July 2011 Entire Research, Vol.-3, Issue-III 1 Inhibition Efficiency of N-Cetyl-N, N, N-Trimethyl Ammonium Bromide on 304 Stainless Steel in NaCl Solution Dr. R. S. Dubey: Chemistry Research Laboratory, Dept. of Chemistry, R. J. College of Arts, Science and Commerce (University of Mumbai), Ghatkopar (W), Mumbai-400 086, India. Abstract N-Cetyl-N, N, N-Trimethyl Ammonium Bromide (CTAB)-C19H42NBr is used as corrosion inhibitor for protection of 304 Stainless Steel in 1.5% NaCl solution. The inhibition effect of the compound was investigated by using electrochemical polarization techniques i.e. potentiodynamic and open circuit potential in the concentration ranges 5-50ppm. Scanning electron microscope (SEM) examined the changes in surface morphology of the specimen in absence and presence of this inhibitor. The results obtained reveals that N-Cetyl-N, N, N-Trimethyl Ammonium Bromide is a very good corrosion inhibitor and shows best performance at a very low concentration of 15 ppm. Potentiodynamic curves indicate, that compound is a mixed type of inhibitors having heteroatom in the chain of the compound. SEM observations also show that in the presence of inhibitor, there is less attack of the metal surface. Keywords: Corrosion, 304 Stainless Steel, Inhibitors, and Electrochemical techniques. Introduction Coatings, paints and use of organic compounds are the some way of corrosion mitigation. The organic compounds especially, heterocyclic compounds containing heteroatoms like S, N, O, Se with loosely bound lone pair of electrons and compounds with π electrons, undergo adsorption on the metal surface and protects the material from the aggressive environment. Various workers have used organic compounds for corrosion inhibition of metals like Cu, iron, mild steel, and stainless steel, Al etc. at different concentrations in acidic, basic and salt solutions1-11. Stainless steel, due to its high strength, workability and high corrosion resistance property are used in various engineering applications like chemical and pharmaceutical industry 12-13, food and beverage industry14, petrochemical industry15-17, oil and water pipe lines18, ship and Naval structures 19-20; architectural applications, water supply and desalination plants 13. The corrosion inhibition actions of the organic compounds containing heteroatoms such as undecanoic acid hydrazide, 2-mercaptobenzothiazole, and 2-hydrazinobenzothiazole on carbon steel in HCl solution21, morpholinium caprylate, morpholinium sebacate and laurate22-23, morpholinium oleate24 and morpholinium stearate25 have been investigated for steel. Al-Suhybani et al26 investigated the corrosion inhibition efficiency of azoles: 2-mercaptobenzoazole (CBA), and its derivatives (2-mercaptobenzoimidazole, 2-mercaptobenzoxazole, ISSN 0975-5020 July 2011 Entire Research, Vol.-3, Issue-III 2 2-mercapto benzothiazole); 2-methyl benzoazole and its derivatives (2-methyl benzimidazole, 2-methyl benzoxazole, 2-methyl benzothiazole and 2-methyl benzoselenazole) for 304 stainless steel in acidic solution where some provides inhibition efficiency up to 90% at a concentration of 5x10-4 M and stated efficiency of the heteroatoms in the decreasing order as Se > S > N > O. Dubey et al27-28 investigated the corrosion inhibition efficiency of some heterocyclic organic compounds like Ketoconazole, Fluconazole, Roxythromycin, Amoxycillin, Ampicillin; and some benzimidazole derivatives like 2-methylbenzimidazole, 2- ethylbenzimidazole, and 2-benzylbenzimidazole for 304 stainless steel in marine environment. The aim of the present investigation was to find out the suitable inhibitor for control of corrosion of 304 stainless steel in marine environment. Experimental Procedure: 304 Stainless Steel of commercial grade in sheet form having composition as follows: C -0.06%, Si - 0.53%, Mn- 0.10%, P- 0.032%, S-0.016%, Ni- 8.16%, Cr- 18.17%; and Iron- balance, were used in the present investigation. For electrochemical polarization, samples of 1cm x 3cm were sheared from the commercial grade sheets. The surface of these samples was successively polished by using the Emery papers of grades 1 / 0, 2 / 0, 3 / 0, and 4 / 0 obtained from Sianor, Switzerland to obtain a scratch free mirror finish surface. The polished samples were washed with detergent solution, rinsed with distilled water and finally degreased with acetone. The specimens were dried and stored in a desiccators containing silica gel as a dehydrating agent. N-Cetyl-N, N, N-Trimethyl Ammonium Bromide was procured and its inhibition efficiency was determined with electrochemical techniques. A molecular structure of this compound is shown in Fig.1. Fig.1.Structure of N-Cetyl-N,N,N-trimethyl ammonium bromide Pure NaCl obtained from S. D. Fine Chemicals was used to prepare its 1.5% solution with double distilled water. Electrochemical Measurement System, DC 105, containing software of DC corrosion techniques from M/S Gamry Instruments Inc., (No. 23-25) 734, Louis Drive, Warminster, PA-18974, USA has been used for performing corrosion potential and polarization experiments. For electrochemical polarization studies (corrosion potential, and potentiodynamic polarization) flag shaped specimens with sufficiently long tail were cut from the stainless steel sheet. These samples were polished as described earlier leaving a working area of 1cm2 on both sides of the flag and a small portion at the tip for providing electrical contact. Rest of the surface was isolated from the corroding solution by coating with enamel lacquer including side edges. The test specimen was connected to the working electrode holder with the ISSN 0975-5020 July 2011 Entire Research, Vol.-3, Issue-III 3 help of a screw. About 50ml of the corrosive medium was taken in a mini corrosion testing electrochemical cell. This volume was appropriate to permit desired immersion of electrodes. The electrochemical investigation was carried out using microprocessor based corrosion measurement system (CMS-105, Gamry Instruments Inc., USA.). The three-electrode i.e. working electrode, reference electrode (calomel), and counter electrode (graphite rod), system cell was used throughout the electrochemical measurements. Open circuit potential measurement and potentiodynamic polarization of the samples were investigated in the concentration ranges 5 , 10 ,15 ,20 ,30 , 40 and 50 ppm of the inhibitors. The value of inhibition efficiency in terms of corrosion current density: E = 100 x (io – i) / io ......................... … ………………………………………….1 Where io and i are the corrosion current density of the uninhibited and inhibited samples. Scanning Electron Microscopy (SEM) Surface morphology of the specimens before and after corrosion experiments was examined using the scanning electron microscope (Model No. JEOL-JSM 840, JAPAN). Results and Discussion: Open circuit potential (OCP) Open circuit potential (potential vs. time) plots for 304 Stainless steel xposed to 1.5%NaCl in absence and presence of N-Cetyl-N, N, N-trimethyl mmonium bromide as inhibitor in the concentration range 5-40ppm is shown in Fig.2.In presence of inhibitor the potential shifts towards more positive direction in compare to the blank (Curve No.7). The potential shift in +ve direction is maximum corresponding to the conc. 15ppm. Fig. 2. Open Circuit Potential of 304 Stainless Steel Exposed to 1.5% NaCl Solution with different concentrations (in ppm) of N-Cetyl-N, N, N-Trimethyl Ammonium Bromide. Potentidynamic polarization Potentiodynamic polarization (potential vs. current density) consisting of anodic and cathodic polarization curves is recorded and indicates the partial ISSN 0975-5020 July 2011 Entire Research, Vol.-3, Issue-III 4 electrochemical reactions i.e. anodic and cathodic reactions. Fig.3. Shows the potentiodynamic polarization curves of 304 Stainless steel exposed to 1.5% NaCl solution with presence of N-Cetyl-N, N, N-trimethyl ammonium bromide in the conc. ranges 5-50 ppm and in the absence of the inhibitor. Fig. 3. Potentiodynamic polarization of 304 Stainless Steel Exposed to 1.5% NaCl Solution with different concentrations (in ppm) of N-Cetyl-N, N, N- Trimethyl Ammonium Bromide. In presence of inhibitor the potential shifts towards the noble direction and decreasing simultaneously the corrosion current density, indicates the interference of the inhibitor to the anodic and cathodic reaction processes. The effect of different concentration of the inhibitor on various electrochemical parameters like corrosion potential (Ecorr), corrosion current density (Icorr), anodic Tafel constant (βa), cathodic Tafel constant (βc), corrosion rate and % inhibition efficiency etc. of 304 Stainless steel is shown in Table-1. Among all the conc. of the inhibitor, 15ppm is the optimum concentration, which gives highest % inhibition efficiency (98.05%), lowest anodic Tafel‘s slope (218.7e-3 V/decade) and highest noble corrosion potential (79.00 mV). Table-1. Electrochemical Parameters for Inhibition of Corrosion of 304 Stainless Steel Exposed to 1.5% Sodium Chloride with Different Concentration of N-Cetyl-N, N, N-Trimethyl Ammonium Bromide. _________________________________________________________________ Concentration a c Icorr Ecorr Corr. Rate % Inhibition (ppm) (V/dec.) (V/dec.) (µA/cm-2) (mV) (mpy) Efficiency ________________________________________________________________ -- 737.7e-3 171.0e-3 1.930 -317.0 882.7e-3 N-Cetyl-N, N, N-Trimethyl Ammonium Bromide 5 246.2e-3 235.0e-3 0.07940 -34.10 33.69e-3 95.88 10 394.5e-3 266.9e-3 0.08300 21.00 35.22e-3 95.70 15 218.7e-3