resistance of the film toward the bacteria which affects the film efficiency. Thus, hydrogen evolution and corrosion behavior of 316L stainless steel was investigated in 0.5 M H2SO4 acid solution containing different newly synthesized organic inhibitors (A–D) [9]. Antibacterial activity of these organic inhibitors was studied. Different techniques were employed such as potentiodynamic polarization, impedance spectroscopy (EIS) and Scanning electron microscopy (SEM).

Section snippets

Materials preparation

The tested 316L stainless steel rod has cross-sectional area of 0.2 cm2. The composition of the stainless steel is as follows (wt %): C = 0.016, Cr = 16.71, Mo = 2.07, Ni = 10.28, N = 0.067, Mn = 1.66, Si = 0.48, P = 0.02, S = 0.00006, Cu = 0.12 and balance Fe. The test aqueous solutions contained naturally aerated solution, as present in natural environment (without agitation) H2SO4 (Aldrish) analytical reagents with concentration (0.5 M). Triple distilled water was used for preparing the

Results and discussion

The method for synthesis of triazoquinoline derivatives that are used as inhibitors (compounds A–D) in this work is reported in Scheme 1.The four inhibitors called compounds A–D, where A containing –OCH3 group as substituent, B contains –CH3 group, C contains –Br and D contains –Cl as substituents. To the best of our knowledge, the triazoloisoquinoline 4 required for this study have not yet been reported and prepared via cycloaddition of nitrilimine 2 (prepared in situ from hydrazonoyl chloride

Conclusions

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    EIS results showed that using 0.5 M sulfuric acid medium containing compound A as inhibitor for 316L alloy gives the highest corrosion resistance (RT) value relative to the other used compounds (B, C and D).

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    Polarization results showed that corrosion current density (icorr) value or hydrogen evolution rate is the lowest for compound A and these results confirmed well EIS results.

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    The corrosion (icorr) and hydrogen evolution rate, for compound A, were found to increase with either increasing

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