Corrosion inhibition effect of Allium sativum extracts on mild 2016-10-05آ  Corrosion inhibition effect

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    Journal of Chemical and Pharmaceutical Research, 2016, 8(2):216-230

    Research Article ISSN : 0975-7384 CODEN(USA) : JCPRC5

    216

    Corrosion inhibition effect of Allium sativum extracts on mild steel in HCl and H2SO4

    Cleophas A. Loto1,2, Roland T. Loto1 and Ohwofasa J. Oshogbunu1

    1Department of Mechanical Engineering, Covenant University, Canaan land, Ota, Nigeria 2Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria,

    South Africa _____________________________________________________________________________________________ ABSTRACT The effect of Allium sativum(garlic) extract as a ‘green’ inhibitor on mild steel corrosion in 0.5M HCl and 0.5M H2SO4 was studied at ambient temperature. Weight loss/corrosion rate and potentiostatic polarization measurement techniques were used for the experimental work. Potentiostatic polarization measurement was performed using a potentiostat (Autolab PGSTAT 30 ECO CHIMIE) interfaced with a computer for data acquisition and analysis. Results obtained showed effective corrosion-inhibition of the extract on the mild steel test-specimens in the different concentrations of HCl and H2SO4 used. There was increasing inhibition performance with increasing concentration of inhibitor. The best inhibition performance was achieved with the 100% (as extracted) garlic concentration. In 0.5M HCl, 100% garlic gave the optimal performance with weight loss at 8 days of the experiment of -0.15g, polarization resistance value of 2.78E+03Ω, corrosion rate, CR, of 9.47E – 02 mm/yr and current density (Icorr) value of9.46E-02 A/cm2. A similar result was observed in 0.5M H2SO4 where 100% garlic gave the best results of - 0.145g weight loss, polarization resistance value of2.79E+03Ω;corrosion rate, CR, value of9.46E-02 mm/yr and current density of9.20E-06 mm/yr. Results of ba and bc indicate a mixed type inhibitor. Key words: Corrosion, Allium Sativum, mild steel, inhibition, sulphuric acid, hydrochloric acid. _____________________________________________________________________________________________

    INTRODUCTION

    Mild steel is apparently one of the most versatile metallic materials that is widely used in construction, manufacturing, marine and diverse areas of other industrial and engineering purposes. However, the versatility of mild steel and hence its engineering performance is continually being threatened as it is subject to corrosive environmental degradation in service. One of the means to mitigate this destructive phenomenon which can be disastrous and with economic and technological consequences is the use of chemical inhibitors. These are chemical compounds that are adsorbed on the metal surfaces to minimize, control and/or prevent corrosion destructive processes and reactions. In very recent time, the use of plant extracts as inhibitors for the corrosion of metals/alloys, has gained very wide interest among researchers [1-12]. In many cases, the corrosion inhibitive effect of some plants’ extracts has been attributed to the presence of tannin in their chemical constituents [7-9]. Also associated with the presence of tannin in the extracts is the bitter taste in the bark and /or leaves of the plants. Extracts of plants used as inhibitors are environment friendly and this generates further additional interest in research in this area. In this present work, extract of garlic, Allium Sativum, was investigated. Garlic is of the Genus Onions; Class: Equisetopsida in the family of Amaryllidaceae. Garlic has been cultivated for thousands of years and is used throughout the world for its aromatic, spice and health giving properties. It is known to consist of calcium, Vitamin C, Vitamin B-6, Iron and Magnesium. It also contains protein, carbohydrates, potassium and sodium. With the major

  • Cleophas A. Loto et al J. Chem. Pharm. Res., 2016, 8(2):216-230 ______________________________________________________________________________

    217

    chemical constituents, garlic contains 0.1-0.36% of a volatile oil. These volatile compounds are generally considered to be responsible for most of the pharmacological properties of garlic. Garlic contains at least 33 sulphur compounds like aliin, allicin(diallylthiousulphinate or diallyl disulphide), ajoene, allylpropl, diallyl trisulphide, sallylcysteine, vinyldithiines, S-allylmercaptocystein, and others. Besides suphur compounds garlic contains 17 amino acids and their glycosides, arginine and others. Minerals such as selenium and enzymes like allinase, peroxidases and myrosinase. Garlic contains a higher concentration of sulphur compounds than any other Allium species. The sulphur compounds are responsible both for garlic’s pungent odour and many of its medicinal effects. The odour is formed by the action of the enzyme allinase on the sulphur compound alliin. The two major compounds in aged garlic, S-allylcysteine and S-allylmercapto-L-cysteine, had the highest radical scavenging activity. In addition, some organosulphur compounds derived from garlic, including S-allylcysteine, have been found to retard the growth of chemically induced and transplantable tumors[13]. Garlic sulphur-containing compounds are classified as oil- and water-soluble compounds. Oil-soluble compounds include sulphides, such as diallyl sulphide (DAS), diallyl disulphide (DADS), diallyl trisulphide and allyl methyl trisulphide, dithiins, and ajoene. Water-soluble compounds include cysteine derivatives, such as S-allyl cysteine (SAC), S-allylmercaptocysteine (SAMC) and S-methyl cysteine, and gamma-glutamyl cysteine derivatives, all as previously mentioned above. Oil-soluble sulphur compounds are odorous, whereas water-soluble compounds are odourless. Moreover, water-soluble compounds are more stable and safer than oil-soluble compounds. Garlic was also found to contain unique non-sulphur compounds, such as allixin and saponins and recent studies have revealed the important contribution of these compounds to garlic’s health benefits [14]. With the complex structural chemical compounds of the extract of garlic such as shown below (i-iii), a reasonable amount of exhibition of electrochemical corrosion activities of inhibition of the mild steel in the very corrosive acid environments used in this work is expected. Such a positive result will be economically and technologically beneficial.

    (i) Allicin [15]

    (ii) S-allylcysteine (SAC)[16]

    (iii) S–allylmercaptocysteine (SAMC)(17)

    EXPERIMENTAL SECTION

    2.1. Preparation of specimens The mild steel specimen used as test specimens was obtained from a local rolling mill in Nigeria. It has a per cent nominal composition as shown in Table 1. The cylindrical steel sample was cut into average size of 20 mm x 20 mm coupons for weight loss measurements and 20 mm x 20 mm coupons for potentiostatic polarization measurements. A total number of 24 samples used for the weight loss experiment were de-scaled with a wire brush, ground with various grades of emery paper and then polished to 6 µm,. They were further rinsed in distilled water to remove any

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    corrosion products and then cleaned with acetone to degrease. The samples were fully immersed thereafter preventing further exposure to moisture in the atmosphere. Another set of 24 samples for the corrosion polarization experiments were cleaned in the same manner as those for the weight loss experiment except that they were mounted in resin to ensure that only the surface of the samples were exposed to the corrosive medium. Before mounting, copper wire was spot welded to each of the samples.

    Table 1: Summary of per cent nominal composition of mild steel

    2.2. Preparation of Garlic (allium sativum) Extracts and Test Media The experiment was performed in (i) hydrochloric acid medium, 0.5M HCl and (ii) sulphuric acid medium, 0.5M H2SO4 both of AnalaR grade. 0.5M HCl was prepared by diluting 41.39 cm

    3 of concentrated HCl in 1 liter of distilled water while 0.5M H2SO4 was prepared by diluting 44.44cm

    3 of concentrated H2SO4 in 1 liter of distilled water. Garlic was obtained from the neighbourhood of the Covenant University, Ota, Nigeria.1Kg of the garlic was chopped into pieces and soaked with 2.5litres ethanol for 24 days. At the end of the soaking period, the chopped garlic was filtered to obtain a liquid solution of ethanol and garlic organic matter. The liquid was separated with the use of a rotary evaporator which extracted the ethanol from the liquid solution leaving behind the solution of garlic organic matter. The organic solution was stored in a refrigerator until it was used. The garlic extract (allium sativum) inhibitor test solutions were prepared in the percentage concentrations of 20, 40, 60, 80 and 100 respectively from the stock solution. This entailed taking 20 ml of the extract and 80 ml of the acidic medium to make 20% concentration. While for preparing 40% concentration requires taking 40ml of the garlic extract and 60ml of any of the acidic medium.100ml of the stock inhibitor solution was used as 100% allium sativum inhibitor concentration. The same procedure was followed to obtain 60% and 80% inhibitor concentrations. The HCl and H2SO4acidic media were separately used in turns for the preparation of percent concentrations of the extract inhibitors. 2.3. Weight loss experiment Weighed test specimens were totally immersed in each of the test media contain