Electrochimica Acta 51 (2005) 1076–1084

Formation and behaviour study of an environment-friendly corrosion inhibitor by electrochemical methods P. Bommersbach, C. Alemany-Dumont ∗ , J.P. Millet, B. Normand Laboratoire de Physico-Chimie Industrielle, INSA de Lyon-Bˆat. L´eonard de Vinci 20, Avenue Albert Einstein, F 69621 Villeurbanne Cedex, France Received 28 February 2005; received in revised form 13 May 2005; accepted 6 June 2005 Available online 7 July 2005

Abstract This paper deals with the characterization of an environment-friendly corrosion inhibitor formulated for industrial cutting fluids. Polarization measurements and electrochemical impedance spectroscopy (EIS) tests reveal the formation of a 3D film at the interface metal/elecrolyte. This film blocks iron ions oxidation by forming a barrier on the metallic surface. Studies concerning, respectively, inhibitor concentration, immersion time and temperature show that effects of these three parameters are strongly linked and influence considerably the protective effect of the inhibitor. XPS analyses confirm formation of an inhomogeneous layer submitted to a water-uptake with time when inhibitor is not added in necessary concentration. © 2005 Elsevier Ltd. All rights reserved. Keywords: Corrosion inhibitor; RDE; EIS; XPS

1. Introduction In metal industry, cutting fluids are an important topic of research [1]. They are devoted to cool and lubricant tools and workpieces, making life longer and guaranteeing the machined surface quality. Over these thermal and tribological regards, lubricant fluids must insure the corrosion resistance of working parts and cooling systems. In this way, the inhibitors using is largely widespread [2,3]. Due to restrictive environmental laws, inorganic corrosion inhibitors such as chromate or nitrites are replaced by organic compounds [4]; organic inhibitors are less or not toxic and so present a good compromise allying efficiency with environment and human health protection [5,6]. Role and mechanisms of corrosion prevention by most of inhibitors are well-known [7] but all research in this field consists now to design new environment-friendly inhibitor. This approach is particularly advisable regarding the toxicological and epidemiological studies carried out on the ∗

Corresponding author. Fax: +33 4 72 43 87 15. E-mail address: [email protected] (C. Alemany-Dumont). 0013-4686/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2005.06.001

genotoxicity of industrial cutting fluids [8]. The work developed in this paper takes place in this topic. Studied inhibitor could be submitted to several aggressive conditions (high speed machining, high temperature, etc.) and must keep its integrity to improve productivity and machining precision. Tertiary amine and carboxylic acid are constitutive of the studied inhibitor. It is considered like an inhibitor mixture expected to provide better inhibition than either of the individual inhibitor. Nitrogen is considered like the active centre of the amine. It is able to exchange electrons liberated by the metal during first step of anodic dissolution. Physisorbed species block electrochemical reaction and react with first corrosion products to form a precipitate layer on the steel surface, which decreases the corrosion kinetic. This latter is principally decreased by coverage with oxide layer and small amount of complex precipitate [9,10]. Tertiary amines are well-known like basic compounds; their combinations with steel corrosion products induce interfacial pH increasing. To adjust this one, carboxylic acid is added in inhibitor formulation and expected to react with corrosion products and none adsorbed extremity of the tertiary amine. This synergistic effect of carboxylic acid and

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

tertiary amine on thickness increasing of the barrier layer can be expected [10,11]. Before to take into account specific high speed cutting conditions (shear stresses, temperature, etc.), this paper concerns the growth and the stability of the interface layer versus time in laminar flow simulating cooling lubricant. Thus, electrochemical tests were performed with rotating disk electrode (RDE), which ensures well defined hydrodynamic conditions. EIS technique is particularly a pertinent tool for investigations concerning formation and growth of the inhibitor film [12,13]. Inhibitor concentration, immersion time and also temperature parameters were studied in order to characterize their influence on inhibitor behaviour. Electrochemical studies have been associated to XPS analyses for two different analyzing angles in order to identify compounds constituting the inhibitive layer in depth and in surface.

1077

reference electrode was placed in a thermostated adaptator maintaining ambient temperature closed to 18–20 ◦ C. 2.2. XPS conditions Analyses were carried out on two disk mild steel samples (diameter 6 mm). They were immersed during 24 h. Sample 1 was exposed in solution A and sample 2 in solution A with 0.5 wt.% of inhibitor. After this immersion time, both samples were removed from solutions and dried in air flow. X-ray photoelectrons spectra were recorded on an ESCALAB 200RVG Scientific Spectrometer, using a Al K␣ X-ray source (1486.6 eV). For sample 2 (with corrosion inhibitor), two take-off angles ␣ were chosen to characterize the film structure grown on the sample 2 (90◦ and 30◦ ). Analysis depth concerned at 30◦ is twice lower than one reached with 90◦ .

3. Results and discussion 2. Experimental conditions 3.1. Influence of inhibitor concentration 2.1. Electrochemical experiments The corrosion tests were performed with classic threeelectrode configuration: a graphite rod as counter-electrode, a saturated calomel electrode (SCE) as reference electrode. A cylinder rod of studied material (SAE 1038) was embedded in epoxy resin delimiting the working surface of 0.28 cm2 . Specimen was previously covered by cataphoretic epoxyamine base paint to avoid electrolyte infiltrations between metal and resin interface. Deposit conditions were described elsewhere [14]. This system was machined to form a rotatingdisk electrode and made the working electrode. Just before each experiment, the surface was polished by emery-paper up to 2400 grade, rinsed with distilled water and dried under an air flow. The aqueous electrolyte (called solution A) was prepared with de-ionised water and 100 ppm of each salt: Na2 SO4 , Na2 CO3 and NaCl. These contents correspond to a “synthetic” corrosive solution that increases the severity of the test over that produced by distilled water [15]. The studied inhibitor is composed by a tertiary amine and a carboxylic acid and its formulation is in validation. Inhibitor content was ranging from 0 to 5 wt.% for an electrolyte volume fixed to 100 mL. Electrochemical impedance spectra were obtained with Gamry equipment (model FAS 1), controlled by software EIS 300 and DC 105 (Bioritech). The impedance data were collected at the open-circuit potential over a frequency range between 65 kHz and 10 mHz at ten points per decade, a sine wave with 10 mV amplitude is applied. The parametric adjustment of the experimental data was carried out by the logicial ZSimWin 3.10 (EChem Software). The disk rotation speed was fixed at 1600 rpm. Temperature tests were ranged from 20 ◦ C to 80 ◦ C. Its control was insured by a thermostatic double walls cell. The

3.1.1. Polarization curves Fig. 1 presents the potential evolution versus time for different inhibitor concentrations. Curve referred Blank corresponds to the corrosion potential curve recorded with steel immersed in inhibitor-free solution. After 20 min, potential reaches a steady state near −500 mV/SCE. When solution contains inhibitor, potential value increases drastically. It increases with inhibitor content. Nevertheless, with 0.2 wt.% of inhibitor, the open-circuit potential decreases after 40 min of immersion. This content is not sufficient to insure a steady state potential evolution. Polarization curves illustrate the same trend. They are reported in Fig. 2. The anodic domain curves were obtained by applying −200 to 1000 mV/Ecorr (Fig. 2a) and the cathodic field curves were obtained by applying +20 to −800 mV/Ecorr (Fig. 2b). Both domains were drawn with a scanning rate of 0.5 mV s−1 . Blank curve exhibits the more cathodic potential and the higher current density. Inhibitor in the solution

Fig. 1. Open-circuit potential evolution vs. time, for mild steel SAE1038 in solution A with different inhibitor concentrations (T = 20 ◦ C, ω = 1600 rpm).

1078

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

Fig. 3. Impedance Nyquist plots for mild steel SAE1038 after 2 h of immersion in solution A with different inhibitor concentrations (T = 20 ◦ C, ω = 1600 rpm).

potential towards more noble values, its presence in solution does not disturb the cathodic reaction and the anodic plateau is more consequent when inhibitor concentration increases. 3.1.2. Electrochemical impedance spectroscopy Impedance spectra measured at open-circuit potential are recorded after 2 h of immersion. Nyquist and Bode plots are shown in Figs. 3 and 4. In the insert presented in Fig. 3, Fig. 2. Polarization curves recorded for mild steel SAE1038 after 2 h of immersion in solution A for different inhibitor concentrations (T = 20 ◦ C, ω = 1600 rpm): (a) in the anodic field and (b) in the cathodic one.

insures a corrosion potential ennoblement to reach a maximum value near −300 mV/SCE. In the cathodic field, same behaviour for both inhibitor-free solution and solution containing inhibitor curves are obtained after −800 mV/SCE. That shows inhibitor does not act on dissolved oxygen reduction. In the anodic field, corrosion potential value of −300 mV/SCE is obtained from 0.3 wt.% inhibitor content. The higher inhibitor content, the more extent potential field is, corresponding to the lower anodic current density. Over a certain potential, current density increases. This potential value increases with inhibitor content. This illustrates also that inhibitor content has a beneficial effect. From these polarization curves, corrosion current density can be extrapolated for different solutions. Anodic current exhibits a plateau. Its extrapolation allows calculating inhibitive efficiency. It follows this expression: Inhibitive efficiency (%) =

icorr − iinh corr × 100 icorr

(1)

where icorr and iinh corr correspond to the corrosion current density without and with inhibitor, respectively. Inhibitive efficiency reaches 78% for 0.2 wt.% inhibitor content in solution and more than 95% from 0.3 wt.%. Studied inhibitor can be considered like an anodic inhibitor. Added in corrosive solution, it shifts the corrosion

Fig. 4. Impedance Bode plots: (a) angle phase and (b) impedance modulus, for mild steel SAE1038 after 2 h of immersion in solution A at different inhibitor concentrations (T = 20 ◦ C, ω = 1600 rpm).

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

1079

zoomed graph displayed the very high frequencies behaviour. Impedance modulus and depressed loops increase notably with inhibitor content. This type of diagram is usually interpreted as a mechanism of charge transfer on an inhomogeneous surface [16]. As can be seen in Fig. 4a, only one time constant is detected on the Bode plots for inhibitor contents ranging from 0.2 to 0.4 wt.%. Polarization resistances values estimated from the Nyquist plots confirm the good efficiency from 0.3 wt.%. That is in good accord with previous results obtained with polarization curves. With solution containing 5 wt.% of inhibitor, a second time constant appears; it was already distinguished for 0.5 wt.%. This behaviour illustrates two different contributions. The first one, located in high frequencies, can be associated to the film and the second one to the charge transfer at the interface. These observations attest the formation of a barrier layer closely related to the inhibitor content in solution. The Bode plot recorded with 5 wt.% permits to conclude that this layer evolutes versus inhibitor content. This evolution could be associated to the film growth. 5 wt.% content gives a sufficient thickness to characterize a film contribution in the impedance measurements that explains two time constants presence [17,18]. For solutions containing less than 0.5 wt.% of inhibitor, the film contribution cannot be measured after 2 h of immersion. The following part of the study discusses about the evolution of the impedance spectra with immersion time. 3.2. Influence of immersion time 3.2.1. Electrochemical impedance spectroscopy Previous results have shown that a good inhibition efficiency occurs after 2 h from 0.3 wt.%. This fact is clearly illustrated in Figs. 1 and 2. From longer immersion times, it was possible to characterize the layer surface modification by EIS results analyses. Tests on 60 h are carried out with two different inhibitor concentrations (0.3 and 0.5 wt.%). Impedance spectra reported in Fig. 5 for the two concentrations show an increase of the total impedance of the system with immersion time. This evolution suggests a strong inhibition of the dissolution processes occurring on the surface [19]. After 6 h of immersion and also for the two studied concentrations, Bode plots present a widening of the phase, which can be attributed to the film contribution (Fig. 6a and b). Impedance Nyquist spectra obtained for 0.3 wt.% of inhibitor (Fig. 5a) exhibit a decrease of capacitive loop since 42 h; moreover, at 48 h of immersion, an inductive loop in the low frequencies range characterizes the relaxation of corrosion products adsorption and desorption on the metallic surface, revealing the inhibitor efficiency loss. On the contrary, the evolution of impedance spectra for 0.5 wt.% of inhibitor in Fig. 5b reveals that inhibitor efficiency subsists in time (until 60 h and beyond). This concentration of 0.5 wt.% will be fixed for the following studies because protective efficiency is maintained at least during 60 h.

Fig. 5. Nyquist plots for mild steel SAE1038 vs. time in solution A in addition with (a) 0.3 wt.% of inhibitor and (b) 0.5 wt.% of inhibitor (T = 20 ◦ C, ω = 1600 rpm).

3.2.2. Electrical equivalent circuit (EEC) From EIS results, an electrical equivalent circuit (EEC) could be proposed to model the electrolyte/sample interface. Presented in Fig. 7, this EEC is classically proposed for coating [20]. It is constituted of two constant phase elements, respectively, composed of a component Q and a coefficient α. The coefficient α can characterize different physical phenomena like surface inhomogeneousness resulting from surface roughness, impurities, inhibitor adsorption, porous layer formation,etc [21,22]. Thus, the capacitance is calculated by the following relation: C = Q(ωmax )α−1

(2)

In this equation, ωmax = 2f, where f represents the frequency at which the imaginary value reaches a maximum on the Nyquist plot. The EEC is constituted of elements describing properties of inhibitor film (Qf and Rf ) and other relative to the corrosion processes (Rct and Qdl ) on steel surface. By fitting impedance experimental diagrams, this EEC contributes to establish an evolution of physical parameters related to the inhibitor film and to the corrosion processes with time. A good correlation between experimental and simulated data were obtained (the error of the fitted parameters is done by the chi-squared χ2 , which is included for all adjustments

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

1080

Fig. 8. Evolution of charge transfer resistance (Rct ) and double layer capacitance (Cdl ) values vs. time in solution A with 0.3 wt.% of inhibitor (T = 20 ◦ C, ω = 1600 rpm).

Fig. 6. Impedance Bode plots for mild steel SAE1038 vs. time in solution A with (a) 0.3 wt.% of inhibitor and (b) 0.5 wt.% of inhibitor (T = 20 ◦ C, ω = 1600 rpm).

between 1.21E10−3 and 5.48E10−4 ). Evolutions of parameters Cdl , Rct , Cf and Rf , for a 0.3 wt.% inhibitor content, are respectively described in Figs. 8 and 9. The analysis of these parameters evolutions was made to propose assumption on the efficiency loss after 36 h. Rf can be attributed to the electric resistance of ionic transfer through inhibitor film pores. Rf decreases with time corresponding to the penetration of the electrolyte through the organic film pores. Parallel to this phenomenon, the diminution of the film capacitance Cf would be bound to an increase of the film thickness, which would swell under the influence of water-uptake, the film capacitance having this expression: Cf = εε0

A d

where ε denotes the relative dielectric constant of the layer, A the active area and d the film thickness. ε0 is the permittivity of the vacuum (8.85 × 10−14 F cm−1 ). The effect of the increasing dielectric constant with the penetration of the electrolyte, which increases Cf value has only a minor repercussion. The physic interpretation of Rf and Cf is in good agreement with Rct and Cdl respective evolutions during the immersion period. Indeed, a regular Cdl value decrease with a Rct increase are noticed during an immersion of 36 h that indicates a decrease of the corrosion process. This observation shows that film inhibitor pores are not yet opening to the active surface. After this time, the tendency is reverse indicating the corrosion process beginning. At this moment, the water-uptake is so important that the number of pathways, which permits contact between electrolyte and subtract is increasing. All these observations can contribute to propose some assumptions concerning the degradation of inhibitor properties. The anodic inhibitor is adsorbed on the steel surface and forms an inhibitive layer integrating first corrosion products. The growth of this layer increases the corrosion resistance of metal. Nevertheless, the morphology of the layer is likely to let electrolyte infiltrate that induces corrosion phenomena after 36 h. It is at the end of this period that film is completely degraded. In particular this degradation is characterized by a

(3)

Fig. 7. Electrical equivalent circuit for steel coated by inhibitor layer [20].

Fig. 9. Evolution of film resistance (Rf ) and of film capacitance (Cf ) values vs. time in solution A with 0.3 wt.% of inhibitor (T = 20 ◦ C, ω = 1600 rpm).

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

1081

Fig. 10. XPS spectra of Fe 2p for mild steel SAE1038 exposed to the solution A alone (sample 1), to the solution A with 0.5 wt.% of inhibitor (sample 2).

drastic increase of the capacitance Cf . Then film capacitance has no physical sense since the layer does not exist any more [23]. 3.3. XPS analyses XPS analyses were practiced on corroded and protected surface samples referred sample 1 and sample 2, respectively. The analyses were made after 24 h of immersion in the electrolyte because after this time, impedance spectrum obtained for 0.5 wt.% of inhibitor in solution presents a constant efficiency. Fig. 10 shows that sample surface exhibits clear modification according to steel is immersed in free or containing inhibitor. From O 1s line deconvolution presented in Fig. 11, oxygen appears in three chemical states. They related to oxide O–Fe (529.3 eV), hydroxide HO–Fe (531.5 eV) forms and adsorbed H2 O (533.0 eV) [24–26]. Only O2− and OH− can be identified in Fig. 11a, related to the measurement practiced on sample 1 surface. These oxides and hydroxides are constitutive to corrosion products formed on metallic surface immersed in free-inhibitor solution. In Fig. 11b, analyses practiced with an angle of 90◦ (in the layer depth) on sample 2 surface reveal also a significative oxide contribution. This observation reveals that film growth incorporates first corrosion products. In Fig. 11c, analyses practiced with 30◦ angle exhibit less O2− contribution. So less corrosion products subsist on film surface and major contribution comes from organic compound. In fact traces of nitrogen were identified on sample 2, in a more important proportion at the extreme film surface: nitrogen is associated to film inhibitor presence. It is related to the tertiary amine

Fig. 11. (a) O 1s XPS spectra of SAE1038 sample in free-inhibitor solution A; (b) O 1s XPS spectra of SAE1038 sample, in solution A with 0.5 wt.% of inhibitor (analysis angle of 90◦ ); (c) O 1s XPS spectra of SAE1038 sample, in solution A with 0.5 wt.% of inhibitor (analysis angle of 30◦ ).

contribution; nitrogen into amine generates a peak at a binding energy (BE) of 400 eV (Table 1) [25,26]. In Fig. 11b and c, peak identification at 536.5 eV corresponds to the sodium Auger line (precisely a transition Na

Table 1 Binding energies for each component of spectrum (eV)

Sample 1 Sample 2 (θ = 90◦ ) Sample 2 (θ = 30◦ )

Fe 2p3/2

O 1s (O2− )

O 1s (OH− )

O 1s (H2 O)

N 1s

710.5 707 + 709.7 707 + 710

529.5 (59%) 529.3 (47%) 529.3 (30%)

531.0 (41%) 531.5 (38%) 531.6 (50%)

– 533.0 (15%) 532.9 (20%)

399.6 399.5

In bracket, percentage data values correspond to peak area ratio.

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

1082

Table 2 Measured chemical data from XPS measurements

Sample 1 Sample 2 (θ = 90◦ ) Sample 2 (θ = 30◦ )

C/Fe

O/Fe

N/Fe

Na/Fe

1.1 4.4 11.9

2.7 2.6 4.9

– 0.2 0.4

0.1 0.6 1.4

KL1 L23 ) [27]. Its presence can be associated to the composition of the electrolyte. This detection is in accord with an infiltration of the electrolyte into the film, particularly on the outer part of the film (Table 2). Corrosion products contribution in the inhibitor layer demonstrated previously could explain the high value of film capacitance revealed in Fig. 9. 3.4. Influence of temperature The influence of temperature was tested from 20 ◦ C to

80 ◦ C. These temperatures reflect the using conditions of the

inhibitor. All tests were carried out with 0.5 wt.% of inhibitor; this content insures good protection of the sample, even for immersion times higher than 60 h at 20 ◦ C. In Fig. 12, evolution of free potential versus time reveals that temperature factor has not the same effect on the whole investigated range. Thus, two domains can be distinguished: the 20–40 ◦ C field and the 50–80 ◦ C one.

Fig. 13. Voltametric curves for mild steel SAE1038 in solution A with 0.5 wt.% of inhibitor for different temperatures (ω = 1600 rpm).

of charge transfer at the interface. The size of the capacitive loops decreases with temperature, which can be correlated to the evolution of the anodic current density described previously. At 40 ◦ C, capacitive loops increase with immersion time (Fig. 15). This phenomenon was already discussed in the Section 3.2.1 and was attributed to an increase of inhibitive efficiency connected to a film thickening. Then, the same type of impedance spectra and the same evolution of these diagrams with time are obtained. The film formation mechanisms at the steel interface and its evolution with time are

3.4.1. The temperature range 20–40 ◦ C For temperatures included between 20 and 40 ◦ C, a potential ennoblement characterizes the film formation. Polarization curves recorded in this domain of temperature are presented in Fig. 13: these curves exhibit a higher current density for the anodic plateau from 30 ◦ C. In order to understand this evolution, electrochemical impedance spectra were drawn at the corrosion potential, on the one hand, after 2 h of immersion at different temperatures (Fig. 14a and b), and on the other hand, at 40 ◦ C for different immersion times (Fig. 15). For these studied temperatures, after 2 h of immersion, same types of impedance spectra are obtained which present only one time constant, characteristic

Fig. 12. Open-circuit potentials vs. time in solution A with 0.5 wt.% of inhibitor at different temperatures (ω = 1600 rpm).

Fig. 14. (a) Impedance Niquist plots and (b) Impedance Bode plots (angle phase) for mild steel SAE1038 in solution A with 0.5 wt.% of inhibitor (ω = 1600 rpm) for different temperatures.

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

1083

Fig. 16. Polarization curves after 2 h of immersion in solution A with and without inhibitor at 60 ◦ C and 80 ◦ C (ω = 1600 rpm), respectively.

Fig. 17a informs that 5 wt.% of inhibitor added in solution A at 80 ◦ C induces a potential evolution versus time identical to a content of 0.5 wt.% at 20 ◦ C (Fig. 12). This result reveals the adsorption feasibility but with a greater adding of inhibitor for 80 ◦ C. An anodic plateau is observed on polarization curve presented in Fig. 17b and the inhibitive efficiency is close to 80%. This observation shows that inhibitor would act even at high temperature (80 ◦ C) on condition that a more important content is supplied. Fig. 15. (a) Impedance Niquist plots and (b) Impedance Bode plots (angle phase) for mild steel SAE1038 in solution A with 0.5 wt.% of inhibitor (ω = 1600 rpm) at 40 ◦ C.

unchanged in the temperature range 20–40 ◦ C. Temperature would rather act on film morphology; the film would become less resistant to corrosion. 3.4.2. The temperature range 50–80 ◦ C Temperatures ranging from 50 ◦ C to 80 ◦ C promote a significative free potential decreasing (Fig. 12) characteristic of the steel sample corrosion. Steel surface seems to be exempt of protective layer, since no anodic plateau characteristic of the sample protection by the film is detected on potentiodynamic curves (Fig. 13). In addition, potentiodynamic curves obtained with and without inhibitor at 60 and 80 ◦ C are similar (Fig. 16). Inhibitive efficiencies (calculated with Eq. (1)) are equals to 28.4% and 1.2%, respectively for these two temperatures. Finally, for temperatures higher than 50 ◦ C, electrochemical impedance spectra present two capacitive loops (Fig. 14a). The high frequencies loop can be attributed to charge transfer at the interface and the low frequencies loop to the iron ions diffusion through the layer of corrosion products [16]. Temperature acts on iron dissolution kinetic. Indeed, when temperature increases, dissolution of steel electrode is more important and the quantity of iron ions formed at the interface increases. The ratio between inhibitor molecules and ferrous oxides or hydroxides is not respected anymore, which would have an important effect on the film formation mechanism.

Fig. 17. (a) Open-circuit potential and (b) polarization curves, for mild steel SAE1038 in solution A at 80 ◦ C with and without inhibitor (ω = 1600 rpm).

1084

P. Bommersbach et al. / Electrochimica Acta 51 (2005) 1076–1084

4. Conclusion This study points out the mechanism of inhibitive layer formation and/or degradation versus three different parameters: inhibitor concentration, immersion time and temperature. The studied inhibitor, made up of amine and carboxylic acid forms a three-dimensional film on the steel surface, by using first corrosion products. It acts principally on anodic dissolution and it is efficient from 0.3 wt.% after 2 h of immersion at ambient temperature. The evolutions of Cf and Rf with time at this concentration describe a water-uptake responsible of the film degradation. 0.5 wt.% is then necessary to ensure a protection of steel in time. Temperature influence was then tested from 20 ◦ C to 80 ◦ C in order to simulate using conditions of inhibitor. • For temperatures higher than 60 ◦ C, low protective efficiency (<30%) is connected to a great increase of iron dissolution kinetics, which disturbed the formation of the protective layer. • On the contrary, for temperatures below 50 ◦ C, film formation mechanism is conserved. The decrease of the protective efficiency in this temperature range is attributed to an evolution of the film morphology. • Finally, the good effectiveness obtained at 80 ◦ C, for 5 wt.% of inhibitor content proves the existence of a critical ratio between the quantity of iron oxides–hydroxides and inhibitor molecules for the film formation feasibility.

Acknowledgement This work is supported by a grant of French Ministry of Research and inhibitors have been proposed by ASCOTEC Comp which is supported by Rhˆone–Alpes Region. The authors are indebted to H. Takenouti for his precious advices with regard to the electrode preparation procedure. They express their gratitude to Robert Di Folco for his great help and know-how concerning experimental devices.

References [1] D.U. Braga, A.E. Diniz, G.W.A. Miranda, N.L. Coppini, J. Mater. Process. Tech. 122 (2002) 127.

[2] F. Mansfeld, M.W. Kendig, W.J. Lorentz, J. Electrochem. Soc. 132 (1985) 290. [3] I. Felhosi, R. Ekes, P. Baradlai, J. Electroanal. Chem. 480 (2000) 199. [4] P. Kern, D. Landolt, Electrochim. Acta 47 (2001) 589. [5] A. Aballe, M. Bethencourt, F.J. Botana, M. Marcos, J. Alloys Compd. 323 (2001) 855. [6] K. J¨uttner, W.J. Lorentz, M.W. Kendig, F. Mansfeld, J. Electrochem. Soc. 135 (1988) 332. [7] K.L. Vasanth, in: S.D. Cramer, B.S. Covino (Eds.), Corrosion: Fundamentals, Testing, and Protection, vol. 13A, ASM Handbook, 2003, p. 871, ISBN 0-87170-705-5. [8] M. Kleber, W. F¨ollmann, M. Blaszkewiscz, Toxicol. Lett. 151 (2004) 211. [9] N. Tsuji, K. Nozawa, Corros. Sci. 42 (2000) 1523. [10] T. Suzuki, H. Nishihara, K. Aramaki, Corros. Sci. 38 (1996) 1223. [11] M. Duprat, F. Dabosi, F. Moran, S. Rocher, Corros. Nace 37 (1981) 262. [12] H. Takenouti, in: B. Normand, N. P´eb`ere, C. Richard, M. W´ery (Eds.), Pr´evention et lutte contre la corrosion, Presses Polytechniques et Universitaires Romandes, Lausanne, 2004, p. 123, ISBN 2-88074543-8. [13] L. Bousselmi, C. Fiaud, B. Tribollet, E. Triki, Corros. Sci. 39 (1997) 1711. [14] K. Es-Salah, M. Keddam, K. Rahmouni, A. Shriri, H. Takenouti, Electrochim. Acta 49 (2004) 2771. [15] ASTM, Standard Test Method for Corrosion Test for Engine Coolants in Glassware, ASTM D 1384-93, ASTM, Philadelphia, 1993. [16] M. Duprat, Thesis, Toulouse: Institut National Polytechnique de Toulouse, France, 1981. [17] N. Ochoa, G. Baril, F. Moran, N. P´eb`ere, J. Appl. Electrochem. 32 (2002) 497. [18] N. Ochoa, Thesis, Toulouse: Institut National Polytechnique de Toulouse, France, 2004. [19] H.E. Jamil, A. Shriri, R. Boulif, C. Bastos, M.F. Montemor, M.G.S. Ferreira, Electrochim. Acta 49 (2004) 2753. [20] L. Beaunier, I. Epelboin, J.C. Lestrade, H. Takenouti, Surf. Technol. 4 (1976) 237. [21] S. Veleda, A. Popova, S. Raicheva, Proceedings of the 7th European Symposium on Corrosion Inhibitors, Ferrara, 1990, p. 149. [22] W.J. Lorenz, Dechema Monographs 101, VerlagChemie, Weinheim, 1986, p. 185. [23] L. Diguet, Thesis, Lyon: INSA de Lyon, France, 1996. [24] I. Felhosi, Zs. Keresztes, F.H. Karman, E. Kalman, J. Electrochem. Soc. 146 (1999) 961. [25] A. Welle, J.D. Liao, K. Kaiser, M. Grunze, U. M¨ader, N. Blank, Appl. Surf. Sci. 119 (1997) 185. [26] F. Bentiss, M. Traisnel, L. Gengembre, M. Lagren´ee, Appl. Surf. Sci. 152 (1999) 237. [27] J. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, in: J. Chastain (Ed.), Handbook of X-ray Photoelectron Spectroscopy, second ed., Perkin-Elmer Corporation (Physical Electronics), 1992.

Formation and behaviour study of an environment ...

300 and DC 105 (Bioritech). ... The paramet- ric adjustment of the experimental data was carried out by ..... Perkin-Elmer Corporation (Physical Electronics), 1992.

708KB Sizes 14 Downloads 223 Views

Recommend Documents

Formation and behaviour study of an environment ...
research [1]. They are devoted to cool and lubricant tools ..... Process. Tech. 122 (2002) 127. [2] F. Mansfeld, M.W. Kendig, W.J. Lorentz, J. Electrochem. Soc. 132.

TELANGANA MOVEMENT AND STATE FORMATION STUDY ...
TELANGANA MOVEMENT AND STATE FORMATION STUDY MATERIAL.pdf. TELANGANA MOVEMENT AND STATE FORMATION STUDY MATERIAL.pdf.

A study of the formation of microporous material SAPO-37
Mar 29, 2013 - diffraction (PXRD). Scanning electron microscopy (SEM) was uti- lized to observe the morphological changes. Further, the nucleation and crystal growth were examined by atomic force microscopy. (AFM). The combination of these techniques

Militarization and the Environment: A Panel Study of ...
proposed theorization and highlight the need for social scientists to consider the ..... being equal, nations with relatively larger non-dependent adult populations ...

A study of the formation of microporous material SAPO-37
Mar 29, 2013 - For. DGC, SAPO-37 crystallizes from a semi-crysta lline layered precursor containing large pores and ... (DGC), was introduced years ago as an alternative method to HTS ... The silicon, aluminum, and phosphorous sources were fumed ...

Militarization and the Environment: A Panel Study of ...
proposed theorization and highlight the need for social scientists to consider the ..... equal, nations with relatively larger non-dependent adult populations will ...

Militarization and the Environment: A Panel Study of ...
1991:152): “We are in the business of protecting the nation, not the ...... Posted on TomDispatch Website, .... Nature's Economy: A History of Ecological Ideas.

Formation of Molecular Clouds and Global Conditions for Star Formation
Dec 11, 2013 - of molecular clouds in interarm regions, and Koda et al. (2009) apply similar arguments to the H2-rich galaxy M51. They find that, while the largest GMC complexes reside within the arms, smaller (< 104 M⊙) clouds are found in the int

numerical study of the behaviour for elastic- viscoplastic ...
Abstract : The variation of stress during creep convergence of a horizontal circular galleries excavated in rock salt is studied. Examples are given for rock salt by N. Cristescu ([1], [2]). A non-associated elasto-viscoplastic constitutive equation

Using Transformation and Formation Maps to Study the ...
was produced using the MIT general circulation model. (MITgcm) (Marshall et al. 1997a,b) data assimilation technology (ECCO), which fits the model trajectory as closely as is possible to all modern datasets, including. Argo profiles, surface altimetr

Formation of thiadiazole, thiadiazine, thiadiazepine and ... - Arkivoc
resulted in a green coloration of the solution which later turned to dark brown. ..... at room temperature to a solution of 2 (2.0 mmol) in ethyl acetate (20 mL).

Formation of Networks and Coalitions
being modeled may not have any “money” (more generally a private good). Alternatively ...... like the United Nations Security Council or the European Council.

Formation and Stabilization of Anisotropic ... - CSIRO Publishing
Sep 23, 2008 - mission electron microscopy. Rapid microwave heating resulted in 'star-shaped' palladium nanoparticles, but platinum nanoparticles were ...

An Overlapping Generations Model of Habit Formation ...
when the tax rate is high enough (i.e., exceeds a ”critical” tax rate, which can be as low as zero ... Both savings and interest on savings are fully con- sumed. c2 t+1 = (1 + ..... be misleading if habit formation is taken into account. The intu

An inclusion-based mechanism of chain formation ...
3. (13). [TP JohnC [T' was [VP kissed JohnuC]]]. This representation is not legible at PF since, by definition, uninterpretable features (uFF) cause the crash of the derivation at the interfaces. Thus, it is necessary to assume that some kind of oper

An Overlapping Generations Model of Habit Formation ...
financial support. 1 ...... Utility and Probability, New York, London: W.W. Norton & Company. ... Satisfaction, New York and Oxford: Oxford University Press.

Pattern forming method including the formation of an acidic coating ...
Apr 29, 1996 - Foreign Application Priority Data. Dec. 9, 1991 [JP] Japan . .... form ?ner patterns by using electron beam or X-ray with a shorter wavelength.

Formation of thiadiazole, thiadiazine, thiadiazepine and ... - Arkivoc
Mar 15, 2018 - thiadiazolidine C-5 at δC 162.92 as well as the absence of C=S favor structure 10b. The 1H NMR spectrum of 10b showed the presence of ...

A Wizard-of-Oz environment to study Referring ...
will be used to build user simulation mod- ... tion to build data-driven user simulations. How- ever, our study ... like environment with a desktop computer, phone.