Benzyl Nicotinate as an Efficient Corrosion Inhibitor for Cold Rolled Steel in a 1 M HCl Solution

Portugaliae Electrochimica Acta 2017, 35(5), 253-268 DOI: 10.4152/pea.201705253 PORTUGALIAE ELECTROCHIMICA ACTA ISSN 1647-1571 Benzyl Nicotinate as an Efficient Corrosion Inhibitor for Cold Rolled Steel in a 1 M HCl Solution M.R. Vinutha,a T.V. Venkatesha,a,* and Vinayak Bhatb a Department of Chemistry, School of Chemical Science, Jnana Sahyadri Campus, Kuvempu University, Shankaraghatta-577451, Karanataka, India b Department of Physics, Shri Madhwa Vadiraja Institute of Technology and Management, Bantakal, Udupi – 574115, India Received August 27, 2016; accepted April 02, 2017 Abstract The ability of benzyl nicotinate (BN) to inhibit the corrosion process of cold rolled steel (CRS) in a 1 M HCl solution has been investigated by weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopic methods. The potentiodynamic polarization study revealed that BN acts as a mixed type inhibitor. The effect of temperature range (303-333 K) on the corrosion of steel was studied at different concentrations of BN. The efficiency of this inhibitor increases with an increase in its concentration, and decreases with rise of temperature. Free energy values revealed that BN molecule undergoes comprehensive adsorption. The adsorptive behavior of BN on CRS obeys Langmuir adsorption. The thermodynamic and activation parameters calculation helped in getting insight into the inhibitor mechanism. The DFT (density functional theory) studies of BN molecule also supported our experimental findings. Keywords: BN, corrosion, EIS, quantum studies. Introduction Hydrochloric acid is widely used as pickling liquor for processes like descaling, pickling, acid cleaning and oil-well acidizing, etc. Steel (mild steel-MS, cold rolled steel-CRS, and stainless steel-SS) of various forms is employed in all industries for many purposes, such as storage tanks, containers, boilers, carrier pipes, etc. But, during its surface treatment, steel gets damaged due to the corrosive nature of acid solution, thereby reducing its service life. This corrosive damage occurs as a result of electrochemical reactions at the surface, which cause the failure of materials [1]. To avoid this, various preventive methods were developed by the researchers, and the use of corrosion inhibitors is one of the best practical methods. * Corresponding author. E-mail address: M.R. Vinutha et al. / Port. Electrochim. Acta 35 (2017) 253-268 Corrosion inhibitors are organic compounds containing heteroatoms like P, S, O and N in their ring structure, which show good corrosion inhibition properties in acidic media [2-8]. Inhibitors act through the process of adsorption, and their adsorptive nature depends upon the electronic density at the donor site, aromaticity, steric factor, molecular mass, presence of functional groups like – C=O,-N=N-,-OH,-COOR, temperature and potential developed at the metal solution interface. Literature survey reveals that derivatives of Schiff bases, triazoles, thiozoles, pyridine and many other organic compounds were reported as good corrosion inhibitors in acidic media [9-12]. A few researchers have reported the use of nicotinic acid derivatives, namely, M.P. Chakravarthy et al. [13-14], which have studied the inhibitive effect of two nicotinamide derivatives and two isonicotinic acid derivatives of indole and pyrrol on mild steel in 0.5 M HCl. The anti-corrosive effect using nicotinic acid hydrazide and its benzalidine derivatives as inhibitors in a 1 M HCl solution studied by Hemapriya et al. [15] showed a as high as 90% and 94% inhibition efficiency, respectively. Jun Zhao et al. [16] have used cigarette butts as a corrosion inhibitor for N80 steel in an HCl solution; they contain nicotine and nicotine derivatives as major components, which show 92% inhibition efficiency in 5% by weight of inhibitor solution in 10% HCl. The inhibitors containing nicotine heterocycle are less reported in the literature, so we have chosen benzyl nicotinate (BN) (Fig. 1). Figure 1. Structure of benzyl nicotinate (BN). Previously, we have verified the inhibitory effect of BN on the corrosion of CRS in a 0.5 M H2SO4 solution [17]. In the present work, studies on the theoretical, adsorptive and electrochemical behavior of BN on the corrosion of CRS in a 1 M HCl solution are evaluated. Experimental Sample The experiments were performed with CRS specimens with the compositions of 0.14% C, 0.4% Mn, 0.025% P, 0.0008% S, 0.025% Si, 0.003% Al and remaining of Fe. 254 M.R. Vinutha et al. / Port. Electrochim. Acta 35 (2017) 253-268 Solutions The aggressive solutions of 1 M HCl AR-grade were prepared using double distilled Millipore water. The tested inhibitor benzyl nicotinate (BN) of AR grade was purchased from Sigma-Aldrich Chemicals, Bangalore. The different concentrations of inhibitor (0 to 500 ppm) were prepared in a 1 M HCl solution. Weight loss measurement The CRS coupons of dimension 4 cm × 2 cm × 0.5 cm were used for weight loss measurements. The coupons were treated with a series of emery paper from 220, 330, 400, 600 and 1200 grades to obtain a uniform surface. Then, the specimens were washed several times with distilled water, then with acetone, and dried using a stream of air. The weight loss incurred by CRS specimens was determined by weighing the samples before and after immersion in 100 cm3 of 1 M HCl, in the absence and presence of various concentrations of BN at different temperature ranges of 303, 313, 323, and 333 K. The experiments were performed in triplicate and the mean value is reported. The experiments were carried out in a static aerated condition. The corrosion rate (νcorr) of CRS was determined using the following relation: ν = corr ∆m St (1) where νcorr is the corrosion rate of mild steel (g cm−2 h−1), Δm is the corrosion weight loss of mild steel (g), S is the surface area of mild steel specimen (cm2), and t is the time of exposure. The percentage inhibition efficiency was calculated using the relationship: % IE = o ν corr − ν corr × 100 o ν corr (2) where ν0corr and νcorr are the corrosion rates of CRS in the absence and presence of BN, respectively. Electrochemical measurements Electrochemical measurements were conducted in a conventional glass cell using a CHI 660D electrochemical analyzer (USA made). The CRS specimen of 1 cm2 exposed areas with a 5 cm2 long stem isolated with araldite resin was used as working electrode; platinum electrode and calomel electrode were used as counter and reference electrodes, respectively. Prior to polarization and electrochemical impedance spectroscopic measurements (EIS), a steady state open circuit potential (OCP) was measured. Each experiment was carried out in triplicate and the average values of corrosion parameters were reported. EIS measurements were done at OCP in the frequency range from 100 kHz to 0.01 Hz, with an amplitude of 5 mV. The inhibition efficiency of EIS measurements was calculated using charge (...truncated)