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Corrosion inhibition of Eichhornia crassipes acid extract on low carbon steel in hydrochloric acid

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  • Save International Journal of M aterials and Chemistry 2012, 2(4): 158-164 DOI: 10.5923/j.ijmc.20120204.08 Corrosion Inhibition of Mild Steel in Hydrochloric Acid by Acid Extracts of Eichhornia Crassipes S. B. Ulaeto1,2,3, U. J. Ekpe1,*, M. A. Chidiebere3, E. E. Oguzie3 1Corrosion and Electrochemistry Research Group, Department of Pure and Applied Chemistry, University of Calabar, PM B 1115, Calabar, Niger ia 2Department of Physical and Chemical Sciences, Rhema University, Aba, Abia State, Nigeria 3Electrochemistry and M aterial Science Research Laboratory, Department of Chemistry, Federal University of Technology, PM B 1526, Owerri, Nigeria Abstract Acid extracts from leaves and roots of Eichhornia crassipes (water hyacinth) were tested as corrosion inhibitors for mild steel in hydrochloric acid solutions using a gasometric technique. The effects of temperature and concentration on the inhibition performance of the extracts have been studied. The results show that both the leaf and root extracts functioned as effective corrosion inhibitors, with the leaf ext racts exerting a greater effect. Fitt ing of the experimental data to the Arrhenius and transition state equations revealed that the organic constituents of the extracts were physically adsorbed on the corroding mild steel surface. The adsorption characteristics of selected extract constituents were theoretically evaluated by mo lecular dynamics simulations in the framework of the density functional theory and confirm d istinct adsorption of the e xtract organic matter on the mild steel surface. Our findings provide ready eco-friendly applicat ion for the problematic fresh water weed Eichhornia crassipes. Keywords Acid Corrosion Inhibit ion, Gasomet ric Technique, Mild Steel, Eichhornia Crassipes, Molecular Dynamics Simu lation 1. Introduction Iron and its alloys are used as materials of choice in diverse industrial and structural applications. Acid solutions are often used in drilling operations in oil and gas exp loration, as well as for cleaning, decaling and pickling of steel structure; processes which are normally acco mpanied by considerable dissolution of the metal and it is very important to add corrosion inhibitors to decrease the corrosion rate in such situations. Organic heterogeneous compounds containing these elements have been reported to be efficient corrosion inhibitors[1-8]. These co mpounds contain nitrogen, oxygen, sulphur and aromatic ring in their mo lecular structures and function via adsorption of the molecules on the metal surface creating a barrier to corrodent attack. The use of natural products of plant origin as corrosion inhibitors has been widely reported by several authors[9-19]. Such interest derives fro m their inexpensive and eco-friendly nature, easy availability and wide variety. Also the use of these biomass products is justified by the phytochemical compounds present therein with mo lecular and electron ic structures bearing close similarity to conventional organic * Corresponding author: (U. J. Ekpe) Published online at Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved inhibitor mo lecules[11]. The yield of these compounds as well as the corrosion inhib ition abilities vary widely depending on the part of the plant and its geographical location[13]. E. crassipes is noted as one of the most important and noxious freshwater weeds[20], ranked 8th in the list of the worlds ten most serious weeds according to[21]. It is a floating aquatic plant with inflated petioles and native to tropical A merica[22]. It is believed that the weed o rig inated in Brazil[23] but found its way into Nigerian waters fro m a lagoon in the Port Novo area of the Republic of Benin which opens into the Badagry creek enroute to the Atlantic ocean [22]. Since then Eichhornia crassipes has become a major weed in Nigeria, having successfully invaded and established itself on the entire Badagary Creek, the Yewa Lagoon, Ologe Lagoon, the Lagos Lagoon and the waterways of Okitipupa, it was reported in 1982 in local newspapers as a weed that is spreading fast and paralyzing the fishing industry[22]. Despite its long list of harmful effects, in recent years it has been found useful in animal feeds, compost, paper, energy (fro m biogas), b iological waste water treat ment and heavy metals uptake[20]. In recent times, studies have been carried out to identify more useful applications of this abundant noxious weed and certain active co mpounds with antio xidant activit ies such as chlorophylls and carotenoids, phenols, alkaloids and terpenoids have been successfully obtained fro m E. 159 International Journal of M aterials and Chemistry 2012, 2(4): 158-164 Crassipes extracts[24]. The antio xidants showed corrosion inhibit ion efficiency on magnesium alloy and it may be due to the presence of a great number of double bonds, amine and hydroxyl groups known for their o xygen scavenging and hydrogen donating antioxidant activit ies[24]. However, to the best of our knowledge, the plant has not been studied for corrosion inhibition abilities on mild steel. The present study investigates the inhibitive effect of leaves (ELV) and roots (ERT) extracts of Eichhornia crassipes on mild steel corrosion in HCl solutions using gasometric technique and its modelled structures provides additional insight into the mechanis m of inhib itory action. 2. Materials and Methods 2.1. Metal S peci men The mild steel sheets used in this present work have the composition presented in Table 1. Before measurements, the mild steel coupons were mechanically polished with series of emery paper of variab le grades starting with the coarsest and proceeding in steps to the finest (1200) grade, degreased with absolute ethanol, dipped into acetone and air dried. A ll experiments were conducted on mild steel coupons of dimension 2.0 x 0.08 x 5.0 cm (with a surface area of 21.12 cm2). Table 1. Chemical composition of the mild steel C Si Mn S P Ni Cr Mo Cu 0.19 0.26 0.64 0.05 0.06 0.09 0.08 0.02 0.27 2.2. Preparati on of Plant Extracts Leaves and roots of E. crassipes were collected fro m a water dam in the Un iversity of Ibadan, Nigeria. They were cleaned fro m ep iphytes, washed, dried to a constant weight, ground and kept in labelled glass jars till use. Stock solutions of the leaves and roots extracts were prepared by soaking 4.0 g of the dried and ground leaves and roots in 1000 ml of 5 M HCl solution. The resultant solution was kept for 24 hours, filtered and stored. Fro m the stock solution (4.0 g/l), inhibitor test solutions (concentrations of 0.1, 0.5, 1.0 and 2.0g/l) were prepared. 2.3. Gasometric Experiments Gasometric measurements were carried out as previously described[25, 26]. Experiments were conducted at 30, 40, 50 and 60℃. Gasometric technique is based on the principle that corrosion reactions in aqueous acidic media are characterized by the evolution of gas resulting fro m the cathodic reaction of the corrosion process, which is proportional to the rate of corrosion[27]. The rate of evolution of the gas (RH) is determined fro m the slope of the graph of volume of gas evolved (V) versus time (t) and the degree of surface coverage (θ) and hence inhibition efficiency (η%) determined using equations (1) and (2), res p ectiv ely . θ = (1 - RHi/ RHo) (1) η% = (1 - RHi/ RHo) x 100 (2) where RHo and RHi are the rates of hydrogen evolution in the absence and presence of the inhibiting mo lecules, respectively. Results obtained using the gasometric technique have been corroborated by other well established corrosion rate determinat ion techniques, including weight loss, thermo metric and electrochemical techniques[3, 28, 29]. 2.4. Quantum Chemical Calcul ati ons All theoretical calculat ions were performed using the density functional theory (DFT) electronic structure programs Forcite and DMol3 as contained in the Materials Studio 4.0 software (Accelrys, Inc.). We modeled the mo lecular electronic structures of the co mpounds, including the distribution of frontier molecular orbitals and Fukui indices in order to establish the active sites as well as the local reactivity of the mo lecules. The calculat ions were performed by means of the DFT electronic structure program DMol3 using a Mulliken population analysis[30,31]. Electronic parameters fo r the simulat ion include restricted spin polarizat ion using the DND basis set and the Perdew Wang (PW) local correlation density functional. Geo metry optimization was achieved using COMPASS force field and the Smart minimize method by high-convergence criteria. Forcite quench molecular dynamics was used to sample many different low energy adsorption configurations of the different molecu les on Fe[32,33]. The Fe crystal was cleaved along the (110) plane. Calcu lations were carried out in a 12 x 8 supercell using the COMPASS fo rce field and the Smart algorith m with NVE (microcanonical) ensemble, a time step of 1 fs and simu lation time 5 ps. Temperature was fixed at 350 K. 3. Results and Discussion We have employed gas-volumetric measurements to investigate mild steel corrosion in 5 M HCl solutions in the absence and presence of ELV and ERT ext racts, which are studied herein for corrosion-inhibit ing efficacy. 3.1. Corrosion Rates Figure 1 shows the representative hydrogen evolution plots for mild steel in uninhib ited 5 M HCl at 30 – 60℃. The data presented are means of triplicate determinations, with standard deviation ranging from 0 to 0.003. Hydrogen gas evolution can be seen to increase with increase in temperature resulting in degradation of the mild steel. Figure 2 illustrates the hydrogen gas evolution rates of the mild steel specimen in 5 M HCl in the presence of different concentrations of ELV (Figure 2a) and ERT (Figure 2b) at different temperatures. The plots indicate that the extracts actually retarded mild steel corrosion at all concentrations in 5 M HCl and the inhibiting effect becomes mo re pronounced at higher extract concentrations. The data in Figures 1 and 2 S. B. Ulaeto et al.: Corrosion Inhibition of M ild Steel in Hydrochloric Acid by Acid Extracts of Eichhornia Crassipes 160 also indicate that the rates of steel corrosion in absence and presence of the extracts increased with rise in temperature. This is because an increase in temperature usually accelerates corrosive processes, particularly in med ia in which H2 gas evolution accompanies corrosion, giving rise to higher dissolution rates of the metal. 55 30oC 50 40oC 45 50oC 40 60oC 35 30 VH/(cm3) 25 20 15 10 5 0 -5 0 5 10 15 20 25 30 Time/(min) Figure 1. Hydrogen evolution plots for mild steel in uninhibited 5 M HCl at 30 – 60℃ 3.5 (a) 30oC 3.0 40oC 50oC 60oC 2.5 Quantitative characterization of the inhib iting effect of PNG ext ract on the free corrosion of mild steel was carried out by an assessment of the inhibition efficiency (IE %) defined by Eq. 2 above. Figures 3a and 3b show the variation of inhibit ion efficiency with extract concentration and temperature in 5 M HCl. Inhibit ion efficiency increased steadily with increasing extract concentration and decreases with rise in temperature. The increase in efficiency of inhibit ion with ext ract concentration indicates that more of the extract constituents are adsorbed on the metal surface at higher concentration, leading to greater surface coverage. Declining efficiency with rise in temperature suggests a possible shift of the adsorption–desorption equilibriu m towards desorption of adsorbed inhibiting species, since the interface beco mes increasingly agitated due to higher rates of hydrogen gas evolution, thus perturbing the adsorbed species. Additionally, the roughening of the metal surface as a result of enhanced corrosion could also reduce the ability of the inhibitor to be adsorbed on the metal surface at high temperatures. 80 30oC (a) 40oC 70 50oC 60 60oC 50 40 Inhibition efficiency/(%) Corrosion rate(cm3min-1) 2.0 30 20 1.5 10 1.0 0 0.5 0.1 0.5 1.0 2.0 Extract Concentration/(gl-1) 5 (b) 4 4.0 30oC 40oC 50oC 60oC 0 1 2 3 4 Extract concentration/(gl-1) 80 30oC 40oC (b) 50oC 60 60oC 40 Inhibition efficiency/(%) Corrosion rate(cm3min-1) 3 20 0 2 -20 1 0 0 1 2 3 4 Extract concentration/(gl-1) Figure . 2. Variation of corrosion rates with extracts concentration for mild steel in 5 M HCl containing (a) ELV and (b) ERT 3.2. Inhi bi tion Efficiency and Adsorption Considerations -40 0 1 2 3 4 Extract concentration/(gl-1) Figure 3. Variation of inhibition efficiency with extracts concentration for mild steel in 5 M HCl containing (a) ELV (b) ERT In accounting for the observed protective effect, it should be noted that the ext racts comprise a mixture of organic and resinous matter. So me of which are known to exhib it good 161 International Journal of M aterials and Chemistry 2012, 2(4): 158-164 corrosion inhibiting abilities. The comp lex chemical compositions make it rather difficult to assign the inhibiting action to a particular constituent. Nevertheless, the net adsorption of the e xtract organic matter on the meta l surface creates a barrier to charge and mass transfer, thus protecting the metal surface fro m corrodent attack [8]. Interestingly, Shanab et al.[24] isolated, characterized and assessed the corrosion inhibiting e fficacies of diffe rent active antioxidant fract ions of E. Crassipes extracts on magnesium corrosion in saline environments. The obtained fractions include the alkalo id (18,19-Secoyohimban-19-oic acid, 16, 17,20, 21-tetradehydro-16-(hydro xy methyl)-methyl ester) and several phthalate derivatives ((i) Methyl dioctyl phthalate, 1,2-Ben zene dicarbo xylic acid, mono-(2-ethylhexy l ester) (ii) 1,2 Ben zene dicarbo xy lic acid, dioctyl ester (iii) Methyl dioctyl phthalate, (iv) 1,2 Ben zene dicarbo xylic acid, diisooctyl ester). The results indicate that all the different fractions inhib ited the corrosion reaction under the studied conditions, which was attributed to the chemical structure with many double bonds, hydroxyl and amine groups which have high o xygen scavenging activity leading to oxygen reduction in the corroding s ys tem and cons equently reduces the rate of metal corrosion by forming an adsorbed layer on the metal surface. The often complex processes associated with metal-inhibitor interactions can be theoretically investigated at the molecular level using computer simulations of suitable models in the framework of the density functional theory (DFT). We have performed such calculat ions to model the electronic and adsorption structures of above mentioned phytochemica l constituents of E. Crassipes. resemblance to those of conventional organic corrosion in h ib ito rs [3 4- 3 8]. The corresponding optimized (lowest energy) adsorption structures for the different molecules on Fe (110) surface are presented in Figures 5 a-e and show that all the mo lecules maintain a flat-lying adsorption orientation on the Fe surface. The motivation for the computational studies is not so much to provide in depth explanation of the adsorption of the extract, but rather to provide some insight into the nature of their individual interactions with the mild steel surface and their possible contributions to the overall inhibit ing effect. The high negative values of the corresponding adsorption energies[Eads = Etotal - (Emol + EFe)]; where Emol, EFe and Etotal correspond respectively to the total energies of the molecule, Fe (110) slab and the adsorbed Mol/Fe (110) couple, point towards strong interaction of the molecules with the metal surface and is responsible for the observed corrosion inhibit ing effect of the ext racts. (a) Eads =-178 kcal/mol (i) (ii) (iii) (a) (b) Eads = -160 kcal/mol (c) Eads = -241 kcal/mol (b) (c) (d) (d) Eads = -342 kcal/mol (e) Eads = -221 kcal/mol (e) Figure 4. (COLOUR ONLINE) Electronic properties of (a) (18 ,1 9-Secoy oh imban-1 9-o icacid,16 ,1 7,20 ,21 -t etradeh y dro -16 -(hy dro xym ethyl)-, methyl ester, (15 beta,16 E); (b) 1,2-Benzene dicarboxylic acid, mono-(2-ethylhexyl ester); (c) 1,2 Benzene dicarboxylic acid, dioctyl ester; (d) Methyl dioctyl phthalate; (e) 1,2 Benzene dicarboxylic acid, diisooctyl ester: (i) total electron density (ii) HOMO orbital (iii) LUMO orbital. (Atom legend: whit e = H; gray = C; red = O; blue = N Figure 4 depicts the highest occupied molecular orb ital (HOMO), lowest unoccupied molecular orb ital (LUM O) and the total electron density, all of which bear close Figure 5. Molecular dynamics models of adsorption of the different extract constituents on Fe (110) surface; (a) (18 ,1 9-Secoy oh imban-1 9-o icacid,16 ,1 7,20 ,21 -t etradeh y dro -16 (hydroxymethyl), methyl ester, (15 beta,16 E);(b) 1,2-Benzene dicarboxylic acid, mono-(2-ethylhexyl ester); (c) 1,2 Benzene dicarboxylic acid, dioctyl ester; (d) Methyl dioctyl phthalate; (e) 1,2 Benzene dicarboxylic acid, diisooctyl ester 3.3. Thermodynamics Parameters The Arrhenius-type relationship between the corrosion rate (k) of mild steel in acidic med ia and temperature (T) as often expressed by the Arrhenius equation was used to determine the activation energies (Ea): S. B. Ulaeto et al.: Corrosion Inhibition of M ild Steel in Hydrochloric Acid by Acid Extracts of Eichhornia Crassipes 162 k = A exp (-Ea/ RT) (3) A is the preexponential factor and R the universal gas constant. The variation of logarith m of corrosion rate with reciprocal of absolute temperature is shown in Figure 6 and Figure 7 for mild steel corrosion in 5 M HCl containing ELV and ERT respectively. The calculated values of Ea are given in Table 2. Addition of the extracts can be seen to increase Ea for the corrosion reaction, imply ing that the extracts would be more effective at lower temperatures, wh ich in agreement with the observed trend of inhib ition efficiency with temperature as well as the proposed physisorption mechanis m for the adsorption of the extract organic matter. Log CR 0.6 0.5 0.4 Blank 0.1g/l 0.3 0.5g/l 0.2 1.0g/l 2.0g/l 0.1 4.0g/l 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 3.00 3.05 3.10 3.15 3.20 3.25 3.30 1/Tx10-3(K-1) Figure 6. Arrhenius plots for mild steel corrosion in 5 M HCl in the absence and presence of different concentrations of ELV Log CR 0.8 0.7 0.6 Blank 0.5 0.1g/l 0.5g/l 0.4 1.0g/l 0.3 2.0g/l 0.2 4.0g/l 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 3.00 3.05 3.10 3.15 3.20 3.25 3.30 1/Tx10-3(K-1) Figure 7. Arrhenius plots for mild steel corrosion in 5 M HCl in the absence and presence of different concentrations of ERT Some other activation parameters such as the enthalpy change of activation (∆H*) and entropy change of activation (∆S*) were obtained fro m the Eyring transition state equation[39]: CR = RT exp ∆S°  exp − ∆H°  (4) Nh  R   RT  where R is molar gas constant; T is absolute temperature, N is Avogadro’s number, h is Planck’s constant. Table 2. Calculated values of activation energy, activation enthalpy and activation entropy for mild steel in 5 M HCl containing ELV and ERT System Con c. (gl -1 ) Ea (KJmol -1) ∆Ho (KJmol -1) ΔSo (Jmol -1 K-1 ) Blank 0 46.27 43.63 -104.50 0.1 52.42 0.5 44.28 49.78 41.64 -86.23 -85.22 ELV 1.0 54.43 51.79 -84.56 2.0 58.29 4.0 57.70 55.65 55.06 -74.04 -78.61 0.1 65.65 63.01 -43.85 0.5 ERT 1.0 65.86 73.47 63.22 70.83 -45.14 -22.71 2.0 73.52 70.88 -24.25 4.0 61.93 59.29 -62.23 Straight lines were obtained fro m the Eyring plots (Figures 8 and 9) with slope ∆H* /R and intercept [ln (R/ NAh) + ∆S*/R]. The calculated values of ∆H* and ∆S* obtained from these plots are also given in Table 2. The positive values of ∆H* both in absence and presence of inhibitor reflect the endothermic nature o f the steel dissolution process. It is also clear that the activation enthalpies vary in the same manner as the activation energies, supporting the proposed inhibition mechanism. Large and negative values of entropies imply that the activated complex in the rate determining step represents an association rather than a dissociation step, mean ing that a decrease in disordering takes place on going from reactants to the activated complex. Log(CR/T) -1.9 -2.0 Blank -2.1 0.1g/l 0.5g/l -2.2 1.0g/l -2.3 2.0g/l 4.0g/l -2.4 -2.5 -2.6 -2.7 -2.8 -2.9 -3.0 -3.1 -3.2 -3.3 -3.4 3.00 3.05 3.10 3.15 3.20 3.25 3.30 1/Tx10-3/(K-1) Figure 8. Eyring plots for mild steel corrosion in 5 M HCl without and with ELV 163 International Journal of M aterials and Chemistry 2012, 2(4): 158-164 Log(CR/T) -1.8 -1.9 Blank -2.0 0.1g/l 0.5g/l -2.1 1.0g/l -2.2 2.0g/l 4.0g/l -2.3 -2.4 -2.5 -2.6 -2.7 -2.8 -2.9 -3.0 -3.1 -3.2 3.00 3.05 3.10 3.15 3.20 3.25 3.30 1/TX10-3/(K-1) Figure 9. Eyring plots for mild steel corrosion in 5 M HCl without and with ERT [5] P. C. Okafor, E.E. Ebenso, U.J. Ibok, U.J. Ekpe, M.I. Ikpi (2003) Trans. SAEST, 38: 91 [6] K. F. Khaled, N. Hackerman (2003) M ater. Chem. Phys., 82: 949 [7] P. C. Okafor, E.E. Ebenso, U.J. Ekpe (2004) Bull. Chem. Soc. Ethiopia, 18: 181 [8] E. E. Ebenso, E.E. Oguzie (2005) M ater. Lett. 59(17): 2163 [9] F. Zucchi, H. I. Omar (1985) Surface Tech., 24(4): 391 [10] S. P. Ramesh, K. V. Kumar, M . G. Sethuraman (2001) Bull. of Electrochem., 17(3): 141 [11] P.C. Okafor, U.J. Ekpe, E.E. Ebenso, E.E. Oguzie, N.S. Umo, A.R. Etor (2006) Trans. SAEST, 41: 82 [12] M . Abdel-Gaber, B. A. Abd-El-Nabel, I. M . Sidahmed, A. M . El-Zayady, M. Saadawy (2006) Corros. Sci., 48: 765 [13] E.E. Oguzie (2006) Pigm. Res. Tech., 35(2): 63 4. Conclusions The aim of this research was to determine the feasibility of exploit ing the bothersome weed (Eichhornia crassipes ) for materials corrosion control. Our findings show that the leaf (ELV) and root extracts (ERT) of E. crassipes effectively inhibited mild steel corrosion in 5 M HCl. At higher concentrations and lower temperatures, the extracts performed better, whereas at low concentrations and high temperature, their inhib ition efficiency decreased. ELV inhibited better than ERT at ordinary temperature and highest concentration of 4 g/l. The inhibit ing potential of the extracts were theoretically confirmed via, DFT based quantum chemical co mputations of parameters associated with the electronic and adsorption structures of selected phytochemical co mponents of the e xtract. These results propose a ready industrial application for the problemat ic fresh water weed for the control of the acid corrosion of mild steel. [14] P. C. Okafor, E. E. Ebenso (2007) Pigm. Res. Tech., 36(3): 134 [15] P. C. Okafor, V. I. Osabor, E. E. Ebenso (2007) Pigm. Res. Tech., 36(5): 299 [16] E. E. Oguzie (2008) Corros. Sci.50: 2993-2998 [17] P. C. Okafor, M . E. Ikpi, I.E., Uwah, E.E., Ebenso, U.J Ekpe, S.A. Umoren (2008) Corros. Sci., 50: 2310 [18] P.C. Okafor, I.E. Uwah, O.O. Ekerenam, U.J. Ekpe (2009) Pig. Res. Tech., 38(4): 236 [19] E. E. O guzie, C. K. Enenebeaku, C. O Akalezi, S. C. Okoro, A. A. Ayuk, E. N. Ejike, J. (2010) Colloid Interf. Sci., 349: 283 [20] B. Gopal (1987) Water Hyacinth: Aquatic plant studies 1. New York: Elsevier Science Publishing Company. [21] K. R. Reddy, D. L. Sutton (1984) J. of Environ. Quality, 13: 1 [22] O. A. Akinyemiju (1987) J. of Aquatic Plant M gt., 25: 24 [23] T. D. Center, M . P. Hill, H. Cordo, M . H. Julien (2002) USDA Forest Service Publication FHTET-2002-04: 41 ACKNOWLEDGEMENTS The authors acknowledge Patrick Asuquo for technical assistance in performing some measurements [24] S. M . M . Shanab, M . A. Ameer, A. M . Fekry, A. A. Ghoneim and E. A. Shalaby (2011) Int. J. Electrochem. Sci.,6: 3017 [25] U. J. Ekpe, U.J. Ibok, B.I. Ita, O.E. Offiong, E.E. Ebenso (1995) M ater. Chem. Phys., 40(2): 87 [26] B. I. Ita, O.E. Offiong (1997) M ater. Chem. Phys., 48(2): 164 REFERENCES [1] V. U. Khuzhaeu, S. F. 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