Journal Information
Share
Share
Download PDF
More article options
Visits
54
Original Article
DOI: 10.1016/j.jmrt.2018.09.010
Open Access
Two ditetrazole derivatives as effective inhibitors for the corrosion of steel in CH3COOH solution
Visits
54
Shuduan Denga,
Corresponding author
dengshuduan@163.com

Corresponding author.
, Xianghong Lib, Guanben Dua
a Faculty of Materials Science and Engineering, Southwest Forestry University, Kunming 650224, PR China
b College of Chemical Engineering, Southwest Forestry University, Kunming 650224, PR China
This item has received
54
Visits

Under a Creative Commons license
Article information
Abstract
Full Text
Bibliography
Download PDF
Statistics
Figures (11)
Show moreShow less
Tables (4)
Table 1. Parameters of the straight lines of c/θ−c and standard adsorption free energy (ΔG0) in 2.5M CH3COOH at 20°C (weight loss method, immersion time is 24h).
Table 2. Potentiodynamic polarization parameters for the corrosion of CRS in 1.0M CH3COOH containing different concentrations of BT and NTBC at 20°C.
Table 3. EIS parameters for the corrosion of CRS in 2.5M CH3COOH containing BT and NTBC at 20°C.
Table 4. Quantum chemical parameters for inhibitor molecules at GGA/BLYP/DND/COSMO level.
Show moreShow less
Abstract

The inhibition performance of two ditetrazole derivatives of blue tetrazolium (BT) and nitrotetrazolium blue chloride (NTBC) on cold rolled steel (CRS) in 2.5M CH3COOH solution was studied by weight loss, electrochemical techniques and scanning electron microscope (SEM). Quantum chemical calculations of BT2+ and NTB2+ were performed to theoretically investigate the adsorption mechanism. The results show that both BT and NTBC behave as effective inhibitors, and their maximum inhibition efficiency values are higher than 92% at 0.20mM. The inhibition follows the order of NTBC>BT. The adsorption of either BT or NTBC on steel surface follows Langmuir isotherm. BT and NTBC can be arranged as mixed-type inhibitors. The presence of BT or NTBC increases the charge transfer resistance, and decreases the corrosion degree of steel surface in CH3COOH. The adsorption centers are mainly focused on two tetrazole rings as well as the linkers of two benzene rings.

Keywords:
Corrosion inhibitor
Acetic acid
Steel
Blue tetrazolium
Nitrotetrazolium blue chloride
Adsorption
Full Text
1Introduction

A large number of N-heterocyclic compounds have been already used as effective inhibitors to retard the steel corrosion in various acids media [1–3]. The adsorption of N-heterocyclic inhibitor onto steel surface is mainly through the N-heterocyclic ring, in which coordinate bonds could be formed between Fe 3d empty orbits and electron pairs of N hetero-atom(s) as well as π electrons of N-heterocyclic ring. If a N-heterocyclic ring contains more N atoms, it could strongly interact with metal surface. The tetrazole ring is a five-member ring with four N atoms, and so tetrazole derivatives meet the structural characteristics of potential good corrosion inhibitors, and their inhibitions have been increasingly received some attentions. Kertit and Hammouti [4] reported that 1-phenyl-5-mercapto-1,2,3,4-tetrazole (PMT) was an effective inhibitor for pure iron in 1.0M HCl with inhibition efficiency (η) of 98% at 2.0mM, but other two tetrazole derivatives of 1-H-tetrazole (TTZ) and 1-methyl-5-mercapto-1,2,3,4-tetrazole (MMT) reversely accelerates steel corrosion with negative η values of −1.5% and −0.5% at 2.0mM, respectively. Also, the optimum η of 1.0mM PMT was as high as 98% for the corrosion of steel in both 1/2M H2SO4 and 1/3M H3PO4 solutions [5]. According to another previous work studied by Morales-Gil et al. [6], 5-mercapto-1-tetrazoleacetic sodium salt (MTAc) is a moderate inhibitor for steel 1.0M H2SO4, and the maximum η was about 69% at 200mgl−1. Although these tetrazole derivatives are widely studied as corrosion inhibitors for steel in inorganic acids (HCl, H2SO4 and H3PO4), there is little work in organic acid medium.

Acetic acid (CH3COOH) is widely used in acid pickling and acidification in the oil and gas industry [7]. Most important of all, CH3COOH accounts for about 50%–90% of the total organic acids in produced fluids during oil and gas systems [8]. Despite CH3COOH is weak acid (Kaθ=1.8×10−5), it still shows strong corrosive attack on steel. During past decades, many studies [9–11] have been dedicated to investigating the corrosion behavior and mechanism of steel in CH3COOH media. Regarding protection of steel from CH3COOH corrosion, organic inhibitors are always added to the acetic acid solution. The inhibition performance of some N-heterocyclic compounds on steel in CH3COOH media have been reported, such as pyridine derivative [12], thiadiazole derivatives [13], thiazoles [14] and triazoles [15]. Obviously, there is no published literature regarding the tetrazole derivatives as corrosion inhibitors in CH3COOH solution.

Our work team has been doing some research work about the corrosion inhibition of tetrazole derivatives of steel in inorganic acid media, like red tetrazolium [16], 5-aminotetrazole [17], triazolyl blue tetrazolium bromide [18], blue tetrazolium (BT) [19] and nitrotetrazolium blue chloride (NTBC) [20]. It is found that the type of tetrazole compound with double N-heterocyclic rings exhibits more inhibitive efficiency than the traditional tetrazole compound with only one tetrazole ring. Here, in continuation of our previous work, the aim of the present work is study the inhibition effect of two ditetrazole derivatives of BT and NTBC on cold rolled steel (CRS) in 2.5M CH3COOH solution. Besides experimental methods of weight loss, electrochemical techniques and SEM, quantum chemical calculation was applied to further explore the adsorption mechanism and structural–property relationship. It is expected to fully elucidate the inhibitive action and mechanism of ditetrazole derivatives on steel in acetic acid media.

2Experimental2.1Materials

The element compositions (wt.%) of tested CRS specimens are 0.07% C, 0.3% Mn, 0.022% P, 0.010% S, 0.01% Si, 0.030% Al and the remainder Fe. Both BT (C40H32N8O2Cl2, molecular weight: 727.7gmol−1) and NTBC (C40H30N10O6Cl2, molecular weight: 817.6gmol−1) are purchased from Sinopharm Chemical Reagent Co. Ltd. of China, and their chemical molecular structures are illustrated in Fig. 1. Both BT and NTBC are easily dissolved in water, and the additive inhibitor concentrations are 0.01–0.20mM. The aggressive solution of 2.5M CH3COOH (calculated pH=2.17, measured pH=2.10) were prepared by dilution of analytical grade 99.5% acetic acid glacial (Sinopharm Chemical Reagent Co. Ltd. of China) with distilled water. A freshly prepared corrosive electrolyte was used for each experiment.

Fig. 1.
(0.1MB).

Chemical molecular structures of two ditetrazole derivatives: (a) blue tetrazolium (BT); (b) nitrotetrazolium blue chloride (NTBC).

2.2Weight loss method

For each gravimetric test, three parallel CRS (the dimension of one CRS specimen is 2.5cm×2.0cm×0.06cm) were weighed accurately by digital balance (±0.1mg) to obtain the initial mass, then suspended using glass rods and hooks, and then totally immersed in a beaker with 250ml CH3COOH test solution at a constant temperature kept by a water ultra-thermostat (±0.1°C). After immersion for 24h, CRS sheets were taken out, subsequently immersed in ASTMG1-90 standard solution (Clark solution: 100ml HCl+2% Sb2O3+5% SnCl2) to remove the corrosion products, then washed with distilled water and acetone, dried and reweighed accurately to obtain the final mass. The average weight loss of three parallel CRS sheets is obtained, and then both corrosion rate (v) and inhibition efficiency (ηw) are calculated [20].

2.3Electrochemical measurements

All electrochemical tests were performed on PARSTAT 2273 advanced electrochemical system (Princeton Applied Research) with PowerSuite software. The electrochemical three-electrode cell is used for all electrochemical measurements. A platinum electrode is used as counter electrode, a saturated calomel electrode (SCE) coupled to a fine Luggin capillary as reference electrode, and a square CRS embedded in PVC holder using epoxy resin as working electrode (WE). The exposed surface (1.0cm×1.0cm) of WE was treated as described above (Section 2.1). The electrolyte is the corrosive media of 250ml 2.5M CH3COOH solution without or with a certain concentration of ditetrazole maintained at 20°C under non-stirred conditions. The tip of Luggin capillary was located about 3mm close to WE to minimize the ohmic drop of the solution, and the exposed surface of WE was put right against the platinum plate to form uniform electric field. Prior to electrochemical measurements, WE was immersed in corrosive electrolyte for 2h at OCP to reach a stationary value (±0.5mV). The polarization curves were conducted in the potential range from −250 to +250mV versus OCP at a sweep rate of 0.5mVs−1. EIS was carried out at stable OCP within the frequency range from 100kHz to 10mHz, and the signal amplitude is 10mV root mean square. Each test was run at least three times to verify the reliable results. Inhibition efficiency values of polarization curves (ηp) and EIS (ηp) are calculated according to corrosion current density and charge transfer resistance, respectively [20].

2.4SEM examinations

The morphologies of CRS samples after 24h of immersion in 2.5M CH3COOH solutions without and with 0.2mM BT or NTBC at 20°C were examined by FEI QUANTA 200 scanning electron microscope (America).

2.5Quantum chemical calculations

Quantum chemical calculations were respectively performed with DMol3 in Materials Studio 7.0 software from Accelrys Inc. [21]. Quantum chemical calculations based on density function theory (DFT) of BT2+ and NTB2+ were done at the GGA/BLYP [22]/DND [23]/COSMO [24] level without any symmetry and spin constraints. Both optimized geometric structures of BT2+ and NTB2+ are verified that their vibrations have no imaginary frequency through frequency calculations. The parameter criteria for the convergence tolerances of energy, maximum force, maximum displacement and SCF convergence criteria k-point set are 1.0×10−5Ha, 2.0×10−3Ha/Å, 5.0×10−3Å and 1.0×10−6, respectively [25].

3Results and discussion3.1Weight loss measurements

The relative standard deviation (RSD) values of both v and ηw for three parallel CRS specimens obtained from weight loss method are below 5%, which confirms that the reproducibility for experimental data in present system is very precise.

3.1.1Effect of BT and NTBC on corrosion inhibition

In blank 2.5M CH3COOH solution, v is 1.296gm−2h−1 (RSD=3.4%), but it greatly decreases for all additive concentrations of ditetrazoles. To directly understand the inhibitive ability, the corresponding inhibition efficiency (ηw) values against inhibitor concentrations of BT and NTBC (c) for CRS in 2.5M CH3COOH solution at 20°C are plotted in Fig. 2. Inspection of Fig. 2 reveals that ηw sharply increases with increasing the inhibitor concentration from 0.01 to 0.08mM, but it mildly changes within the inhibitor concentration from 0.08 to 0.20mM. This behavior is attributed to that the adsorption amount of inhibitor covering steel surface increases to more extent firstly, but when it is near to the saturated state, it slightly changes with the further increase of added inhibitor concentrations from 0.10 to 0.20mM. At the inhibitor concentration of 2.0mM, the maximum ηw values of BT and NTBC are 96.4% and 92.6%, respectively. Thus, both BT and NTBC act as effective inhibitors for steel in CH3COOH. It is apparent that NTBC has higher inhibitive performance than BT, which could be assigned to two additional substituted nitro-groups in NTBC as compared to BT.

Fig. 2.
(0.09MB).

Relationship between inhibition efficiency (ηw) and concentration of inhibitor (c) in 2.5M CH3COOH at 20°C (weight loss method, immersion time is 24h).

3.1.2Adsorption isotherm and standard adsorption free energy (ΔG0)

Two ditetrazoles of BT and NTBC exhibit their inhibitive ability via the adsorption on steel surface. In order to elucidate the adsorption behavior of inhibitor on steel surface, some adsorption isotherms such as Frumkin, Langmuir, Temkin, Freundlich, Bockris–Swinkels and Flory–Huggins are utilized to fit the experimental data. By far, Langmuir adsorption isotherm is found to be the best description for the present adsorption behavior, and it is described by Eq. (1)[26]:

where c is the inhibitor concentration (mM) and K is the adsorptive equilibrium constant (M−1). θ is the degree of surface coverage, and its value approximately equals to inhibition efficiency [27].

Two linear fitted straight lines and experimental data of c/θ versus c for BT and NTBC at 20°C are plotted in Fig. 3, and the corresponding linear regression parameters and the adsorption parameter of K are listed in Table 1. From Table 1, both linear correlation coefficients (r) and slope are very close to 1, confirming the adsorption of either BT or NTBC on steel surface completely obeys Langmuir adsorption isotherm. Larger K is generally related to stronger interaction of inhibitor molecule with metal surface. As can be seen from Table 1, K (NTBC)>K (BT) means that NTBC exhibits a stronger tendency to be adsorbed onto steel surface than BT.

Fig. 3.
(0.1MB).

Langmuir adsorption isotherm modes of BT and NTBC on CRS surface in 2.5M CH3COOH at 20°C from weight loss measurement.

Table 1.

Parameters of the straight lines of c/θc and standard adsorption free energy (ΔG0) in 2.5M CH3COOH at 20°C (weight loss method, immersion time is 24h).

Inhibitor  r  Slope  K (M−1ΔG0 (kJmol−1
BT  0.9997  1.02  8.16×104  −37.35 
NTBC  0.9999  1.01  1.42×105  −38.71 

Another important thermodynamic parameter of standard adsorption free energy (ΔG0) could be obtained from K given by the following equation [28]:

where the value 55.5 is the concentration of water in test solution expressed in M [28].

The calculated ΔG0 values of BT and NTBC as shown in Table 1 ranges from −40 to −20kJmol−1, it is thus to deduce that the adsorption of BT and NTBC on steel surface could be the mixed adsorption process that involves both physical and chemical adsorption [29]. ΔG0 (NTBC)<ΔG0 (BT) again demonstrates that NTBC has more stronger adsorptive ability on steel surface than BT between two studied ditetrazole derivatives.

3.2Potentiodynamic polarization studies

Potentiodynamic polarization curves for CRS electrode in 2.5M CH3COOH media at 20°C with the addition of different concentrations (0.02, 0.10 and 0.20mM) of BT and NTBC are shown in Fig. 4(A) and (B). Comparing with uninhibited 2.5M CH3COOH bank solution, the addition of either BT or NTBC moves both anodic and cathodic curves to the lower current densities, which indicates that both anodic and cathodic reactions of the corrosion of CRS are significantly inhibited by two ditetrazole compounds of BT and NTBC. Each potentiodynamic curve is parallel with each other, which suggests that the electrochemical reactions of CRS in CH3COOH are not changed upon with the addition of the tested ditetrazoles. The appearance of polarization curves indicates that both cathodic hydrogen permission and anodic ferrous dissolution are activatedly controlled. The cathodic reaction of steel in CH3COOH solution is the hydrogen evolution reaction [9–11]. Accordingly, the proposed cathodic mechanism follows the steps (4)–(6)[30]:

Fe+H+(FeH+)ads
(FeH+)ads+e(FeH)ads
(FeH)ads+H++eFe+H2

Fig. 4.
(0.19MB).

Potentiodynamic polarization curves for CRS in 2.5M CH3COOH without and with different concentrations of inhibitors at 20°C (immersion time is 2h): (A) BT; (B) NTBC.

Two (FeH)ads may combine together to liberate hydrogen (H2) via following reaction [31]:

(FeH)ads+(FeH)ads2Fe+H2

According to the mechanism for the corrosion of mild steel in aqueous solutions of CH3COOH [9–11], the anodic dissolution of CRS in CH3COOH solutions may be assumed as follows:

Fe+CH3COO(FeCH3COO)ads

(FeCH3COO)ads(FeCH3COO)ads+e

(FeCH3COO)ads(FeCH3COO+)+e

(FeCH3COO+)Fe2++CH3COO

Thus, the adsorption of CH3COO ions on the CRS surface would be the prerequisite for the anodic steel dissolution to be occurred.

The corrosion parameters including corrosion current densities (icorr), corrosion potential (Ecorr), cathodic Tafel slope (bc) and anodic Tafel slope (ba) are obtained by extrapolation of the Tafel lines. Table 2 lists the fitting corrosion parameters and inhibition efficiency (ηp). As can be seen from the data in Table 2, icorr decreases prominently after adding BT or NTBC to CH3COOH media, and it decreases gradually with increasing of the concentration of ditetrazoles. icorr is as high as 225.4μAcm−2 in CH3COOH blank solution, but it falls to only 22.1μAcm−2 in the presence of 2.0mM BT; and 15.5μAcm−2 in the presence of 2.0mM NTBC. Correspondingly, ηp increases with the inhibitor concentration, and the best ηp of 2.0mM BT and 2.0mM NTBC are 90.20% and 93.12%, respectively. Thus, both BT and NTBC are good inhibitors in 2.5M CH3COOH, and NTBC is a better inhibitor than BT. Ecorr is not changed in the presence of either BT or NTBC with respect to blank solution, which indicates both ditetrazole compounds of BT and NTBC behave as mixed-type inhibitors for CRS in CH3COOH [32]. Moreover, the electrochemical mechanism of ditetrazole inhibitors of BT and NTBC is caused by geometry blocking effect [32]. In the other words, both BT and NTBC diminish the available reactive surface areas to be corroded in CH3COOH. Two Tafel constants of bc and ba are not changed with the addition of BT and NTBC, again indicating that both BT and NTBC impedes the electrode corrosion by merely blocking the reaction sites of electrode surface without affecting both anodic dissolution of steel and cathodic hydrogen evolution reaction mechanism [33].

Table 2.

Potentiodynamic polarization parameters for the corrosion of CRS in 1.0M CH3COOH containing different concentrations of BT and NTBC at 20°C.

Inhibitor  c  Ecorr  icorr  bc  ba  ηp 
  (mM)  (mV vs. SCE)  (μAcm−2(mVdec−1(mVdec−1(%) 
—  −481  225.4  305  95  — 
BT0.02  −478  92.8  313  102  58.83 
0.10  −484  30.8  312  107  86.34 
0.20  −471  22.1  328  103  90.20 
NTBC0.02  −476  70.5  282  87  68.72 
0.10  −482  26.7  328  103  88.15 
0.20  −477  15.5  303  80  93.12 
3.3Electrochemical impedance spectroscopy (EIS)

Fig. 5(A) and (B) represents the Nyquist plots for CRS electrode in 2.5M CH3COOH without and with the addition of BT and NTBC at 20°C after an exposure immersion time of 2h, respectively. It is evident that all Nyquist spectra obtained exhibit one single capacitive loop, which indicates that the corrosion of steel in CH3COOH solution is mainly controlled by the charge transfer process [34]. The diameter of the capacitive loop in the presence of BT or NTBC is much bigger than that in the absence of inhibitor (blank solution), and increases with the inhibitor concentration from 0.02 to 0.20mM. Thus, the impedance of inhibited substrate is enhanced owing to the introduction of ditetrazole compound BT or NTBC.

Fig. 5.
(0.22MB).

Nyquist plots for CRS in 2.5M CH3COOH without and with different concentrations of inhibitors at 20°C (immersion time is 2h): (A) BT; (B) NTBC.

The Bode modulus and phase angle plots for CRS in 2.5M CH3COOH containing different concentrations of BT and NTBC at 20°C are given in Figs. 6 and 7, respectively. Comparing with the Bode of the blank solution, the absolute impedance in the presence of ditetrazole compound is drastically increased at low frequencies in Bode modulus, which corresponds slowing down the corrosion of steel and confirms the higher protection of ditetrazole compounds of BT and NTBC, owing to the adsorption of the inhibitor molecules on the CRS surface. As can be seen from Fig. 7(A) and (B), there is only one phase peak in phase angle plots, which confirms that there is only one time constant related to the capacitive loop. Irrespective of adding any concentrations of BT or NTBC to CH3COOH, the shapes of Nyquist and Bode plots are not altered throughout all tested inhibitor concentrations. Thus, there is almost no alter in the corrosion mechanism whether the inhibitor is added to the corrosive media [35,36].

Fig. 6.
(0.24MB).

Bode modulus for CRS in 2.5M CH3COOH without and with different concentrations of inhibitors at 20°C (immersion time is 2h): (A) BT; (B) NTBC.

Fig. 7.
(0.26MB).

Bode phase angle plots for CRS in 2.5M CH3COOH without and with different concentrations of inhibitors at 20°C (immersion time is 2h): (A) BT; (B) NTBC.

Noticeably, all these capacitive loops in Nyquist grams are not perfect semicircles, and the peak angles are lower than 90° in phase angle plots (Fig. 7), which could be attributed to the frequency dispersion effect as a result of the roughness and inhomogeneousness of electrode surface or electrode/solution interface [37].

In summary, the hydrogen depolarisation of CRS in CH3COOH solution is the charge transfer controlling step with only one time constant. Thus, the simplest model of EIS could be the electrochemical resistance in parallel to the double layer capacitance connected with the resistance of the electrolyte. However, there is the frequency dispersion effect that will result in a deviation from ideal double layer capacitance. Accordingly, constant phase element (CPE) is more accurate to replace the double layer capacitance (Cdl), and then EIS data are simulated using the equivalent circuit shown in Fig. 8, in which Rs and Rt are the solution resistance and charge transfer resistance, respectively. The fitted solid lines in Figs. 5–7 agrees well with experimental data, which confirms that this equivalent circuit best fit the experimental data.

Fig. 8.
(0.01MB).

The equivalent circuit model of EIS.

CPE is composed of a component Qdl and a dispersion coefficient a that quantifies the inhomogeneousness degree of electrode/solution interface resulting from surface roughness, inhibitor adsorption, porous layer formation, etc. The double layer capacitance (Cdl) can be obtained via CPE from the following equation [38]:

where fmax represents the frequency at which the imaginary value reaches a maximum on the Nyquist plot. The electrochemical parameters of Rs, Rt, CPE, a, Cdl, fmax, chi-squared (χ2) and ηR are summarized in Table 3.

Table 3.

EIS parameters for the corrosion of CRS in 2.5M CH3COOH containing BT and NTBC at 20°C.

Inhibitor  c  Rs  Rt  CPE  a  χ2  Cdl  ηR 
  (mM)  cm2cm2(μΩ−1sacm−2    (μFcm−2(%) 
–  132.2  139.1  288.2  0.7049  5.48×10−5  117  — 
BT0.02  131.4  307.3  205.4  0.8036  5.44×10−5  106  54.73 
0.1  130  1008  106.8  0.7799  1.78×10−4  51  86.2 
0.2  129.7  1860  75.6  0.823  4.41×10−4  46  92.52 
NTBC0.02  130  546.6  125.3  0.8637  2.01×10−4  82  74.55 
0.1  133.8  1385  94.6  0.8995  3.81×10−4  49  89.96 
0.2  133.5  2131  68.7  0.89  4.64×10−4  44  93.47 

All χ2 values are rather as low as 10−5 to 10−4, which verifies that the fitted data are in good coincidence with the experimental data. It is observed that Rs is about 100Ωcm2 for 2.5M CH3COOH test solution, which implies that the test solution is not very conductive owing to the weak deionization of CH3COOH. Rt is about 139.1Ωcm2 for the blank solution, and is increased to remarkable about 1860Ωcm2 in the presence of 2.0mM BT; and 2131Ωcm2 in the presence of 2.0mM NTBC. A large charge transfer resistance (Rt) is associated with a slower corroding system. Rt of two ditetrazole compounds follows the order: Rt (BT)<Rt (NTBC), which again confirms that inhibitive performance of NTBC is better than that of BT.

If the electrode surface is homogeneous and plane, the dispersion coefficient of a equals to 1 and the electrode surface can be treated as an ideal capacitance. The value of a is used to account for the roughness of the electrode. The lower the value of a is related to the rougher electrode surface. All a values are lower than 1, which confirms that there is frequency dispersion on electrode surface. In presence of BT or NTBC, the value of a increases to some extent, which suggests that CRS electrode surface becomes smoother due to formation of a non-porous and dense monolayer of inhibiting film.

As shown in Table 3, Cdl becomes lower when BT or NTBC is added to CH3COOH medium, which can be explained on Helmholtz model:

where ɛ0 is dielectric constant of vacuum, ɛ the dielectric constant of electrolyte, d the thickness of the electrical double layer, and S is the surface area. Comparing CRS electrode in uninhibited solution with that in inhibited solution, ɛ0 and S remain unchangeable, thus the decrease in Cdl in inhibited solution, which could result from a decrease in ɛ and/or an increase in d, suggests that the inhibitor molecules function by adsorption at the metal/solution interface to replace the adsorbed water molecules [39]. ηR increases with the concentration of ditetrazole derivative, and follows the consequence: ηR(NTBC)>ηR (BT). The maximum ηR values at 2.0mM are 92.52% and 93.47% for BT and NTBC, respectively. Thus, two ditetrazole derivatives act as effective inhibitors for CRS in CH3COOH solution.

Inhibition efficiencies obtained from EIS are in good accordance with those from weight loss and polarization methods.

3.4SEM surface examination

In order to further determine the inhibitive action of ditetrazole compounds, SEM microstructures of CRS surfaces are shown in Fig. 9. It can be seen from Fig. 9(A) that CRS surface after immersion in uninhibited 2.5M CH3COOH blank system for 24h is drastically damaged by the aggressive media. The corrosion products distributed on the whole steel surface appear too uneven, and are rather rough. Fig. 9(B) shows that corrosion degree of the steel surface decreases in the presence of 2.0mM BT, and the surface seems much smoother. Fig. 9(C) clearly shows that the corrosion of steel surface in the presence of 2.0mM NTBC is significantly hindered; where the corrosion specimen surface is more flat and compact. Both observations in Fig. 9(B) and (C) reveals that there are compact and rigid layers on steel surfaces treated with ditetrazoles, which could efficiently protect steel from corrosion in CH3COOH. In summary, either BT or NTBC could be adsorbed onto steel surface to form a good protective film, thus impeding the corrosion of steel surface in CH3COOH media.

Fig. 9.
(0.7MB).

SEM micrographs of CRS surface: (a) after 24h of immersion at 20°C in 2.5M CH3COOH; (b) after 24h of immersion at 20°C in 0.20mM BT+2.5M CH3COOH; (c) after 24h of immersion at 20°C in 0.20mM NTBC+2.5M CH3COOH.

3.5Quantum chemical calculations of DFT

Quantum chemical calculation has been proved the useful method to theoretically elucidate the metal-inhibitor and inhibitive mechanism of inhibitor molecule [40]. Both BT and NTBC could be easily ionized in water solution to cationic parts of BT2+ and NTB2+ and anionic chloride ion (Cl):

BTBT2++2Cl
NTBCNTB2++2Cl

The organic parts of BT2+ and NTB2+ could be deemed as vital effective components for BT and NTBC, respectively. Accordingly, quantum chemical calculations of BT2+ and NTBC2+ based on DFT were done to elucidate the adsorption inhibitive mechanism on molecular level. Fig. 10 shows the full optimized spatial molecular structures of BT2+ and NTB2+ under BLYP/DND/GGA/COSMO level. For either BT2+ or NTB2+, two tetrazole rings and four benzene rings are not in one plane. In view of molecular structures of BT2+ and NTB2+, the adsorption involves two main adsorption modes: physisorption and chemisorption.

Fig. 10.
(0.15MB).

Optimized molecular structures of two ditetrazole derivatives: (a) BT2+; (b) NTB2+.

The physisorption is correlated with the quantum parameter of dipole moment (μ) that is used to determine the polarity of a molecule [41]. The physisorption of organic inhibitor molecules on metal surface arises as a result of electrostatic attraction between the organic dipole and the charged metal surface. The inhibitor molecules incorporated in the electric double layer on the metal/solution interface compete with the adsorbed H2O molecules for sites at the metal surface. The inhibitor molecules with a high dipole moment exert significant effect on the dielectric properties of the electric double layer. Thus, the inhibitor molecule with larger μ value is more likely to interact with steel surface through electronic force [42]. The calculated μ value of BT2+ is 18.3615 D, and that of NTB2+ is 18.6669 D. As mentioned above in Section 3.2, CH3COO could be firstly adsorb on electrode surface during the anodic reaction process in CH3COOH media. Meanwhile, the chloride ions (anionic part of ditetrazole derivative) can penetrate into the inner layer of the double-layer structure, and could specifically adsorb on steel surface.

The adsorption of these anions (CH3COO and Cl) on steel surface create negative charged steel surface. Then, the positive charged molecules of BT2+ and NTB2+ could adsorb on the negatively charged metal surface through electrostatic interactions. In other words, the adsorption of CH3COO and Cl leads to the enhancement of the adsorption of BT2+ and NTB2+ at the steel electrode. It should be noted that μ (NTB2+)>μ (BT2+), which indicates that the better inhibitive action of NTB2+ than BT2+ may be arisen from intermolecular electrostatic force.

The frontier molecular orbitals are applied to study the global reactivity of two ditetrazoles studied. HOMO (the highest occupied molecular orbital) is related to the capacity of a molecule to donate electrons, whereas LUMO (the lowest unoccupied molecular orbital) represents the ability of the molecule to accept electrons [40]. The electric/orbital density distributions of HOMO and LUMO for BT2+ and NTB2+ molecules are shown in Fig. 11. As can be seen from Fig. 11(A) and (C), that the electron densities of HOMO for both BT2+ and NTB2+ are mostly localized on the linkers of two benzene rings and two oxygen atoms in methoxy groups, which could be deemed as the donor of the electrons to the metal surface. For BT2+, LUMO as shown in Fig. 11(B) is mostly located on two tetrazole rings, which reflects two tetrazole rings could be acceptor of electrons from steel surface. Inspection of Fig. 11(D) reveals that the distributions of LUMO for NTB2+ are found on two tetrazole rings and two nitro-groups (–NO2). Thereby, comparing with BT2+, it is reasonable to assume that the two substituted –NO2 groups of NTB2+ have extra additional ability to accept electrons from d-orbitals of metal to form back-donating bond, which could be assigned to the main reason of inhibition order of NTB2+>BT2+. Noticeably, there are π conjugation systems for either HOMO parts of two benzene rings (Fig. 11(A) and (C)) or LUMO parts of two tetrazole rings (Fig. 11(B) and (D)), which make them suitable for π-interaction with metal surface [43] and back donation of metal d-electrons to the π*-orbitals of inhibitor molecule [44]. The aromatic π-electrons intensify the chemisorption, which make two studied ditetrazoles to be considered as efficient inhibitors.

Fig. 11.
(0.31MB).

The frontier molecule orbital density distributions of two ditetrazole derivatives: (a) BT2+ (HOMO); (b) BT2+ (LUMO); (c) NTB2+ (HOMO); (d) NTB2+ (LUMO).

The quantum parameters of energy of highest occupied molecular orbital (EHOMO), energy of lowest unoccupied molecular orbital (ELUMO) and the separation energy (ELUMOEHOMO, ΔE) are also presented in Table 4. Higher value of EHOMO causes more tendency of inhibitor molecule to donate electrons to empty 3d orbitals of Fe [45], while lower ELUMO suggests more probable of inhibitor molecule to accept electrons from steel [45]. From Table 4, EHOMO has a slight difference value of 0.055eV between two studied ditetrazoles owing to that the HOMO distribution of BT2+ (Fig. 11(A)) is same as that of NTB2+ (Fig. 11(C)). In contrast, ELUMO obeys the order: NTB2+<BT2+, which is in complete agreement with the experimental inhibition consequence of NTBC>BT. Thus, there is a good correlation between ELUMO and inhibition efficiency.

Table 4.

Quantum chemical parameters for inhibitor molecules at GGA/BLYP/DND/COSMO level.

Molecule  EHOMO (eV)  ELUMO (eV)  ΔE (eV)  β (eV)  γ (eV)  s (eV−1ΔN 
RT2+  −6.096  −3.975  2.121  5.036  1.061  0.943  0.926 
NTB2+  −6.151  −4.350  1.801  5.250  0.900  1.110  0.972 

The parameter of ΔE means the reactivity of inhibitor molecule toward the adsorption on metallic surface. The lower ΔE is, the higher reactivity of inhibitor molecule is reversely, and facilitates the adsorption, then improves higher inhibitive performance [46]. ΔE values of two ditetrazole compounds follow the order: NTB2+<RT2+, which confirms that NTB2+ exhibits adsorptive ability on steel surface preferably to RT2+.

The energy parameters of EHOMO and ELUMO are related to ionization potential (I) and electron affinity (Y), respectively [47]:

With obtained I and Y, three parameters of absolute electronegativity (β), global hardness (γ) and global softness (s) of inhibitor molecule are approximately calculated as following equations [48]:

The number of electrons transferred from the inhibitor molecule to metallic surface (ΔN) is calculated through β and γ values [49]:

The theoretical values of βFe and γFe are 7eV and 0eV for Fe atom, respectively [50]. The values of β, γ, s and ΔN are also listed in Table 4. According to some studies [50], the parameter of β is related to the chemical potential, and higher β corresponds to better inhibitive performance. Comparing Eq. (18) with Eqs. (15) and (16), γ is equal to ΔE/2, and so the lower γ implies more polarizability and higher inhibitive action. The parameter of s is reciprocal to γ, thus high value of s is related to more efficiency. The parameter of ΔN exhibits inhibitive performance resulted from electrons donations. If ΔN<3.6, the chemisorption and inhibition efficiency increase with increasing in electron-donation ability to the metal surface [50]. For the present studied two ditetrazoles, the inhibition action follows the order: NTB2+>BT2+. Thus, there is a good correlation between inhibition efficiency with the parameters of ELUMO, ΔE, β, γ, s and ΔN.

4Conclusions

  • (1)

    Two ditetrazole derivatives of NTBC and BT act as effective inhibitors for the corrosion of CRS in 2.5M CH3COOH solution, and the inhibitive action follows the order: NTBC>BT. Inhibition efficiency (ηw) increases with the inhibitor concentration, and the maximum ηw values of BT and NTBC at 0.20mM are 96.4% and 92.6% at 20°C. The adsorption of either BT or NTBC on CRS surface completely obeys Langmuir adsorption isotherm.

  • (2)

    Both BT and NTBC are arranged as mixed-type inhibitors in CH3COOH, and the electrochemical inhibitive mechanism is caused by geometry blocking effect. EIS spectra exhibit one depressed capacitive loop with one time constant, and the presence of each ditetrazole derivative enhances Rt while reduces Cdl. SEM micrographs clearly confirms that the corrosion of steel surfaces are prominently retarded by ditetrazoles.

  • (3)

    The higher μ values of BT2+ and NTB2+ facilitates their physisorption. For both BT2+ and NTB2+, the nucleophilic attack sites and LUMO are mainly located on two tetrazole rings, while the electrophilic sites and HOMO densities are focused on the linker of two benzene rings as well as two O atoms in –OCH3. As compared with BT2+, two substituted –NO2 groups of NTB2+ have extra ability to accept electrons from steel surface to form back-donating bond.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

This work was carried out in the frame of research projects funded by National Natural Science Foundation of China (51361027) and Training Program of Young and Middle Aged Academic and Technological Leaders in Yunnan Province (2015HB049, 2017HB030).

References
[[1]]
A.Y. Musa, A.A.H. Kadhum, A.B. Mohamad, M.S. Takriff, A.R. Daud, S.K. Kamarudin
On the inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1,2,4-trizole-3-thiol
Corros Sci, 52 (2010), pp. 526-533
[[2]]
P. Morales-Gil, M.S. Walczak, C. Ruiz Camargo, R.A. Cottis, J.M. Romero, R. Lindsay
Corrosion inhibition of carbon-steel with 2-mercaptobenzimidazole in hydrochloric acid
Corros Sci, 101 (2015), pp. 47-55
[[3]]
Z.Q. Wang, Y.L. Gong, C. Jing, H.J. Huang, H.R. Li, S.T. Zhang
Synthesis of dibenzotriazole derivatives bearing alkylene linkers as corrosion inhibitors for copper in sodium chloride solution: a new thought for the design of organic inhibitors
Corros Sci, 113 (2016), pp. 64-77
[[4]]
S. Kertit, B. Hammouti
Corrosion inhibition of iron 1M HCl by 1-phenyl-5-mercapto-1,2,3,4-tetrazole
Appl Surf Sci, 93 (1996), pp. 59-66
[[5]]
E. Bensajjay, S. Alehyen, M. El Achouri, S. Kertit
Corrosion inhibition of steel by 1-phenyl-5-mercapto 1 2,3,4-tetrazole in acidic environments (0.5M H2SO4 and 1/3M H3PO4)
Anti-Corros Meth Mater, 50 (2003), pp. 402-409
[[6]]
P. Morales-Gil, G. Negrón-Silva, M. Romero-Romoa, C. Ángeles-Chávez, M. Palomar-Pardavé
Corrosion inhibition of pipeline steel grade API 5L X52 immersed in 1M H2SO4 aqueous solution using heterocyclic organic molecules
Electrochim Acta, 49 (2004), pp. 4733-4741
[[7]]
K.Y. Huang
Corrosion characteristics and corrosion inhibitors for metals in acetic acid solution
Appl Chem Indus, 30 (2001), pp. 1-6
[[8]]
P.C. Okafor, S. Nešić
Effect of acetic acid on CO2 corrosion of carbon steel in vapor-water two-phase horizontal flow
Chem Eng Commun, 194 (2007), pp. 141-157
[[9]]
Y.M. Gao, S.M. Wang, Y.X. Xu, W.T. Wu
Corrosion behavior and mechanism of A3 steel in acetic acid
Corros Prot, 27 (2006), pp. 11-13
[[10]]
T. Tran, B. Brown, S. Nešić, B. Tribolet
Investigation of the electrochemical mechanisms for acetic acid corrosion of mild steel
Corrosion, 70 (2014), pp. 223-229
[[11]]
M.M. Singh, A. Guapta
Corrosion behavior of mild steel in acetic acid solutions
Corrosion, 56 (2000), pp. 371-379
[[12]]
S. Abd El Wanees, M.I. Alahmdi, M.H.E. Abd El Azzem
Ahmed, 4,6-dimethyl-2-oxo-1,2-dihydro-pyridine-3-carboxylic acid as an inhibitor towards the corrosion of C-steel in acetic acid
Int J Electrochem Sci, 11 (2016), pp. 3446-3448
[[13]]
M.Z.A. Rafiquee, S. Khan, N. Saxena, M.A. Quraish
Influence of some thiadiazole derivatives on corrosion inhibition of mild steel in formic and acetic acid media
Port Electrochim Acta, 25 (2007), pp. 419-434
[[14]]
M.A. Quraishi, H.K. Sharma
Thiazoles as corrosion inhibitors for mild steel in formic and acetic acid solutions
J Appl Electrochem, 35 (2005), pp. 33-39
[[15]]
M.A. Quraishi, H.K. Sharma
Inhibition of mild steel corrosion in formic and acetic acid solutions
Indian J Chem Technol, 11 (2004), pp. 331-336
[[16]]
X.H. Li, S.D. Deng, H. Fu
Synergism between red tetrazolium and uracil on the corrosion of cold rolled steel in H2SO4 solution
Corros Sci, 51 (2009), pp. 1344-1355
[[17]]
X.H. Li, S.D. Deng, X.G. Xie, G.B. Du
Synergistic inhibition effect of 5-aminotetrazole and 4 6-dihydroxypyrimidine on the corrosion of cold rolled steel in H3PO4 solution
Mater Chem Phys, 181 (2016), pp. 33-46
[[18]]
X.H. Li, S.D. Deng, H. Fu
Triazolyl blue tetrazolium bromide as a novel corrosion inhibitor for steel in HCl and H2SO4 solutions
Corros Sci, 53 (2011), pp. 302-309
[[19]]
X.H. Li, S.D. Deng, H. Fu
Blue tetrazolium as a novel corrosion inhibitor for cold rolled steel in hydrochloric acid solution
Corros Sci, 52 (2010), pp. 2786-2792
[[20]]
S.D. Deng, X.H. Li, H. Fu
Nitrotetrazolium blue chloride as a novel corrosion inhibitor of steel in sulfuric acid solution
Corros Sci, 52 (2010), pp. 3840-3846
[[21]]
Materials Studio 7.0, Accelrys Inc., 2013.
[[22]]
A.D. Becke
A multicenter numerical integration scheme for polyatomic molecules
J Chem Phys, 88 (1988), pp. 2547-2553
[[23]]
C. Lee, W. Yang, R.G. Parr
Development of the Colle–Salvetti correlation-energy formula into a functional of the electron density
Phys Rev B, 37 (1988), pp. 785-789
[[24]]
A. Klamt, G. Schüürmann
COSMO: a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient
J Chem Soc Perkin Trans, 2 (1993), pp. 799-805
[[25]]
S.D. Deng, G.B. Du, X.H. Li, A. Pizzi
Performance and reaction mechanism of zero formaldehyde-emission urea-glyoxal (UG) resin
J Taiwan Inst Chem Eng, 45 (2014), pp. 2029-2038
[[26]]
I. Langmuir
The constitutions and fundamental properties of solids and liquids. II. Liquids
J Am Chem Soc, 39 (1917), pp. 1848-1906
[[27]]
M.H. Hussin, A.A. Rahim, M.N.M. Ibrahim, N. Brosse
Improved corrosion inhibition of mild steel by chemically modified lignin polymers from Elaeis guineensis agricultural waste
Mater Chem Phys, 163 (2015), pp. 201-212
[[28]]
E. Cano, J.L. Polo, A. La Iglesia, J.M. Bastidas
A study on the adsorption of benzotriazole on copper in hydrochloric acid using the inflection point of the isotherm
Adsorption, 10 (2004), pp. 219-225
[[29]]
N. Soltani, H. Salavati, N. Rasouli, M. Paziresh, A. Moghadas
Adsorption and corrosion inhibition effect of Schiff base ligands on low carbon steel corrosion in hydrochloric acid solution
Chem Eng Commun, 203 (2016), pp. 840-854
[[30]]
G. Bereket, A. Yurt, H. Türk
Inhibition of the corrosion of low carbon steel in acidic solution by selected polyelectrolytes and polymers
Anti-Corros Meth Mater, 50 (2003), pp. 435-442
[[31]]
M.M. Singh, A. Gupta
Corrosion behavior of mild steel in formic acid solutions
Mater Chem Phys, 46 (1996), pp. 15-22
[[32]]
C. Cao
On electrochemical techniques for interface inhibitor research
Corros Sci, 38 (1996), pp. 2073-2082
[[33]]
S.S. Abd El Rehim, M.A.M. Ibrahim, K.F. Khalid
The inhibition of 4-(2’-amino-5’-methylphenylazo) antipyrine on corrosion of mild steel in HCl solution
Mater Chem Phys, 70 (2001), pp. 268-273
[[34]]
X.W. Zhen, S.T. Zhang, W.P. Li, L.L. Yin, J.H. He, J.F. Wu
Investigation of 1-butyl-3-methyl-1H-benzimidazolium iodide as inhibitor for mild steel in sulfuric acid solution
Corros Sci, 80 (2014), pp. 383-392
[[35]]
N. Labjar, M. Lebrini, F. Bentiss, N.E. Chihib, S. El Hajjaji, C. Jama
Corrosion inhibition of carbon steel and antibacterial properties of aminotris-(methylnephosnic) acid
Mater Chem Phys, 119 (2010), pp. 330-336
[[36]]
K.F. Khaled
The inhibition of benzimidazole derivatives on corrosion of iron in 1M HCl solutions
Electrochim Acta, 48 (2003), pp. 2493-2503
[[37]]
F. Manfeld
Electrochemical impedance spectroscopy (EIS) as a new tool for investigating methods of corrosion protection
Electrochim Acta, 35 (1990), pp. 1533-1544
[[38]]
H.H. Hassan
Inhibition of mild steel corrosion in hydrochloric acid solution by triazole derivatives Part II: time and temperature effects and thermodynamic treatments
Electrochim Acta, 53 (2007), pp. 1722-1730
[[39]]
E. Gutiérrez, J.A. Rodríguez, J. Cruz-Borbolla, J.G. Alvarado-Rodríguez, P. Thangarasu
Development of a predictive model for corrosion inhibition of carbonsteel by imidazole and benzimidazole derivatives
Corros Sci, 108 (2016), pp. 23-25
[[40]]
I.B. Obot, D.D. Macdonald, Z.M. Gasem
Density functional theory (DFT) as a powerful tool for designing new organic corrosion inhibitors. Part 1: an overview
Corros Sci, 99 (2015), pp. 1-30
[[41]]
R.M. Issa, M.K. Awad, F.M. Atlam
Quantum chemical studies on the inhibition of corrosion of copper surface by substituted uracils
Appl Surf Sci, 255 (2008), pp. 2433-2441
[[42]]
M. Lashkari, M.R. Arshadi
DFT studies of pyridine corrosion inhibitors in electrical double layer: solvent, substrate, and electric field effects
Chem Phys, 299 (2004), pp. 131-137
[[43]]
Z. Salarvand, M. Amirnasr, M. Talebian, K. Raeissi, S. Meghdadi
Enhanced corrosion resistance of mild steel in 1M HCl solution by trace amount of 2-phenyl-benzothizole derivatives: experimental, quantum chemical calculations and molecular dynamics (MD) simulation studies
Corros Sci, 114 (2017), pp. 133-145
[[44]]
M. Hosseini, S.F. Mertens, M. Ghorbani, M.R. Arshadi
Asymmetrical Schiff bases as inhibitors of mild steel corrosion in sulphuric acid media
Mater Chem Phys, 78 (2003), pp. 800-808
[[45]]
T. Ghailane, R.A. Balkhmima, R. Ghailane, A. Souizi, R. Touir, M. Ebn Touhami
Experimental and theoretical studies for mild steel corrosion inhibition in 1M HCl by two new benzothiazine derivatives
Corros Sci, 76 (2013), pp. 317-324
[[46]]
Sudheer, M.A. Quraishi
Electrochemical and theoretical investigation of triazole derivatives on corrosion inhibition behavior of copper in hydrochloric acid medium
Corros Sci, 70 (2013), pp. 161-169
[[47]]
H. Tian, W. Li, K. Cao, B. Hou
Potent inhibition of copper corrosion in neutral chloride media by novel thiadiazole derivatives
Corros Sci, 73 (2013), pp. 281-291
[[48]]
M.A. Hegazy, A.M. Badawi, S.S. Abd El Rehim, W.M. Kamel
Corrosion inhibition of carbon steel using novel N-(2-(2-mercapto acetoxy)ethyl)-N,N-dimethyl) dodecan-1-aminium bromide during acid pickling
Corros Sci, 69 (2013), pp. 110-122
[[49]]
N. Kovačević, A. Kokalj
The relation between adsorption bonding and corrosion inhibition of azole molecules on copper
Corros Sci, 73 (2013), pp. 7-17
[[50]]
H. Ju, Z.P. Kai, Y. Li
Aminic nitrogen-bearing polydentate Schiff base compounds as corrosion inhibitors for iron in acidic media: a quantum chemical calculation
Corros Sci, 50 (2008), pp. 865-871
Copyright © 2018. Brazilian Metallurgical, Materials and Mining Association
Journal of Materials Research and Technology

Subscribe to our Newsletter

Article options
Tools
Cookies policy
To improve our services and products, we use cookies (own or third parties authorized) to show advertising related to client preferences through the analyses of navigation customer behavior. Continuing navigation will be considered as acceptance of this use. You can change the settings or obtain more information by clicking here.