Synthesis of tertiary amines and their inhibitive performance on carbon steel corrosion

Corrosion Science 49 (2007) 1833–1846 www.elsevier.com/locate/corsci

Synthesis of tertiary amines and their inhibitive performance on carbon steel corrosion Guo Gao a, Cheng Hao Liang

a,b,*

, Hua Wang

a

a

b

School of Chemical Engineering, Dalian University of Technology, Dalian 116012, China Electromechanics & Materials Engineering College, Dalian Maritime University, Dalian 116026, China Received 1 December 2005; accepted 21 August 2006 Available online 1 February 2007

Abstract Some tertiary amines in the series of 1,3-di-amino-propan-2-ol, referred as 1,3-di-morpholin-4-ylpropan-2-ol (DMP) and 1,3-bis-diethylamino-propan-2-ol (DEAP), had been synthesized by alkylation reaction. These compounds were checked by MS, IR, 1H NMR and 13C NMR. The electrochemical performance of these products was investigated through potentiodynamic polarization measurement and electrochemical impedance spectroscopy (EIS) under thin electrolyte layer with thickness of 100 lm, and their inhibition efficiencies were measured using gravimetric method. These compounds, retarding the anodic dissolution of iron by the protective layer bonding on the metal surface, were anodic inhibitors under thin electrolyte layer. Polarization data indicated that the inhibitive performance of DMP for carbon steel was improved with the increasing of concentration, whereas DEAP showed a maximum inhibiting power at 2.5 · 102 M. The values of the charge transfer resistance, obtained from impedance plots of carbon steel, showed that DEAP was a promising inhibitor. The gravimetric results showed that the inhibition efficiency of DEAP at 2.5 · 102 M was 95%. The adsorption on the carbon steel surface followed Langmuir isotherm model. The Fourier transform spectroscopy (FTIR) was used to analyze the surface adsorbed film.  2006 Elsevier Ltd. All rights reserved. Keywords: Tertiary amine; Volatile corrosion inhibitor; Carbon steel; Thin electrolyte layer

* Corresponding author. Address: School of Chemical Engineering, Dalian University of Technology, Dalian 116012, China. Tel.: +86 411 88993926; fax: +86 411 88993926. E-mail address: [email protected] (C.H. Liang).

0010-938X/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2006.08.014

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1. Introduction The metal is easily suffered from atmospheric corrosion due to the variation of temperature and humidity during transport and storage. It is known that the application of volatile corrosion inhibitor (VCI) is one of the most practical methods for protection of metal against atmospheric corrosion [1–4]. The advantage of VCI is that the vaporized inhibitive molecules can reach hard-to-reach areas at room temperature, and form a relatively stable layer on the metal surface. As the protective layer of VCI is very thin, it will not interfere with the subsequent process of treatment for the protected surface [5]. The research of VCIs has been vastly studied and a number of them successfully protect the metal corrosion, such as dicyclohexylamine (DICHAN) and carbonates of monocyclohexylamine (CHC) effectively inhibit the carbon steel corrosion. However, the application of these available inhibitors has been confined for their toxicity. Recently, the amino-compounds of low toxicity like triethylamine, triethanolamine, (CnH2n+1)2NCH2CH2OH and bis-morpholin-4-ylmethyl-amine acting as VCIs on carbon steel has been reported by researchers [6–10]. Jamil et al. [11] suggested that some amino-based inhibitors could effectively reduce the corrosion rate of the reinforcing steel in simulated concrete interstitial electrolyte. Damborenea et al. [12] investigated several primary aliphatic amines as corrosion inhibitors for mild steel in 2 M hydrochloric acid and found that the inhibition efficiency improved when the alkyl chain length of the inhibitors was increased. Moretti et al. [13] studied tryptamine as an effective corrosion inhibitor for iron in 0.5 M deaerated sulphuric acid. Skinner [14] suggested a series of heterocyclic amines as VCIs for steel. Magidson and Rubtsov [15] found that the toxicity of compounds will be decreased by introduction of side-chain –NHCH2CH(OH)CH2NR2. It was logical to extend this idea to the compound of 1,3-di-morpholin-4-yl-propan-2-ol (DMP) and 1,3-bis-diethylamino-propan-2ol (DEAP). However, the inhibitive performance of these new compounds on carbon steel has been studied poorly. The research of DMP and DEAP can be contributed to the ‘‘green VCIs’’ building blocks. In this paper, DMP and DEAP have been synthesized by alkylation reaction. The inhibitive effect was investigated using electrochemical measurements and gravimetric method. The FTIR was used to characterize the surface adsorbed film. 2. Experimental 2.1. Synthesis The synthesis of these compounds were accomplished through epichlorohydrin with appropriate secondary amine in the molar ratio of 1:3.2. The reactants were heated to refluxing over an oil bath about 6–8 h. Then the reaction mixture was cooled to room temperature, and 20% sodium hydroxide solution was added. The excess amine and water were removed by distillation. The residue was purified through chromatography on silica gel eluting by acetone-ethyl acetate (40:60). Their structures of DMP and DEAP were shown in Fig. 1. These products were characterized by mass spectra, IR, 1H NMR and 13C NMR. Mass spectra DMP (ESI+) (m/z):(M+1)+ = 231. DEAP (ESI+) (m/z):(M+1)+ = 203.

G. Gao et al. / Corrosion Science 49 (2007) 1833–1846

a H2 C O C H2

a

b H2 C

H2 H2 d H2 C C H C N C N c C C OH H2 H2

1835

H2 C O C H2

b

H2 H2 H2 d H2 H3C C C CH3 C H C N C N c C CH3 H3C C OH H2 H2 Fig. 1. Molecular structures of DMP and DEAP. (a) 1,3-di-morpholin-2-propanol (DMP), (b) 1,3-bisdiethylamino-2-propanol (DEAP).

Infrared spectroscopy DMP: m max (KBr cm1): 3420 (m O–H), 2800–3000 (m C–H), 1456 (d C–H2), 1274 (m C–N), 1115(m C–O–C), 1069 (m C–O). DEAP: m max (KBr cm1): 3425 (m O–H), 2800–3000 (m C–H), 1460 (d C–H2), 1384 (d C–H3) 1202(m C–N), 1063 (m C–O). Spectral characteristics DMP. 1H NMR (400 MHz, d, DMSO/TMS): (a) t, 3.6 ppm; (b) t, 2.4 ppm; (c) dd, 2.2– 2.3 ppm; (d) m, 3.8 ppm. DMP. 13C NMR (400 MHz, d, DMSO): (a) 66.4 ppm; (b) 54.1 ppm; (c) 63.4 ppm; (d) 65.1 ppm. DEAP. 1H NMR (400 MHz, d, DMSO/TMS): (a) t, 0.9 ppm; (b) q, 2.4 ppm; (c) dd, 2.2–2.3 ppm; (d) m, 3.5 ppm. DEAP. 13C NMR (400 MHz, d, DMSO): (a) 11.8 ppm; (b) 47.1 ppm; (c) 57.8 ppm; (d) 66.5 ppm. 2.2. Materials and medium The electrolyte solution was simulated atmospheric corrosion water (0.1 g/L NaCl, 0.1 g/L NaHCO3, 0.1 g/L Na2SO4), which was prepared by analytical reagents and distilled water. Specimens were made from carbon steel with the following chemical composition (wt%): C 0.18; P 0.01; Si 0.02; Mn 0.47; S 0.02; Fe balance. Before experiment, the specimens were polished with grit emery paper to 2000 grade, degreased by ethanol, washed by distilled water and dried in air. 2.3. Potentiodynamic measurements Early electrochemical test of VCI was customarily conducted in bulk electrolyte medium. The results had a distinct difference with that of the actual atmospheric corrosion

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a

c

b

100μm

2 1 3

RE

6 4

CE

5

WE

20mm 22mm Fig. 2. Schematic diagram of the electrochemical experimental arrangement. (a) 1 SCE, 2 Pt, 3 jar lid, 4 phenolic resin, 5 bracket, 6 working electrode, (b) top view of the working electrode, (c) side view of the working electrode.

condition. Literatures [16,17] had pointed out that when the electrolyte layer was thicker than 200 lm, the results were similar to that of the body solution. But in the range of 100–200 lm, the results of electrochemical measures were relatively approach to the atmospheric corrosion condition. The experimental equipment was shown in Fig. 2. A polyester film with a gap of 2 mm was fixed around the working electrodes. A thin electrolyte layer (about 100 lm) could be obtained by corresponding thickness of the polyester film. Electrochemical measurements were performed by a three-electrode system, the working electrode in the form of a disk having a working area of 1.43 cm2, with a platinum as counter electrode and a saturated calomel electrode (SCE) as the reference one. The potential values in this paper were referred to SCE. The working electrode was stabilized in the solution for 30 min before test. Then the potentiodynamic measurements were started by changing stepwise (2 mV/s) on a PAR M173 potentiostat/galvanostat.

2.4. EIS measurements The cell configuration of EIS test was the same as the potentiodynamic polarization test, yet the EIS measurement was done on a potentiostat/galvanostat PAR M283 and a PAR M1025 frequency response detector. The employed amplitude of the sinusoidal signal is ±10 mV, frequency ranging from 10 kHz to 5 mHz.

2.5. Gravimetric measurements The carbon steel specimens were polished with grit emery paper to 2000 grade in order to eliminate heterogeneities caused by the drilling and cutting of the test specimens, then, degreased by ethanol, washed by distilled water and dried in air. The corrosion test employed in the absence and presence inhibitors was carried out according to the JB/T 6071 standard with a few modifications. The chamber used in this test was a 250 cm3 conical flask containing 30 cm3 of an electrolyte/inhibitor solution, with an airtight lid holding the steel specimen. Each test was carried out with three specimens at the same time to give reproducible results. The test process included cyclic warming and cooling for the samples in a corrosion testing chamber of varying humidity. One cycle included an 8 h exposure in

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the thermostat (50 ± 1 C), and 16 h exposure in room temperature. The period of gravimetric measurement was 7 d. 2.6. FTIR spectra The adsorbed film on the carbon steel surface during gravimetric tests in the presence of inhibitors were washed by distilled water, dried and used for subsequent spectra analysis. Infrared spectra were obtained from KBr discs using NEX-US spectrometer. 3. Results and discussion 3.1. Potentiodynamic polarization measurements Polarization curves of samples in the solution without and with DMP and DEAP inhibitors at different concentrations are shown in Figs. 3 and 4. When the concentration of inhibitors increases, the anodic current densities of carbon steel decrease and the corrosion potentials of carbon steel have a remarkable shift toward positive direction. The corrosion potential changes from 552 mV to 391 mV in the presence of DMP at 5 · 102 M, and to 445 mV with DEAP at 2.5 · 102 M. The electrochemical performance of carbon steel has been improved due to the addition of DMP and DEAP. It indicates that these compounds predominate as anodic inhibitors for carbon steel [18]. From Fig. 3, the anodic polarization of carbon steel shows a passive trend with the concentration of DMP at 5 · 102 M, and the values of the anodic current densities are varied between 10.8 lA/cm2 and 22.5 lA/cm2 when the potential increased from 230 mV to 46 mV. In Fig. 4 the anodic current densities maintain 13.7 lA/cm2 in the potential interval from 210 mV to 65 mV. However, the anodic current densities increase rapidly when the polarization potential increases over 65 mV, and the metal surface protected by the inhibitive molecules of DEAP was no longer ‘‘stabilization’’. A plateau of anodic current 0.6

blank DMP -3 10 M -2 10 M -2 2.5×10 M -2 5×10 M

0.4

E vs. SCE / V

0.2

0.0

-0.2

-0.4

-0.6

-0.8

-4

-3

-2

-1

0

log i / mAcm-2

Fig. 3. Polarization curves of carbon steel with DMP at different concentrations.

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0.6

0.4

E vs. SCE / V

0.2

blank DEAP -3 10 M -2 10 M -2 2.5×10 M -2 5×10 M

0.0

-0.2

-0.4

-0.6

-0.8 -4

-3

-2

-1

0

log i / mAcm-2

Fig. 4. Polarization curves of carbon steel with DEAP at different concentrations.

density appeared owing to the desorption rate of DEAP on the metal/interface is faster than adsorption. It should be noted that the inhibitive performance decrease when the concentration of DEAP at 5 · 102 M. One of the primary reasons is that the adsorption turns from horizontal configuration to vertical form, and active positions at metal surface increase due to the influence of steric hindrance of molecules. Since oxygen in air easily permeates the thin solution layer to the metal surface, the corrosion reaction of carbon steel occurs in thin electrolyte layer. However, DMP and DEAP can bond a stable protective layer on the metal surface. The anodic dissolution of iron has been obstructed by the protective layer. The inhibitive effect of these compounds is independent on blocking the diffusing of oxygen. 3.2. EIS tests The aim of EIS is to obtain more information concerning the dynamics and interface of working electrode in the presence of DMP or DEAP. Nyquist complex plane plots of the carbon steel with these compounds at different concentration are given in Figs. 5 and 6. All experimental plots approximately have a semicircular shape in the complex plane, with the center under the real axis, which is a typical behavior for solid electrodes that suggest the frequency dispersion of the impedance data [19]. The impedance measurements show that the inhibition of DMP and DEAP is characterized by an increase in the diameter of capacitive arc which is acting the resistance. On the other hand, the impedance complex plane plots are similar to a depressed semicircle approaching a capacitor which indicates that a homogeneous protective layer is formed on the metal surface, and the corrosion process become more difficult in the presence of investigated compounds. According to the corrosion process of carbon steel under thin electrolyte layer with inhibitors, a general equivalent circuit model [20] may be used to analyze the electrical behavior in the presence of inhibitors (see Fig. 7). This model represents the parallel

G. Gao et al. / Corrosion Science 49 (2007) 1833–1846 100

3200

1839

blank

80

-Zim/ohm·cm2

2800

-Zim/ohm·cm2

2400

60 40 20

2000

0

1600

0

20

40

60

80

100

120

140

160

Zre/ohm·cm2

DMP

1200

-3

10 M -2 10 M -2 2.5·10 M -2 5·10 M

800 400 0

0

1000

2000

3000

4000

5000

6000

7000

8000

9000 10000

Zre/ohm·cm2

Fig. 5. Nyquist complex plane plots of the carbon steel in the absence and presence of DMP at different concentrations.

3200 2800

-Zim/ohm·cm2

2400 2000 1600

DEAP -3

1200

10 M -2 10 M -2 2.5×10 M -2 5×10 M

800 400 0 0

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Zre/ohm·cm2

Fig. 6. Nyquist complex plane plots of the carbon steel with DEAP at different concentrations.

and/or series junction of a number of resistance and capacitance, simulating the evolution of both the protective properties of adsorbed layer and the kinetics of carbon steel corrosion process. Rsol is the solution resistance between the reference and working electrode. Ra and Ca are adsorption resistance and adsorption capacitance of inhibitor film, respectively. Once the aggressive chemicals such as water, oxygen and ionic species permeate the inhibitor film to the active sites of the metal, the corrosion of metal becomes measurable so that its associated parameters, the double layer capacitance Cdl and the charge transfer resistance Rct, can be estimated. Taking into account the non-ideal frequency response of the display data, a constant phase element (CPE) was used instead of an ideal capacitance. CPE can represent all frequency-dependent electrochemical phenomena, such as

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(CPE)dl Rsol

Rct (CPE)a

(CPE)dl

Rsol Ra

Rct

Fig. 7. Equivalent circuit of carbon steel in thin electrolyte layer. (a) Blank, (b) in the presence of inhibitors.

double-layer capacitance, diffusion processes and local frequency dispersion due to the microscopic roughness of the metal surface [21,22]. The impedance of a CPE is described by the expression [23]: Z CPE ¼ Y 1 ðiwÞn p where Y is a proportional factor, ‘i’ is 1, w is 2pf and n has the meaning of a phase shift, n is a factor satisfying the condition 0 6 n 6 1. The fitted data follows almost the same pattern as the experimental results with R(Q(R(QR))) equivalent circuit using the software of ZsimpWin. This suggested that there are two time constants in this system. In the high frequency range, the first time constant represented the impedance of a surface adsorption layer and can be described adsorption capacitance and adsorption resistance. In the low frequency range, the second time constants can be explained by the charge transfer resistance and the double layer capacitance in the electrode/electrolyte interface. The low frequency time constant was related to diffusion processes of iron cations (Rct(CPE)dl arrangement) through the adsorbed film [24]. The characteristic parameters associated to EIS are given in Table 1. The values of Ya and Ydl (Ya and Ydl can be regarded to be approximation to the value of the adsorption capacitance and double layer capacitance, respectively) has decreased trend for the adsorption of the inhibitor on the metal surface, suggesting the inhibitor molecules displace the water molecules and other ions originally adsorbed on the metal surface. The evolution is correlated with an improvement of the quality of the inhibitor film. The values of na associated with (CPE)a are found in the 0.86-1 interval revealing that adsorbed film are relatively homogeneous. On the other hand, the different values of na is due to a modification of the chemical composition of the adsorbed film in combination with their thickness as suggested by the Ra values. The values of ndl related to (CPE)dl are found in the 0.53– 0.84 interval indicating the electrode surface are partially heterogeneous.

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Table 1 The electrochemical parameters of EIS equivalent circuit Cinhibitor M(mol/l)

Ya (X1 cm2 sna 104)

na

Ra (X cm2)

Ydl (X1 cm2 sndl 104)

ndl

24.0

0.81

1902

155

Cdl (lF cm2)

Rct (X cm2)

g%

Blank DMP 103 102 2.5 · 102 5 · 102

–

5.8 10.0 2.1 1.7

0.89 0.86 0.97 1

523 742 1004 1459

61.0 89.0 5.4 4.4

0.72 0.84 0.56 0.53

8166 11434 1187 863

347 420 2038 4857

55.3 63.1 92.4 96.8

DEAP 103 102 2.5 · 102 5 · 102

12.0 1.6 1.4 1.5

0.88 1 1 1

634 1471 1809 1310

5.2 4.5 4.3 4.4

0.78 0.56 0.56 0.54

428 981 1423 1141

966 5993 10657 6953

84.0 97.4 98.5 97.8

The inhibition efficiency (g%) is calculated from the charge transfer resistance values using [25].   Rct g% ¼ 1  0  100 Rct where Rct and R 0 ct represented, respectively, the charge transfer resistance in the absence and presence of the inhibitor. It is worth noting that the Rct values of DEAP is prominent higher than that of DMP at the same concentration, which indicates the inhibitive performance of DEAP is superior to that of DMP. On the other hand, the values of Rct, from which the corrosion rate can be calculated, increase with DMP concentration, yet have a maximum with DEAP at 2.5 · 102 M. This optimum concentration for DEAP is related to the diffusion processes of iron cations through the adsorbed film, depending on the properties of the configuration of adsorbed film, thickness and porosity [26]. The value of Rct reaches 10657 X cm2 at this optimum concentration, indicating the iron diffusion is quite slower. The variation exhibited is due to a modification of the adsorbed film configuration, which can be evaluated by the thickness of film relating the double layer capacitance. The double layer capacitance Cdl was calculated by the following equation [27]. C dl ¼

ðY dl  Rct Þ1=n Rct

It is found that the Cdl value decreases from 1423 lF cm2 (2.5 · 102 M) to 1141 lF cm2 (5 · 102 M) in the presence of DEAP, indicating the thickness of film at 2.5 · 102 M is less than that at 5 · 102 M. This proves the hypothesis that the adsorption turns from horizontal configuration to vertical form when the concentration of DEAP at 5 · 102 M. According to the values of Ra, this evolution also suggests that the adsorbed film (2.5 · 102 M) is relatively compact which is retarding the diffusion of iron cations, whereas the adsorbed film (5 · 102 M) is porosity, suggesting that iron cations mobility in the film is more unrestricted.

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The investigated amino-compounds have shown inhibitive properties for carbon steel in simulated atmospheric water. The chemical structure influenced their inhibition performance. DEAP is constituted by four non-terminal hydrophobic groups and three hydrophilic groups per molecule, separated by a spacer. The hydrophobic groups may act as an effective barrier effect from the aggressive medium. The symmetrical adsorption centers (N atoms) capable of forming bonds with the metal surface by electron transfer in which the metal acted as an electrophile and DEAP molecule acts as a Lewis base. Moreover, the presence of electron releasing character of –OH group may be attributed to the increased electron density leading to electron transfer mechanism from functional group to metal surface. The inhibition efficiency of DMP is less efficiency than that of DEAP because the active groups of DEAP has a cooperative effect, whereas the binding force of DMP on the metal surface has been decreased for the competitive adsorption of multi adsorption-center. On the other hand, it is known that the –CH2CH3 group can be attributed to the increase of the electron donating ability to the vacant d-orbital of metal. Thus, the adsorption of DMP on the carbon steel surface decreases due to the absence of the electron donating groups. In order to analyze the adsorption mechanism, the Langmuir adsorption isotherm is postulated. C 1 ¼ þC h K The degree of surface coverage h is approximately equal to the inhibition efficiency obtained from EIS, K is the equilibrium adsorption constant of the adsorption process. The plots of C/h versus C for DMP and DEAP are represent in Fig. 8. The data appear to fit straight line indicating that the applicability of Langmuir isotherm model to describe the adsorption process of inhibitors on carbon steel surface under thin electrolyte layer.

0.06

DMP 0.05

DEAP

0.04

C/θ

0.03 0.02 0.01 0 -0.01 -0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

C,M

Fig. 8. Langmuir adsorption plots of carbon steel under thin electrolyte layer containing different concentrations of DMP and DEAP.

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3.3. Gravimetric measurements The mass loss is determined after removing the corrosion products from the metal surface in accordance with the procedures recommended by the ASTM G1-67 standard. Then the corresponding inhibition efficiency (g%) is calculated by the equation [28]: g% ¼ ð1  w=w0 Þ  100 where w and w 0 are the corrosion rate in the presence and absence of inhibitors, respectively. The corrosion rate of carbon steel was calculated by the relation: w¼

Dm St

where Dm and S represented the weight loss and the exposed area of specimen, t was the testing period. Table 2 shows the values of w and g% at different concentration of inhibitors. According to Table 2, the inhibitive efficiency of DEAP at 2.5 · 102 M was 95%. This result indicates that DEAP acts as an excellent volatile corrosion inhibitor. From all the measurements carried out, the variation of inhibitive performance versus concentration shows the same trend. 3.4. Analysis of FTIR spectra The FTIR analysis of the investigated compounds and their iron complexes was carried out between 500 and 4000 cm1. The spectra were shown in Figs. 9 and 10. The O–H stretch of DMP showed an intense peak around 3420 cm1. The peak between 2800 and 3000 cm1 was assigned to C–H stretch. The C–N stretch was shown 1274 cm1 and the C–O–C stretch were shown a sharp intense peak at 1115 cm1. The FTIR spectra of DMP and its iron complex were shown in Fig. 9. The broad envelope between 3000 and 3700 cm1 was assigned to the O–H stretch of DMP and water. The broadening of the O–H stretch clearly demonstrates the formation of iron complex containing water, through hydrogen bonding interaction. The presence of DMP over Table 2 Gravimetric results of carbon steel corrosion without and with addition of inhibitors Inhibitors

M (mol/L)

w (mg m2 h1)

g%

Blank DMP

0

43.54

–

103 102 2.5 · 102 5 · 102

27.01 15.65 10.29 5.70

38 64 76 87

103 102 2.5 · 102 5 · 102

10.58 2.94 2.20 2.53

76 93 95 94

DEAP

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G. Gao et al. / Corrosion Science 49 (2007) 1833–1846 DMP DMP iron complex 100

%Transmittance

80

60

40

20

0 4000

3000

2000

1000

Wave number/cm-1

Fig. 9. FTIR spectra of DMP and its iron complex.

DEAP DEAP iron complex

100

%Transmittance

80

60

40

20

0 4000

3000

2000

1000

Wave number/cm-1

Fig. 10. FTIR spectra of DEAP and its iron complex.

the complex surface was evidenced by the C–H stretch lying just about 2968 cm1 and the C–O–C stretch at 1115 cm1. The O–H stretch of DEAP was shown around 3425 cm1. The peak between 2800 and 3000 cm1 was attributed to the C–H stretch. The C–N stretch was shown 1202 cm1 and the C–O stretch was shown a sharp intense peak around 1063 cm1. The FTIR spectra of DEAP and its iron complex were shown in Fig. 10. The broad envelope in the higher energy side can be assigned to –OH stretch of DEAP and water. The peak at 1642 cm1 is due to –OH2 bend. The peak at 2973 cm1 clearly established the presence of DEAP over the iron surface.

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4. Conclusion (1) 1,3-di-morpholin-4-yl-propan-2-ol (DMP) and 1,3-bis-diethylamino-propan-2-ol (DEAP) have been synthesized by alkylation reaction, purified and characterized by MS and IR, 1H NMR, 13C NMR. (2) Polarization curves indicate that DMP and DEAP act as anodic inhibitors for carbon steel in thin electrolyte layer. The inhibitive performance is improved by increasing the concentration of DMP, whereas showed a maximum inhibiting power of DEAP at 2.5 · 102 M. (3) The impedance measurement shows that the adsorbed protective layer on the metal surface obstructs the anodic dissolution of iron. The maximum of charge transfer resistance of DEAP is attributed to the formation of a compact adsorbed layer. The inhibitive effect of DEAP is superior to that of DMP. (4) All results show that DEAP has a perfect inhibitive performance on carbon steel in simulated atmospheric water medium, and the inhibitive efficiency of DEAP at 2.5 · 102 M is 95%. (5) The adsorption mechanism of DMP and DEAP on the carbon steel obeyed the Langmuir adsorption isotherm model. The adsorbed film containing the investigated compounds was identified by FTIR.

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