**2. Materials and methods**

#### **2.1 Preparation of samples and corrosion test solutions**

Banana peels were sourced locally. The peels were washed under running water and air dried until a constant mass was recorded. It was milled into powder using a hammer-mill and ball-mill to achieve finesse of powder (about 0.25 mm diameter size). The powdered peel was extracted using 95% ethanol. Five grams of powder

*Corrosion Inhibitors*

tions occurring at the anode and cathode are:

Cathode surface:

At anode:*Fe*

gas evolution.

Anode surface:*Fe* → *Fe*

*2Fe + H<sup>+</sup> → Fe*

\_1

<sup>2</sup> *<sup>O</sup>*<sup>2</sup> <sup>+</sup> *<sup>H</sup>*2*<sup>O</sup>* <sup>+</sup> <sup>2</sup> *<sup>e</sup>*

Galvanic corrosion is the most common type of corrosion and it occurs regularly in marine vessels, metal structures, and oil pipelines. Furthermore, the phenomenon is commonly observed in water treatment plant, boilers, storage vessels, oil pipelines, etc. In fact, what makes corrosion challenging is that it starts on the internal part of the metal structure, which makes early detection difficult. Other than water and oxygen, galvanic corrosion is affected by: types of metal, agitation, the presence and type of inhibitors, and environmental factors (pH, temperature, humidity, salinity, etc.) [9]. In addition, the dissolution of mild steel in HCl is given as:

2+ + 2*OH*<sup>−</sup> → *FeO*.(*H*2*O*)–hydrated iron oxide (brown rust)

*2+ + H2*

The rate of this reaction is dependent on: metal (its position in the electromotive series), acidity, ferrous ion concentration (by the law of mass action, the increase in ferrous ions should correspond to the decrease in rate of corrosion), and hydrogen

Three techniques are often used for the assessment of corrosion rates namely, weight loss technique, electrochemical impedance spectroscopy, and hydrogen gas evolution method. The weight loss method is considered the most fundamental, against which the accuracy of the other methods is determined. However, the limitations of this method are: (1) the weight loss expressed is the average of the weight of the corroding specimen over a period of time but the changes in corrosion rate over this period is not accounted for; (2) in order to accurately determine the weight loss caused by corrosion, all the corroded particles need to be removed from the specimen surface without removing the uncorroded metal, which practically is unrealistic. Electrochemical technique has been successfully used in many corrosion studies to determine the rate of corrosion [4, 7, 10]. Particularly, it has certain advantages over the weight loss method, due to its ease of corrosion rates determination. With this method, instantaneous corrosion rates as well as changes in corrosion rates over a period of time can be determined. However, during the electrochemical dissolution process for some metals and metal alloys, the atypical polarization performance at the anode is a challenge. Moreover, hydrogen removal can occur in two ways: hydrogen gas evolution and depolarization via oxidation by

Corrosion is an electrochemical process; it is the propensity for metals to revert to their natural ore state. It takes place in the presence of moisture and oxygen, involving chemical reaction and the flow of electrons on the surface of the corroded cells, which greatly accelerate the transformation of metal back to the low-grade ore. The process involves the oxidation of a metal atom, whereby it loses one or more electrons. The resultant effect of corrosion is metal degradation, that is, the breakup of bulk metal, causing it to lose its useful properties [6]. This electrochemical process, often referred to as galvanic cell, occurs when two different metals in physical or electrical contact are immersed in a common electrolyte with different concentrations. Consequently, the more active metal (anode) gets corroded while the more noble metal (cathode) is protected [7, 8]. The fundamental chemical reac-

> 2+ + 2 *e* −

> > −

<sup>→</sup> <sup>2</sup>*OH*<sup>−</sup>

**42**

#### **Figure 1.**

*Flow process for banana peel extract (BPE) as corrosion inhibitor.*

was dissolved in 200 ml ethanol for 14 days and thereafter filtered. The filtrate was rotatory evaporated in order to remove excess ethanol, and then diluted with 1 M HCl in distilled water to obtain the corrosion inhibition test solutions in the concentration ratio of 1.0, 2.5, 5, 7.5, and 10% (v/v). **Figure 1** shows the various stages involved in the extraction of banana peels.

In addition, the mild steel used was mechanically press-cut into coupons of dimensions 4 × 2.5 × 0.1 cm. Each coupon was degreased by washing with ethanol, dried in acetone, and immediately transferred into the simulated test solutions. Note that the dried coupons can be preserved in a desiccator until use. Similarly, control experiments were set up but without the addition of the inhibitor. All reagents used were of analytical grade. Banana peel is composed of starch (3%), total dietary fiber (43.2–49.7%), crude fat (3.8–11%), crude protein (6–9%), polyunsaturated fatty acids, pectin, micronutrients (K, P, Ca, and Mg), and amino acid [28]. Also, the mild steel sheet used has the following compositions (% wt): Fe—99.3, Mn—0.34, Cu—0.069, Co—0.069, Ca—0.087, Ni—0.043 and Al—0.03.

#### **2.2 Evaluating the physical properties of banana peel extract as a corrosion inhibitor**

#### *2.2.1 Viscosity measurement*

This was determined by the Cannon-Fenske viscometer and a circulatory bath with temperature control. Viscosity was calculated using ASTM Method D445–97 [29]. The viscosity *η* of each sample was calculated using the formula below:

$$
\eta = k\rho T,\tag{1}
$$

**45**

tor and *V0*

*2.3.2 Thermometric method*

was calculated as shown in Eq. 4:

*RN* (

ℰ = (

reaction number of solution with inhibitor.

*Exploring Musa paradisiaca Peel Extract as a Green Corrosion Inhibitor for Mild Steel Using…*

a 100 ml beaker. A platinum ring was then lowered into the solution of banana peel extract in the beaker. It was then brought up to the water sample interface, where the actual measurement takes place. The force required to pull the ring through the interface was measured by a tension meter as the surface tension of the extract

The measurement of the flash point for the BPE sample was done using ASTM D-92 method [29]. An open cup containing BPE sample was heated at a specific rate while flame was periodically passed over its surface. The lowest temperature at which the BPE

vapor ignites without sustaining the flame was recorded as the flash point.

**2.3 Evaluating the corrosion inhibition efficiency of banana peel extract**

This method was adopted in this study as described by Ekpe et al. [23], and carried out at the following temperatures: 303, 308, 313, 318, and 323 K, which were achieved using a water bath. The coupons immersed in the prepared test solutions were recovered after 6 h, washed in detergent solution, and rinsed with distilled water, and air dried. The volume of gas evolved from the cathodic reaction during the corrosion process was determined. Hence, gasometric method correlates the quantity of gas evolved to the rate of corrosion. The graph of the volume of gas liberated per minute gives the rate of gas evolution, while the inhibition efficiency () and degree of surface coverage (θ) were determined from Eqs. 2 and 3, respectively.

> \_\_\_\_*H V*0

where *V\*H* is volume of hydrogen gas evolved at time *t* in the presence of inhibi-

*<sup>H</sup>* is the volume of hydrogen evolved in the absence of inhibitor.

Temperature determination was carried out as reported by Ebenso et al. [30]. Using the value for the rise in temperature per minute, the reaction number (RN)

where *Tm* and *Ti* are the maximum and initial temperatures, respectively, attained by the system and *t* is the time. Similarly, the inhibition efficiency was

> \_\_\_\_\_\_\_\_ *RNo* − *RNi*

where *RNo* is the reaction number of solution without inhibitor, while *RNi* is the

°

determined by the reaction number correlation (Eq. 5).

\_\_\_\_*H V*0

*<sup>H</sup>*) <sup>×</sup> <sup>100</sup> (2)

*<sup>H</sup>*) (3)

*C*/*min*)= (*Tm* − *Ti*)/*t* (4)

*RNo* ) <sup>×</sup> <sup>100</sup> (5)

*DOI: http://dx.doi.org/10.5772/intechopen.82617*

).

<sup>ℰ</sup> <sup>=</sup> (<sup>1</sup> <sup>−</sup> *<sup>V</sup>*<sup>∗</sup>

<sup>θ</sup> <sup>=</sup> (<sup>1</sup> <sup>−</sup> *<sup>V</sup>*<sup>∗</sup>

solution (dynes cm<sup>−</sup><sup>1</sup>

*2.3.1 Gasometric method*

*2.2.4 Flash point measurement*

where *k* is the instrument constant, *ρ* is the density of banana peel extract sample, and *T* efflux time (sec) for banana peel extract sample.

#### *2.2.2 Specific gravity determination*

The extract of banana peel was transferred into a narrow glass cylinder (SP0121-V Osaka, Japan) and a hydrometer was set into the sample and allowed to stabilize. The value of the specific gravity was taken from the markings on the stem of the hydrometer at the surface of the extract sample.

#### *2.2.3 Surface tension determination*

This study employed the American System of Testing Materials D-971 [29] method. Two grams of banana peel extract was added to 50 ml of distilled water in *Exploring Musa paradisiaca Peel Extract as a Green Corrosion Inhibitor for Mild Steel Using… DOI: http://dx.doi.org/10.5772/intechopen.82617*

a 100 ml beaker. A platinum ring was then lowered into the solution of banana peel extract in the beaker. It was then brought up to the water sample interface, where the actual measurement takes place. The force required to pull the ring through the interface was measured by a tension meter as the surface tension of the extract solution (dynes cm<sup>−</sup><sup>1</sup> ).

#### *2.2.4 Flash point measurement*

*Corrosion Inhibitors*

**Figure 1.**

**inhibitor**

*2.2.1 Viscosity measurement*

*2.2.2 Specific gravity determination*

*2.2.3 Surface tension determination*

was dissolved in 200 ml ethanol for 14 days and thereafter filtered. The filtrate was rotatory evaporated in order to remove excess ethanol, and then diluted with 1 M HCl in distilled water to obtain the corrosion inhibition test solutions in the concentration ratio of 1.0, 2.5, 5, 7.5, and 10% (v/v). **Figure 1** shows the various stages

In addition, the mild steel used was mechanically press-cut into coupons of dimensions 4 × 2.5 × 0.1 cm. Each coupon was degreased by washing with ethanol, dried in acetone, and immediately transferred into the simulated test solutions. Note that the dried coupons can be preserved in a desiccator until use. Similarly, control experiments were set up but without the addition of the inhibitor. All reagents used were of analytical grade. Banana peel is composed of starch (3%), total dietary fiber (43.2–49.7%), crude fat (3.8–11%), crude protein (6–9%), polyunsaturated fatty acids, pectin, micronutrients (K, P, Ca, and Mg), and amino acid [28]. Also, the mild steel sheet used has the following compositions (% wt): Fe—99.3, Mn—0.34,

**2.2 Evaluating the physical properties of banana peel extract as a corrosion** 

This was determined by the Cannon-Fenske viscometer and a circulatory bath with temperature control. Viscosity was calculated using ASTM Method D445–97 [29]. The

η = *kT*, (1)

where *k* is the instrument constant, *ρ* is the density of banana peel extract

The extract of banana peel was transferred into a narrow glass cylinder (SP0121-V Osaka, Japan) and a hydrometer was set into the sample and allowed to stabilize. The value of the specific gravity was taken from the markings on the stem

This study employed the American System of Testing Materials D-971 [29] method. Two grams of banana peel extract was added to 50 ml of distilled water in

involved in the extraction of banana peels.

*Flow process for banana peel extract (BPE) as corrosion inhibitor.*

Cu—0.069, Co—0.069, Ca—0.087, Ni—0.043 and Al—0.03.

viscosity *η* of each sample was calculated using the formula below:

sample, and *T* efflux time (sec) for banana peel extract sample.

of the hydrometer at the surface of the extract sample.

**44**

The measurement of the flash point for the BPE sample was done using ASTM D-92 method [29]. An open cup containing BPE sample was heated at a specific rate while flame was periodically passed over its surface. The lowest temperature at which the BPE vapor ignites without sustaining the flame was recorded as the flash point.

#### **2.3 Evaluating the corrosion inhibition efficiency of banana peel extract**

#### *2.3.1 Gasometric method*

This method was adopted in this study as described by Ekpe et al. [23], and carried out at the following temperatures: 303, 308, 313, 318, and 323 K, which were achieved using a water bath. The coupons immersed in the prepared test solutions were recovered after 6 h, washed in detergent solution, and rinsed with distilled water, and air dried. The volume of gas evolved from the cathodic reaction during the corrosion process was determined. Hence, gasometric method correlates the quantity of gas evolved to the rate of corrosion. The graph of the volume of gas liberated per minute gives the rate of gas evolution, while the inhibition efficiency () and degree of surface coverage (θ) were determined from Eqs. 2 and 3, respectively.

$$\mathcal{E} = \left(\mathbf{1} - \frac{V\_H^\*}{V\_H^0}\right) \times \mathbf{100} \tag{2}$$

$$\boldsymbol{\Theta} = \left( \mathbf{1} - \frac{\boldsymbol{V}^\*\_{\,\,H}}{\boldsymbol{V}^0\_{\,\,H}} \right) \tag{3}$$

where *V\*H* is volume of hydrogen gas evolved at time *t* in the presence of inhibitor and *V0 <sup>H</sup>* is the volume of hydrogen evolved in the absence of inhibitor.

#### *2.3.2 Thermometric method*

Temperature determination was carried out as reported by Ebenso et al. [30]. Using the value for the rise in temperature per minute, the reaction number (RN) was calculated as shown in Eq. 4:

$$\text{RNV} \stackrel{\circ}{\text{C}} \text{/} \stackrel{\circ}{\text{cm}} \text{/} \text{=} \begin{pmatrix} \text{Tm} \text{ -- } \text{Ti} \text{\textdegree t} \end{pmatrix} \text{/t} \tag{4}$$

where *Tm* and *Ti* are the maximum and initial temperatures, respectively, attained by the system and *t* is the time. Similarly, the inhibition efficiency was determined by the reaction number correlation (Eq. 5).

$$\mathcal{E} = \left(\frac{RN\_o - RN\_l}{RN\_o}\right) \times 100\tag{5}$$

where *RNo* is the reaction number of solution without inhibitor, while *RNi* is the reaction number of solution with inhibitor.
