A study on the corrosive inhibition ability of CT3 steel in 1 M HCl solution by caffeine and some characteristics of the inhibition process - Truong Thi Thao

Vietnam Journal of Chemistry, International Edition, 54(6): 742-746, 2016 DOI: 10.15625/0866-7144.2016-00397 742 A study on the corrosive inhibition ability of CT3 steel in 1 M HCl solution by caffeine and some characteristics of the inhibition process Truong Thi Thao * , Hoang Thi Phuong Lan, Ngo Duong Thuy Faculty of Chemistry, Thai Nguyen University of Science, Thai Nguyen University Received 2 June 2016; Accepted for publication 19 December 2016 Abstract Caffeine was isolated from dry green tea leaves and used as corrosion inhibitor. The aim of this paper is to study the corrosion inhibition behavior of caffeine with its different concentrations (from 0.01 g/L to 3.00 g/L) for CT3 steel in 1M HCl solution by the curve polarization measurements and surface examination studies. Experiment result showed that: as the concentration of caffeine increases, the inhibition efficiency increases; %IE max is approximately 83.27% at concentration of caffeine 3.00 g/L. The experimental data from all measurements was found to fit well with the Langmuir caffeine adsorption isotherm. Calculated values of free energy of adsorption Gads are -14.71 kJ/mol. It shown that, the adsorption is spontaneous and consistent with the mechanism of physical adsorption. It showed that, the adsorption is spontaneous and consistent with the mechanism of physical adsorption. As temperature increase from 298 to 318 K, the inhibition efficiency is relatively stable: decrease slightly from 83.27 % down 78.50 %. Calculated values of the heat of adsorption Hads are ranged from -6.38 kJ/mol to -19.89 kJ/mol, indicating that the adsorption of caffeine on the surface of CT3 steel is exothermic. The increasing of activation energy in corrosion process which presents caffeine 3.00 g/L compared to absent caffeine proved that caffeine have corrosion occurred more difficult. Keywords. Caffeine, corrosion inhibitor, adsorption. 1. INTRODUCTION Using plant extracts as green corrosion inhibitors is a trend that is being tested extensively in both of Vietnam and many parts of the world in recent years [1-11]. However, one of the drawbacks of the plant extracts is that they are unstable. They are decomposed quickly over time and lose inhibition corrosion property. To overcome this drawback, we are looking for the pure substances which have inhibiting corrosion capability in those extract. Based on some our studies and some research of other authors in the world [1-4, 8], we have realized that, extracts of plants such as green tea, tobacco, coffee,... have shown good inhibitory property. These extracts contain caffeine. So that, caffeine was isolated from dry green tea leaves and used as corrosion inhibitor [12-14]. The present work (i) evaluates the inhibition efficiency of caffeine concentration in controlling corrosion of CT38 steel in 1M HCl acid solution, (ii) examines the inhibition efficiency of 3.00 g/L caffeine at different temperatures, (iii) observes microscopic surface by SEM method. 2. EXPERIMENTAL 2.1 Caffeine Extraction Leaves of Green tea were collected in Thai Nguyen City. The clean air-dried leaves were grounded and entered to 100 ml heatproof cup. The the lime water was pouring flooded more than 3 cm, heated to boiling, then simmer for 150 minutes. Filtering out by the pulp, the solution is neutralized by instillation 5 M HCl and then is extracted three times with chloroform. The chloroform solution was dried by anhydrous sodium sulphate then chased solvent by rotary vacuum. The final product is used to prepare solutions with its different concentrations in 1 M HCl solution. 2.2 Preparation of the specimens The working electrode was made from CT3 carbon steel (produced in Thai Nguyen, composition: 0.154%C; 0.636%Mn; 0.141%Si; 0.019%P; 0.044%S and Fe). Prior to each measurement, the electrode surface was mechanically treated by grinding and polishing with different grades of emery paper, degreased in VJC, 54(6) 2016 Truong Thi Thao, et al. 743 ethanol and rinsed in twice distilled water. The exposed geometric area was 0.785 cm 2 . A new electrode surface was used for each run. 2.3. Method 2.3.1. Electrochemical measurements All experiments were done in unstirred and nondeaerated solutions at room temperature after immersion for 60 min in 1 M solution with and without addition of inhibitor. Corrosion tests were performed electrochemically at room temperature (~ 25 o C). Electrochemical measurements were performed using a potentiostat manufactured by PAR (Model PARSTAT 4000, Princeton Applied Research, USA) at Institute of Materials, Vietnam academy of Science and Technology. The test specimens were placed in a glass corrosion cell, which was filled with fresh electrolyte. A silver/silver chloride electrode and a piece of stainless steel with large area were employed as pseudo-reference and counter electrode, respectively. The linear polarization study was carried out from −20 to +20 mV versus corrosion potential (Ecorr) at a scan rate of 0.1 mV.s −1 to determine the polarization resistance (Rp). Tafel curves were obtained by changing the electrode potential automatically from −250 to +250 mV versus corrosion potential (Ecorr) at a scan rate of 3 mV.s −1 . The linear Tafel segments of anodic and cathodic curves were extrapolated to corrosion potential to obtain corrosion current densities (Icorr). The inhibition efficiency has been calculated from the equation: (2) Where v0 and vt are the corrosion rate of CT3 steel in absence and in presence of inhibitor in working solution, respectively. 2.3.2. Surface examination study The surface morphology after 60 minutes immersion in the test solution was analyzed by scanning electron microscopy (SEM) and EDS, using Quanta 3D scanning electron microscope (model AL99/D8229) at Institute of Materials, Vietnam Academy of Science and Technology. 2.3.3. Some thermodynamic parameters of adsorption and corrosion process The Langmuir adsorption isotherm applied to investigate the adsorption mechanism [9-11] is: 1 KC KC (3) or (4) Where C is the inhibitor concentration in the electrolyte, K is the equilibrium constant of the adsorption process, is the degree of surface coverage ( = IE(%) /100). The standard free energy of adsorption is calculated according to the following equation [10, 11]: G 0 = -2.303RTlog(55.5×K) (5) Where R is the molar gas constant, T is the absolute temperature and 55.5 is the concentration of water in solution expressed in molar. Values of the heat of adsorption are calculated according to equation [9-11]: Hads = 2.303Rx 12 21 TT xTT 1 1 2 2 1 log 1 log (6) Where Hads is entanpi of adsorption (kJ/mol); T1, T2 are test temperatures, respectively; 1 and 2 are the degree of surface coverage of the inhibitor at corresponding temperature. Activation energy of corrosion process (E*, kJ/mol) is calculated according to the equation Arrhenius [9]: v= A.C.e -E*/RT (7) or logv = -E*/RT + log(A.C) (8) Where: C = reactant concentration. 3. RESULTS AND DISCUSSION 3.1. Effects of caffeine concentrations to inhibit corrosion ability 3.1.1. Polarization measurements Polarization curves measurements for mild steel are shown in figure 1. The calculation of the corrosion rate and inhibition efficiency is given in table 1. VJC, 54(6) 2016 A study on the corrosive inhibition ability 744 Figure 1: Polarization curves in absence and presence of different concentrations of caffeine in 1 M HCl solution 1 – 0.00 g/L; 2 – 0.01 g/L; 3 – 0.05 g/L 4 – 0.50 g/L; 5 – 2.00 g/L; 6 – 3.00 g/L Table 1: The corrosion rate of CT3 steel in 1M HCl solution and inhibition efficiency of caffeine by polarization curves measurements Caffeine (g/L) Ecorr(V) R(Ω) vx10 (mm/year) H% 0.00 -0.466 77.71 8.76 0.01 -0.472 84.10 8.01 7.60 0.05 -0.469 91.12 7.40 14.72 0.10 -0.474 135.59 4.94 42.69 0.50 -0.470 246.96 2.81 68.53 1.00 -0.477 354.65 1.91 78.09 2.00 -0.462 391.27 1.73 80.14 3.00 -0.467 464.49 1.44 83.54 Figure 1 and table 1 show that the presence of caffeine reduces the corrosion rate, vcorr (v). The decrease in vcorr values is due to the decrease of the aggressive acid attacking on the mild steel surface, attributed to the adsorption of inhibitor molecule. Furthermore: - The anodic current density decreased as the concentration of caffeine increase from 0.01 g/L to 3.00 g/L but when its concentrations is less than or equal to 0.05 g/L, cathode current density did not change compared to the curve in the background, when the concentration of caffeine increased from 0.10 g/L to 3.00 g/L, the current density decreased rapidly. - The corrosion potential Ecorr shifted to the positive side when caffeine concentrations increase from 0.01 g/L to 0.05 g/L but after that, when caffeine concentrations increase from 0.10 g/L to 3.00 g/L, Ecorr ascending gradually translated into the negative again. Thus, at low concentrations (≤ 0.05 g/L), caffeine expressed as anodic inhibitors, at concentrations > 0.05 g/L, caffeine acts as an inhibitor mixture. It means that, the inhibitors were adsorbed on the mild steel surface, which prevented the metal dissolution reaction and thus controlling the corrosion process. The results obtained are in good agreement with those obtained from the weight loss measurements. 3.1.2 Surface examination study The SEM photomicrography and analysis EDS steel surface which were soaked in 1M HCl solution in the absence and presence 3.00 g/L caffeine after 60 minutes immersion have been done. Results shown in figure 2 and table 2. Figure 2: SEM micrographs of CT3 steel in without and with 3.00 g/L caffeine Table 2: EDS analysis CT3 steel surfaces after immersion in corrosive solution 60 minutes Atom Fe O Cl C Other Blank 86.26 10.6 0.75 1.9 0.49 Inhibitor 97.91 0.39 0.18 1.41 0.11 We can easily see that: CT3 steel surface immersion in HCl solution without caffeine has the thick corrosion centers density, corrosion points are large and corrosion products are pushed to the surface while sample soaking in the 1 M HCl with 3.00 g/L caffeine has the center density corrosion significantly reduced. This result was also confirmed that in 1 M HCl and caffeine presence 3.00 g/L the CT3 steel corrosion has been significantly limited compared with a solution without caffeine. 3.2. Effects of temperature to inhibit corrosion ability of caffeine for CT3 steel in 1 M HCl solution To examine the effect of temperature to corrosion and ability of caffeine to inhibit corrosion for CT3 steel, the work electrodes were measured for the polarization resistance and polarization curve in corrosive solution with and without 3.00 g/L caffeine at 25 °C, 35 °C and 45 °C. The corrosion rate calculated from polarization measurement is VJC, 54(6) 2016 Truong Thi Thao, et al. 745 given in table 3. Table 3: The typical parameters of CT3 steel corrosion process in 1 M HCl solution with and without 3.00 g/L caffeine at different temperatures Solution Ecorr (V) RP (Ω) V (mm/year) H% Blank 25 o C -0.466 77.71 0.876 Blank 35 o C -0.473 48.23 1.411 Blank 45 o C -0.463 26.51 2.568 inhibitor 25 o C -0.467 464.49 0.144 83.27 inhibitor 35 o C -0.467 241.78 0.282 82.36 inhibitor 45 o C -0.477 123.23 0.552 78.52 As the temperature rises. For the solution with or without caffeine. the polarization resistance of corrosion process is reduced so the corrosion rate increases. However. the protective effect of caffeine 3.00 g/L at different temperatures relatively stable. temperatures rising but the protective effect decreases dramatically. 3.3. Some characteristics of corrosive inhibition and corrosion process 3.3.1. Mechanism of corrosive inhibition process The result of 3.1 can showed that the values of surface coverage increases, the corrosion rate decreases with the rise in inhibitor concentration as a result of more inhibitor molecules adsorption on the steel surface. Now assuming that the adsorption of caffeine belongs to monolayer adsorption and the lateral interaction between the inhibitor molecules is ignored. By plotting values of C/ versus C (table 1) following equation (4), straight line graphs were obtained (Fig. 3) which proves that Langmuir adsorption isotherm is obeyed over the range of studied concentrations. The degree of linearity of Langmuir adsorption isotherm as measured by values of R 2 is nearly equal to 1 which indicates that the assumption and the deduction were correct. In other words, the adsorption of caffeine on steel surface in 1 mol.L -1 HCl solution is well described by the Langmuir adsorption isotherm [9-11]. The considerable deviation of the slopes from unity shows that the isotherm cannot be strictly applied. This deviation is attributable to interaction between adsorbate species on the metal surface. A modified Langmuir adsorption isotherm [9, 10] could be applied to this phenomenon, which is given by the corrected equation: Figure 3: Langmuir isotherm for the adsorption of caffeine on the surface of CT3 steel in 1 M HCl C n nC K (9) The equilibrium constant and the standard free energy of adsorption process calculated from equation (5) are: K = 6.82 and G o = -14.71 kJ/mol. The negative values of G o suggest that the adsorption of caffeine onto steel surface is spontaneous. Furthermore, the obtained values of G o ads indicate that adsorption of caffeine occurs via physical adsorption mechanism [7, 8]. Values of Hads were calculated according to equation (6) are ranged from -6.38 kJ/mol to -19.89 kJ/mol, indicating that the adsorption of caffeine on the surface of CT38 steel is exothermic. This is another indication that the adsorption process is essentially physical adsorption. 3.3.2. The activation energy of corrosive process We construct a graph showing the relationship between the log and 1/T (equation (8)) according to the data in table 3. Figure 4: Arrhenius equation for the corrosion of CT3 steel in 1M HCl solution with and without caffeine 3.00 g/L Empirical equations have high correlation coefficients (R 2 ~ 1) demonstrating that the corrosion obeys Arrhenius equation. C (g/L) 3.00 g/L VJC, 54(6) 2016 A study on the corrosive inhibition ability 746 Following the equation (8) calculated the activation energy of CT3 steel corrosion in 1 M HCl with and without caffeine 3.00 g/L is: E*(CT3/1M HCl) = 42.1486 kJ; E*(CT3/1M HCl + caffeine 3.00 g/L) = 52.5781 kJ. The value activation energy increases when present caffeine in solution proved corrosion occurs more difficult, requiring higher energy. It is due to caffeine adsorbed onto the surface so H + ion and/or dissolve O2 attack the steel surface more difficult, or absorption that leads to change surface potential and electrode reactions occur more difficult. 4. CONCLUSIONS - Caffeine has corrosion inhibition ability for CT3 steel in 1M HCl solution. Inhibition efficiency increases with the rise in caffeine concentration, Inhibition efficiency max is approximately 83 % at concentration of caffeine 3.00 g/L. - As temperature increases from 298 to 318 K, the inhibition efficiency is relatively stable: decreases slightly from 83.27 % down 78.5 %. - Mechanism of corrosion inhibition is physical adsorption, obeys the Langmuir adsorption isotherm. The adsorption of caffeine onto steel surface is spontaneous and exothermic. - Calculated The activation energy of CT3 steel corrosion in 1 M HCl with and without 3.00 g/L caffeine was calculated. This value proved caffeine inhibits corrosion process. Those results indicate that caffeine is a very good corrosion inhibitor for CT3 steel in 1 M HCl solution. It also open up the great possibility of practical application because caffeine is quite cheap, easy to obtain and safe for environment and human. REFERENCES 1. W. Bogaerts, V. T. T. Ha, L. Q. Hung, N. N. Phong, R. Addul. Use of different natural Extracts from Tropical plants as Green Inhibitors for Metals, Nanotech conference&Expo 2009, May 3-7, Houston, TX 2. T. T. Thao, V. T. T. Ha, L. Q. Hung. Evaluate the inhibtion of Thai Nguyen steel corrosion in 1M HCl solution by local green tea extract, J. Chemistry, 49(2ABC), 815-820 (2011). 3. T. T. Thao, P. T. H. Luong, N. D. Vinh. Inhinitive ability and adsorption characteristics of water extract of Thai Nguyen green tea leaves for corrosion of mild steel in 1 M HCl solution, Journal of Analytical Sciences, 19, 93-98 (2014). 4. P. T. Giang, V. T. T. Ha and L. Q. Hung. Screening Vietnamese natural products for new environmentally friendly materials for corrosion protection, International scientific conference on ‘Chemistry for Developmant and Integration’, Hanoi, 977-985 (2008). 5. V. T. T. Ha, P. T. Giang, L. Q. Hung, P. H. Phong. Use of Cyclic Polarisations to Evaluate Corrosion Iinhibitive Properties of Ginger Extract, Journal of Chemistry, 47(5A), 168-173 (2009). 6. V. T. T. Ha, P. T. Giang, P. H. Phong and L. Q. Hung. Electrochemical Behaviour of Artemisia as Corrosion Inhibitor of Iron in Aqueous Media, Journal of Chemistry, 47(6B), 67-72 (2009). 7. P. H. Phong, V.T. T. Ha and L. Q. Hung. Investigation of Rhizophora xtract-a new natural product used for corrosion inhibition of carbon steel, International scientific conference on ‘Chemistry for Developmant and Integration’, Hanoi, 895-901 (2009). 8. Smith D. M., Wang Z., Kazi A., Li L. H., Chan T. H., Dou Q. P. Synthetic analogs of green tea polyphenols as proteasome inhibitors, Mol. Med., 8(7), 382-392 (2002). 9. E. E. Ebenso, N. O. Eddy and A. O. Odiongenyi. Corrosion inhibitive properties and adsorption behaviour of ethanol extract of Piper guinensis as a green corrosion inhibitor for mild steel in H2SO4, African Journal of Pure and Applied Chemistry, 2(11), 107-115 (2008). 10. S. A. Umoren, I. B. Obot, E. E. Ebenso, P. C. Okafo. Eco-friendly Inhibitors from Naturally Occurring Exudate Gums for Aluminium Corrosion Inhibition in Acidic Medium, Portugaliae Electrochimica Acta, 26, 267-282 (2008). 11. I. B. Obot, N. O. Obi-Egbedi, S. A. Umoren, E. E. Ebenso. Synergistic and Antagonistic Effects of Anions and Ipomoea invulcrata as Green Corrosion Inhibitor for Aluminium Dissolution in Acidic Medium, Int. J. Electrochem. Sci., 5, 994-1007 (2010). 12. F. S. Souza, R. S. Gonçalves, A.Spinelli. Assessment of caffeine adsorption onto mild steel surface as an eco-friendly corrosion inhibitor, J. Braz. Chem. Soc., 25(1) (2014). 13. Senka gudić, Emeka E. Oguzie, Ani Radonić, Ladislav Vrsalović, Ivana smoljko, Maja kliškić, Inhibition of copper corrosion in chloride solution by caffeine isolated from black tea, Macedonian journal of chemistry and chemical engineering, 33(1), 13-25 (2014) 14. G. Bolat, A. Cailean, D. Sutiman and D. Mareci. Electrochemical behaviour of austenitic stainless steel in 3.5 wt% NacCl solution in the presence of caffeine environmental friendly corrosion inhibitor, Rev. Roum. Chim., 59(1), 53-59 (2014). Corresponding author: Truong Thi Thao Faculty of Chemistry, Thai Nguyen University of Science, Thai Nguyen University Tan Thinh award - Thai Nguyen City - Thai Nguyen E-mail: thao.truong671@gmail.com; Telephone: 0915216469.