EVALUATION OF NEW CATIONIC SURFACTANT AS CORROSION INHIBITOR FOR CARBON STEEL IN A METAL WORKING FLUID

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1 112 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI EVALUATION OF NEW CATIONIC SURFACTANT AS CORROSION INHIBITOR FOR CARBON STEEL IN A METAL WORKING FLUID N. TANTAWY Department of Chemistry, University College for Girls, Ain Shams University, Cairo, Egypt ABSTRACT Metal working straight oil contain large quantities of additive such as corrosion inhibitors, in this paper we study the following additive as corrosion inhibitor before will be use. The corrosion inhibition of carbon steel by di dodecyl benzyl tri ethyl ammonium chloride (CS) is investigated in 1M H 2 SO 4 using weight loss measurements and galvanostatic polarization curves. The corrosion rate decreases with the inhibitor concentration from 10 to 130 ppm. It is found that the corrosion rate decreases with immersion time from 5 to 20 days and then tends to be constant. The results have shown that the lowest corrosion rate is for 75 ppm for (CS). The effect of temperature on corrosion inhibition has been studied and the activation energy for optimum conditions of the inhibitor has been evaluated. The corrosion inhibition of carbon steel in 1M H 2 SO 4 containing (CS) has been attributed to adsorption of inhibitors over the carbon steel surface. Results are correlated will to the chemical structure of the inhibitor. Some electrochemical parameters such as I corr, E corr, b a and b c are evaluated from galvanostatic polarization technique. The results of inhibition efficiency evaluated from galvanostatic polarization technique are in a good agreement with those obtained from weight loss technique. Furthermore, Scanning Electron Microscopy (SEM) is used to examine the surface morphology of the carbon steel samples both in absence and presence of each inhibitor at optimum conditions. KEYWORDS: corrosion inhibition, carbon steel, cationic surfactants, weight loss. 1. INTRODUCTION: Acids are widely used in various technological processes in industry, e.g., in pickling baths, in the extraction and processing oil and gas and in other chemical and petrochemical industries. Also, in the technical cracking of petroleum, acids appear as a result of hydrolysis of salts and may have destructive effect on the equipment. Corrosion due to acids are important and expensive problem in the petroleum refining units and it represents a significant portion of loss as a result of lost production, inefficient operation, high maintenance and the cost of corrosion control chemicals. Inhibitors are compounds that control, reduce, or prevent reactions between a metal and its surroundings when added to the medium in small quantities. Inhibitors should be effective in low concentrations for economy. The use of inhibitors is one of the most practical methods for protection against corrosion, especially in acidic media [1]. Most of the well-known acid inhibitors are organic compounds containing nitrogen, sulphur and oxygen atoms. The influence of organic compounds containing nitrogen, such as amines and heterocyclic compounds, on the corrosion of steel in acidic solutions has been investigated by several workers [2-5]. In previous studies, ethoxylated fatty acid [6], ethoxylated fatty amines [7], and propenethoxylated diol [8] had been used as corrosion inhibitors for steel and aluminum in acidic solutions. The existing data show that the most organic inhibitors act by adsorption on the metal surface. This phenomenon is influenced by the nature and the surface charge of metal, by the type of aggressive electrolyte and by the chemical structure of inhibitors [9]. The inhibition efficiency (E %) depends on the parameters of the system (temperature, ph, duration, and metal composition) and on the structure of the inhibitor molecule. It is well known that heterocyclic compounds containing nitrogen atoms are good corrosion inhibitors for many metals and alloys in various aggressive media [1, 2, 5, 9, 10-16]. In the present investigation the corrosion inhibition of carbon steel in 1M H 2 SO 4 solutions in

2 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI 113 absence and in presence of a new cationic surfactant compound (di dodecyl benzyl tri ethyl ammonium chloride) (CS) has been studied using weight loss and galvanostatic polarization techniques. The effect of temperature and time of immersion on corrosion inhibition have been studied. The inhibitive effect upon using the best concentration of the inhibitor in 1M H2SO4 is also examined using scanning electron microscopy. 2. EXPERIMENTAL RESEARCH 2.1. Materials and Solutions Chemical composition of samples Rectangular samples of size 10x10 mm were cut from a sheet of carbon steel alloy for Weight Loss Measurements, circular sheets of 100mm 2 area for Scanning Electron Microscopy, and a rectangular samples of size 5x20 mm and 100mm 2 area exposed to the tested solutions for Galvanostatic Polarization Technique. The chemical composition of the carbon steel alloy is listed in Table 1. Table 1. Chemical Composition of Carbon Steel Alloy. Element C Mn P Si S Fe Analysis (%) Inhibitor and Solutions Inhibitor: New cationic inhibitor supplied by Omar and prepared as described previously [17] and listed in table 2. It is added in different concentrations from 10 ppm to 130 to 1 M H 2 SO 4 acid solution. Solutions: All solutions are prepared from 96 % sulphuric acid solution with distilled water. Table 2: Structure and name of the inhibitor Name: Di dodecyl benzyl tri ethyl ammonium chloride Type of surfactant: Cationic (CS) Structure: C 12 H 25 CH2N + (CH2CH3)3 Cl - C 12 H Surface Tension Measurement The surface tension was measured with Du Noy tensiometer (KRUSS 8451) for various concentrations of the surfactant solution (1M H 2 SO 4 ) and at different temperatures 30ºC to 50ºC. Accuracy of the surface tension measured was ± 0.2 mn/m Procedures Used for Corrosion Measurements Weight Loss Technique The specimens are polished with different grades of emery papers ( ), cleaned with distilled water, and then dried with absolute ethyl alcohol. All the specimens are immersed in the same volume of solution (50 ml) Galvanostatic Polarization Technique Polarization experiments are carried out in a conventional three-electrode glass cell with a capacity of 500 ml with a platinum counter electrode and a saturated calomel electrode (SCE) as reference with a fine Luggin capillary bridge to avoid ohmic polarization. All tests were performed in deaerated solutions under continuously stirred conditions. The procedure adopted for the polarization measurements was the same as described elsewhere [18]. A platinum electrode is used as an auxiliary electrode and all potential values are measured against a saturated calomel electrode (SCE) Scanning Electron Microscopy A JEOL (5400) Scanning Electron Microscope (Japan) is utilized to document the surface morphology of various specimens of carbon steel. All micrographs of corroded specimens are taken at a magnification of X= RESULTS AND DISCUSSION The surface tension ( γ ) as a function of logarithm of the molar concentration of cationic surfactant (CS) in 1 M H 2 SO 4 at different temperatures is shown in figure 1. From the intersection points in the γ - log C curve, critical micelle concentration was determined. The obtained critical micelle concentration (CMC) shows a increasing trend with the increasing temperature (Table 3), due to decrease in the hydration of hydrophilic group which favour micillization. Table 3. Some physical properties of the synthesized CS Parameters Temperatures 30 o C 40 o C 50 o C CMC G mic Kj/mol γ CMC mn /m

3 114 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI Fig. 1. Relation between surface tension and different concentration of cationic surfactant (C). The corresponding surface tension γ CMC and free energy of micellization G mic show decreasing trend with the increasing temperature. The weight loss of carbon steel in 1M sulphuric acid with the addition of various concentrations of cationic (CS) surfactant as chemical inhibitor is measured and plotted in figure 2. It shows the effect of adding various concentrations (10 ppm ppm) of (CS) on the corrosion of carbon-steel at 30 o C. From this figure we notice that the corrosion rate decreases and the inhibitor efficiency increases with increasing immersion time from 5 to 20 days, then it give a constant value. This means that, the values of surface coverage (θ) and the percentage inhibition efficiencies % (P) increase markedly with increase of inhibitor concentration. This behavior confirm the dependence of inhibition efficiency on carbon number of hydro- carbon chain length, where each molecule of (CS) contains two-dodecyl chain per molecule (C12) which act as octopus at adsorption. As the results the surface coverage (θ) of compound is increasing more clearly. This surface coverage (θ) is calculated using the following equation: 0 R ' θ = (1) 0 where ' R0 and ' R are the corrosion rates in the absence and in the presence of a given inhibitor CS respectively. The percentage inhibition efficiency, (P%), of (CS) is calculated by applying the following equation [19-20]: P (%) = (2) 0 Fig. 2. Variation of the inhibition efficiency of (CS) with concentrations on carbon steel in 1M H2 SO4 at different time intervals.

4 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI 115 Table 4. Inhibition efficiencies of carbon steel: in different concentrations of (CS) in 1M H 2 SO 4 solution at different times of immersion. Cationic Inhibitor Concentration (ppm) Number of days θ P% θ P% θ P% θ P% Table 5. Inhibition efficiencies of carbon steel in different concentrations of (C) and in 1M H 2 SO 4 solution at different times of immersion. Surface coverage (θ) and corrosion inhibition efficiency P (%) Time of immersion (days) Cationic inhibitor concentration (ppm) θ P θ P θ P θ P The measured surface coverage (θ) and the percentage inhibition efficiency (P%) are represented in Table 4. It may be suggested that, cationic inhibitor CS contact between the steel surface and the acid solution. It exists at the interface and attaches or adsorb to the metal surface. The adsorption takes place by head group-n+- and tail group (hydrocarbon chain) of each molecule forming barrier film. The hydrophilic group-n+- with its counter chloride ion is adsorbed onto the steel surface by electrostatic attraction while the hydrophobic (two dodecyl group C12H25) covered the steel. The adsorption takes place by dipole induced interaction with the steel surface as a result of π electron polarization. Tail Head C 12 H 25 C 12 H 25 CH2N + (C2H5)3 At same time, immersion of carbon steel in 1M H 2 SO 4 show an adsorption of the sulphate ions on the steel surface leading to the availability of more negative sites on the metal surface. As the result, hydrophilic group prefer adsorptions on the steel surface. The optimum concentration of CS is 75 ppm, this value represents the critical micelle concentration (CMC) of (CS) (fig. 1). The decreasing in efficiency with time can be interpreted in terms of inverse direction of hydrophilic group adsorption of the cationic surfactant CS and increase repulsion forces between the adsorbed molecules of the inhibitor. At 1M of sulfuric acid, the inhibition efficiency decreases sharply with the increase in temperature from o C (table 5). This can be attributed to destruction of the inhibitive layer formed on the steel surface at higher temperature. Also the adsorbed molecules tend to deadsorptions due to increase repulsion forces between chains of CS molecules, as results the inhibitor molecule tend to form CMC in solution / air interface and increases values of CMC (table 2). It can be concluded that, the increase of temperature distorted the adsorbed layer and retard micellization process. The specific adsorption of the anion having a smaller degree of hydration, such as chloride ions is expected to be more pronounced. Being specifically adsorbed, they create an excess negative charge towards the solution and favour more adsorption of the cations. Moreover data in figure 2 and table 5 reveal that the corrosion rate decreases with time of immersion up to 20 days then tend to be constant, this is due to the formation of oxide layer (Fe 2 O 3 ) according to the following equation 2FeSO 4 (S) + 3 H 2 O Fe 2 O 3 + 2H+ + 2H 2 SO 4 + 2e- The activation energies of the metal dissolution reaction (E a ) for solution of 1M H 2 SO 4 containing various concentrations of each inhibitor can be determined from the Arrhenius relation: Ea k = A exp (3) RT

5 116 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI Fig. 3. Variation of logarithm of corrosion rate with the reciprocal of absolute temperature for carbon steel in 1 M H 2 SO 4 containing 75 ppm CS for different time of immersion. Fig. 4. Galvanostatic polarization curves for carbon steel in 1M H 2 SO 4 in the presence 75 ppm CS inhibitor. That is, by determination of the slopes of the straight lines that depict the linear dependence of the logarithm of the corrosion rate, ln(k), on the reciprocal value of the absolute temperature. The activation energies increases up to 20 days and then tend to be in a stable value as shown in figure 3. The dissolution reaction in presence of (CS) is higher than blanck. The obtained results of activation energies are all tabulated in Table Galvanostatic Polarization Technique At optimum conditions the polarization curves for these inhibitors are shown in figure 4, onto the metal surface without affecting the anodic and cathodic reaction mechanisms. Electrochemical parameters such as corrosion potential (E corr ), corrosion current density (I corr ), and Tafel slopes (i.e., cathodic [bc] and anodic [ba] Tafel slopes) are calculated from Tafel plots and are given in table 7. The lower I corr is for 1M H2SO4 containing 75 ppm of (C), E corr values not show any significant variations for 1M H 2 SO 4 containing 75 ppm and none of the inhibitor showed significant changes in ba and bc slopes, indicating that (CS) is adsorbed.

6 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI 117 Corrosion inhibition efficiency P(%) is calculated using equation: P = 1 Icorr 100 Icorr, o (4) where I corr,o and I corr are the corrosion current densities in the absence and in the presence of inhibitor, respectively. The comparison between the values of inhibition efficiencies by weight loss and galvanostatic polarization techniques after 25 days at 30 o C are compared in table 8. Table 6. Activation energies of carbon steel at optimum concentrations of (CS) in 1M H 2 SO 4 solution at different times of immersion Time E a (k J mol -1 ) (Days) Cationic Inhibitor Table 7. Polarization parameters for the corrosion of carbon steel in 1M H 2 SO 4 containing 75 ppm of (CS). Inhibitor concentration (ppm) Ecorr (mv) Icorr (ma/cm 2 ) 1M H 2 SO ppm of (C) bc (mv.dec -1 ) ba (mv.dec -1 ) surface of another carbon steel specimen after immersion for the same time interval in 1M H2SO4 solution containing 75 ppm of the inhibitor (CS). Fig. 5. Scanning electron micrograph of carbon steel sample after immersion in 1M H 2 SO 4 solution. The micrograph reveals that, there is a decrease in the corrosion sites and pits over the surface of the carbon steel. In figure 6 it appears that the surface of the specimen is covered greatly due to formation of surface film of the inhibitor. From these observations we can say that the cationic inhibitor give a good inhibition effect for the carbon steel and this confirms the results obtained from the other techniques. Table 8. Inhibition efficiencies P(%) from weight loss and galvanostatic polarization techniques for carbon steel in 1M H 2 SO 4 containing optimum concentrations of (C) at 30 o C. Inhibition efficiency P (%) Inhibitor concentration (ppm) using Polarization Technique using Weight loss Technique 75 ppm of (CS) It is observed that the results of surface coverage in presence of inhibitor (CS) are in a good agreement with those given by weight loss technique. This means that the inhibition efficiency calculated by the help of galvanostatic polarization technique is nearly equal to the values obtained by weight loss technique Scanning Electron Microscopy Figure 5 shows SEM image of the surface of the carbon steel specimen after immersion in 1M H 2 SO 4 solution for 20 days at 30 o C. The micrograph reveals that, the surface is strongly damaged in the absence of the inhibitors (active corrosion). Figure 5 and SEM image of the Fig. 6: Scanning electron micrograph of carbon steel samples after immersion in 1M H 2 SO 4 solution in presence of 75 ppm of inhibitor (CS). 4. CONCLUSIONS Di dodecyl benzyl tri ethyl ammonium chloride (CS) behaves as inhibitor for carbon steel corrosion in 1M H 2 SO 4 from 5 days to 20 days at 30 o C, it was found that, the corrosion rate decreases with time of immersion up to 20 days then it tends to be constant. The corrosion rate increases with temperature. The results of SEM indicate that the inhibitive efficiencies

7 118 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI of each inhibitor are high and the most effective inhibitor is the cationic one, which is in a good agreement with the studied techniques. ACKNOWLEDGEMENT The author gratefully acknowledges Assistant Professor Dr. A.M.A. Omar, Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt for his assistance and support. REFERENCES 1. Tadros A.B.,. Abdenaby B.A, 1988, J. Electroanal. Chem. 246, pp Stoyanova A.E., E.I. Sokolova E.I., Raicheva S.N., 1997, Corrosion Science, 39, pp Alshkel A.G., Hefny M.M., Ismail A.R., 1987, Corrosion Prevent. Control, Omar A.M.A., Abdel Khalek N.A., 1998, J. Chem. Eng. Data, (USA), 43, pp El-Etre A.Y., Abdallah M., 1994, Bull. Of Electrochem., 10. pp Mernari B., El Attari H., Traisnel M., Bentiss F., Lagrenée M., 1998, Inhibiting effects of 3,5-bis (n-pyridyl)-4-amino-1,2,4 - triazoles on the corrosion for mild steel in 1 M HCl medium, Corrosion Science, vol. 40, no. 2/3, pp Bentiss F., Lagrenée M., Traisnel M., Hornez J.C., 1999, Corrosion Science, 41, pp Bentiss F., Lagrenée M., Traisnel M., Hornez J. C., 1999, Corrosion, 55,, pp Bentiss F., Traisnel M., Lagrenée M., 2000, Corrosion Science, 42, pp Zucchi F., Trabanelli G., Brunoro G., 1992, Corrosion Science, 33, pp Growcock F.B., Lopp V.R., 1998, Corrosion Science, 28, pp Thomas J.G.N., in: Proc. 5 th. European Symposium on Corrosion Inhibitors, Ann. Univ. Ferrara, N.S., Sez. V, 8 (1980) pp O M. Bockris J., Yang B., 1991, J. Electrochem. Soc. 138, pp Haladky K., Collow L., Dawson J., 1980, Br. Corros. J. 15, pp Lagrenée M., 1998, Corrosion Science, 40, pp Abdallah M., 1994, Annali di Chimica (Rome), 84, pp Abdallah M., 2000, Bull. Of Electrochem., 16, pp Bartos M., Hackerman N., 1992, Electrochem J.. Soc. 139, pp Elachouri M., Haji M. S., Kertit S., Essassi E. M., Salem M., Coudert R., 1995, Corrosion Science, 37, pp Chatterjee P., Benerjee M.K., Mukherjee K.P., Indian J. Technology, 29 (1991), pp Abdel Hamid Z., Soror T.Y., EL-Daham H.A., Omar A.M.A., 1998, Anti-corrosion and materials, 45, 5, pp

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