113 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 Adenine as Environmentally- Friendly Corrosion Inhibitor for Stainless Steel in Sodium Chloride Acid Solution Wisal A. Isa Marwa S. Hussain Dept. of Chemistry / College of Education For Pure Sciences( Ibn Al- Haitham)/ University of Baghdad Received in: 28 October 2014، Accepted in: 21 December 2014 Abstract The corrosion behavior and the influence of the concentration of adenine (AD) on the corrosion of 316L stainless steel in 0.6 mol.dm-3 sodium chloride acid solutions were studied. The research was performed in two pH values (pH=2 and pH=4) over the temperature range (293- 308)K. The investigation involved electrochemical polarization method using potentiostatic technique. Tafel polarization study revealed that (AD) acted as a mixed inhibitor. The inhibition efficiency increased with an increase in the concentration of adenine, but decreased with increase in temperature. (efficiency= 87% at 0.01 M AD & at T= 293K). The adsorption of (AD) has been found to occur on the surface of 316L stainless steel according to the Langmuir isotherm. The kinetic and thermodynamic parameters for stainless corrosion and adenine adsorption respectively were determined and discussed. Key Words: Stainless steel; Adenine, Tafel polarization, kinetic parameters, Thermodynamic parameters. 114 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 1. Introduction Stainless steel has found very wide applications both in modern chemical industries and other places such as desalination plants, construction materials, pharmaceutical industry thermal power plants, chemical cleaning and pickling process due to high strength, workability and weldability. The corrosion of stainless steel in acidic solutions has become a fundamental academic and industrial concern that have received a considerable amount of attention, since aggressive acid solutions are widely used for industrial purposes[1]. The anticorrosive properties of the stainless steel materials which a chromium contained higher than 12% are assigned to the spontaneous formation on the surface of a passive thin film layer, mainly composed of chromium and iron oxide/ hydroxides[2]. The rate of corrosion of stainless steel can be reduced by a thin oxide layer formed naturally on the metal surface[3]. Passive films an surface of stainless steel form in an aqueous acid environment are usually very thin, compact and highly enriched in chromium[4,5]. Despite the established corrosion resistance of stainless steel can be chemically attacked by acids, and some organic compounds. The passive layer of the steel is eroded by these acids resulting in corrosion of the stainless steel. Corrosion control is important in extending the life of equipment. Organic compounds with functional groups containing nitrogen, sulfur and oxygen are widely used as corrosion inhibitors to prevent or minimize material loss during contact with acid. The inhibitors can be adsorbed on the metal surface through donation of electrons such as  electrons in aromatic rings or unpaired electrons and multiple bonds[6,7]. Physisorption and chemisorption are two types of interactions between organic inhibitors and metal surface. The adsorption of inhibitors depends on several factors such as type of acid, distribution of charge in molecule, nature and surface charge of metal and type of interactions between inhibitors and metallic surface[8,9]. Most of the inhibitors are toxic in nature, therefore, their replacement by environmentally benign inhibitors is necessary. These compounds include such amino acids and its derivatives which have tested in acid solutions of various metals[10,11]. An important N-hetero cyclic compound, purine (Pu) and purine derivatives are non toxic and biodegradable, which makes the investigation of their inhibiting properties significant in the context of the current priority to produce eco-friendly inhibitors. Recently, purine and adenine (AD) have been studied as[12] corrosion inhibitors of copper in aggressive solutions. However, it appeared that purine considerably slows down corrosion of stainless steel[13,14]. The industrial consumption and development of new corrosion inhibitors have been continuously increasing of the years. The present work reported the inhibitive effect concentration of adenine (AD) and temperature on the corrosion of 316L stainless steel in sodium chloride acid solution. 2. Experimental Part 2.1 Materials The experiments were performed with stainless steel type 316 L specimens in the form of disks with the following composition in Table(1). All chemicals and reagents used are with analytical grade and used without further purification, they include: a. Sodium chloride (analar grade) was used for preparation of the electrolyte solution of concentrations (0.1, 0.3 and 0.6) mol. dm-3. b. Hydrochloric acid (analar grade). c. Adenine C5H5N5 (> 99.4%) was purchased from merck (Darmstadt, Germany) 2.2 Solutions The aggressive solutions used were made of AR sodium chloride to prepare three different concentrations (0.1, 0.3 and 0.6) mol. dm-3 in two pH values (pH=2 and pH=4). Double 115 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 distilled water was used for preparation, and for each experiment a freshly made solution was used. 2.3 Potentiostatic polarization measurements: The potentiostatic polarization measurements were carried out with specimens of 316L stainless steel which were cut in circular form [2cm diameter and 0.2 cm thickness] having an exposed surface area of 1 cm2 to corrosive medium. The working electrode (316 L SS) was abraded mechanically and successively with different grades of emery paper [100,200, 400, 800, 1200 and 2000] and washed with double distilled water. Further the samples were degreased with acetone and thoroughly washed with distilled water then dried in air and kept in a desicator until use. Polarization experiments were carried out in a conventional three- electrodes cell with 316L SS specimens of 1cm2 exposed area, a platinum electrode and silver- silver chloride in saturated KCl were used as working, auxiliary (counter) and reference electrodes respectively. The measurements were performed using M lab potentiostat/ Galvanostat 200 Germany obtained from Bank Electronic Intelligent controls Gnb H. it was connected to personal by computer desktop. The M lab software cares for controlling the potentiostat, recording and processing data. It provides with electrochemical calculations like tafel line evaluation, re- scaling of the potential and integration. The experiments were performed in the electrolyte solutions of (0.1, 0.3 and 0.6)mol.dm-3 NaCl in two values of pH (2 and 4) in absence and presence of three different concentrations of the inhibitor (adenine) over the temperature range (293- 308) K. The experiments were carried out at a scan rate of 10 mV/s. corrosion current density (icorr) and corrosion potential (Ecorr) were determined from the polarization curve, in addition other information were obtained such tafel slopes (bc and ba), weight loss and penetration. In order to test the reproducibility of the results, the experiments were done in triplicate. 3. Results and Discussions Figures 1 and 2 show the anodic and cathodic polarization curves of 316L stainless steel in 0.6mol.dm-3 NaCl solution at four temperatures in the range of (293-308)K and two pH values (pH= 2 and pH= 4). Tafel extrapolation method was used to calculate the corrosion parameters from the polarization curves. The resulting data were displayed in Table (2) and these data show that corrosion current density (icorr) increases with increasing temperature and concentration of NaCl solution. Also it was noticed that all values of (icorr) at pH= 2 are more than those at pH= 4 at all temperatures of study which indicate that 316L SS has more tendency to corrode in more acidic medium, and this result is enhanced by the values of penetration and weight loss. (Table2) Corrosion potential (Ecorr) values, mostly show less negative values at pH=2 than pH=4 at all temperatures. The shift of the corrosion potential to the noble direction (Less negative) implies generally the tendency of 316L SS specimen for corrosion under certain conditions, also the variation of Ecorr reflects the heterogeneous reaction on 316L SS surface. Anodic and cathodic tafel slopes show variation in their values which can be attributed to the variation of the rate determining step (r.d.s) of the metal dissolution reaction (Anodic) and the charge transfer process (desorption or electrochemical desorption) cathodic.[16] 3.1 Temperature dependence of the corrosion current density The rate of 316L SS corrosion (r) (Which is expressed by icorr) at a given concentration increased considerably with the rise of temperature. The dependence of the corrosion current density (icorr) on temperature followed Arrhenius equation [17]: 116 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 rate (r)=icorr= A exp (- Ea/RT)………..(1) Which can be expressed in logarithmic form : Log i LogA E 2.3RT ……… 2 Where A and Ea are respectively the pre-exponential factor and the activation energy of corrosion reaction. A typical linear plot relating values of log icorr to the reciprocal of temperature is shown in Figures 3 and 4. The values of Ea could be derived from the slope of the line, and when the linear plot of Figures 3 and 4 was extrapolated to log icorr value at 0, the value of A could be obtained. Table 3 presents the values of Ea and the pre-exponential factor A for 316L SS corrosion in two pH values 2 and 4. It was found that there is a direct relation between the values of Ea and A, i.e. simultaneous increase or decrease in Ea and log A for particular system which can be ascribed to the compensation effect which describe the kinetics of catalytic and tarnishing reaction on the metal [18]. Entropy of activation (∆S*) was calculated from the value of A using the relationship: . ∆ ∗ …………..(3 ) Where K is Boltzmann constant, h is Plank constant, R is the universal gas constant and T the temperature of the solution. The negative values of the entropy of activation (∆S*) for 316L SS corrosion implies a loss in the over-all degrees of freedom throughout the formation of the activated complex for the reaction of 316L SS constituent with negative species (Cl- & OH-) leading to the formation of corrosion product, when the activated complex results. Only after considerable arrangements of the structure of reaction molecules, making the complex a less probable structure, ∆S* is negative and the reaction will be slower [19]. 3.2 Corrosion inhibition of 316 L stainless steel (SS) by adenine Figures 5 and 6 show the typical polarization curves of 316L SS in 0.6 mol.dm-3 NaCl solutions containing three different concentrations of adenine as inhibitor over the temperature range (298-303) K. Table 4 presents the polarization data (Ecorr and Icorr) and from these data it can be noticed that the addition of adenine caused a decrease in corrosion current densities of 316L SS, and the inhibition effect of adenine increases as the concentration of the inhibitor increased in the range (10-2 – 10-3) mol.dm-3 at all temperatures of study. Table (5) shows the values of inhibition efficiencies (IE%) which are calculated from equation (4): IE% ° ° ………..(4) Where: ° and are corrosion current densities in absence and presence of the inhibitor respectively. The activation parameters such as: the activation energy Ea* and the entropy of activation (∆Sa*) in the range of studied temperatures (293-308)K for corrosion inhibition of 316L stainless steel in 0.6 mol.dm-3 NaCl solution in the presence of various concentrations of adenine were calculated from Arrhenius -type plot: A exp E RT ………. . 5 The calculated values Ea and ∆Sa are summarized in Table (6). In the presence of adenine, an increase in Ea values was observed, the variation of activation energy Ea in the presence of different concentrations of adenine can be illustrated as follows [20]: higher values of (Ea) were 117 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 found in presence of inhibitor than those without inhibitor, i.e., the addition of adenine raises the energy barrier for the corrosion process of 316L SS in sodium chloride acid solution[21]. The entropy values of activation, ∆S*a in the presence of adenine are negative implying the rate determining step for the activated complex is the association rather than the dissociation step. In the presence of the inhibitor ∆Sa* moves in the direction of negative values Table (6) which impels the adsorption process is accompanied by an decrease in entropy, which is the driving force for the adsorption of adenine onto the 316L stainless steel surface [22]. 3.4 Thermodynamic parameters of the adsorption isotherm The efficiency of organic molecules as good corrosion inhibitors depends mainly on their adsorption ability on the metal surface. Basic information about the interaction between inhibitor and metal can be provided by the adsorption isotherm. The investigation of the relation between corrosion inhibition and adsorption of inhibitor is of great importance. The surface coverage Table (7) and the concentration of adenine solution (CAD) were tested by fitting to various isotherms like: Langmuir, Temkin and Freundlich. However, the fit was obtained with Langmuir isotherm as shown in Figure (7) which is given by the following equation [20]: C ………….. (6) Where kads. is the equilibrium constant of the adsorption/desorption processes, and it reflects the affinity of the inhibitor molecules towards surface adsorption sites . From the intercepts of the straight lines on the CAD/θ axis Fig (7) leads to the equilibrium constant for the adsorption/desorption of adenine process Table (7). The high value of kads reveals that the AD molecule possesses strong adsorption ability onto the 316L SS. However, kads decreased with an increase of temperature indicating that adsorption of adenine onto the metal surface was favorable at lower temperatures. The equilibrium constant of the adsorption/desorption (Kads) was related to the standard free energy of adsorption according to equation,[23] : ∆S°ads= -RT ln (55.5 kads)…………… (7). Where R is the universal gas constant, T is the absolute temperature, and value 55.5 is concentration of water in solution. The standard free energy of adsorption was calculated and is given in Table (8) .Generally the standard free energy of adsorption values of -24 kJ.mol-1 or less negative is associated with an electrostatic interaction between charged metal surface or more negative involves charge sharing or transfer from the inhibitor molecules to the metal surface to form a co-ordinate covalent bond .So it can be concluded that adsorption of adenine onto steel surface takes place through both physical and chemical adsorption[24] . It is generally accepted that the first step in the adsorption of adenine on the metal surface usually involves the replacement of one or more water molecules adsorbed at the metal surface. AD(sol) + H2O (ads) ⇆ AD(ads) + H2O (sol)………(8) The inhibitor adenine may then combine with freshly generated Fe+2 ions on the stainless steel surface , forming metal inhibitor complex[25] Fe Fe+2+ 2e−………(9) Fe+2 + ADads. [ Fe –AD]ads. ……(10) Valuable information about the mechanism of corrosion inhibition can be provided by the values of thermodynamic parameters for the adsorption of inhibitor .Thermodynamically , ∆G°ads were related to the standard enthalpy, ∆H°ads and standard entropy, ∆S°ads according to[17] : ∆G°ads= ∆H°ads – T ∆S°ads…………….(11) 118 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 and the standard enthalpy of adsorption can be calculated on basis of the Van't Hoff formula: nk ∆ ° constant ……….. (12 ) A plot of ln kads vs.1/T gives a straight line as shown in Fig (8). The slope of straight line is ∆ ° The negative sign of ∆H°ads reveals that the adsorption of inhibitor molecules is an exothermic process. Generally, an exothermic adsorption process suggests either physisorption or chemisorption while endothermic process is attributed to chemisorption. The unshared electron pairs in investigated molecules may interact with d-orbitals of SS type 316L to provide a protective chemisorbed film[26]. The values of ∆S°ads in the presence of inhibitor are negative that is accompanied with exothermic adsorption process. ∆S°ads of inhibitor can be calculated from equation (13) according to: [17] ∆S° ∆ ° ∆ ° ………..(13) 119 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. 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"Corrosion inhibition of steel in molar HCl by tripheylin-2- thiophene carboxylate", Corros. Sci., 49, 373, 2985 and 3953. 13. Scendo, M. (2008). "Influence of purine on brass behavior on neutral and alkaline sulphate solution", ", Corros. Sci., 50, 1584. 14. Scendo, M.; Radek, N. and Trela ,J. (2012). "Corrosion inhibition of carbon steel in acid chloride solution by Schiff base of N (2-chlorobenzylidene -4- acetylaniline", ", Corros. Rev., 30-33. 15. General Company for testing and rehabilitation engineering (2014).Baghdad, Iraq. 16. Bockris ,J. Ó. M. and Reddy, A. K. N. (1970). "Modern electrochemistry, Phenum press, New York. 2 ,883. 17. Murgules, I. G. and Radoviei O. (1961). "Metal corrosion", Int. Congr., 10-15 April, London,. 202-205. 18. Zarrouki, A.; Warad, I. and Hammouti, B. (2012). "Kinetic parameters of activation", Int. J. Electrochem. Sci., 5, 1516-1526. 19. Sinko, P. J. (2000). "Physical, chemical and biopharmaceutical principles in pharmaceutical science, 5th ed. 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"Inhibition of mild steel corrosion in acid solution by pheniramine drug: Experimental and theoretical study", Corros. Sci., 52, 3033. 26. Deng, S.; Li X. and Fu H. (2011). "Adsorption and inhibitive action of ethanol extracts of chlomolaena odoratal. Foe the corrosion of Mild steel in H2SO4 solutions", Corros. Sci., 53, 822. 27. Fouda, A. S.; Hassan, A. F.; Elmorsi, M. A.; Fayed, T. A. and Abdelhakim A. (2014). "Chalcones as environmentally-friendly corrosion inhibitors for stainless steel type 304 in 1M HCl solution", Int. J. Electrochem. Sci. 9, pp. 1298-1320. 121 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 [15]steelable No.(1): The chemical composition of 316L stainless T Stainless steel 316L Wt% C% Si% Mn% P% S% Cr% Mo% 0.044 0.374 1.28 0.026 0.000 19.14 0.261 Ni% Al% Co% Cu% V% Fe% 8.19 0.001 0.109 0.343 0.051 Bal Table No.(2): Data of polarization curve for corrosion of 316L SS in 0.6 mol-dm-3 NaCl solution at pH values (2 and 4) over the temperature range (293-308)K.   Table No.(3): Activation energy (Ea); pre-exponential (A) and entropy of activation (∆S*) for 316L SS corrosion in 0.6 mol.dm-3NaCl solution. pH Ea/kJ.mol-1 -∆S*/J.k-1.mol-1 A/molecule.cm-2.S-1 2 5.90 204.11 10882x1022 4 6.67 202.59 13083x1022           pH T/K Icorr/ μA.cm-2 -Ecorr/ mv ba/mv. decade-1 -bc/mv decade-1 Weight loss/ g.m-2. day-1 Penetration loss/mm.year-1 2 293 16.21 156 472.1 -149.6 3.40 0.158 298 16.59 146 2467.1 -116.2 3.98 0.169 303 17.37 144 567.6 -310.4 4.41 0.205 308 18.62 124 1692.9 -237.5 4.82 0.224 4 293 14.12 126 269.0 -1430.6 2.94 0.137 298 14.79 159 235.2 -466.7 3.50 0.162 303 15.48 183 718.6 -1483.8 4.24 0.197 306 16.59 198 276.7 -503.4 4.74 0.202 122 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 Table No.(4): Values of (-Ecorr, Icorr and inhibitor efficiency percent) with different concentrations of Adenine at temperature range (293-308) K in pH= 2 and 4. pH T/K Inhibitor conc.mol.dm-3 -Ecorr/mv Icorr.μA.cm-2 IE% 2 293 0 146 16.59 - 1×10-3 264 4.36 74 5×10-3 255 2.82 86 1×10-2 295 2.14 87 303 0 144 17.37 - 1×10-3 284 4.67 73 5×10-3 275 3.38 85 1×10-2 323 2.39 86 308 0 124 18.62 - 1×10-3 310 5.62 70 5×10-3 305 4.07 79 1×10-2 345 3.09 84 4 293 0 159 14.79 - 1×10-3 195 5.24 65 5×10-3 165 3.55 76 1×10-2 162 2.81 81 303 0 183 15.48 - 1×10-3 225 5.75 63 5×10-3 186 4.17 73 1×10-2 188 3.31 79 308 0 198 16.59 - 1×10-3 236 6.60 61 5×10-3 203 4.79 71 1×10-2 195 3.98 77 123 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 Table No.(5): Values of inhibition efficiencies (IE%) calculated from Icorr. pH Conc.of AD T/K IE% from icorr 2 1×10-3 298 74 303 73 308 70 5×10-3 298 86 303 85 308 79 1×10-2 298 87 303 86 308 84 4 1×10-3 298 65 303 63 308 61 5×10-3 298 76 303 73 308 71 1×10-2 298 81 303 79 308 77 Table No.(6): Activation energy (Ea), pre-expopential factor (A) and entropy of activation (∆S*) for the corrosion of 316L SS in the pH values 2 and 4 in 0.6 mol.dm-3 NaCl solution and different concentrations of Adenine. Ph Conc. Of Adenine mol.dm-3 Ea/ kJ.mol-1 -∆S*/ J.K-1. mol-1 A/ molecule cm-2. S-1 2 1×10-3 14.20 172.52 80407×1022 5×10-3 19.68 172.76 48595×1023 1×10-2 20.5 187.62 49830×1023 4 1×10-3 12.57 176.47 50571×1022 5×10-3 15.86 183.59 21727×1024 1×10-2 18.59 191.44 31081×1023 124 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 Table No.(7): Chosen corrosion parameter, degree of surface coverage and corrosion inhibition efficiency for 316L stainless steel in 0.6 mol.dm-3NaCl solution with different concentrations of adenine at various temperatures. pH Temp/ K Conc. AD/ mol. dm-3 -Ecorr /mv Icorr/μA. cm-2 θ IE% 2 298 0 146 16.59 - - 1×10-3 264 4.36 0.74 74 5×10-3 255 2.82 0.86 86 1×10-2 295 2.14 0.87 87 303 0 144 17.37 - - 1×10-3 284 4.67 0.73 73 5×10-3 275 3.38 0.85 85 1×10-2 323 2.39 0.86 86 308 0 124 18.62 - - 1×10-3 310 5.62 0.70 70 5×10-3 305 4.07 0.79 79 1×10-2 345 3.09 0.84 84 4 298 0 154 14.79 - - 1×10-3 195 5.24 0.65 65 5×10-3 165 3.55 0.76 76 1×10-2 162 2.81 0.81 81 303 0 183 15.48 - - 1×10-3 225 5.75 0.63 63 5×10-3 186 4.17 0.73 73 1×10-2 188 3.31 0.79 79 308 0 198 16.59 - - 1×10-3 236 6.60 0.61 61 5×10-3 203 4.79 0.71 71 1x10-2 195 3.98 0.77 77       125 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 Table No.(8): Equilibrium constant adsorption/desorption and standard free energy, enthalpy and entropy of adsorption onto 316L SS in 0.6 mol.dm-3NaCl solution in the presence of Adenine at various concentrations. pH T/K Kads mol-1 -∆G°ads kJ.mol-1 -∆H°ads kJ.mol-1 -∆S°ads J.mol-1.K-1 2 298 1000 27.06 57.125 100.87 303 500 25.77 103.47 308 333 25.15 103.79 4 298 500 25.34 34.436 30.49 303 333 24.74 31.97 308 250 24.42 32.51       126 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015     NaCl 3 -No.(1): Polarization curves of (SS) corrosion in pH = 2 with 0.6 mol.dm ureFig solution at four temperatures in the range of (293-308)K. NaCl 3 -No.(2): Polarization curves of (SS) corrosion in pH = 4 with 0.6 mol.dm uerFig solution at four temperatures in the range of (293-308)K. 0.00001 0.0001 0.001 0.01 0.1 -300 -250 -200 -150 -100 -50 0 P ot en ti al / m V v s. S C E 293 K 298 K 303 K 308 K   Current density/ µA.cm-2 0.00001 0.0001 0.001 0.01 0.1 -350 -300 -250 -200 -150 -100 -50 0 P ot en ti al / m V v s. S C E 293 K 298 K 303 K 308 K   Current density/ µA.cm-2 P o te n ti al /m V v s. S C E 127 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 for the corrosion of 316L SS in the T 1 to corr(3): Arrhenius plots relating log i .No uerFig pH=2 in the different NaCl concentration over the temperature range (293-308)K. for the corrosion of 316L SS in the T 1 to corrNo.(4): Arrhenius plots relating log i ureFig pH=4 in the different NaCl concentration over the temperature range (293-308)K                   y = ‐1062.9x + 4.1657 R² = 0.9468 y = ‐405.71x + 2.5314 R² = 0.9798 y = ‐308.57x + 2.2571 R² = 0.9918 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 0.00345 0.1 0.3 0.6 Lo g i c o rr 1/T y = ‐1457.1x + 5.2243 R² = 0.9825 y = ‐497.14x + 2.7943 R² = 0.9875 y = ‐348.57x + 2.3371 R² = 0.9936 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 0.00345 0.1 0.3 0.6 Lo g  i co rr 1/T 128 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015   Current density/ µA.cm‐2   Curren                                                                                                      Figure No.(5): The typical polarization curves of 316L SS in 0.6 mol.dm-3 NaCl solutions containing three different concentrations of adenine as inhibitor over the temperature range (298-303)K.                    0.001 0.01 0.1 1 10 100 1000 -1250 -1000 -750 -500 -250 0 250 500 750 1000 P ot en ti al / m V v s. S C E 298 K 303 K 308 K Current density/ µA.cm ‐2 0.0001 0.001 0.01 0.1 1 10 100 1000 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 P ot en ti al / m V v s. S C E 298 K 303 K 308 K 0.0001 0.001 0.01 0.1 1 10 100 1000 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200 P ot en ti al / m V v s. S C E 298 K 303 K 308 K P o te n ti al /m V v s. S C E P o te n ti al /m V v s. S C E P o te n ti al /m V v s. S C E   Current density/ µA.cm‐2  10 ‐2  mol.dm ‐3      Adenine 5x10 ‐3  mol.dm ‐3      Adenine 10 ‐3  mol.dm ‐3      Adenine 129 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015                                       Figure No.(6):The typical polarization curves of 316L SS in 0.6 mol.dm-3 NaCl solutions containing three different concentrations of adenine as inhibitor over the temperature range (298-303)K. 0.0001 0.001 0.01 0.1 1 10 100 1000 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 P ot en ti al / m V v s. S C E 298 K 303 K 308 K   Current density/ µA.cm‐2 0.001 0.01 0.1 1 10 100 1000 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 P ot en ti al / m V v s. S C E 298 K 303 K 308 K 0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 -1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 P ot en ti al / m V v s. S C E 298 K 303 K 308 K   Current density/ µA.cm‐2    Current density/ µA.cm‐2 P o te n ti al /m V v s. S C E P o te n ti al /m V v s. S C E P o te n ti al /m V v s. S C E 10 ‐2  mol.dm ‐3      Adenine 5x10 ‐3  mol.dm ‐3      Adenine 10 ‐3  mol.dm ‐3      Adenine 130 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 Figure No.(7): Langmuir adsorption plots of adenine on to the 316L SS in 0.6 mol. dm-3 NaCl solution at various temperatures. Figure No. (8): Van't Hoff plot 316 L SS in 0.6 mol.dm-3 NaCl solution containing adenine. y = 0.8852x + 0.0013 y = 1.1066x + 0.0021 y = 1.1066x + 0.0031 0 0.005 0.01 0.015 0 0.002 0.004 0.006 0.008 0.01 0.012 298K 303K 308K C /θ C.of AD/mol.dm‐3 pH=2 y = 0.9959x + 0.0022 y = 0.7746x + 0.0034 y = 0.8885x + 0.0041 0 0.005 0.01 0.015 0 0.002 0.004 0.006 0.008 0.01 0.012 298 303 C /θ C.of AD/mol.dm‐3 C /θ C /θ C.of pH=4 y = 6871.4x ‐ 16.258 0 2 4 6 8 0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 1/T K‐1 pH=2 Ln K a d s. y = 4142.9x ‐ 7.7457 5.4 5.6 5.8 6 6.2 0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 1/T K‐1 pH=4 Ln K a d s. 131 | Chemistry 2015) عام 1العدد ( 28مجلة إبن الھيثم للعلوم الصرفة و التطبيقية المجلد Ibn Al-Haitham J. for Pure & Appl. Sci. Vol. 28 (1) 2015 دينين كمثبط صديق بيئيًا لتآكل الفوالذ المقاوم للصدأ في محلول حامضي اإل لكلوريد الصوديوم العزيز عيسىوصال عبد مروة صباح حسين جامعة بغداد. /)ابن الهيثم(كلية التربية للعلوم الصرفةقسم الكيمياء/ 2014 كانون االول21قبل البحث في :،2014 تشرين االول28استلم البحث في: الخالصة أثير تركيز مثبط 316Lيتناول موضوع في دراسة كھروكيميائية لسلوك تآكل الفوالذ المقاوم للصدأ نوع ( ) وت ). تم mol.dm 0.6-3على اعاقة التآكل في محلول حامضي لكلوريد الصوديوم بتركيز ( [Adenine (AD)]اإلدينين ) كما K 308-293) على مدى من درجات الحرارة (pH = 4و pH = 2اجراء البحث عند قيمتين لألس الھيدروجيني ( ھروكيميائي (استقطاب تافل) باستعمال جھاز المجھاد الساكن ، إذ تم التوصل اشتملت الدراسة على طريقة االستقطاب الك بط ( لوك مث ة س ى معرف ه ال ن طريق وديADع اعلين االن ن التف ل م ل ك ى تقلي ل عل ه يعم اثودي ( ) بان mixedوالك inhibitor ما وجد بان الكفاءة تزداد . ك%87)، أي إنه يقوم بعملية تثبيط تآكل سبيكة الفوالذ المقاوم للصدأ بكفاءة مقدارھا 0.01) المساوي (ADتقع عند تركيز المثبط ( %87بزيادة تركيز المثبط وتقل بزيادة درجة الحرارة؛ اذ ان قيمة الكفاءة M عند درجة حرارة (293K) كما اوضحت الدراسة ان عملية امتزاز مثبط اإلدينين .AD على سطح الفوالذ المقاوم ( ).Langmuir Isotherm for Adsorptionة الحرارة لالمتزاز لالنكمير (للصدأ تتبع متساوي درج على التوالي. ADتم حساب ومناقشة المعلمات الحركية والثرموديناميكية لعمليتي تآكل الفوالذ المقاوم للصدأ وامتزاز مثبط المعلمات الحركية والثرموديناميكية. ,استقطاب تافل ,اإلدينين ,الفوالذ المقاوم للصدأ الكلمات المفتاحية: