**1. Introduction**

Inhibition of corrosion of iron is important for theoretical and practical aspects [1]. Iron and its alloys are of great importance in the industry, prompting vast research on corrosion resistance and its conducts [2]. Acids are wildly used in industries [3], such as industrial acid cleaning, acid descaling, and acid picking, and used to remove mill scale from metallic surfaces. Natural compounds containing sulfur, oxygen, and nitrogen atoms are effective as corrosion inhibitors in acid media; inhibitors are used to reduce the rate of dissolution of metals [4]. Natural plant inhibitors that contain organic compounds are widely used to inhibit minerals in an acidic medium [5] and are called environmentally friendly nontoxic inhibitors [6]. The adsorption of these compounds is influenced by the electronic structure of their content of active compounds, electrons density, aromatic rings, and functional groups possessing free electrons such as, R–OH –CHO, –N=N, etc. [7]. The adsorption of organic inhibitors at the metal/solution interface takes place through the replacement of water molecules by organic inhibitor molecules [8]. The efficiency of these compounds depends mainly on their abilities to be adsorbed on the metal surface with their polar groups moving as the reactive centers. The purpose of this research is to use a nontoxic environment friendly inhibitor formed from turmeric root extract to reduce iron corrosion and study its effect using electrochemical impedance and Tafel polarization methods. Turmeric root extract contains active substances represented by turmeric derivatives with a high percentage (90%), which are phenolic compounds of antioxidant. The most important are curcumin, demethoxycurcumin, and bisdemethoxycurcumin, which have the following chemical formulas (**Figures 1** and **2**) [9]:

the effect of turmeric on solid carbon in a saline medium (3.5% NaCl) was studied

*Electrochemical,Thermodynamic, Surface, and Spectroscopic Study in Inhibition of Iron…*

This phenomenon has not been adequately studied in Syria; therefore, this research is an important step in studying the phenomenon of corrosion and understanding the mechanism of its occurrence and the conditions affecting it with the latest technologies Electrochemical impedance spectrometry and Mott-Schottky plot are used as a basis for future research in order to implement solutions on the

Electrochemical impedance spectrometry is also called alternating current (AC) and impedance spectroscopy (EI). It is a useful tool and the newest method in many studies, especially the study of corrosion of minerals. Impedance is defined as the measurement of the impedance of alternating current passage in each part of the electrical circuit, and it has units of ohm. Electromagnetic impedance spectroscopy measures the sinusoidal changes of the current and potential signals as a function of the frequency at the value of a current, a field of current, a value of a potential, or a field of potential. Frequency changes give rise to a different phase difference between the current and potential signals for each circuit element [1].

Impedance is measured by applying a sinusoidal signal or current and then measuring the resulting response to the corresponding variable in a given frequency range. The following equations show the signal of latency and current response at a

where Et is the latency at time t, E0 is the applied signal amplitude, ω is the angular frequency (radians/second) equal to 2лf, and f (frequency) is the number of

The resulting current response is measured at the same frequency value with a phase difference between the current and potential signals and a difference in signal

where φ is the phase difference in radians and I0 is the signal response amplitude.

The value of the phase difference at the value of a specific frequency is given by

The electromagnetic impedance spectroscopy is distinguished as its results are accurate, as each point of the EIS curve contains information about the electrical

where Zimg is the imaginary impedance and Zreal is the true impedance.

The relationship of impedance is given according to Ohm's law:

Et ¼ E0 sin ð Þ ωt (1)

It ¼ I0 sin ð Þ ωt þ φ (2)

Z ¼ Et*=*It ¼ E0 ð Þ sin ð Þ ωt *=*I0 sin ð Þ ωt þ φ (3)

¼ Z0 ð Þ sin ð Þ ωt *=* sin ð Þ ωt þ φ (4)

tan φ ¼ Zimg*=*Zreal (5)

with Tafel technology; the inhibit corrosion was 91% [12].

*DOI: http://dx.doi.org/10.5772/intechopen.92648*

specific frequency [3], which are found via Eq. (1):

integrated vibrations per second (Hz/s).

amplitude, which are found via Eq. (2):

where Z0 = E0/I0.

**1.2 Features and applications**

**55**

**1.1 Definition of electrochemical impedance spectrometry (EIS)**

ground.

Recent reference studies indicate the use of turmeric root extract in 2012 to inhibit copper metal. The inhibit corrosion was 98% with EIS technology and Tafel polarization [10]. In 2014, the effect of turmeric on steel was studied with Tafel polarization in a petroleum medium. The inhibit corrosion was 92% [11]. In 2017,

**Figure 1.** *Chemical formulas for turmeric derivative compounds [9].*

**Figure 2.** *Sinusoidal signal applied and the sinusoidal current signal produced by a specific phase difference.*

*Electrochemical,Thermodynamic, Surface, and Spectroscopic Study in Inhibition of Iron… DOI: http://dx.doi.org/10.5772/intechopen.92648*

the effect of turmeric on solid carbon in a saline medium (3.5% NaCl) was studied with Tafel technology; the inhibit corrosion was 91% [12].

This phenomenon has not been adequately studied in Syria; therefore, this research is an important step in studying the phenomenon of corrosion and understanding the mechanism of its occurrence and the conditions affecting it with the latest technologies Electrochemical impedance spectrometry and Mott-Schottky plot are used as a basis for future research in order to implement solutions on the ground.

#### **1.1 Definition of electrochemical impedance spectrometry (EIS)**

Electrochemical impedance spectrometry is also called alternating current (AC) and impedance spectroscopy (EI). It is a useful tool and the newest method in many studies, especially the study of corrosion of minerals. Impedance is defined as the measurement of the impedance of alternating current passage in each part of the electrical circuit, and it has units of ohm. Electromagnetic impedance spectroscopy measures the sinusoidal changes of the current and potential signals as a function of the frequency at the value of a current, a field of current, a value of a potential, or a field of potential. Frequency changes give rise to a different phase difference between the current and potential signals for each circuit element [1].

Impedance is measured by applying a sinusoidal signal or current and then measuring the resulting response to the corresponding variable in a given frequency range. The following equations show the signal of latency and current response at a specific frequency [3], which are found via Eq. (1):

$$\mathbf{E\_t = E\_0 \sin\ (\alpha t)}\tag{1}$$

where Et is the latency at time t, E0 is the applied signal amplitude, ω is the angular frequency (radians/second) equal to 2лf, and f (frequency) is the number of integrated vibrations per second (Hz/s).

The resulting current response is measured at the same frequency value with a phase difference between the current and potential signals and a difference in signal amplitude, which are found via Eq. (2):

$$\mathbf{I}\_t = \mathbf{I}\_0 \text{ \(\alpha \mathbf{t} + \mathbf{q}\)} \tag{2}$$

where φ is the phase difference in radians and I0 is the signal response amplitude. The relationship of impedance is given according to Ohm's law:

$$\mathbf{Z} = \mathbf{E}\_t/\mathbf{I}\_t = \mathbf{E}\_0 \left( \sin \text{ (ot)}/\text{I}\_0 \sin \left( \text{ot} + \text{q} \right) \right) \tag{3}$$

$$\mathbf{Z} = \mathbf{Z\_0} \left( \sin \text{ (ot)} / \sin \text{ (ot-}\mathbf{q} \text{)} \right) \tag{4}$$

where Z0 = E0/I0.

The value of the phase difference at the value of a specific frequency is given by

$$\tan\,\,\mathrm{q} = \mathrm{Z}\_{\mathrm{img}} / \mathrm{Z}\_{\mathrm{real}} \tag{5}$$

where Zimg is the imaginary impedance and Zreal is the true impedance.

#### **1.2 Features and applications**

The electromagnetic impedance spectroscopy is distinguished as its results are accurate, as each point of the EIS curve contains information about the electrical

groups possessing free electrons such as, R–OH –CHO, –N=N, etc. [7]. The adsorption of organic inhibitors at the metal/solution interface takes place through the replacement of water molecules by organic inhibitor molecules [8]. The efficiency of these compounds depends mainly on their abilities to be adsorbed on the metal surface with their polar groups moving as the reactive centers. The purpose of this research is to use a nontoxic environment friendly inhibitor formed from turmeric root extract to reduce iron corrosion and study its effect using electrochemical impedance and Tafel polarization methods. Turmeric root extract contains active substances represented by turmeric derivatives with a high percentage (90%), which are phenolic compounds of antioxidant. The most important are curcumin, demethoxycurcumin, and bisdemethoxycurcumin, which have the following

Recent reference studies indicate the use of turmeric root extract in 2012 to inhibit copper metal. The inhibit corrosion was 98% with EIS technology and Tafel polarization [10]. In 2014, the effect of turmeric on steel was studied with Tafel polarization in a petroleum medium. The inhibit corrosion was 92% [11]. In 2017,

chemical formulas (**Figures 1** and **2**) [9]:

*Electrochemical Impedance Spectroscopy*

*Chemical formulas for turmeric derivative compounds [9].*

*Sinusoidal signal applied and the sinusoidal current signal produced by a specific phase difference.*

**Figure 1.**

**Figure 2.**

**54**

process taking place, compared to conventional electrical methods that depend on measuring current changes, electrical charges, or the potential of the electrodes as a function of time, which depends on a certain value of its spectrum, such as a cyclic voltage, which includes current changes in hundreds of points for the potential to obtain a specific value for the peak oxidation and return at the corresponding current and potential value [3].

**2.5 Scanning electron microscopy (SEM) and energy dispersive X-rays (EDX)**

*Electrochemical,Thermodynamic, Surface, and Spectroscopic Study in Inhibition of Iron…*

EDX techniques.

**3. Results and discussion**

and enhances inhibition.

(Rct) is calculated by

**Figure 3.**

**57**

**3.1 Mechanism of inhibition process**

*DOI: http://dx.doi.org/10.5772/intechopen.92648*

The inhibitor film formation of the extracts surface was studied using SEM and

Turmeric root extract (TRE) used here as a corrosion inhibitor can serve as a scale inhibitor as well. This plant is characterized by the existence of a percentage of phenolic compounds (categories of curcumin) of a percentage up to 90%. It is a natural, nontoxic, environmentally friendly material. Active compounds in turmeric root extract are attributed to curcumin, demethoxycurcumin, and

bisdemethoxycurcumin and to the multiple lone pair of electrons, multiple bonds, and/or conjugated л-type bond system [15]. Adsorption of these active molecules forms thin inhibitor films on the metal surface, which isolate the metal surface from the corrosive environment [16]. The oxygen atoms, the aromatic rings, and the bilateral bond of the aromatic rings boost the electronic pair freedom on the surface of the electrode. These compounds adsorb their free electrons on the surface of the electrode, and the iron is oxidized to form positively charged iron, thus forming a double electrical layer, and difference in voltage arises, as schematically presented in **Figure 3**. The inhibitor enhances the free electrons, which reduces iron corrosion

In the corrosion behavior of iron in 0.5 M HCl solution, in the absence and presence of TRE, it is investigated by the EIS, at 298 K after 1 hour of immersion in the acid solution. The double-layer capacitance (Cdl) and the frequency at which the imaginary component of the impedance is maximum (�Zmax) are found via Eq. (6):

The inhibition efficiency %IERct that resulted from the charge transfer resistance

%IERct <sup>¼</sup> Rct � <sup>R</sup><sup>0</sup>

*Schematic presentation of the electric double-layer formation [Chem draw].*

Cdl ¼ 1*=*wmaxRct where wmax ¼ 2πfmax (6)

ct *=*Rct ∗ 100 (7)

**3.2 Electrochemical impedance spectroscopy measurements**

Among the applications of electromagnetic impedance spectroscopy, in addition to studying corrosion processes, electroplating processes, and semiconductors, it studies surface processes that include oxidation and reduction processes on the electrode surface, adsorption processes, electrical adsorption, and diffusion, as well as the kinetics of reactions in solutions, mass transfer, and resistance to solution, cells, and their electrical properties and batteries, determining the effect of each circuit element on impedance [1, 6]. It is also distinguished by not destroying the studied sample after testing [13].
