Inhibitive effect of Prosopis cineraria on mild steel in acidic media

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1 Inhibitive effect of Prosopis cineraria on mild steel in acidic media M. K. Sharma*, P. Arora, S. Kumar, S. P. Mathur and R. Ratnani The alcoholic extracts of stem bark, leaves and fruit from the Prosopis cineraria are tested for their effectiveness to combat corrosion of mild steel in hydrochloric acid, sulphuric acid and in acid mixture (hydrochloric acidzsulphuric acid) by the mass loss method. It was found that the presence of the extracts reduces the corrosion rate of mild steel in acidic solution. The inhibition efficiency increases as the extract concentration is increased. The fruit extract of Prosopis cineraria shows a maximum corrosion inhibition efficiency in the acid mixture solution compared to leaves and stem bark extracts. The Prosopis extract provides a good protection to mild steel against corrosion. Keywords: Prosopis cineraria, Mild steel, Corrosion rate, Mass loss method, Inhibition efficiency Introduction Mild steel is widely used in most of the chemical industries due to its low cost and easy availability for fabrication of various reaction vessels, tanks, pipes, etc. Because it suffers from severe corrosion in aggressive environments, it has to be protected. Hydrochloric acid and sulphuric acid have been used for drilling operations, pickling baths and in decaling processes. Corrosion commonly occurs on metal surface in the presence of oxygen and moisture and involves two electrochemical reactions: oxidation takes place at the anodic site and reduction occurs at the cathodic site. In acidic medium, hydrogen evolution reaction predominates whereas in neutral medium, reduction of oxygen takes place. To reduce the corrosion problems in these environments, inhibitive effects of various corrosion inhibitors have been tried so far. Corrosion inhibitors reduce or prevent these reactions, which are adsorbed onto the metal surface, by forming a barrier to oxygen and moisture by complexing with metal ions or with forming of passivating film on the metal surface. Numerous naturally occurring substances such as Prosopis juliflora, 1 Eugenia jambolans, 2 Lawsonia extract, 3 Opuntia extract, 4 Swertia aungustifolia, 5 Ficus religeosa, 6 Heena 7 and Datura stromonium 8 have been evaluated as potential corrosion inhibitors. The present work is directed to evaluate the extract of Prosopis cineraria as probable acid corrosion inhibitors in hydrochloric acid, sulphuric acid and in acid mixture (hydrochloric acidzsulphuric acid) for mild steel. The results shows that the percentage inhibition efficiency (IE) of Prosopis cineraria is found to be maximum (95?39%) as compare to Swertia aungustifolia (90?00%), 5 Eugenia jambolans (93?00%) 2 and Heena (94?00%). 7 Department of Pure and Applied Chemistry, Maharshi Dayanand Saraswati University, Ajmer, Rajasthan , India *Corresponding author, mann_sharma04@yahoo.co.in Prosopis cineraria (family: Leguminosae) is commonly used in dry land agroforestry in the Indian subcontinent. Prosopis cineraria effectively stabilises sand dunes and can withstand periodical burial. 9 Its flower, bark and pods are endowed with medicinal properties. 10 The pods of Prosopis cineraria are used in times of scarcity. After boiling, they are used as astringent, demulcent and pectoral medicine. The flowers of Prosopis cineraria are powdered mixed with sugar and used by women during pregnancy as a safeguard against miscarriage. 11 The analysis of plant fruit gives the following mineral element composition: 0?14%Ca, 0?16%Mg, 0?29%P, 0?78%K, 0?04%Na and 2?04 ppm Fe. Prosopis cineraria contains alkaloid spicigerine, 12 which is isolated and characterised as w-(3-hydroxy-2- methyl-6-piperidyl)alkanoic acid. The seeds contain fixed oil, fatty acid composition determined as palmitic, stearic, oleic and linoleic acid by GLC. Alkaloids have been reported to inhibit the acid corrosion on mild steel. 13 The alkaloid spicigerine (Fig. 1) is found to be effective for inhibition of mild steel in acidic media. Experimental Rectangular specimens of mild steel of dimension 2?561?560?03 cm containing a small hole of y3 mm diameter near the upper edge were employed for the determination of corrosion rate. The specimens were cleaned by buffing to produce a mirror finish with the help of emery paper and were then degreased. Each specimen was suspended using a glass hook, immersed in a beaker containing 50 ml of test solution at room temperature and left exposed to air. Evaporation losses were made up with doubly distilled water. After the test specimens were cleaned using benzene, duplicate experiments were performed in each case and mean values of the mass loss were calculated. The acidic solution was prepared using doubly distilled water. All chemicals used were of analytical reagent quality. ß 2008 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 15 August 2006; accepted 14 March 2007 DOI / X Corrosion Engineering, Science and Technology 2008 VOL 43 NO 3 213

2 where DM u and DM i are the mass loss of the metal in uninhibited and inhibited solutions respectively. The corrosion rate (mm year 21 ) can be obtained by the following equation 1 Spicigerine The Prosopis extract was obtained by drying, then finely powered and extracted using boiling ethanol. The solvent is distilled off and the residue is treated using inorganic acid, where the bases are extracted as their soluble salts. The free bases are liberated by the addition of any base and extracted using various solvents, e.g. ether, chloroform, etc. The mixture of bases thus obtained is separated by various methods into individual compounds. The percentage inhibition efficiency was calculated as 14 g~100(dm u DM i )=DM u (1) Corrosion rate (mm year {1 )~ mass loss 87 : 6 (2) area time metal density where the mass loss is expressed in mg, the area in cm 2 of metal surface exposed, the time in hours of exposure, the metal density in g cm 23 and 87?6 is the conversion factor. Results and discussion The loss in mass and percentage inhibition efficiency for various concentrations of acid and inhibitors are shown in Tables 1 9. It can be seen that the inhibition efficiency increases with increasing concentration of inhibitor. It is also evident from the tables that the Table 1 Mass loss DM and inhibition efficiency g for mild steel in 0?5 N H 2 SO 4 (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Table 2 Mass loss DM and inhibition efficiency g for mild steel in 1 N H 2 SO 4 (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Corrosion Engineering, Science and Technology 2008 VOL 43 NO 3

3 Table 3 Mass loss DM and inhibition efficiency g for mild steel in 2 N H 2 SO 4 (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Table 4 Mass loss DM and inhibition efficiency g for mild steel in 0?5 N HCl (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Table 5 Mass loss DM and inhibition efficiency g for mild steel in 1 N HCl (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Corrosion Engineering, Science and Technology 2008 VOL 43 NO 3 215

4 Table 6 Mass loss DM and inhibition efficiency g for mild steel in 2 N HCl (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Table 7 Mass loss DM and inhibition efficiency g for mild steel in 0?5 N acid mixture (0?5 N hydrochloric acidz0?5 N sulphuric acid) (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Table 8 Mass loss DM and inhibition efficiency g for mild steel in 1 N acid mixture (1 N hydrochloric acidz1 N sulphuric acid) (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Corrosion Engineering, Science and Technology 2008 VOL 43 NO 3

5 inhibition efficiency improves with increasing concentration of acid and all the inhibitors display maximum efficiency at the highest concentration of acid used (i.e. 2 N). All the inhibitors reduce corrosion rate to a significant extent, showing inhibition efficiencies of.81?24% in 2 N sulphuric acid and 73?05% in 2 N hydrochloric acid solutions. The highest efficiency was displayed by the fruit extract in 2 N sulphuric acid for which a maximum value of 94?20% was obtained at an inhibitor concentration of 0?6% and in hydrochloric acid solution, the fruit extract shows an efficiency of 83?50% at an inhibitor concentration of 0?6%. From the mass loss data, it is concluded that the plant extracts act as a good inhibitor for mild steel in sulphuric acid as compared to hydrochloric acid. Comparison between the both acids and with the acid mixture has also been undertaken. The results for acid mixtures are reproduced in Tables 7 9. It is clear that the inhibitor acts as an efficient corrosion inhibitor for corrosion of mild steel in the acid mixture solutions. The inhibition efficiency improves in the acid mixture solution compare to the sulphuric acid and hydrochloric acid solutions. Maximum inhibition efficiencies of y95?39% are observed at the highest acid mixture concentrations (2 N) above which the maximum inhibition efficiencies in the sulphuric acid solution (2 N) is 94?20% and in hydrochloric acid solution (2 N) 83?50%, indicating the superiority of the inhibitor in the acid mixture to the acid solution (hydrochloric acid, sulphuric acid). It is evident from Table 7 that the maximum inhibition efficiency shown by the fruit extract of Prosopis cineraria is 82?79% in the 0?5 N acid mixture (hydrochloric acidzsulphuric acid) solution. The leaves extract of this plant shows an inhibition efficiency of 81?40% and that of stem bark 82?44% at the same concentration (i.e. 0?5 N) of acid mixture solution. According to Table 8, it can be seen that the fruit extract of Prosopis cineraria shows an inhibition efficiency of 85?43% at 1 N concentration of acid mixture solution. The leaves and stem bark extracts show 82?24 and 83?61% inhibition efficiencies respectively at the same concentration of the acid mixture solution (i.e. 1 N). Tables 7 9 evidenced that the alcoholic extract of Prosopis cineraria acts a good corrosion inhibitor for mild steel in acid mixture solution (hydrochloric acidzsulphuric acid) compared to the hydrochloric acid or sulphuric acid solutions. Generally, the adsorption of organic molecules on metallic surface involves O, N and S atoms. In the case of the plant extract of Prosopis cineraria, the N and O of alkaloid may be responsible for the adsorption. This process may block the active sites, hence decreasing the corrosion rates. The N atom of the alkaloid acts as the reaction centre because of its higher electron density, resulting in the formation of a monolayer on the metal surface. Organic inhibitors with active portions contain generally large C H chains or rings with positively charged amine nitrogen group at the one end. In acids and water, the terminal primary, secondary and tertiary amines groups take additional hydrogen that gives them a net positive or cationic charge. The polar amine group is adsorbed on the metal and the hydrocarbon portion forms an oily water repellant surface film. The molecular shape (dissymmetry) helps these materials act as surfactants and can stabilise emulsions of oil and water. Organic corrosion inhibitors 15 may function by: (i) chemisorptions of the molecule on the metallic surface (ii) complexing of the molecule with the metal ion, which remains in a solid state (iii) neutralising the corrodent (iv) adsorbing the corrodent. They offered large coverage due to the long hydrocarbon chain and by the presence of OH groups. Being hydrophilic in nature, the OH groups counteracted the effects of chain length and ensured higher solubility. It has been observed that the fruit extract of Prosopis cineraria has a maximum inhibition efficiency compared to the leaves and stem bark extracts. This may be attributed to the presence of alkaloids. In the fruit extract, the electron repelling hydroxyl group on the alkaloid is present; as a result, the electron density at the N atom becomes more than any other additives. This process increased the adsorptivity of the fruit extract on the corroding site of the metal. This explains the higher Table 9 Mass loss DM and inhibition efficiency g for mild steel in 2 N acid mixture (2 N hydrochloric acidz2 N sulphuric acid) (24 h), with given inhibitor addition at Uninhibited % % % % % % % % % % % % % % % Corrosion Engineering, Science and Technology 2008 VOL 43 NO 3 217

6 inhibition efficiency displayed by the fruit extract for 0?6% concentration. Conclusions The rate of corrosion of the mild steel in hydrochloric acid, sulphuric acid and acid mixture solution (hydrochloric acidzsulphuric acid) is a function of the concentration of the plant extract of Prosopis cineraria. The inhibition by this additive increased with increasing additive concentration. It may be concluded that the plant extract of Prosopis cineraria is a good corrosion inhibitor for mild steel in acid mixture and acid solution or can be used to replace toxic chemicals. References 1. R. Chowdhary and S. P. Mathur: J. Electrochem. Soc. India, 2005, 54, S. A. Verma and G. N. Metha: Trans. SAEST, 1997, 32, A. Y. El-Etre, M. Abdallah and Z. E. El-Tantawy: Corros. Sci., 2005, 47, A. Y. El-Etre: Corros. Sci., 2003, 45, S. J. Zakvi and G. N. Metha: Trans. SAEST, 1988, 23, T. Jain, R. Chowdhary and S. P. Mathur: Mater. Corros., 2006, 57, A. Chetouani and B. Hammouti: Bull. Electrochem., 2003, 19, G. S. Verma, P. Anthony and S. P. Mathur: J. Electrochem. Soc. India, 2002, 51, P. J. Gates and K. Brown: Outlook Agr., 1988, 17, The useful plants of India, Publication and Information Directorate CSIR, New Delhi, India, NAS: Fire wood crops, Vol. 1; 1980, Washington, DC, National Academy Press. 12. K. Jewers, M. J. Nagler, K. A. Zirvi, F. Amir and F. H. Cottee: Pahlavi Med. J., 1974, 5, G. N. Metha and T. P. Sastry: Proc. 2nd Int. Symp. on Industrial and oriented basic electrochemistry, Chennai, India, J. D. Talati and D. K. Gandhi: Indian J. Technol., 1991, 29, R. H. Hausler: Proc. Int. Conf. on Corrosion inhibition, Dallas, TX, USA, May 1983, Vol. 7, Corrosion Engineering, Science and Technology 2008 VOL 43 NO 3

Corrosion Inhibition and Adsorption Behavior of Clove Oil on Iron in Acidic Medium

ISSN: 0973-4945; CODEN ECJHAO E- Chemistry http://www.ejchem.net 2012, 9(4), 2044-2051 Corrosion Inhibition and Adsorption Behavior of Clove Oil on Iron in Acidic Medium ARCHANA SAXENA* 1, ANURAG SHARMA