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Inhibition of carbon steel corrosion
by 4-vinylbenzyl triphenyl phosphonium
chloride in HCl solution
Ayssar Nahle´, Ideisa...
very well on the metal surface and form a protective layer,
which in turn increases the effectiveness of corrosion inhibit...
workstation presented the resulting data as a plot of logarithm
of the absolute value of the current (LogjIj, mA) against ...
used for weight loss measurements. A 2 mm diameter hole
was drilled close to the upper edge of the specimen and served
to ...
from 1 £ 102 7
to 1 £ 102 4
M are shown in Figure 7. From
this figure, the slope (2(Ea/R)) of each line was determined
and ...
energy (kcal mol21
); R – gas constant (kcal mol2 1
) and T –
absolute temperature (K).
According to equation (6), the str...
large surface area of the metal. The interaction occurs
between the p-electrons of the four rings, the vinyl group
(ZCvCZ)...
Conclusions
4-vinylbenzyl triphenyl phosphonium chloride was found to
be a highly efficient inhibitor for carbon steel in 1...
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  1. 1. Inhibition of carbon steel corrosion by 4-vinylbenzyl triphenyl phosphonium chloride in HCl solution Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Department of Chemistry, College of Arts and Sciences, University of Sharjah, Sharjah, United Arab Emirates Abstract Purpose – The purpose of this paper is to study electrochemically and by weight loss experiments the effect of 4-vinylbenzyl triphenyl phosphonium chloride on the corrosion inhibition of mild steel in 1.0 M HCl solution, which will serve researchers in the field of corrosion. Design/methodology/approach – Electrochemical and weight loss measurements were carried out on carbon steel specimens in 1.0 M HCl and in 1.0 M HCl containing various concentrations (1.0 £ 102 7 to 1.0 £ 102 4 M) of the laboratory synthesized 4-vinylbenzyl triphenyl phosphonium chloride at temperatures ranging from 303 to 343 K. Findings – 4-vinylbenzyl triphenyl phosphonium chloride was found to be a highly efficient inhibitor for carbon steel in 1.0 M HCl solution, reaching about 99 per cent at the concentration of 1 £ 102 4 M at room temperature and about 96 per cent at 303 K, a concentration and temperature considered to be very moderate. The percentage of inhibition in the presence of this inhibitor was decreased with temperature which indicates that physical adsorption was the predominant inhibition mechanism because the quantity of adsorbed inhibitor decreases with increasing temperature. Practical implications – This inhibitor could have application in industries, where hydrochloric acid solutions at elevated temperatures are used to remove scale and salts from steel surfaces, such as acid cleaning of tankage and pipeline, and may render dismantling unnecessary. Originality/value – This paper is intended to be added to the family of phosphonium salt corrosion inhibitors which are highly efficient and can be employed in the area of corrosion prevention and control. Keywords Corrosion inhibitors, Steel, Electrochemistry Paper type Research paper Introduction Most organic inhibitors consist of compounds containing polar groups by which the molecule can become strongly or specifically adsorbed on the metal surface (Damaskin et al., 1968; Okamato et al., 1962). These inhibitors, which include N, P, S, and/or O atoms, are known to be similar to catalytic poisons as they decrease the reaction rate at the metal/solution interface without, in general, being involved in the reaction considered. It is generally accepted that most organic inhibitors act via adsorption at the metal/solution interface. The mechanism by which an inhibitor decreases the corrosion current is achieved by interfering with some of the steps for the electrochemical process. The corrosion inhibition of carbon steel in aggressive acidic solutions has been widely investigated. In industry, hydrochloric acid solutions are often used in order to remove scale and salts from steel surfaces, and for cleaning tanks and pipelines. This treatment may be prerequisite for coating by electroplating, galvanizing or painting techniques. The acid must be treated to prevent an excessive dissolution of the underlying metal. This treatment involves the addition of organic inhibitors to the acid solution that are adsorbed at the metal/solution interface by displacing water molecules on the surface and forming a compact barrier film. The presence of non-bonded (lone pair) and p-electrons in the alkenes, alkynes and aromatic rings would be expected to be involved in chemisorption and/or physisorption onto the metal surface. The corrosion inhibition of many organic cations in acidic media has been studied thoroughly by numerous authors (Mutombo and Hackerman, 1998). However, the manner of inhibition has not been obvious to all authors. Some attributed inhibition to chemisorption through an electron pair on the heteroatom (N, P, S). Others have assumed an electrostatic interaction between the cations and the negatively charged surface of the metal. Phosphonium salts have been found to inhibit iron corrosion in acidic media according to the following mechanism: ðRþ 3 PR0 Þ þ Hþ þ 2e2 ! R3P þ R0 H ð1Þ where R, R0 – alkyl or aryl. If R is phenyl, the triphenyl phosphine (PPh3) has been assumed to adsorb on the metal surface via its lone pair of electrons on the phosphorus atom or/ and through the p-electrons on the phenyl rings, consequently inhibiting corrosion. For example, the cation [(ph)4Pþ ] is adsorbed on the sites of the metal surface where the chloride anion is chemisorbed: FeCl2 þ ðPhÞ4Pþ ! ðFeCl2 2þ PðPhÞ4Þads: ð2Þ The corrosion inhibition of triphenyl phosphonium salts on various metals (Ni, Zn and Fe) and alloys in acidic media was studied by Niass et al. (2001), Said et al. (2005, 2007), Troquet and Pagetti (2004), Bhrara and Singh (2007) and Khamis et al. (2000). In all these studies, the phosphorus atom and the phenyl rings in the compounds were shown to be able to adsorb The current issue and full text archive of this journal is available at www.emeraldinsight.com/0003-5599.htm Anti-Corrosion Methods and Materials 55/4 (2008) 217–224 q Emerald Group Publishing Limited [ISSN 0003-5599] [DOI 10.1108/00035590810887727] 217
  2. 2. very well on the metal surface and form a protective layer, which in turn increases the effectiveness of corrosion inhibition with the increase in the concentration of the inhibitor, reaching in some cases 98 and 99 per cent inhibition (Nahle´ and Walsh, 1995; Bhrara and Singh, 2007), respectively. No studies have been reported on the VTPC inhibitor used in our present work, both in terms of studying the electrochemical effects and the temperature effects on the effectiveness of inhibition of carbon steel corrosion in 1 M HCl solution. Carbon steel was chosen in the present studies because high-temperature aggressive acids are widely used in industry in combination with carbon and low-alloy steels. In this work, the VTPC was prepared via a synthesis that produced a high-percentage yield of this pure compound. The aim of the work was to study, using potentiodynamic and weight loss measurements, the effect of temperature on the corrosion inhibition of carbon steel in 1 M HCl solution by VTPC and to calculate the associated thermodynamic parameters. It was anticipated that the study should provide a building block or perhaps the nucleus of a new family or group of phosphonium derivatives for corrosion inhibitors. Experimental details Synthesis of 4-vinybenzyl triphenyl phosphonium chloride About 2.0 ml of 4-chloromethylstyrene (0.02 M) and 5.26 g of triphenylphosphine (0.02 M) were dissolved in 50 ml of toluene in 100 ml round-bottomed flask equipped with a Teflon coated magnetic stirring bar and a reflux condenser. The reaction mixture was refluxed for 2 h. The mixture then was cooled to room temperature and the product was filtered, washed with toluene and dried under vacuum. Yield 80 per cent, M.P., 2858C (Kanazawa et al., 1993). + 4-Chloromethyl styrene Triphenyl phosphine 4-Vinylbenzyl triphenyl phosphonium chloride Cl P+ Cl–P Electrochemistry Electrode preparation A 5-mm diameter piece cut from a carbon steel rod (IS 226 containing 0.18 per cent C, 0.6 per cent Mn, and 0.35 per cent Si) supplied by “Reliable Steel Traders”, Sharjah, UAE, formed the working electrode (WE) and was mounted, using Araldite epoxy resin, in a glass tube that fitted in the electrochemical cell. Prior to each experiment, the working carbon steel electrode was abraded using a series of carborundum papers starting with 600 grades and ending with 1,200 grade. The electrode surface then was polished with 0.3-mm alumina on cloth, washed with deionized distilled water and rinsed with pure ethanol before being transferred to the electrochemical cell that contained deaerated fresh electrolyte. Instrumentation In this work, an electrochemical cell made at Southampton University, England was used, as in previous studies (Nahle´, 1997, 1998, 2002, 2005; Nahle´ and Walsh, 1995; Nahle´ et al., 2007), as shown in Figure 1. This electrochemical cell consisted of carbon steel WE, a saturated calomel reference electrode (RE), and platinum gauze counter electrode (CE). Prior to each experiment, the electrolyte was deaerated by nitrogen bubbling. The cell was designed in such a way that the nitrogen was allowed to escape into the solution, precluding its collection at the electrode surface. In order to protect the WE from any substance that might be produced at the CE during the electrochemical reactions, the CE compartment was separated from the WE compartment by a glass frit. The following electrochemical equipment and chemicals were used. A PC controlled Sycopel AEW2-1000 electrochemical workstation (supplied from Sycopel Scientific Limited, England) capable of driving currents up to ^1 A with an output potential across the cell of up to ^10 V. Analytical-grade hydrochloric acid (Ajax), 4-chloromethyl styrene, triphenylphosphine and toluene, were obtained from Aldrich Chemical Company and used without further purification. Measuring procedure Electrochemical corrosion measurements (Tafel plots) were carried out on the carbon steel electrode, prepared as described previously, in 1.0 M HCl and in 1.0 M HCl containing various concentrations of VTPC. The concentration of VTPC inhibitor ranged from 1.0 £ 102 7 to 1.0 £ 102 4 M. Owing to the restricted solubility of VTPC in 1.0 M HCl, higher concentrations of inhibitor could not be prepared. The cell was filled with 60 ml of the electrolyte. The solution was deaerated with nitrogen gas and the WE equilibrium potential was monitored and recorded vs SCE until it reached a steady state. The electrode potential was scanned from 2700 to 2300 mV vs SCE at a sweep rate of 1 mV s2 1 . The computer driving the electrochemical Figure 1 The electrochemical cell 1 2 5 8 7 Notes: (1) Gas bubbler; (2) B 12 glass socket; (3) Platinum gauze (CE); (4) glass frit; (5) inlet for nitrogen gas; (6) Luggin capillary (RE); (7) iron rod (WE); (8) epoxy resin; (9) B 24 glass socket; and (10) copper wire 10 6 4 3 9 Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 218
  3. 3. workstation presented the resulting data as a plot of logarithm of the absolute value of the current (LogjIj, mA) against the electrode potential (E, mV) vs SCE. Each experiment was repeated at least three times with a newly-polished electrode and fresh electrolyte, while extreme experimental precautions were taken in order to ensure the reproducibility of the results. Once reproducible plots were obtained, the corrosion currents were then extrapolated from the Log jIj (logarithm of absolute current, mA) vs electrode potential plots (Tafel). Results Figure 2 shows the anodic and cathodic polarization curves (Tafel plot) of the carbon steel electrode in deaerated 1.0 M HCl solution with and without the addition of various concentrations of VTPC. The presence of VTPC inhibitor affects both the anodic and cathodic branches of the curve as can be clearly seen; this indicated that the VTPC acted as a mixed inhibitor. The corrosion current of the carbon steel electrode in each solution was determined by locating the intersections of extrapolated tangents of the anodic and cathodic curves at the corrosion potential (Erest) using the Tafel plot. As a result, the corrosion current was found to decrease with the increase of the concentration of VTPC inhibitor as shown in Table I. In the absence of inhibitor (in 1.0 M HCl), the corrosion current was found to be 0.76 mA., which in turn dropped down to 0.0084 mA when the concentration of VTPC in 1.0 M HCl reached 1.0 £ 1024 M (Table I). The percentage inhibition values of VTPC at various concentrations in 1.0 M HCl were calculated according to the following equation (3) and the results are shown in Table I: Percentage inhibition ¼ ðICorr:ÞUninh: 2 ðICorr:ÞInh: ðICorr:ÞUninh: £ 100 ð3Þ where (ICorr.)Uninh – corrosion current in the uninhibited solution; and (ICorr.)inh. – corrosion current in inhibited solution. Figure 3 shows the plot of the percentage inhibition versus the concentration of VTPC. Figure 3 shows that the percentage inhibition increased steeply from 7.89 per cent (with 1 £ 102 7 M inhibitor) to 95.79 per cent with 1 £ 102 5 M inhibitor. Subsequently, the percentage inhibition increased slightly more to reach 98.89 per cent in the solution containing a concentration of 1 £ 102 4 M inhibitor. Discussion The high-percentage inhibition could be attributed to the best orientation of the three phenyl rings and the benzyl group in the VTPC, which seemed to be as close as possible to the electrode surface. This possible explanation could justify the increase in the inhibition at the 1.0 £ 102 4 M inhibitor concentration. When the electrode was pulled out from the 1.0 M HCl containing 1.0 £ 102 4 M of VTPC inhibitor (at the end of the experiment), the carbon steel surface was extremely clean (as it was initially polished before the immersion) and showed the absence of any oxide layer such as the one encountered in the experiments where lower inhibitor concentrations in 1.0 M HCl were used. The inhibition efficiency of organic compounds depended upon molecular size, molecular structure and the mode of interaction with the metal surface. VTPC is a potential corrosion inhibitor because it contains not only phosphorus but also four phenyl rings and a vinyl group (ZCvCZ). The high-inhibition efficiency may be attributed to the interaction occurs between the p-electrons of the four rings, the vinyl group (ZCvCZ), and the lone pair of electrons on P atom with the positively charged metal surface. In addition, the (ZCvCZ) bond plays a major role in the stabilization of both sides of the VTPC structure. Effect of temperature Specimen preparation Rectangular specimens (1 £ 2.3 £ 0.3 cm) cut from large sheet of 3 mm thick carbon steel (IS 226 containing 0.18 per cent C, 0.6 per cent Mn, and 0.35 per cent Si) supplied by “Reliable Steel Traders”, Sharjah, UAE, were Figure 2 Anodic and cathodic polarization curves of mild steel in an uninhibited 1.0 M HCl solution and in 1.0 M HCl containing various concentrations of 4-vinylbenzyl triphenyl phosphonium chloride −4 −3 −2 −1 0 1 2 −0.70 −0.60 −0.50 −0.40 −0.30 Potential, E / V vs SCE LogI,mA 1 23 4 5 Notes: (1) 1.0 M HCl; (2) 1.0 M HCl + 1.0×10–7 M inhibitor; (3) 1.0 M HCl + 1.0×10–6 M inhibitor; (4) 1.0 M HCl + 1.0×10–5 M inhibitor; and (5) 1.0 M HCl + 1.0×10–4 M inhibitor Table I Tafel corrosion currents and percentage inhibitions of 4-vinylbenzyl triphenyl phosphonium chloride at various concentrations in 1.0 M HCl at room temperature 1.0 M HCl 1.0 M HCl11.031027 M 4-vinylbenzyl triphenyl phosphonium chloride 1.0 M HCl11.03102 6 M 4-vinylbenzyl triphenyl phosphonium chloride 1.0 M HCl11.031025 M 4-vinylbenzyl triphenyl phosphonium chloride 1.0 M HCl 11.0 3 102 4 M 4-vinylbenzyl triphenyl phosphonium chloride Icorrosion/mA 0.76 0.70 0.34 0.037 0.0084 Percentage inhibition – 7.89 55.26 95.79 98.89 Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 219
  4. 4. used for weight loss measurements. A 2 mm diameter hole was drilled close to the upper edge of the specimen and served to be hooked with a glass rod for immersion purposes. Prior to each experiment, the specimens were polished with 600 grade emery paper, rinsed with distilled water, degreased with acetone, dried, and weighed precisely on an accurate analytical balance. Instrumentation The experimental set-up consisted of a 250 ml round bottomed flask fitted with a reflux condenser and a long glass rod on which the specimen was hooked and in turn immersed in a thermally-controlled water bath (Nahle´, 2001; Nahle´ et al., 2005). Analytical-grade hydrochloric acid (Ajax) and VTPC were used as prepared without farther purification. Measuring procedure The flask was filled with 100 ml of 1 M HCl solution either with or without VTPC of various concentrations, then placed in water bath. As soon as the required working temperature was reached, the precisely weighed carbon steel specimen was immersed in the solution, and left there for exactly 6 h, after which period the sample was removed, rinsed with distilled deionized water, degreased with acetone, dried, and finally weighed precisely on an accurate analytical balance. This procedure was repeated with all the samples with a variety of VTPC inhibitor concentrations ranging from 1 £ 102 7 up to 1 £ 102 4 M and at temperatures ranging from 303 to 343 K. Results Weight loss corrosion tests were carried out on the carbon steel in 1 M HCl in the absence or presence of VTPC over a period of 6 h. Table II presents the corrosion rates (mg cm2 2 h2 1 ), and the percentage efficiencies for the studied inhibitor with concentrations varying from 1 £ 1027 to 1 £ 102 4 M at 303, 313, 323, 333 and 343 K, respectively. The percentage inhibition was calculated according to the following equation: Percentage inhibition ¼ WUninh: 2 WInh: WUninh: £ 100 ð4Þ where, WUninh – corrosion rate without inhibitor; and Winh – corrosion rate with inhibitor. Figures 4 and 5 show the plots of the corrosion rate of the carbon steel in 1 M HCl as a function of concentration of VTPC inhibitor at 303, 313, 323, 333 and 343 K. At 303 K (Figure 4), the corrosion rate dropped from 0.961 mg cm2 2 h2 1 (1 M HCl in the absence of VTPC inhibitor) to 0.363 mg cm2 2 h2 1 (62.2 per cent inhibition) when 1 £ 102 7 M of VTPC was present in the 1 M HCl solution. This corrosion rate continued to decrease slightly to reach 0.081 mg cm2 2 h2 1 (91.6 per cent inhibition) at a concentration of 1 £ 102 5 M, followed by a plateau reaching 0.04 mg cm2 2 h2 1 (95.8 per cent inhibition) when the inhibitor concentration was 1 £ 102 4 M. At 313 K (Figure 4), the curve exhibited a similar shape to that obtained at 303 K. At concentrations of VTPC greater than 1 £ 102 5 M, the corrosion rate decreased from 1.394 mg cm2 2 h2 1 (1 M HCl in the absence of VTPC inhibitor) to reach about 0.133 mg cm2 2 h2 1 (90.5 per cent) at 1 £ 102 4 M. At 323 K (Figure 4), the corrosion rate decreased sharply from 2.894 mg cm2 2 h2 1 (38.0 per cent inhibition) with 1 £ 102 7 M down to 1.01 mg cm2 2 h21 (78.4 per cent inhibition) with 1 £ 1025 M. Subsequently, the corrosion rate decreased smoothly to 0.738 mg cm2 2 h21 (84.2 per cent inhibition). At 333 K (Figure 5), the corrosion rate decreased smoothly from 9.0 mg cm2 2 h2 1 (26.4 per cent inhibition) with 1 £ 102 7 M down to 3.612 mg cm22 h21 (70.5 per cent inhibition) with 1 £ 102 5 M until a corrosion rate of 2.454 mg cm2 2 h2 1 (80.0 per cent inhibition) with 1 £ 102 4 M inhibitor. On the other hand, a temperature of 343 K caused a very steep decrease in the corrosion rate between 1 £ 102 7 and 1 £ 102 5 M inhibitor, corresponding to 23.915 mg cm2 2 h2 1 (9.0 per cent inhibition) and 10.348 mg cm22 h2 1 (60 per cent inhibition), respectively, reaching 8.611 mg cm2 2 h2 1 (67.2 per cent inhibition) when the concentration of VTPC inhibitor was 1 £ 102 4 M. Figures 4 and 5 show that as the temperature increased, the effect of the concentration of the VTPC inhibitor on the decrease of the corrosion rate was more significant. Figure 6 shows the plots of the percent inhibition versus the concentration of the VTPC inhibitor at temperatures of 303, 313, 323, 333 and 343 K, respectively. This figure shows that the percent inhibition was affected by the increase of temperature from 303 to 343 K, at all inhibitor concentrations (1 £ 102 7 to 1 £ 102 4 M). The data obtained from the weight loss measurements (Table III) were plotted in accordance with the Arrhenius equation: ln rate ¼ 2 Ea RT þ const: ð5Þ where, Ea – activation energy (kcal mol2 1 ); R – gas constant (kcal mol2 1 ); T – absolute temperature (K), and const. – constant. The Arrhenius plots of the corrosion rate of carbon steel in 1 M HCl solution (ln corrosion rate as a function of 1/T) with or without the presence of VTPC at concentrations ranging Figure 3 Percentage inhibition of different concentrations of 4-vinylbenzyl triphenyl phosphonium chloride on mild steel surface in 1.0 M HCl solution 0 10 20 30 40 50 60 70 80 90 100 1.0E-07 1.0E-06 1.0E-05 1.0E-04 10E-03 Inhibitor Concentration, M %Inhibition Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 220
  5. 5. from 1 £ 102 7 to 1 £ 102 4 M are shown in Figure 7. From this figure, the slope (2(Ea/R)) of each line was determined and used to calculate the activation energy according to equation (5), with R ¼ 1.987 £ 102 3 kcal mol2 1 (Table IV). The increase in concentration of VTPC (from 1 £ 102 7 to 1 £ 102 4 M), increased the activation energies for the corrosion of carbon steel in 1 M HCl (initially 18.27 kcal mol21 ) (Table IV). Table V shows the surface coverage of various concentrations of VTPC (from 1 £ 102 7 to 1 £ 1024 M) on carbon steel surfaces as a function of temperature. These values were extracted from the corresponding percent efficiency values reported earlier in Table II. The plot of surface coverage, u, against the natural logarithm of the concentration of VTPC, ln C, for carbon steel at various inhibitor temperatures is shown in Figure 8. After examining these data and adjusting them to different theoretical adsorption isotherms, it was concluded that the inhibitor was adsorbed on the carbon steel surface according to Temkin isotherm: 22a u ¼ ln KC ð6Þ where, a – molecular interaction constant; u – degree of coverage; K – equilibrium constant for the adsorption reaction; and C – concentration of the inhibitor. The equilibrium constant for the adsorption reaction, K, is related to the standard free energy of adsorption via equation (7) (Damaskin et al., 1968): K ¼ 1 55:5 exp 2 DG RT ð7Þ where, K – equilibrium constant for the adsorption reaction; 55.5 – concentration of water (mol L21 ); DG – standard free Figure 4 Effect of concentration of 4-vinylbenzyl triphenyl phosphonium chloride on the corrosion rate (mg cm2 2 h2 1 ) of mild steel in 1 M HCl at various temperatures 0 0.5 1 1.5 2 2.5 3 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 Concentration, M Notes: 303 K; 313 K; 323 K CorrosionRate,mg.cm−2 .h−1 Figure 5 Effect of concentration of 4-vinylbenzyl triphenyl phosphonium chloride on the corrosion rate (mg cm2 2 h2 1 ) of mild steel in 1 M HCl at various temperatures 0 5 10 15 20 25 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 Concentration, M CorrosionRate,mg.cm−2 .h−1 Notes: 333 K; 343 K Table II Effect of concentration of 4-vinylbenzyl triphenyl phosphonium chloride on the corrosion rate (mg cm2 2 h2 1 ) and percentage efficiency of mild steel in 1 M HCl at various temperatures Temperature/K 303 313 323 333 343 Concentration of inhibitor Corr. rate Efficieny of percentage Corr. rate Efficieny of percentage Corr. rate Efficieny of percentage Corr. rate Efficieny of percentage Corr. rate Efficieny of percentage 1 M HCl 0.961 – 1.394 – 4.671 – 12.225 – 26.280 – 1 M HCl 1 1 3 1027 M 0.363 62.2 0.694 50.2 2.894 38 9 26.4 23.915 9 1 M HCl 1 1 3 1026 M 0.157 83.7 0.413 70.4 2.027 56.6 6.929 43.3 19.646 25.2 1 M HCl 1 1 3 1025 M 0.081 91.6 0.206 85.2 1.01 78.4 3.612 70.5 10.348 60 1 M HCl 1 1 3 1024 M 0.04 95.8 0.133 90.5 0.738 84.2 2.451 80 8.611 67.2 Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 221
  6. 6. energy (kcal mol21 ); R – gas constant (kcal mol2 1 ) and T – absolute temperature (K). According to equation (6), the straight lines shown in Figure 8 will have the following slopes and intercepts: Slope ¼ 2 1 2a ð8Þ Intercept ¼ 2 1 2a ln K ð9Þ Combining equations (8) and (9) leads to the following relationship: Intercept ¼ Slope ðln KÞ ð10Þ Using equation (10), the equilibrium constant for the adsorption reaction, K, was calculated: K ¼ eðIntercept=SlopeÞ ð11Þ The free energy of adsorption of the inhibitor, DG, was calculated from the results in Figure 8, which was used to calculate the equilibrium constant, K, and equation (7) at various temperatures (303-343 K) as shown in Table VI. The enthalpy of adsorption, DH, for the inhibitor was calculated from the following equation and shown in Table VII: DH ¼ Ea 2 RT ð12Þ The entropy, DS, was calculated at various temperatures for the inhibitor using the following equation and shown in Table VIII: DG ¼ DH 2 TDS ð13Þ Discussion The results presented in Table IV show that, the activation energy (Ea) for the corrosion of carbon steel in the presence of the inhibitor VTPC at all concentrations (1 £ 102 7 M to 1 £ 102 4 M) are higher compared to the activation energy in the absence of inhibitor (between 22.77 and 28.50 vs about 18.27 kcal mol2 1 ). This can be attributed to the fact that higher values of Ea in the presence of VTPC inhibitor compared to its absence generally were consistent with a physisorption mechanism, while unchanged or lower values of Ea in inhibited solution suggest charge sharing or transfer from the organic inhibitor to the metal surface to form coordinate covalent bonds (chemisorption). The increase in the activation energies for the corrosion was attributable to a decrease in the adsorption of the inhibitor on the metal surface as the temperature increased. Subsequently, an increase in the corrosion rate will result due to the greater exposed area of the metal surface to the acid. Tables VI-VIII show the thermodynamic data obtained in the presence of the inhibitor at various temperatures. These thermodynamic quantities represent the algebraic sum of the values for adsorption and desorption. The negative value of DG indicates the spontaneous adsorption of inhibitor on the surface of the carbon steel. The free energy, DG, varied from 220.60 kcal mol2 1 at 303 K to 214.37 kcal mol21 at 343 K. The adsorption process is believed to be exothermic and associated with a decrease in entropy (DS) of solute, whereas the opposite is true for the solvent (Sanad et al., 1995). The gain in entropy which accompanies the substitutional adsorption process is attributable to the increase in the solvent entropy (Table VIII). This agrees with the general suggestion that the values of DG increase with the increase of inhibition efficiency (Ateya et al., 1984; Talati et al., 2005) as the adsorption of organic compound is accompanied by desorption of water molecules off the surface. The high-inhibition efficiency may be attributed to the large surface area of this compound that consequently covered a Figure 6 Effect of concentration of 4-vinylbenzyl triphenyl phosphonium chloride on the percent inhibition of mild steel in 1 M HCl at various temperatures 0 10 20 30 40 50 60 70 80 90 100 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 Inhibitor Concentration, M %Inhibition Notes: 303 K; 313 K; 323 K; 333 K; 343 K Table III The data obtained from the weight loss measurements for Arrhenius equation: (I/T ) against Ln corrosion rate Ln corrosion rate (mg cm2 2 h21 ) (1/T ) 3 103 K21 1 M HCl 1 M HCl 11 3 1027 M 1 M HCl 11 3 102 6 M 1 M HCl 11 3 1025 M 1 M HCl 11 3 1024 M 3.30 20.03978 21.01335 21.85151 22.51331 23.21888 3.19 0.332177 20.36528 20.88431 21.57988 22.01741 3.10 1.541373 1.06264 0.706557 0.00995 20.30381 3.00 2.503483 2.197225 1.935716 1.284262 0.896496 2.92 3.268808 3.174506 2.977874 2.336793 2.15304 Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 222
  7. 7. large surface area of the metal. The interaction occurs between the p-electrons of the four rings, the vinyl group (ZCvCZ), and the lone pair of electrons on P atom with the positively charged metal surface. In addition, the (ZCvCZ) bond plays a major role in the stabilization of both sides of the phosphonium structure. These results agree with findings reported by Fouda et al. (1986), who suggested that the inhibition efficiency of organic compounds depends on many factors including their charge density, number of adsorption sites, heat of hydrogenation, mode of interaction with the metal surface, and formation of metallic complexes (Fouda et al., 2005). Table VI The free energy of adsorption (DGads) for mild steel in 1 M HCl in the presence of 4-vinylbenzyl triphenyl phosphonium chloride inhibitor at various temperatures (303-343 K) DG, kcal mol2 1 303 K 313 K 323 K 333 K 343 K 220.60 218.14 216.60 215.46 214.37 Table VII The enthalpy of adsorption (DH) for mild steel in 1 M HCl in the presence of 1 £ 1024 M 4-vinylbenzyl triphenyl phosphonium chloride inhibitor at various temperatures (303-343 K) DH, kcal mol21 303 K 313 K 323 K 333 K 343 K 27.90 27.88 27.86 27.84 27.82 Table VIII The change in entropy (DS) for mild steel in 1 M HCl in the presence of 4-vinylbenzyl triphenyl phosphonium chloride inhibitor at various temperatures (303-343 K) DS, kcal K21 mol21 303 K 313 K 323 K 333 K 343 K 0.160 0.147 0.138 0.130 0.123 Table V Effect of concentration of 4-vinylbenzyl triphenyl phosphonium chloride on surface coverage for mild steel in 1 M HCl at various temperatures Temperature/K 313 323 333 Concentration of inhibitor 303 Surface coverage u 343 1 M HCl 11 3 1027 M 0.622 0.502 0.380 0.264 0.090 1 M HCl 11 3 1026 M 0.837 0.704 0.566 0.433 0.252 1 M HCl 11 3 1025 M 0.916 0.852 0.784 0.705 0.600 1 M HCl 11 3 1024 M 0.958 0.905 0.842 0.800 0.672 Table IV The activation energy (Ea) for the corrosion of mild steel in 1 M HCl with and without 4-vinylbenzyl triphenyl phosphonium chloride inhibitor at various concentrations Activation energy, Ea (kcal mol2 1 ) System 1 3 1024 M 1 3 102 5 M 1 3 102 6 M 1 3 1027 M 1 M HCl 18.27 18.27 18.27 18.27 1 M HCl 1 4-vinylbenzyl triphenyl phosphonium chloride 28.50 26.20 26.03 22.77 Figure 7 Effect of temperature on the corrosion rate of mild steel in 1 M HCl solution with and without the presence of various concentrations of 4-vinylbenzyl triphenyl phosphonium chloride −4 −3 −2 −1 0 1 2 3 4 2.8 3 3.2 3.4 1/T × 103 , K−1 LnCorrosionRate,mg.cm−2 .h−1 Notes: 1 M HCl; 1×10–7 M; 1×10–6 M; 1×10–5 M; 1×10–4 M Figure 8 Effect of concentration of 4-vinylbenzyl triphenyl phosphonium chloride on the surface coverage of mild steel in 1 M HCl at various temperatures 0 0.2 0.4 0.6 0.8 1 −18 −14 −10 −6 Ln Concentration, M SurfaceCoverage Notes: 303 K; 313 K; 323 K; 333 K; 343 K Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 223
  8. 8. Conclusions 4-vinylbenzyl triphenyl phosphonium chloride was found to be a highly efficient inhibitor for carbon steel in 1.0 M HCl solution, reaching about 98.89 per cent at 1.0 £ 102 4 M and room temperature, a concentration considered to be very moderate. Even an inhibitor concentration tenfold lower, 1.0 £ 102 5 M provided a very high and acceptable inhibition of 95.79 per cent at room temperature. 4-vinylbenzyl triphenyl phosphonium chloride is a potential corrosion inhibitor since it contains not only a phosphorus atom, but also the four phenyl rings together with a vinyl group (ZCvCZ). It was apparent from the molecular structure that this compound would be adsorbed onto the metal surface through the lone pair of electrons of phosphorus and p-electrons of the four aromatic rings and the double bond that attached to one of these rings. The percentage inhibition in the presence of this inhibitor decreased with temperature, which indicated that physical adsorption was the predominant inhibition mechanism because the quantity of adsorbed inhibitor decreased with increasing temperature. References Ateya, B.C., El-Anadouli, B.E. and El-Nizamy, F.M. (1984a), “The adsorption of thiourea on mild steel”, Corrosion Science, Vol. 24 No. 6, pp. 509-15. Ateya, B.C., El-Anadouli, B.E. and El-Nizamy, F.M. (1984b), “The effect of thiourea on the corrosion kinetics of mild steel in H2SO4”, Corrosion Science, Vol. 24 No. 6, pp. 497-507. Bhrara, K. and Singh, G. (2007), “Effect of allyl triphenyl phosphonium bromide on electrochemical and corrosion behaviour of mild steel in 0.5 M sulfuric acid”, Corrosion Engineering, Science and Technology, Vol. 42 No. 2, pp. 137-44. Damaskin, B.B., Pietrij, O.A. and Batrokov, W.W. (1968), “Adsorpcja organiczeskich sojedinienij na electrodach”, Moskva. Fouda, A.S., Abd El-Aal, A. and Kandil, A.B. (2005), “The effect of some phthalimide derivatives on the corrosion behaviour of copper in nitric acid”, Anti-Corrosion Methods and Materials, Vol. 52 No. 2, pp. 96-101. Fouda, A.S., Mousa, M.N., Taha, F.I. and Elneamaa, A.I. (1986), “The role of some thiosemicarbazide derivatives in the corrosion inhibition of aluminum in HCl”, Corrosion Science, Vol. 26 No. 9, pp. 719-26. Kanazawa, A., Ikeda, T. and Endo, T. (1993), “Novel polycationic biocides: synthesis and antibacterial activity of polymeric phosphonium salts”, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 31, pp. 335-43. Khamis, E., El-Ashry, E.S.H. and Ibrahim, A.K. (2000), “Synergistic action of vinyl triphenyl phosphonium bromide with various anions on corrosion of steel”, British Corrosion Journal, Vol. 35 No. 2, pp. 150-4. Mutombo, P. and Hackerman, N. (1998), “The effect of some organophosphorus compounds on the corrosion behaviour of iron in 6 M HCl”, Anti-Corrosion Methods and Materials, Vol. 45 No. 6, pp. 413-8. Nahle´, A. (1997), “Electrochemical studies of corrosion inhibition of a series of quaternary ammonium salts for iron in HCl solution”, Corrosion Prevention Control, Vol. 44 No. 7, pp. 99-105. Nahle´, A. (1998), “Inhibition of iron in HCl using benzyl trimethyl and triethyl ammonium chloride”, Corrosion Prevention Control, Vol. 45 No. 4, pp. 124-30. Nahle´, A. (2001), “Effect of temperature on the corrosion inhibition of carbon steel in HCl solutions”, Bulletin of Electrochemistry, Vol. 17 No. 5, pp. 221-6. Nahle´, A. (2002), “Effect of triethanolamine on the electrochemical dissolution of solder in NaOH solution”, Bulletin of Electrochemistry, Vol. 18 No. 3, pp. 105-10. Nahle´, A. (2005), “Inhibition of corrosion of iron in HCl solution by semicarbazides and thiosemicarbazides”, Bulletin of Electrochemistry, Vol. 21 No. 6, pp. 275-81. Nahle´, A. and Walsh, F.C. (1995), “Electrochemical studies of two corrosion inhibitors for iron in HCl: cytyltrimethyl ammonium bromide and tetraphenylphosphonium chloride”, Corrosion Prevention Control, Vol. 42 No. 2, pp. 30-4. Nahle´, A., Abdel-Rahman, I. and Alfarouk, M. (2005), “Effect of temperature on the inhibition of corrosion of carbon steels by semicarbazides and thiosemicarbazides”, Bulletin of Electrochemistry, Vol. 21 No. 8, pp. 353-61. Nahle´, A., Abu-Abdoun, I. and Abdel-Rahman, I. (2007), “Electrochemical studies of the effect of trans-4-hydroxy- 4’-stilbazole on corrosion inhibition of mild steel in HCl solution”, Anti-Corrosion Methods and Materials, Vol. 54 No. 4, pp. 244-8. Niass, S.O., Ebn Touhami, M., Hajjaji, N., Srhiri, A. and Takenouti, H. (2001), “The inhibition effect of quaternary phosphine on Ni-P alloys in 1 M H2SO4”, Journal of Applied Electrochemistry, Vol. 31 No. 1, pp. 85-92. Okamato, G., Nagayama, M., Kato, J. and Baba, T. (1962), “Effect of organic inhibitors on the polarization characteristics of mild steel in HCl solution”, Corrosion Science, Vol. 2 No. 1, pp. 21-7. Said, F., Souissi, N., Dermaj, A., Hajjaji, N., Triki, E. and Srhiri, A. (2005), “Effect of (Rþ, X2) salts addition on nickel corrosion in 1 M sulfuric medium”, Materials Corrosion, Vol. 56 No. 9, pp. 619-25. Said, F., Souissi, N., Es-Salah, K., Hajjaji, N., Triki, E. and Srhiri, A. (2007), “Phosphonium iodine as nickel corrosion inhibitor in 1 M sulfuric acid medium”, Journal of Material Science, Vol. 42 No. 21, pp. 9070-4. Sanad, S.H., Ismail, A.A. and El-Meligi, A.A. (1995), “The effect of temperature on the corrosion and corrosion inhibition of steel alloys in hydrochloric acid solutions”, Bulletin of Electrochemistry, Vol. 11 No. 10, pp. 462-9. Talati, J.D., Desai, M.N. and Shah, N.K. (2005), “Meta- substituted aniline-N-salicylidenes as corrosion inhibitors for zinc in sulfuric acid”, Materials Chemistry Physics, Vol. 93 No. 1, pp. 54-64. Troquet, M. and Pagetti, J. (2004), “Contribution of the electrochemical impedance measurement technique to zinc corrosion inhibition studies in acid media”, Materials and Corrosion, Vol. 40 No. 11, pp. 633-41. Corresponding author Ayssar Nahle´ can be contacted at: anahle@sharjah.ac.ae Inhibition of carbon steel corrosion Ayssar Nahle´, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman Anti-Corrosion Methods and Materials Volume 55 · Number 4 · 2008 · 217–224 224 To purchase reprints of this article please e-mail: reprints@emeraldinsight.com Or visit our web site for further details: www.emeraldinsight.com/reprints

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