**1. Introduction**

In 2016, NACE International estimated the global cost of corrosion at US\$ 2.5 trillion annually. This accounts for about 3.4% of the global gross domestic product (GDP). In the same study, it was discovered that if corrosion prevention best practices are implemented, there could be global savings of between 15 and 35% of the cost of damage [1]. In spite of the technological advancement of this generation, high profile cases of corrosion have continued to emerge [2–4]. Moreover, the extensive application of acid solutions in industrial cleaning and descaling of mild steel makes metal dissolution a common phenomenon Gadiyar et al. [5]. In order to prolong the lifespan of mild steel, to enhance its viability, and to reduce the high cost of production, practical steps need to be employed in corrosion prevention. Failure to prevent or manage corrosion can result to metal losses, loss of production time, leaking vessels, and unwarranted cleanup costs.

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 reactions occurring at the anode and cathode are:

 Anode surface:*Fe* → *Fe* 2+ + 2 *e* −

$$\text{Cathode surface:} \frac{1}{2}O\_2 + H\_2O + 2e^- \rightarrow 2OH^-$$

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

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:

$$2F\_{\epsilon} \star H^{\ast} \rightarrow F\_{\epsilon}^{\ 2\ast} \star H\_{2\ \ast}$$

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 gas evolution.

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

**43**

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

dissolved oxygen or by some other oxidizing agent [11]. Hydrogen gas evolution method seems to be the most significant and reliable in assessing the rate of corrosion as the mole of metal dissolved directly correlates to the amount of hydrogen gas

The application of inhibitors is one of the practical ways to protect metals against corrosion, especially in acidic media. Basically, they function by serving as integuments on metal surface thereby preventing it from chloride ions and oxygen dissolution. Corrosion inhibitors find application in minimizing metallic waste in engineering materials, in addition to the advantages of versatility and cost effectiveness when compared to other corrosion protection methods [10, 13]. Most of the effective inhibitors are either from biomass precursors or chemical compounds containing hetero-atoms such as oxygen, nitrogen, and sulfur with multiple bonds in their molecules through which they are adsorbed on the metal surface [14–16]. This adsorption depends on certain physiochemical properties of the inhibitors: functional group, electron density at the donor atom, n-orbital character, and the electron structure of the molecule. They contain electronegative functional groups and π-electrons in their double bonds, which facilitate their adsorption onto the metal surface. Hence, the strength of an inhibitor to either prevent corrosion reaction from being initiated or slow down the rate of corrosion, is dependent upon the

The major concern with most chemical inhibitors is their toxicity to the environment. Although many of these synthetic compounds have shown good anti-corrosive activity; their applications have been limited due to environmental considerations [17–20]. Particularly, inorganic corrosion inhibitors such as lead and chromium have been found to constitute significant health challenge to human when released into the environment. This has necessitated the quest for environmentally benign precursors as corrosion inhibitors, for which a plethora of organic materials have been reported. Some of these materials are plant extracts of kola nut, tobacco, *Rosmarinus officinalis*, *Cassia auriculata*, *Argemone Mexicana*, unripe fruit of *Musa acuminate*, roasted coffee seed (*Coffea arabica*), *Carica papaya* leaves, cannabis plant, pomegranate, etc. [14, 19, 21–23]. Furthermore, research has revealed that the basic components of plant extracts are alkaloids, steroids, sugars, gallic acid, tannic acid, and flavonoids, which have been found to improve the protection

The use of natural organic plant extracts as corrosion inhibitors is sometimes referred to as green corrosion prevention. These natural organic compounds are relatively cheaper, nontoxic, and readily available, either as agro-waste and/or agroindustrial waste [27]. Therefore, the aim of this study was to investigate the effectiveness of *Musa paradisiaca* (banana) peel extract as a green corrosion inhibitor for mild steel in acidic medium. The rate of corrosion was assessed using the hydrogen gas evolution method. In addition, the interaction effects of concentration and temperature variation on the corrosion inhibition were assessed using full factorial

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

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

molecular structure of the inhibitor molecules.

of metal surface against corrosion [24–26].

design and analyzed with relevant statistical tools.

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

**2. Materials and methods**

given off [12].

dissolved oxygen or by some other oxidizing agent [11]. Hydrogen gas evolution method seems to be the most significant and reliable in assessing the rate of corrosion as the mole of metal dissolved directly correlates to the amount of hydrogen gas given off [12].

The application of inhibitors is one of the practical ways to protect metals against corrosion, especially in acidic media. Basically, they function by serving as integuments on metal surface thereby preventing it from chloride ions and oxygen dissolution. Corrosion inhibitors find application in minimizing metallic waste in engineering materials, in addition to the advantages of versatility and cost effectiveness when compared to other corrosion protection methods [10, 13]. Most of the effective inhibitors are either from biomass precursors or chemical compounds containing hetero-atoms such as oxygen, nitrogen, and sulfur with multiple bonds in their molecules through which they are adsorbed on the metal surface [14–16]. This adsorption depends on certain physiochemical properties of the inhibitors: functional group, electron density at the donor atom, n-orbital character, and the electron structure of the molecule. They contain electronegative functional groups and π-electrons in their double bonds, which facilitate their adsorption onto the metal surface. Hence, the strength of an inhibitor to either prevent corrosion reaction from being initiated or slow down the rate of corrosion, is dependent upon the molecular structure of the inhibitor molecules.

The major concern with most chemical inhibitors is their toxicity to the environment. Although many of these synthetic compounds have shown good anti-corrosive activity; their applications have been limited due to environmental considerations [17–20]. Particularly, inorganic corrosion inhibitors such as lead and chromium have been found to constitute significant health challenge to human when released into the environment. This has necessitated the quest for environmentally benign precursors as corrosion inhibitors, for which a plethora of organic materials have been reported. Some of these materials are plant extracts of kola nut, tobacco, *Rosmarinus officinalis*, *Cassia auriculata*, *Argemone Mexicana*, unripe fruit of *Musa acuminate*, roasted coffee seed (*Coffea arabica*), *Carica papaya* leaves, cannabis plant, pomegranate, etc. [14, 19, 21–23]. Furthermore, research has revealed that the basic components of plant extracts are alkaloids, steroids, sugars, gallic acid, tannic acid, and flavonoids, which have been found to improve the protection of metal surface against corrosion [24–26].

The use of natural organic plant extracts as corrosion inhibitors is sometimes referred to as green corrosion prevention. These natural organic compounds are relatively cheaper, nontoxic, and readily available, either as agro-waste and/or agroindustrial waste [27]. Therefore, the aim of this study was to investigate the effectiveness of *Musa paradisiaca* (banana) peel extract as a green corrosion inhibitor for mild steel in acidic medium. The rate of corrosion was assessed using the hydrogen gas evolution method. In addition, the interaction effects of concentration and temperature variation on the corrosion inhibition were assessed using full factorial design and analyzed with relevant statistical tools.
