Scientific paper Protection of Copper Surface With Phytic Acid Against Corrosion in Chloride Solution Dunja Peca,1 Boris Pihlar2 and Ingrid Milo{ev1* 1 Jozef Stefan Institute, Department of Physical and Organic Chemistry, Jamova 39, SI-1000, Ljubljana, Slovenia 2 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, SI-1000 Ljubljana, Slovenia * Corresponding author: E-mail: ingrid.milosev@ijs.si tel.: + 386 1 4773 452 Received: 13-12-2013 Dedicated to the memory of Prof. Dr. Marija Kosec. Abstract Phytic acid (inositol hexaphosphate) was tested as a corrosion inhibitor for copper in 3% sodium chloride. Phytic acid is a natural compound derived from plants, it is not toxic and can be considered as a green inhibitor. Electrochemical methods of linear polarization and potentiodynamic polarization were used to study the electrochemical behaviour and evaluate the inhibition effectiveness. To obtain the optimal corrosion protection the following experimental conditions were investigated: effect of surface pre-treatment (abrasion and three procedures of surface roughening), pre-formation of the layer of phytic acid, time of immersion and concentration of phytic acid. To evaluate the surface pre-treatment procedures the surface roughness and contact angle were measured. Optimal conditions for formation of phytic layer were selected resulting in the inhibition effectiveness of nearly 80%. Morphology and composition of the layer were further studied by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The layer of phytic acid with thickness in the nanometer range homogeneously covers the copper surface. The obtained results show that this natural compound can be used as a mildly effective corrosion inhibitor for copper in chloride solution. Keywords: Copper, phytic acid, chloride solution, corrosion, corrosion inhibitor 1. Introduction Copper has a high thermal and electrical conductivity, resistance to micro-organisms and good mechanical properties.1 Moreover, it forms many alloys, which increases its use in industry and in daily life. Pure copper exhibits a good corrosion resistance at the atmospheric conditions, but in many aggressive media the corrosion rate increases. For example, in chloride solutions uniform and pitting corrosion may occur, as chloride ions accelerate dissolution of copper.2 One of the important ways to protect metals against corrosion is the use of corrosion inhibitors. Up to date, mainly organic molecules which contain heteroatoms have been investigated as inhibitors. A coordinative bond between heteroatoms and copper modifies the surface resulting in the formation of protective surface layer. The most widely used inhibitors such as azoles and amines have shown a high level of inhibition.3 However, some of these compounds are at high price, or are toxic and should be thus use with restriction. Due to these reasons, contemporary research is dedicated to search for new, environmentally friendly reagents available at reasonable price. Phytic acid is in chemical structure inositol hexaphosp-hate (IP6), with a molecular formula C6H6[OPO (OH)2]6. It contains six phosphates with 12 replaceable protons (Fig. 1) and expresses highly pH dependent chelating properties, so it is able to interact with many metal ions, such as Cu2+, Zn2+ and Fe2+.4,5 It may be assumed that the interaction between phytic acid and copper would lead to the surface modification and, consequently, to the surface protection. Phytic acid is a natural compound derived from plant sources. It can be found in cereals, nuts, seeds, corn, Figure 1. The structure of phytic acid (inositol hexaphosphate, wheat, rice and soybeans.6 Hitherto is this compound used as a cleansing agent, water treatment agent, food additive and cosmetic additive.4'7 Phytic acid is a non-toxic and environmentally friendly reagent. Moreover, it is soluble in water and available at low cost.8 9 Due to these properties phytic acid and its salts have recently attracted interest as potential corrosion inhibitors on different metals.4-15 Phytic acid extract from rice bran inhibited corrosion of copper almost to 95%.10 The inhibition effect was the highest at the concentration of 5 mg/L IP6, as determined from the weight-loss measurements. In addition to the electrochemical methods, Shen et al. used surface enhanced Raman scattering to investigate the composition of copper surface in 3% NaCl containing IP6.11 Formation of self-assembled monolayers was achieved on roughened surfaces obtained through oxidation-reduction process. Namely, in order to enhance subsequent adsorption of IP6, in majority of studies the surface roughening in KC-l4,5,1315 or H2SO411 were used. In some studies no surface roughening was used prior immersion in IP6 solution.8,9 Phytic acid acted as a cathodic inhibitor with values of AGads close to -40 kJ mol1 indicating that chemisorp-tion may be the operative mechanism.11 The binding of Na phytate on copper was determined using Raman spectros-copy and electrochemical methods in 0.1 M KCl.5 The chemical adsorption was proposed to occur through two phosphate groups leading to the inhibition effectiveness (IE) of 41.2%.5 Na phytate achieved high inhibition in 0.1 M NaOH (ca. 90%).7 Phytate was shown to promote the formation of the cuprous species, but strongly inhibited the subsequent oxidation to cupric corrosion product. The inhibition effectiveness was strongly dependent on NaOH concentration.7 In domestic water, the IE value of copper corrosion was dependent on the type of the phytate salt; the IE for Ca and Mg salts was 90%, but that of Na phytate only 65.3%.12 Electrochemical studies performed on silver electrode showed that IP6 can form dense monola-yers and protect silver in acidic and in alkaline condi- tions.13 Further, phytic acid is able to interact with brass4 and cupronickel (copper-nickel alloy).14,15 The aim of this work was to consider the use of phytic acid as an inhibitor of copper corrosion in chloride solution. In order to stimulate the adsorption of phytic acid at the copper surface, three different surface roughening procedures were examined. In the first set of experiments the electrochemical measurements were carried out directly in 3% NaCl solution containing phytic acid. In the second set of experiments, the sample was first immersed in the solution of phytic acid, and then electrochemical measurements were performed in 3% NaCl solution. The corrosion parameters and inhibition effectiveness were deduced from electrochemical polarization measurements. Surface roughness, contact angle, surface morphology and composition were analysed using confo-cal microscope, tensiometer, scanning electron microscope, energy dispersive X-ray spectrometer and X-ray photoelectron spectrometer. 2. Experimental 2. 1. Materials and Chemicals Working electrode used for electrochemical measurements was copper (purity 99.9%) purchased in the shape of 2 mm-thick foil (Goodfellow, Cambridge, UK). Samples were cut into the shape of discs with diameter 15 mm. Electrode was first abraded on SiC papers under water stream up to 4,000-grit (Struers Labo-Pol-5), rinsed with water, ultrasonically cleaned with ethanol and dried by a stream of nitrogen gas. All experiments were performed on freshly prepared copper surface. Electrochemical measurements were performed in 3% sodium chloride (Carlo Erba Reagenti, p.a. quality). Phytic acid was supplied by Acros organics (purity 50%), H2SO4 (96%) by Carlo Erba Reagenti, HNO3 (65%) by AppliChem, and KCl by Sigma Aldrich. Solutions were prepared using Milli-Q deionized water with the resistivity of 18.2 Mfi cm at 25 °C (Millipore, Billerica, MA). 2. 2. Surface Pre-treatment To increase the surface roughness three procedures on freshly abraded copper electrodes were performed -two types of oxidation-reduction cycle (ORC) and etching: (i) oxidation-reduction cycle was performed elec-trochemically in 0.1 M KCl. Sample was subjected to potential cycle between -0.4 and 0.4 V vs. saturated calomel electrode (SCE) with a potential scan rate of 30 mV/s and then hold at the final potential for 5 seconds.5 This procedure was repeated three times. This procedure was denoted as "ORC in KCl". (ii) oxidation-reduction cycle was performed elec- trochemically in 2 M H2SO4. Sample was polarized with a potential scan rate of 30 mV/s from -0.55 V up to the potential at which the current reached the value of 215 mA/cm2.11 This procedure was denoted as "ORC in H2SO4". (iii) etching was performed by immersing the sample into 10% HNO3 for 30 seconds. This procedure was denoted as "etching in HNO3". Following the roughening step the surface was always rinsed with distilled water and dried. 2. 3. Formation of Layer of Phytic Acid Two procedures were used to form the layer of phyt-ic acid on abraded surface (without roughening step) and roughened copper surface. The first comprised the immersion of the electrode directly in 3% NaCl solution containing various concentrations of phytic acid (0.01, 0.05, 0.1, 0.5 and 1 mM) as inhibitor. Immersion time was up to 6 hours followed by electrochemical measurements. Second procedure included the pre-treatment the electrode, i.e. immersion of the sample into solution of various concentrations of phytic acid (0.01, 0.1 and 1 mM) for various immersion times (1, 4, 6 and 8 hours) to form the protection layer. The sample was then transferred into another cell to perform electrochemical measurements in 3% NaCl solution. 2. 4. Electrochemical Measurements Electrochemical measurements and oxidation-reduction cycles were performed in a three-electrode cell (volume 1000 mL, Autolab, Metrohm Autolab, Utrecht, The Netherlands). Copper sample as working electrode was embedded in a Teflon holder with the area exposed to solution of 0.95 cm2. Saturated calomel electrode (SCE, E = 0.250 V vs. SHE) was used as a reference electrode and carbon rod served as a counter electrode. A Parstat potentiostat/galvanostat model 263A (PAR) controlled by PowerSuite software was used for ORC and electrochemical measurements. Before the electrochemical measurement, the sample was allowed to stabilize at the open circuit potential (Eoc). Linear polarization was then performed using a potential scan rate of 0.167 mV/s in potential range ± 10 mV with respect to the stabilized value of Eoc to obtain the polarization resistance (Rp). The value of Rp was determined as the slope of the current vs. potential curve. Potentiodynamic curve started 250 mV more negative with respect to Eoc in the anodic direction with a potential scan rate 1 mV/s up to 0.8 V. The values of corrosion potential, Ecorr and corrosion current density (jcorr) were deduced by the analysis of the Tafel region. Measurements were repeated at least twice and the results presented are the mean values. Inhibition effectiveness, IE, of the samples immersed into IP6 solution was calculated according to the equation: 1EC%) = _ Jcorr(bare) -/corr(mod} i corr(bare) * 100 (1) where Ware) icorr(mod) is corrosion current density for bare surface and surface modified by phytic acid. 2. 5. Surface Analysis Surface roughness (Ra) was determined using a con-focal optical microscope (Axio, CSM 700, Zeiss). 3-D profiles were measured using an objective of 50x magnification. The vertical resolution was 0.05 pm, and the scanning range 10 pm. The results are expressed as average surface roughness, Ra, as the average of the absolute value of height Z(x,y) in the measurement length, l, of the roughness curve in x and y direction.16 The value of l was 1 mm. A tensiometer Kruss DSA 20E 20 (Kruss GmbH, Hamburg, Germany) was used for contact angle measurements (CA) of water drop on copper surface. The measurements were carried out at room temperature. Contact angles were determined based on the image of the deioni-zed water drop on the sample surface using Drop-shape-analysis software which enables the fitting of the water drop on the surface and allows a precise determination of the contact angle value. Each contact angle value is the average of at least three measurements made on different locations of the same sample. For surface analysis a field emission scanning electron microscopy (FEG-SEM; Joel JSM-7600F) equipped with energy dispersive X-ray spectroscopy (EDS, Oxford Instruments, INCA) were used. Further, X-ray photoelec-tron spectroscopy (XPS) was performed with a TFA Physical Electronics Inc. spectrometer using mono-chro-matized Al Ka radiation (1486.6 eV) and a hemispherical analyser. The measurements were conducted at three different take-off angles (detection angle) with respect to the surface plane, 15°, 45° and 75°. Information closer to the surface is obtained at small angles, whereas at large angles information closer to the inner interface with the bulk is obtained. The energy resolution was 0.5 eV. Survey scan spectra were recorded at a pass energy of 187.85 eV, and individual high-resolution spectra at a pass energy of 29 eV with an energy step of 0.1 eV. 3. Results and Discussion 3. 1. Corrosion Measurements in 3% NaCl Solution Containing Phytic Acid The effects of the concentration of phytic acid (IP6), the pre-treatment of the surface and immersion time at the Eoc on the copper corrosion 3% NaCl were investigated. First, measurements were carried out on abraded copper surface. Linear polarization (Fig. 2) and potentiodynamic curves (Fig. 3) were measured following the stabilization at the Eoc for six hours (denoted as tstab). Electrochemical parameters (Rp, Ecorr, jcorr) and inhibition effectiveness (IE) deduced from electrochemical measurements are presented in Table 1. During stabilization at the Eoc, the potential shifted in the negative direction within the first 1000 s and then remained approximately constant. Copper sample in NaCl solution without IP6 inhibitor achieved the most negative value of Eoc (Table 1). The highest polarization resistance and, consequently, highest resistance to uniform corrosion, exhibited the sample immersed in the solution containing 0.05 mM phytic acid (Fig. 2). It is noteworthy that Rp and jcorr values were not completely correlated, i.e. high Rp values were not always followed by low jcorr values, probably due to the insufficient protection of the surface by IP6 molecules once the surface was polarized to catho-dic direction. Further, in NaCl solution without inhibitor the copper sample exhibited only slightly lower Rp value than the sample immersed in 0.05 mM phytic acid; samples immersed in solutions containing other concentrations of IP exhibited lower R values. 6p Polarization curves in 3% NaCl solution with and without addition of IP6 (Fig. 3) showed typical shape characteristic for chloride solution.17 Cathodic reaction in the vicinity of Ecorr is related to the reduction of oxygen. In neutral chloride solution, anodic reaction is formation of cuprous ions followed by the formation of the main initial corrosion product cuprous chloride (CuCl).2 CuCl reacts to produce cuprous oxide reflecting in the formation of plateau in the range from -0.3 to -0.2 V (Fig. 3). The mechanism of cuprous oxide production in the presence of chloride ions is usually taken as precipitation reaction.2 At potentials more positive than -0.2 V the current density increases again leading to the formation of anodic peak at 0 V due to the formation of CuCl. The current minimum denotes the maximum surface coverage with cuprous chloride. CuCl species do not attain the sufficient protection and the current density progressively increases resulting in the formation of cupric ions. In the presence of IP6 the value of Ecorr is shifted to more positive values up to 40 mV. The shape of the curve changed; the current density in the cathodic branch decreased, and in the anodic branch the current plateau disappeared. At potentials more positive than -0.2 V the presence of inhibitor did not affect the shape of the curve significantly. Decreased values of jcorr resulted in the '-g -C.23 0) O Q. -C.Z4 / / / j w .* A ......*" X NaCl 0.01 mM IP6 ..... 0,1 mM IPg - 1.0 mM IPg current density (pA cm ) Figure 2. Linear polarization curves recorded for abraded Cu in 3% NaCl, and in 3% NaCl with the addition of different concentrations of phytic acid (IP6). dE/dt = 0.167 mV/s, t b = 6 h. Figure 3. Potentiodynamic polarization curves recorded for abraded Cu in 3% NaCl, and in 3% NaCl with the addition of different concentrations of phytic acid (IP6). dE/dt = 1 mV/s, tstab = 6 h. Table 1. Electrochemical parameters (open circuit potential, Eoc, polarization resistance, Rp, corrosion potential, Ecorr, corrosion current density, jcorr, and inhibition effectiveness, IE) deduced for abraded Cu in 3% NaCl, and in 3% NaCl containing different concentrations of phytic acid (IP6).The sample was stabi- solution Eoc (mV) Rp (a cm2) Ecorr (mV) Jcorr ■M- y»L~-''ÜX- lO.OkV LEI 3EM a/12/2013 VTO 15. Osa B 33: 19 Figure 8. SEM images and images of water drop during contact angle measurements (inset) of Cu surface after immersion for 6 hours in 0.1 mM solution of phytic acid (a) abraded Cu; (b) roughened by ORC in H2SO4. i.e. CA = 71.4° on roughened and CA = 65.7° on abraded surface (Fig. 8, inset). Values obtained did not differ significantly from those obtained on bare surface, i.e. CA = 78.6° on roughened and CA = 67.0° on abraded surface (Table 2). For both samples the EDS analysis identified only signal of copper. As the depth of the EDS analysis is approximately 1 pm, we can assume that the layer formed in phytic acid is thinner; therefore, signals of phosphorus and oxygen related to phytic acid could not be identified by EDS. To prove the formation of protective layers, XPS with the analysis depth of approximately 10 nm was explored. Survey XPS spectrum recorded at the surface of Cu sample immersed for 6 h in 0.01 mM IP6 solution identified the presence of copper, oxygen, phosphorus and car- Figure 9. Survey spectra of the surface layer formed on roughened copper surface after 6 hours immersion in 0.1 mM phytic acid. Take-off angle 45°. The composition deduced from survey spectrum is given in inset. Surface was roughened by ORC in H2SO4. bon (Fig. 9). The presence of phosphorous confirms that the molecule of phytic acid has interacted with copper surface and formed a surface layer. As the ratio P:O in phytic acid is 1:4, the expected content of oxygen would be around 10 at.% if only phytic layer would be present at the surface. As the measured oxygen content is over 30 at.% it may be assumed that copper oxide is formed along with the layer of phytic acid molecules. The content of carbon expected from the atomic ratio in IP6 should not exceed that of phosphorus, so we can conclude that the vast majority of measured carbon is related to adventitious carbon. High resolution spectra were recorded to analyse the presence of various chemical species at the surface. The position of Cu 2p3/2 peak is at the binding energy, Eb, of 932.8 eV, in accordance with literature data for Cu and Cu2O (Fig. 10a). Copper and cuprous compounds cannot be differentiated in Cu 2p spectra due to the small chemical shift.18 The presence of cupric species is noted by the satellite peak approximately 10 eV above the main Cu 2p3/2 peak. The absence of the peak proves that cupric species are not present the surface (Fig. 10a). In order to differentiate between copper and cuprous species Auger peak in the XPS spectrum is used (Fig. 10b). Auger [Cu(L3M4 5M4 5)] spectra of Cu and Cu2O are significantly different and allow them to be differentiated.18 The metal shows an Auger peak centred at a binding energy, Eb, of 568.2 eV, while in Cu2O this peak is centred at Eb of 570.6 eV.19 Each of the Auger peaks can be deconvoluted using four peaks.18 The Auger peak of the sample immersed in phytic acid showed both peaks, at 568.0 eV and 570.8 eV (Fig. 10b) proving the presence of copper and cuprous oxide species. The peak at lower Eb, 565.5 eV, is related mainly to Cu. The intensity of peaks related to Cu metal (at 565.5 eV and 568.0 eV) decreased with decreasing take-off angle, i.e. from interface with metal substrate to la- yer surface, indicating that cuprous species (at 570.8 eV) are mainly present at the surface layer. The O 1s peak was centred at 531.5 eV at take-off angle of 45° (Fig. 10c). This peak comprises contribution from different oxygen species: O2- (Eb from 530.1 to 530.3 eV), hydroxide, OH- (Eb from 53b.4 to 531.6 eV) and water, H2O (Eb from 532.3 to 532.5 eV). In the presence of phosphorus (Fig. 9) the presence of phosphate species, PO43- should be considered which are located at slightly higher Eb range than OH- species, i.e. from 531.6 to 533.0 eV.20 The shape and position of the O 1s spectrum (Fig. 10c) indicates that the surface layer formed comprised oxide, hydroxide and phosphate species. The intensity of peak related to species at 532.4 eV related to phosphate increased at smaller take-off angle, indicating that these species are enriched at the layer surface. The phosphorus 2p spectrum should theoretically be a non-resolved doublet with 2p1/2 and 2p3/2 components at ABE of only 0.8 eV.20 At smaller and larger take- off angles the shape of the peak changed indicating that the distribution of different phosphorus species across the layer.21 At take-off angle of 45° the peak was centred at 133.4 eV. In phytic acid, phosphorus may be bonded to carbon (C-P), single-bonded to oxygen (P-OH) and double-bonded to oxygen (P=O). At larger take-off angle, i.e. closer to interface with substrate, another peak is observed at 133.8 eV. Further, in the case of binding with copper surface, it can also be bonded to oxygen of cuprous oxide. Detailed deconvolution of XPS signal is beyond the scope of this work as at this point of investigation it was important to prove that phytic acid is bonded to copper surface. Angle resolved XPS analysis represents a non-destructive method of surface profiling analysing the surface depth of approximately 10 nm. Spectra recorded at close to layer surface (15) and closer to interface with metal (75°) are similar indicating that the layer thickness is in the range of 10 nm. Figure 10. High resolution XPS spectra (a) Cu 2p, (b) Cu Auger, (c) O 1s, and (d) P 2p, of the surface layer formed on roughened Cu samples electrode after immersion in 0.1 mM phytic acid for 6 hours. Surface was roughened by ORC in H2SO4. Spectra were recorded at different take-off angles (15°, 45° and 75°). Vertical lines denote the position of reference species. 4. Conclusions Corrosion protection of copper in 3% NaCl was investigated with electrochemical and surface analytical techniques. Phytic acid was selected as a "green" corrosion inhibitor due to its availability from plants, non-toxi-city and reasonable price. Present study proves that its use as corrosion inhibitor is justified but only when used under optimal preparation conditions which were tested in details. When adding phytic acid directly to NaCl solution, the roughening of the sample surface can be omitted as a pre-treatment. Compared to roughened surface, abraded surface achieves better inhibition effectiveness when immersed for sufficient immersion time and at sufficient acid concentration. At optimal conditions, 6 h immersion time and 0.1 mM concentration, the corrosion was reduced for 65% compared to bare surface. Potentiodynamic measurements show that phytic acid acts as a cathodic inhibitor. When sample is pre-treated in solution of phytic acid before exposure to chloride solution, surface roughening is necessary. Optimal conditions were achieved for surface roughened by oxidation-reduction cycle in 2 M H2SO4, immersion time of 6 h and concentration of phytic acid of 0.1 mM. The layer formed under these conditions at copper surface achieved inhibition effectiveness of 77% when exposed to chloride solution. SEM analysis confirmed that surface roughening was required to achieve the bonding between copper surface and phytic acid and the formation of homogeneous layer. This layer shows higher contact angle than bare copper surface. Due to small thickness of the layer formed it was necessary to use X-ray photoelectron spectroscopy to analyse the surface composition. The bonding of phytic acid to the copper surface is proved by the presence of phosphorus peak. Copper surface is covered by a cuprous oxide layer. Therefore, when bonded to the surface, phyt-ic acid is bonded to Cu2O. The thickness of the layer formed is nanometer sized. 5. Acknowledgements The authors thank Prof. B. Malič,dr. J. Kovač and dr. Z. Samardžija from the Jožef Stefan Institute for contact angle, XPS measurements and SEM analysis, respectively. The financial support by the Slovenian Research Agency is acknowledged (grant No. P2-0148). 6. References 1. J. R. 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Wen, H.-F.Yang, Appl. Surf. Sci., 2013, 276, 167-173. 12. T. Notoya, V. Otieno-Alego, D. P. Schweinsberg, Corros. Sci., 1995, 37, 55-65. 13. H. F. Yang, J. Feng, Y. L. Liu, Y. Y., Z. R. Zhang, G. L. Shen, R. Q. Yu, J. Phys. Chem., 2004, 108, 17412-17417. 14. Q.-J. Xu, Z.-Y. Wan, G.-D. Zhou, R.-H. Yin, W.-M. Cao, An-ti-Corros. Method. M, 2009, 56, 95-102. 15. C. Hao, R.-H. Yin, Z.-Y. Wan, Q.-J. Xu, G.-D. Zhou, Corros. Sci., 2008, 50, 3527-3553. 16. I. Milošev, B. Kapun, Mater. Sci. Eng. C, 2012, 32, 10681077. 17. I. Milošev, M. Metikoš-Hukovic, J. Electrochem. Soc., 1991, 138, 61-67. 18. I. Milošev, H.-H. Strehblow, J. Electrochem. Soc., 2003, 150, B517-B524. 19. T. Kosec, D. Kek Merl, I. Milošev, Corros. Sci., 2008, 50, 1987-1997. 20. NIST X-ray Photoelectron Spectroscopy Database, NIST Standard Reference Database 20, Version 3.5, Data compiled and evaluated by C. D. Wagner, A. V. Naumkin, A. Kraut-Vass, J. W. Allison, C. J. Powell, J. R. Rumble, Jr., http://sr-data.nist.gov/xps/. 22. I. Milošev, M. Metikoš-Hukovic, Ž. Petrovic, Mat. Sci. Eng. C, 2012, 32, 2604-2616. Povzetek Raziskali smo inhibicijo korozije bakra s fitinsko kislino (inozitol heksafosfat) v 3 % natrijevem kloridu. Fitinska kislina je naravna spojina pridobljena iz rastlinskih virov in jo lahko zaradi svoje nestrupenosti označimo kot zeleni inhibitor. Z uporabo elektrokemijskih metod linearne polarizacije in potenciodinamske polarizacije smo študirali elektroke-mijsko vedenje ter ovrednotili inhibicijsko učinkovitost. Z namenom, da bi dosegli optimalno korozijsko zaščito, smo spreminjali naslednje eksperimentalne pogoje: predpripravo površine (brušenje in trije postopki povečanja hrapavosti), način tvorbe plasti fitinske kisine, čas potopitve in koncentracijo fitinske kisline. Vpliv postopkov predpriprave površine smo ocenili z merjenjem hrapavosti in kontaktnih kotov. Pri izbranih optimalnih pogojih tvorbe plasti fitinske kisline smo dosegli skoraj 80 % inhibicijsko učinkovitost. Morfologijo in sestavo zaščitne plasti smo analizirali z vrstično elektronsko mikroskopijo, spektroskopijo energijske porazdelitve rentgenskih žarkov ter rentgensko fotoelektronsko spektroskopijo. Ugotovili smo, da plast fitinske kisline z debelino do 10 nanometrov homogeno prekrije bakrovo površino. Rezultati raziskave so pokazali da to naravno spojino lahko uporabljamo v praksi kot relativno učinkovit inhibitor korozije bakra v kloridni raztopini.