*3.2.1 Gasometric method*

The efficiency of corrosion inhibition by BPE was determined using gasometric method according to Eq. 1, for the various concentrations of 1.0, 2.5, 5.0, 7.5, and 10.0 g/L (**Table 2**).


#### **Table 1.**

*Physical properties of banana peel extract (BPE).*


**47**

**Figure 2.**

*3.2.2 Thermometric method*

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

The volume of gas evolved from the cathodic reaction during the corrosion study

As shown in **Figure 2**, the volume of H2 evolved decreased with increasing concentration of the extract. This can be attributed to increased adsorption forces at higher concentrations. However, hydrogen gas evolution increased with time, until after 8 min before equilibration. This is expected since adsorption decreases with time. From the chemical equation, the dissolution of 2 M of ferrous generates one molecule of hydrogen gas. This means that the evolution of one molecule of hydrogen gas corresponds to the dissolution of 2 M of iron. Theoretically, by mole ratio, it implies that the rate of iron dissolution doubles the rate of hydrogen gas evolution. From the anodic and cathodic reactions, the flow of chloride ion from cathode caused the dissolution of iron at the anode and the metal gets corroded, which is the formation of hydrated iron (II) chloride. Hence, prevention of corrosion is possible if the chloride ion is prevented from having contact with the metal surface. The corrosion of mild steel in HCl solutions has been reported to be a first order reaction [36], which increases with increased acid concentration. In addition, the dissolution of iron steel in hydrochloric acid is dependent upon chloride ion over acidic range of pH. Also, the pH of HCl solution decreased with increased immersion time of the mild steel (**Figure 3**). This was obviously due to increased acidity of the solution. Moreover, as described in Section 2.3, the volume of hydrogen gas evolution was used to determine the corrosion inhibition efficiency at different temperatures and concentrations of the biomass extract. Consequently, experimental design was used to assess the effects of these independent parameters that ultimately led to peak process performance and the discovery of optimum conditions. The experimental design was generated using a MINITAB 17.0 software (Stat-Ease Inc., USA). Each variable was analyzed at five levels with a total of 25 experiments being performed representing a full factorial. The system response, which is the corrosion inhibition efficiency,

(**Figure 2**) is correlated to inhibition efficiency by gasometric method.

*Volumetric rate of hydrogen gas during corrosion of mild steel in 1 M HCl acid solution.*

was determined by gasometric and thermometric methods (**Tables 3** and **4**).

Similarly, using thermometric method given in Eq. 4, the percentage corrosion inhibition was evaluated for the concentrations 1.0, 2.5, 5.0, 7.5, and 10.0 g/L, and

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

**Table 2.** *Experimental design.* *Exploring Musa paradisiaca Peel Extract as a Green Corrosion Inhibitor for Mild Steel Using… DOI: http://dx.doi.org/10.5772/intechopen.82617*

#### **Figure 2.**

*Corrosion Inhibitors*

were the input variables.

**Table 1**.

of the inhibitor.

*3.2.1 Gasometric method*

10.0 g/L (**Table 2**).

**Density (g/L cm3 )**

**3. Results and discussion**

**3.1 Physical properties of BPE**

**2.4 Effects of concentration and temperature variations on corrosion inhibition**

The data obtained from the banana peel extraction experiments were analyzed statistically using factorial method to obtain a linear fit for the inhibition of mild steel corrosion under varied concentration and temperature. The mathematical model was generated by a MINITAB 17.0. Regression analysis was performed to correlate the response variable to the independent variables. The quality of the fit of the model was evaluated using analysis of variance (ANOVA), where the response was the inhibition efficiency; while concentration and temperature of BPE solution

The physical properties determined for the banana peel extract are presented in

The efficiency of corrosion inhibition by BPE was determined using gasometric method according to Eq. 1, for the various concentrations of 1.0, 2.5, 5.0, 7.5, and

> **Surface tension (dynes cm<sup>−</sup><sup>1</sup>**

**)**

**Specific gravity**

**Flash point (°C)**

**Levels 1 2 3 4 5** Concentration (g/L), X1 1.0 2.5 5.0 7.5 10.0 Temperature (K), X2 303 308 313 318 323

1.56 32.04 18.0 1.55 237

The viscosity of the banana peel extract (BPE) compares favorably well with those previously reported for BPE and other biomaterials. For instance, similar viscosities were reported for extracts from *Citrullus lanatus*, *Phyllanthus*, and banana peels [31, 32]. Viscosity is the property of a fluid that makes it resist flow and sustain frictional force. It is an important property of a good inhibitor, which makes it stick to the surface of metals thereby forming a protective barrier against corrosion. It represents the ability of the extract to adhere longer to metal surfaces, thus enhancing corrosion inhibition. Corrosion inhibitors often contain one or more surfactants, which lowers the surface tension of corrosive fluids [33]. Similarly, the flash point of BPE extract is within the range reported by Kliskic et al. [34] and Betiku et al. [35]. This indicates the flammability or combustibility

**3.2 Evaluation of BPE efficiency as a corrosion inhibitor**

**Dynamic viscosity (cp)**

*Physical properties of banana peel extract (BPE).*

**46**

**Table 2.**

**Table 1.**

*Experimental design.*

*Volumetric rate of hydrogen gas during corrosion of mild steel in 1 M HCl acid solution.*

The volume of gas evolved from the cathodic reaction during the corrosion study (**Figure 2**) is correlated to inhibition efficiency by gasometric method.

As shown in **Figure 2**, the volume of H2 evolved decreased with increasing concentration of the extract. This can be attributed to increased adsorption forces at higher concentrations. However, hydrogen gas evolution increased with time, until after 8 min before equilibration. This is expected since adsorption decreases with time. From the chemical equation, the dissolution of 2 M of ferrous generates one molecule of hydrogen gas. This means that the evolution of one molecule of hydrogen gas corresponds to the dissolution of 2 M of iron. Theoretically, by mole ratio, it implies that the rate of iron dissolution doubles the rate of hydrogen gas evolution. From the anodic and cathodic reactions, the flow of chloride ion from cathode caused the dissolution of iron at the anode and the metal gets corroded, which is the formation of hydrated iron (II) chloride. Hence, prevention of corrosion is possible if the chloride ion is prevented from having contact with the metal surface. The corrosion of mild steel in HCl solutions has been reported to be a first order reaction [36], which increases with increased acid concentration. In addition, the dissolution of iron steel in hydrochloric acid is dependent upon chloride ion over acidic range of pH. Also, the pH of HCl solution decreased with increased immersion time of the mild steel (**Figure 3**). This was obviously due to increased acidity of the solution.

Moreover, as described in Section 2.3, the volume of hydrogen gas evolution was used to determine the corrosion inhibition efficiency at different temperatures and concentrations of the biomass extract. Consequently, experimental design was used to assess the effects of these independent parameters that ultimately led to peak process performance and the discovery of optimum conditions. The experimental design was generated using a MINITAB 17.0 software (Stat-Ease Inc., USA). Each variable was analyzed at five levels with a total of 25 experiments being performed representing a full factorial. The system response, which is the corrosion inhibition efficiency, was determined by gasometric and thermometric methods (**Tables 3** and **4**).

#### *3.2.2 Thermometric method*

Similarly, using thermometric method given in Eq. 4, the percentage corrosion inhibition was evaluated for the concentrations 1.0, 2.5, 5.0, 7.5, and 10.0 g/L, and

*Variation of pH of HCl solution with immersion time of mild steel in the presence of banana peel extract (BPE).*


**Table 4.**

**3.3 Modeling and statistical analysis**

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

**Run order Concentration (g/L) (X1) Temperature (K) (X2) Inhibition, Ɛ (%)** 7.5 303 62.4 5.0 313 41.93 1.0 303 41.58 10.0 313 59.85 2.5 308 49.25 7.5 318 44.98 7.5 313 51.73 2.5 318 33.94 5.0 308 54.13 2.5 313 40.31 10.0 323 48.77 1.0 323 21.75 2.5 303 51.75 10.0 303 71.56 1.0 313 29.95 7.5 308 57.92 7.5 323 40.86 1.0 318 24.86 5.0 323 37.72 5.0 303 60.01 1.0 308 35.32 5.0 318 41.93 10.0 308 65.70 10.0 318 53.62 2.5 323 31.56

at various temperatures. The experimental results presented in **Tables 3** and **4** show that at constant concentration of the extract; say, at 10 or 7.5 g/L, corrosion inhibition efficiency decreased with increasing temperature. In the same vein, it was observed that at constant temperature; say, 303 K, corrosion inhibition efficiency increased with increasing inhibitor concentration. In a similar study, Gunavathy and Murugavel [37] have reported that the inhibition efficiency of mild steel corrosion in acid medium by *Musa acuminata* fruit peel extract increases with the increase in concentration but decreases with increase in temperature. The same trend was reported by Mayanglambam et al. [38] for *Musa Paradisiaca* extract on mild steel in sulfuric acid solution. Lai et al. [39] have also worked on the inhibition of mild steel in HCl acid solution with a synthetic inhibitor, and/or synthetic mixed-type inhibitors as revealed by potentiodynamic polarization measurement. It was equally reported that the efficiency of the inhibitors decreased with increasing temperature as well as acid concentration.

*Corrosion inhibition efficiency determination using thermometric method.*

Suitable statistical models were chosen to model the interactions between the different experimental variables and their effect on the efficiency of corrosion inhibition, based on the "Fit Regression Model" of MINITAB 17.0 (Pen, USA). The response was modeled with a response surface quadratic model and

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

**Table 3.** *Corrosion inhibition efficiency determination using gasometric method.*


*Exploring Musa paradisiaca Peel Extract as a Green Corrosion Inhibitor for Mild Steel Using… DOI: http://dx.doi.org/10.5772/intechopen.82617*

#### **Table 4.**

*Corrosion Inhibitors*

**Figure 3.**

*(BPE).*

**Run order Concentration (g/L) (X1) Temperature (K) (X2) Inhibition, Ɛ (%)** 7.5 303 64.14 5.0 313 51.11 1.0 303 44.40 10.0 313 61.75 2.5 308 49.53 7.5 318 49.25 7.5 313 53.14 2.5 318 40.28 5.0 308 56.31 2.5 313 44.43 10.0 323 49.21 1.0 323 24.75 2.5 303 54.73 10.0 303 72.03 1.0 313 34.00 7.5 308 59.00 7.5 323 44.17 1.0 318 29.15 5.0 323 41.62 5.0 303 61.51 1.0 308 39.20 5.0 318 29.15 10.0 308 66.83 10.0 318 54.62 2.5 323 34.92

*Variation of pH of HCl solution with immersion time of mild steel in the presence of banana peel extract* 

**Table 3.**

*Corrosion inhibition efficiency determination using gasometric method.*

*Corrosion inhibition efficiency determination using thermometric method.*

at various temperatures. The experimental results presented in **Tables 3** and **4** show that at constant concentration of the extract; say, at 10 or 7.5 g/L, corrosion inhibition efficiency decreased with increasing temperature. In the same vein, it was observed that at constant temperature; say, 303 K, corrosion inhibition efficiency increased with increasing inhibitor concentration. In a similar study, Gunavathy and Murugavel [37] have reported that the inhibition efficiency of mild steel corrosion in acid medium by *Musa acuminata* fruit peel extract increases with the increase in concentration but decreases with increase in temperature. The same trend was reported by Mayanglambam et al. [38] for *Musa Paradisiaca* extract on mild steel in sulfuric acid solution. Lai et al. [39] have also worked on the inhibition of mild steel in HCl acid solution with a synthetic inhibitor, and/or synthetic mixed-type inhibitors as revealed by potentiodynamic polarization measurement. It was equally reported that the efficiency of the inhibitors decreased with increasing temperature as well as acid concentration.
