Corrosion and corrosion inhibition of alloyed zinc electrode were investigated in neutral chloride solution using electrochemical techniques. The purpose of this study is to study the corrosion inhibition of acetanilide and para hydroxy acetanilide as organics inhibitors for corrosion control of alloyed zinc electrode in NaCl 3 per cent solution.
A volt lab PGZ 301, assembled using alloyed zinc working electrode, a platinum counter electrode and a saturated calomel electrode as the reference electrode, was used in the experiment. This research was conducted using potentiodynamic polarization and electrochemical impedance spectroscopy techniques.
Acetanilide, para hydroxy acetanilide and their mixture provided inhibitions efficiencies of 88 per cent at 40 ppm, 87 per cent with 80 ppm and 99.86 per cent with (40 ppm AC + 80 ppm PHA), respectively. The study also discusses the corrosion inhibition mechanism of the protective layers. The adsorption of acetanilide and para hydroxy acetanilide on metal surface obeyed Langmuir’s adsorption isotherm. Polarization measurements showed that the acetanilide and the para hydroxy acetanilide, and their mixture acted as cathodic inhibitors in NaCl solution, and the inhibitor molecules followed physical adsorption on the surface of alloyed zinc.
The other new inhibitors which are very efficient inhibitors and to be applied in the field of prevention and control against corrosion.
Zouied, D., Zouaoui, E., Medjram, M., Chikha, O. and Dob, K. (2018), "The para hydroxy acetanilide and acetanilide mixture for the protection from corrosion of alloyed zinc", Anti-Corrosion Methods and Materials, Vol. 65 No. 1, pp. 1-10. https://doi.org/10.1108/ACMM-02-2017-1754Download as .RIS
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Zinc is an important structural metal extensively used in many applications. Owing to its good corrosion resistance and relatively low price (Chung et al., 2000), it is generally used as sacrificial anode in cathodic protection of steel against corrosion (de la Fuente et al., 2007). The most important application of zinc is a coating for steel corrosion protection. In addition, zinc is an important component in paints, cosmetics, pharmaceuticals, storage batteries, electrical equipment and an endless list of other capital applications (Nady, 2016). In general, zinc-based coatings corrode in the order of 100 times slower than cold rolled steel because of the inhibiting or barrier effect of zinc-based corrosion products (de la Fuente et al., 2007). The corrosion mechanism of zinc has been studied in field exposures as well as in laboratory under controlled environments (Mouanga et al., 2010). According to the composition of environments, zincite (ZnO) and zinc hydroxide (Zn(OH)2) are often the first compounds formed, but they are rapidly transformed in to hydrozincite (Zn5(CO3)2 (OH)6_H2O), or simonkolleite (Zn5(OH)8Cl2_H2O), which forms the white rust of zinc (Mouanga et al., 2010; Chen et al., 2008).
Sodium chloride (NaCl), which is mainly from the ocean, is probably one of the most important salt particles for atmospheric corrosion, and it can be used as a corrosion stimulator in accelerated tests of metals exposed to marine environments. Because of its importance, much work has been done in recent decades to explore the effect of NaCl particles on the atmospheric corrosion of metals (Shanhua and Zhuoyuan, 2013). Lindström et al. (2002) showed that the corrosion rate of zinc was related to a number of chloride ions as well as a number of sodium ions present on the surface. The corrosion and electrochemical studies of zinc dissolution in sodium chloride solution have been investigated in the literature (Nady, 2016). The deposition of chloride is known to be one of the main factors that influence zinc corrosion in the atmosphere (Falk, 1998). The presence of a surface electrolyte greatly increases the corrosion rate and affects the composition of the corrosion products. However, zinc is a kind of active metal and can be easily corroded in acid medium.
The searching of an effective inhibitor to zinc is significant for the protection during zinc corrosion (Huang and Zhao, 2006). The effect of organic inhibitors (Aramaki, 2001), such as sodium benzoate (NaBz) and sodium N-dodecanoylsarcosinate (NaDS), S-Octyl-3-thiopropionate (NaOTP), 8-quinolinol (8-QOH) and 1,2,3-benzotriazole (BTAH) on corrosion of zinc in aerated 0.5 M NaCl solution was investigated using potentiodynamic polarization measurements. Cerium (III) chloride CeCl3 and sodium octylthiopropionate C8H17S(CH2)2COONa (NaOTP) (Aramaki, 2002) are effective inhibitors for zinc corrosion in 0.5 M NaCl. The inhibition effects of chromate-free (Aramaki, 2001), environmentally acceptable anion inhibitors were examined on the corrosion of zinc in an aerated 0.5 M NaCl solution using polarization measurements; sodium silicate Na2Si2O5 and phosphate Na3PO4 were remarkably effective on zinc corrosion. Recently, plant extracts have again become important as an environmentally acceptable (Khamis and Al-Andis, 2002; Rushing et al., 2003), readily available and renewable source for a wide range of needed inhibitors. The aqueous extract of the leaves of henna (lawsonia) (El-Etre et al., 2005) was tested as a corrosion inhibitor of zinc in neutral solutions, using the polarization technique.
It was found that the extract acted as a good corrosion inhibitor in the tested media.
In this research, we introduce the acetanilide and para hydroxy acetanilide inhibitors to control the corrosion of zinc in a stagnant, naturally aerated, neutral NaCl solution. The corrosion rate and corrosion inhibition efficiency were calculated using different concentrations of the inhibitor. In this respect, conventional electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used. The experimental impedance data were fitted to theoretical values according to equivalent circuit models enables understanding the corrosion inhibition mechanism and the suggestion of the suitable model that explains the electrochemical behavior of the metal/solution interface under different conditions.
The inhibitors molecules used in this research were synthesized from laboratory, and the scheme of the structures of AC and PHA compounds is shown in Scheme 1 and Figure 1. As can be seen, they have different active groups, which can act as adsorption centers. The chemical composition of alloyed zinc electrodes used in this study is as follows: Fe, 0.038 per cent; Cr, 0.002 per cent; Mn, 0.029 per cent; Pb, traces; and Al, 2 per cent.
The electrode was mounted into glass tubes by two-component epoxy resin, leaving a surface area of 0.196 cm2 to interact the corrosive medium. The electrochemical cell was a three-electrode all-glass cell, with a platinum counter electrode and saturated calomel reference electrode. Before each experiment, the working electrode was mechanically polished using successive grades of emery papers down to 1200 grit, and then washed thoroughly with triple distilled water. The corrosion-inhibition by acetanilide and para hydroxy acetanilide was carried out in solutions containing NaCl 3 per cent. The NaCl 3 per cent was prepared by dissolving analytical grade 30 g NaCl in 1,000 ml deionized water. The concentration range of inhibitors used was 20, 40 and 60 ppm (AC) and 20, 40, 60, 80 and 100 ppm (PHA).
The polarization experiments and EIS investigations were performed using a Voltalab PGZ 301 “All-in-one” potentiostat/Galvanostat system.
The potentials were measured against and referred to the saturated calomel electrode. To achieve quasi-stationary condition, the polarization experiments were carried out using a scan rate of 10 mV/s.
Actually, the potential of measure was between −1,200 and −200 mv. Impedance Z and phase shift Ɵ was recorded in the frequency domain of 100 KHZ at 100 mHZ. The superimposed ac-signal was at 10 mV peak-to-peak amplitude.
Results and discussion
Figure 1(a) and (b) presents potentiodynamic polarization plots for alloyed zinc in NaCl 3 per cent solution in the absence and presence of AC and PHA, at 298°C.
From the curves obtained in Figures 1(a) and 1(b), we observe that the addition of AC and PHA causes a decrease in speed of zinc corrosion alloy in the solution of NaCl 3 per cent. Table I gives the electrochemical parameters of curves of polarization (current density of corrosion (icorr), the potential of corrosion (Ecorr), anodic slope (ba) and cathodic slope (bc).
The inhibitive efficiency of AC and PHA is calculated by the following relation:
According to the Table I, we observe that the icorr in the solution NaCl 3 per cent decreases considerably with the increase in concentration, with a maximal efficiency of 88 per cent for 40 ppm AC and 87 per cent for 80 ppm PHA.
For all the concentrations of AC and PHA, the general shift of the corrosion potential in the positive direction because ΔE is super de 85 mV, which indicates that AC and PHA act as anodic-type inhibitors (Li et al., 2008; Abd El-Maksoud, 2004).
Electrochemical impedance measurements
The parameters deduced from the impedance diagrams are shown in the Table II.
The corrosion inhibitory efficiency of zinc alloy is calculated from the values of the charge transfer resistance Rct according to the following relationship:
From Table II, we note that as the inhibitor concentration increases, Rct increases with decreasing CPE.
Figure 2 represents diagrams of impedance for the alloyed zinc in a solution of NaCl 3 per cent in the absence and presence of the various concentrations of AC and PHA to 298 K. The Nyquist plots show a depressed semicircular shape with their centers below the real axis.
According to the Curve (a.1), we notice that every curve possesses one only one capacitive layer. This layer increases according to the concentration until a maximal concentration of 40 ppm, or we observe two capacitive layers.
The isotherms of adsorption give the relation of interaction between the adsorbed molecules as well as the interaction of these molecules with the surface.
For the studied inhibitors, we notice that the isotherm of Langmuir is the only one that verifies. Their relation is as follows:
After calculating, we obtain a value of ΔG that is equal to −10.44 KJ/mol for the AC inhibitor and −9.85 KJ/mol for the PHA inhibitor.
Negative values of ΔG indicate that the adsorption of the molecules of inhibitor on the metallic surface is a spontaneous process.
Generally, values of ΔGads are around − 20 KJ mol−1 or lower are consistent with the electrostatic interaction between charged molecules and the charged metal surface (physisorption); those around −40 KJ mol−1 or higher involve charge sharing or transfer from organic molecules to the metal surface to form a coordinate type of metal bond (chemisorption; Bentiss et al., 2005). In the present work, the calculated ΔGads values are almost slightly less negative than −20 KJ mol−1, indicating that the adsorption of inhibitor molecules is physisorption.
Effect of temperature
Temperature effect was studied at 298 to 313 K, without and with the presence of 40 ppm of AC and 80 ppm of PHA presence (Figure 5). Increase in the temperature leads to an increase in the corrosion rate in the absence and presence of these inhibitors (Table III). The effect of temperature on the corrosion parameter can be deduced by comparing the activation energy in the presence and absence of the inhibitor. The Arrhenius and transition state plot were used to determine the activation energy (Ea), activation enthalpy (ΔH) and activation entropy (ΔS) for the corrosion of alloyed zinc in NaCl 3 per cent solution. The activation energy can be obtained by the Arrhenius equation and Arrhenius plot (Musa et al., 2011):
The values of ΔHa and Ea are nearly the same, and are higher in the presence of the inhibitor. This indicates that the energy barrier of the corrosion reaction increased in the presence of the inhibitor without changing the mechanism of dissolution. The positive values of ΔHa for both corrosion processes with and without the inhibitor reveal the endothermic nature of the alloyed zinc dissolution process, and indicate that the dissolution of alloyed zinc is difficult (Behpour et al., 2008; El-Ouali et al., 2010).
The large negative value of ΔSa alloyed zinc in NaCl 3 per cent implies that the activated complex is the rate-determining rather than the dissociation step. In the presence of the inhibitor AC and PHA, the value of ΔSa increases and is generally interpreted as an increase in disorder as the reactants are converted to the activated complexes (Musa et al., 2011). The positive values of ΔSa reflect the fact that the adsorption process is accompanied by an increase in entropy, which is the driving force for the adsorption of the inhibitor onto the alloyed zinc surface.
Potentiodynamic polarization curves
Figure 7 shows the potentiodynamic polarization curves for alloyed zinc in NaCl 3 per cent solution in the absence and presence of different concentrations of the mixture (AC + PHA). In the absence of inhibitors, it is the anodic dissolution reaction of zinc and cathodic reactions related to the oxygen and proton reduction:
These reactions were accompanied by hydrolysis and the hydroxide precipitation of zinc reactions:
In the presence of inhibitors, an evident effect was observed on the anodic parts of the polarization curves, with a shift in the corrosion potential Ecorr. These findings indicate that the use of inhibitors can be classified as anodic-type. The associated electrochemical parameters and the inhibition efficiency values are listed in Table V. Maximal efficiency is obtained for the mixture (40 AC + 80 PHA) from 98.94 per cent.
The curves of impedance (Figure 8) obtained for the alloyed zinc in a solution of NaCl 3 per cent with and without the addition of different concentration of mixture (AC + PHA) were made in a potential of circuit opened after 1 h of emersion. Their experimental data were extracted using the same electrical equivalent circuit, as presented in Figure 3(b). According to Table VI, the mixture (AC + PHA) increases the charge transfer resistance Rct and decreases the double layer capacitance Qdl. These evolutions can be because of the increase in the quantities of inhibitors molecules adsorbed on the metallic surface (Wieczorek and Szklarska-Smialowska, 1972; Aramaki and Hackerman, 1987).
It is important to underline that Aramaki and Nishihara (1987) explained the effect of synergy using a competitive adsorption by a cooperative adsorption between both compounds. In the first case, both compounds are adsorbed on different sites on the surface of the electrode, while in the second case, one is chemisorbed on the surface of the metal and the other one comes to be physisorbed on this one. Then, the synergism parameter S was calculated from the impedance data according to the equations described in literature (Rochdi et al., 2014). If S < 1, it is a competitive adsorption, and if s > 1, it is a cooperative adsorption. According to the obtained results, the value of S is greater than to the unity which indicates a cooperative adsorption between AC and PHA (Azaroual et al., 2016).
The acetanilide, para hydroxyl acetanilide PHA and their mixture were investigated as corrosion inhibitors for alloyed zinc in 3.0 per cent NaCl solution using electrochemical techniques.
Potentiodynamic polarization curves showed that the AC, PHA and their mixture (AC + PHA) reduced anodic reactions and, thus, act as anodic-type inhibitors. A corrosion inhibition efficiency of about 88.91 per cent in the presence of 40 ppm AC, 88.6 per cent of 80 ppm PHA and 99.86 per cent of this mixture was obtained.
Electrochemical parameters and inhibitor efficiencies derived from the polarization curves for the alloyed zinc in NaCl 3 per cent as a function of inhibitor concentration of AC and PHA at 25°C
|C(ppm)||−E(i = 0)(mv)||Icorr(A/cm2)||Ba(V)||−Bc(v)||Ɵ||E (%)|
Impedance electrochemical parameters derived from the Nyquist plots in NaCl 3 per cent solution in the absence and presence of the inhibitors AC and PHA at 25°C
Corrosion rate and inhibition efficiency values for the corrosion of alloyed zinc in the absence (blank) and in the presence of 40 ppm of AC and 80 ppm of PHA, at different temperatures
|T||C(ppm)||−E(i = 0)(v)||Icorr(µA/cm2)||Ba||−Bc||Ɵ||E(%)|
Corrosion kinetic parameters in NaCl 3 per cent in the presence and absence of 40 ppm of AC and 80 ppm of PHA
|C(ppm)||E°a (KJ/mol)||ΔH°a (KJ/mol)||ΔS (J/mol.K)|
Electrochemical parameters and inhibitor efficiencies derived from the polarization curves for the alloyed zinc in NaCl 3% as function of inhibitor concentration of mixture (AC + PHA) at 25°C
|Cinh(ppm)||−E(i = 0)||Icorr(µA/cm2)||Ba(mV)||−Bc(mV)||Ɵ||E(%)|
|20AC + 20PHA||829.486||0.392||244.2||302.4||0.9845||98.45|
|20AC + 40PHA||951.158||0.614||265||293.7||0.9758||97.58|
|40AC + 80PHA||970.794||0.268||284||288.9||0.9894||98.94|
|40AC + 40PHA||417.715||1.832||312.3||297.8||0.928||92.8|
|20AC + 60PHA||870.557||0.407||155.6||236.9||0.984||98.4|
|40AC + 20PHA||945.61||0.58||222.1||242.9||0.9665||96.65|
|60AC + 20PHA||1007.8||0.85||236.2||238||0.9771||97.71|
the electrochemical parameters from EIS for alloyed zinc in NaCl 3 per cent solution with different concentrations of the mixture (AC + PHA)
|20AC + 20PHA||5244||0.2153e−9||1||46747||9.871e−6||0.617||74344||0.9976||99.76|
|20AC + 40PHA||5003||0.2279e−9||1||31478||11.81e−6||0.622||45741||0.9964||99.64|
|40AC + 80PHA||5466||0.212e−9||1||82258||6.832e−6||0.511||74299||0.9986||99.86|
|20AC + 60PHA||2449||0.2201e−9||1||14484||17.73e−6||0.584||40442||0.9903||99.03|
|60AC + 20PHA||2724||0.4229e−9||0.944||13732||11.54e−6||0.613||34789||0.9919||99.19|
|40AC + 20PHA||4231||0.265e−9||1||13905||14.21e−6||0.676||42713||0.992||99.2|
|40AC + 40PHA||4385||0.7788e−9||1||3434||14.51e−6||0.668||31426||0.9677||96.77|
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