Al-Cu-Fe alloy powder, a highly effective lubrication-oil additive, was coated by conventional sol-gel method employing tetraethyloxysilane (TEOS) as the precursor for purpose of improving its corrosion resistance [78]. The sol-gel method was modified by employing ultrasound to study the effects of both ultrasonic power and irradiation time on the coating process. The coated powder had a high corrosion resistance in the acid media of pH 1. Vignesh et al. used 3-mercaptopropyltrimethoxysilane (MPTMS) as the precursor for sol-gel coating on aluminum metal [79]. The results brought to light the potential of MPTMS as a precursor in the development of sol-gel coating over Al metal. The FTIR studies revealed the mechanism of the gelation of MPTMS and the formation of Si─O─Al linkage on the metallic substrate. The formed film was found to be stable up to 350°C as evident from thermogravimetric analysis. The X-rays diffraction (XRD) data also confirmed the formation of sol-gel coating on the metal surface. The electrochemical impedance spectroscopy (EIS) analysis of MPTMS coating on aluminum showed the inhibition of the corrosion by acting as a barrier to the electrolyte by impeding its contact with the metal

concerning the use of sol-gel coatings for corrosion control in metals and metal alloys.

**10.** Hybrid silica sol-gel coatings are of growing interest as corrosion protection materials for metals as these coatings have good adhesion to metallic substrates and offer good corrosion resistance by combining properties of organic polymers and properties of ceramics [73, 74].

### *2.3.2. Limitations of sol-gel coatings*

Common sol-gel limitations can be summarized in the following points [7]:

#### *2.3.3. Applications of sol-gel coatings*

#### *<IP_ADDRESS>. Spin-coating*

Spin coating has been used for several decades for the application of thin films. In this process, a small drop of the coating material is loaded onto the center of a substrate, which is then spun at a controlled high speed. In the spin-coating process, the substrates spin around an axis which should be perpendicular to the coating area. As a result, the coating material spreads forming a thin film on the surface. Film properties, such as thickness, will be affected by several factors such as: viscosity, surface tension, drying ease and the rotation speed [75].

#### *<IP_ADDRESS>. Dip coating*

This method can be achieved by immersing a metal into a tank containing the coating material then withdrawing it to obtain a homogeneous film. Compared to the spin coating, the film obtained by dip coating is thicker [76].

#### *<IP_ADDRESS>. Spray coating technique*

Spray coating technique is a process in which molten or softened particles are applied by impact onto a substrate to produce a coating. This is done by using a vessel under pressure that pumps loading through a spray gun. The operation occurs in a totally enclosed system to minimize radiation of coating and product wastes [75].

#### *<IP_ADDRESS>. Flow-coating process*

**8.** Highly porous materials and nanocrystalline materials may be prepared in this way.

machining or melting.

68 Corrosion Inhibitors, Principles and Recent Applications

*2.3.2. Limitations of sol-gel coatings*

• Precursors are sensitive to moisture;

• The process is time-consuming; and

*2.3.3. Applications of sol-gel coatings*

obtained by dip coating is thicker [76].

minimize radiation of coating and product wastes [75].

*<IP_ADDRESS>. Spray coating technique*

[73, 74].

attention.

speed [75].

*<IP_ADDRESS>. Dip coating*

*<IP_ADDRESS>. Spin-coating*

**9.** Since liquid precursors are used, it is possible to cast ceramic materials in a range of complex shapes and to produce thin films or fibers as well as monoliths, without the need for

**10.** Hybrid silica sol-gel coatings are of growing interest as corrosion protection materials for metals as these coatings have good adhesion to metallic substrates and offer good corrosion resistance by combining properties of organic polymers and properties of ceramics

• The dimensional change can occur on densification, shrinkage, cracking on drying, require

Spin coating has been used for several decades for the application of thin films. In this process, a small drop of the coating material is loaded onto the center of a substrate, which is then spun at a controlled high speed. In the spin-coating process, the substrates spin around an axis which should be perpendicular to the coating area. As a result, the coating material spreads forming a thin film on the surface. Film properties, such as thickness, will be affected by several factors such as: viscosity, surface tension, drying ease and the rotation

This method can be achieved by immersing a metal into a tank containing the coating material then withdrawing it to obtain a homogeneous film. Compared to the spin coating, the film

Spray coating technique is a process in which molten or softened particles are applied by impact onto a substrate to produce a coating. This is done by using a vessel under pressure that pumps loading through a spray gun. The operation occurs in a totally enclosed system to

Common sol-gel limitations can be summarized in the following points [7]:

• Precursors are expensive, limiting large-scale manufacture;

In flow-coating process, the liquid-coating system is more or less poured over the substrate to be coated. The coating thickness depends on the angle of inclination of the substrate, the coating-liquid viscosity and the solvent evaporation rate. Thus, nonplanar large substrates can be readily coated [76].

There are many studies, investigate the ability of the sol-gel method to protect metals from corrosion, will be discussed in the following section.

#### *2.3.4. Corrosion control by using sol-gel coatings*

Sol-gel-coated layers can exhibit good adhesion to the metal substrate due to the formation of chemically adsorbed M─O─Si bonds, as shown in **Figure 3**, resulting in a good anticorrosion performance. The following section summarizes a brief collection of recent and novel studies concerning the use of sol-gel coatings for corrosion control in metals and metal alloys.

Al-Cu-Fe alloy powder, a highly effective lubrication-oil additive, was coated by conventional sol-gel method employing tetraethyloxysilane (TEOS) as the precursor for purpose of improving its corrosion resistance [78]. The sol-gel method was modified by employing ultrasound to study the effects of both ultrasonic power and irradiation time on the coating process. The coated powder had a high corrosion resistance in the acid media of pH 1. Vignesh et al. used 3-mercaptopropyltrimethoxysilane (MPTMS) as the precursor for sol-gel coating on aluminum metal [79]. The results brought to light the potential of MPTMS as a precursor in the development of sol-gel coating over Al metal. The FTIR studies revealed the mechanism of the gelation of MPTMS and the formation of Si─O─Al linkage on the metallic substrate. The formed film was found to be stable up to 350°C as evident from thermogravimetric analysis. The X-rays diffraction (XRD) data also confirmed the formation of sol-gel coating on the metal surface. The electrochemical impedance spectroscopy (EIS) analysis of MPTMS coating on aluminum showed the inhibition of the corrosion by acting as a barrier to the electrolyte by impeding its contact with the metal

**Figure 3.** Bonding of silane precursors to the metallic surface [77].

surface. The polarization studies revealed that MPTMS sol-gel coating on aluminum blocked the anodic sites of the metal and thereby reduced the metal dissolution into the electrolyte solution, while SEM confirmed the protective nature of the MPTMS coating over aluminum substrate.

by the addition of cerium salts due to its self-healing abilities. The sol-gel coating doped with

in 0.5 M HCl solution pretreated with various mono- and bilayered sol-gel films [85]. It was found that the bilayer morphology is similar to that of the outer layer. The protection abilities of mono- and bi-films are discussed in terms of film structure and functionality. The hybrid bifunctional organic coating (i.e. contains two different organic functional groups) is more efficient than monofunctional one. Hybrid monolayer has higher protection ability than its corresponding bilayers. Rahimi et al. reported the corrosion- and wear-resistance characterization of environmentally friendly sol-gel hybrid nanocomposite coating on aluminum. The hybrid nanocomposite coatings have been synthesized from TEOS and GPTMS precursors. The multilayer coatings were prepared by dip-coating technique. Effects of different layers on corrosion and wear resistance were studied. The coatings were found to increase the electrochemical corrosion resistance of aluminum. The maximum corrosion resistance properties, as determined by using electrochemical cyclic polarization testing, were observed for triple solgel-coated layer. The results suggested that crack-free plain organic-inorganic hybrid nano-

network could be obtained on aluminum substrate by sol-gel synthesis. Atomic-force microscopy height images showed smooth nanostructural surface with root mean square less than 4 nm and the existence of organic and inorganic components in coatings could be a result of excellent wear and mechanical properties. Shi et al. studied that the sol-gel coatings were prepared using GPTMS and TEOS as precursors, diethylentriamine as curing agent. Inhibition effect of 2-methyl piperidine on magnesium alloy in 0.005, 0.05 and 0.5 wt.% NaCl solution is

The protection abilities of unmodified and modified GPTMS-VTMS sol-gel films with different Ti- and Al-alkoxides concentrations against zinc corrosion in 0.5 M HCl solution are reported by Ali et al. [85]. It was shown that the presence of the modifiers, either Ti or Al, facilitates the formation of the network structure and increases slightly the thermal stability of sol-gel materials. Weight-loss and electrochemical measurements proved that the highest protection ability of sol-gel coatings is assigned with low modifiers concentrations. The protection efficiency is increased from 69.2 to 96.2% and 95.8% upon modification with 0.005 M of Ti and Al modifiers, respectively. On the other hand, higher modifier concentrations may cause a galvanic corrosion which results in lower protection efficiency values. Corrosion inhibitors and nanoparticles can be added in the silane sol-gel network to improve corrosion resistance [86]. Balan et al. examined the effect of adding activated cerium nitrate nanoparticles into a coated sol-gel matrix on low-carbon steel substrates. Hybrid sol-gel films have been prepared from mixture of TEOS and GPTMS. Silica, alumina and their equimolar mixtures are used as nanoparticles with a concentration of 250 ppm. The SEM confirmed crack-free surface for prepared substrates with different pretreatments. Inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles reported by Tavandashti et al. [87]. Organosiloxane sol was prepared by mixing GPTMS, TEOS and isopropanol to obtain a sol with 75 mol.% organic content. The high corrosion-resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at

has the highest corrosion resistance due to the utilized hydrolysis and conden-

. Ali et al. investigated the corrosion behavior of zinc substrates

group incorporated into a silica

Green Methods for Corrosion Control http://dx.doi.org/10.5772/intechopen.72762 71

Ce(CH3

investigated.

COO)3

sation provided by CH3

COO−

composite coatings with Si-O-Si structure backbone and CH2

Seifzadeh et al. have studied the novel and crack-free nanocomposites based on sol-gel process for corrosion protection of copper [80]. The best results have been obtained after addition of sodium montmorillonite nanoclay at 0.01% concentration. Also, the phenyltrimethoxysilane sol-gel coating becomes more hydrophobic after addition of nanoclay at low concentrations (0.01 and 0.1%). Results indicated that phenyltrimethoxysilane coating provided a high protection from corrosion when compared with copper substrate. The addition of nanoclays resulted in a crack-free sol-gel coating and enhanced protective properties of the coating. A conversion coating was formulated and applied on mild steel prior to sol-gel Al2 O3 coating to improve the corrosion resistance of mild steel reported by Tiwari et al. [81]. The comparison was made between conversion coated and conversion followed by sol-gel Al2 O3 -coated mild steel. The modified surfaces, produced by conversion coating and conversion followed by sol-gel Al2 O3 coating, were characterized by XRD and X-ray photoelectron spectroscopy (XPS) and SEM. The corrosion resistance of the sol-gel coating was evaluated in 3.5 wt.% NaCl solution by one-component plasma (OCP), polarization and EIS measurement. By examining the surface morphology of solgel after Al2 O3 coating (0.36 ± 0.03 μm thickness), the surface seems smooth with featureless topography. The sol-gel Al2 O3 coating is free from any defect and is homogeneous. No change in the coating morphology is seen after long immersion (240 h) in 3.5 wt.% NaCl solution and repeated anodic polarization. The conversion coating by using silica sol and aluminum oxyhydroxide followed by heat treatment at 500°C produced mild steel surface suitable for sol-gel Al2 O3 coating. The conversion coating formed a composite oxide containing Al2 O3 , SiO2 , α-Fe2 O3 and Fe3 O4 on the surface. The Al2 O3 coating is amorphous and stable for 240 h in 3.5 wt.% NaCl solution. The protective nature of a coating composed of a hybrid sol-gel and a phosphate-based conversion layer for magnesium-alloy corrosion was investigated by Li et al. [82]. The sol-gel coating itself has a good anticorrosion performance; however, the presence of an additional conversion layer highly enhanced the protection ability. The corrosion process was examined by EIS which showed that the presence of the conversion layer increases the system resistance upon immersion in a 0.05 M NaCl solution, as compared to the single sol-gel coating. Hassannejad et al. studied the effects of cerium doping on corrosion resistance of amorphous silica-titania coating [83]. Potentiodynamic polarization and EIS spectroscopy have been used to study the corrosion behavior of composite coating in 3.5% NaCl solution. Results showed that ceria doping presented higher corrosion resistance than undoped silica-titanium composite layer and also the passive region of the doped films in potentiodynamic tests expanded with respect to undoped silica-titanium composite layer. The film corrosion resistance is noticed due to the inhibition action of cerium. There is a critical cerium concentration, above it cracking occurs, this can be related to the high expansion coefficient of cerium oxide. Mei et al. examined the effects of cerium salts on corrosion behaviors of Si-Zr hybrid sol-gel coatings [84]. The Si-Zr hybrid sol-gel coatings on aluminum substrate were prepared through hydrolysis and condensation of GPTMS and zirconium(IV) n-propoxide, used as inhibitors for corrosion, three types of cerium salts (Ce(NO3 ) 3 , CeCl3 and Ce(CH3 COO)3 ) were doped into the sol-gel coatings. The corrosion process is retarded by the addition of cerium salts due to its self-healing abilities. The sol-gel coating doped with Ce(CH3 COO)3 has the highest corrosion resistance due to the utilized hydrolysis and condensation provided by CH3 COO− . Ali et al. investigated the corrosion behavior of zinc substrates in 0.5 M HCl solution pretreated with various mono- and bilayered sol-gel films [85]. It was found that the bilayer morphology is similar to that of the outer layer. The protection abilities of mono- and bi-films are discussed in terms of film structure and functionality. The hybrid bifunctional organic coating (i.e. contains two different organic functional groups) is more efficient than monofunctional one. Hybrid monolayer has higher protection ability than its corresponding bilayers. Rahimi et al. reported the corrosion- and wear-resistance characterization of environmentally friendly sol-gel hybrid nanocomposite coating on aluminum. The hybrid nanocomposite coatings have been synthesized from TEOS and GPTMS precursors. The multilayer coatings were prepared by dip-coating technique. Effects of different layers on corrosion and wear resistance were studied. The coatings were found to increase the electrochemical corrosion resistance of aluminum. The maximum corrosion resistance properties, as determined by using electrochemical cyclic polarization testing, were observed for triple solgel-coated layer. The results suggested that crack-free plain organic-inorganic hybrid nanocomposite coatings with Si-O-Si structure backbone and CH2 group incorporated into a silica network could be obtained on aluminum substrate by sol-gel synthesis. Atomic-force microscopy height images showed smooth nanostructural surface with root mean square less than 4 nm and the existence of organic and inorganic components in coatings could be a result of excellent wear and mechanical properties. Shi et al. studied that the sol-gel coatings were prepared using GPTMS and TEOS as precursors, diethylentriamine as curing agent. Inhibition effect of 2-methyl piperidine on magnesium alloy in 0.005, 0.05 and 0.5 wt.% NaCl solution is investigated.

surface. The polarization studies revealed that MPTMS sol-gel coating on aluminum blocked the anodic sites of the metal and thereby reduced the metal dissolution into the electrolyte solution, while SEM confirmed the protective nature of the MPTMS coating over aluminum substrate.

Seifzadeh et al. have studied the novel and crack-free nanocomposites based on sol-gel process for corrosion protection of copper [80]. The best results have been obtained after addition of sodium montmorillonite nanoclay at 0.01% concentration. Also, the phenyltrimethoxysilane sol-gel coating becomes more hydrophobic after addition of nanoclay at low concentrations (0.01 and 0.1%). Results indicated that phenyltrimethoxysilane coating provided a high protection from corrosion when compared with copper substrate. The addition of nanoclays resulted in a crack-free sol-gel coating and enhanced protective properties of the coating.

to improve the corrosion resistance of mild steel reported by Tiwari et al. [81]. The comparison

steel. The modified surfaces, produced by conversion coating and conversion followed by

and SEM. The corrosion resistance of the sol-gel coating was evaluated in 3.5 wt.% NaCl solution by one-component plasma (OCP), polarization and EIS measurement. By examining the

homogeneous. No change in the coating morphology is seen after long immersion (240 h) in 3.5 wt.% NaCl solution and repeated anodic polarization. The conversion coating by using silica sol and aluminum oxyhydroxide followed by heat treatment at 500°C produced mild steel

stable for 240 h in 3.5 wt.% NaCl solution. The protective nature of a coating composed of a hybrid sol-gel and a phosphate-based conversion layer for magnesium-alloy corrosion was investigated by Li et al. [82]. The sol-gel coating itself has a good anticorrosion performance; however, the presence of an additional conversion layer highly enhanced the protection ability. The corrosion process was examined by EIS which showed that the presence of the conversion layer increases the system resistance upon immersion in a 0.05 M NaCl solution, as compared to the single sol-gel coating. Hassannejad et al. studied the effects of cerium doping on corrosion resistance of amorphous silica-titania coating [83]. Potentiodynamic polarization and EIS spectroscopy have been used to study the corrosion behavior of composite coating in 3.5% NaCl solution. Results showed that ceria doping presented higher corrosion resistance than undoped silica-titanium composite layer and also the passive region of the doped films in potentiodynamic tests expanded with respect to undoped silica-titanium composite layer. The film corrosion resistance is noticed due to the inhibition action of cerium. There is a critical cerium concentration, above it cracking occurs, this can be related to the high expansion coefficient of cerium oxide. Mei et al. examined the effects of cerium salts on corrosion behaviors of Si-Zr hybrid sol-gel coatings [84]. The Si-Zr hybrid sol-gel coatings on aluminum substrate were prepared through hydrolysis and condensation of GPTMS and zirconium(IV)

coating, were characterized by XRD and X-ray photoelectron spectroscopy (XPS)

O3

on the surface. The Al2

O3

O3

coating is amorphous and

) 3 , CeCl3

coating (0.36 ± 0.03 μm thickness), the surface seems

coating. The conversion coating formed a composite oxide

O3

coating is free from any defect and is

coating

A conversion coating was formulated and applied on mild steel prior to sol-gel Al2

was made between conversion coated and conversion followed by sol-gel Al2

O3

O4

n-propoxide, used as inhibitors for corrosion, three types of cerium salts (Ce(NO3

) were doped into the sol-gel coatings.  The sol-gel Al2

, α-Fe2 O3

O3

and Fe3

The protection abilities of unmodified and modified GPTMS-VTMS sol-gel films with different Ti- and Al-alkoxides concentrations against zinc corrosion in 0.5 M HCl solution are reported by Ali et al. [85]. It was shown that the presence of the modifiers, either Ti or Al, facilitates the formation of the network structure and increases slightly the thermal stability of sol-gel materials. Weight-loss and electrochemical measurements proved that the highest protection ability of sol-gel coatings is assigned with low modifiers concentrations. The protection efficiency is increased from 69.2 to 96.2% and 95.8% upon modification with 0.005 M of Ti and Al modifiers, respectively. On the other hand, higher modifier concentrations may cause a galvanic corrosion which results in lower protection efficiency values. Corrosion inhibitors and nanoparticles can be added in the silane sol-gel network to improve corrosion resistance [86]. Balan et al. examined the effect of adding activated cerium nitrate nanoparticles into a coated sol-gel matrix on low-carbon steel substrates. Hybrid sol-gel films have been prepared from mixture of TEOS and GPTMS. Silica, alumina and their equimolar mixtures are used as nanoparticles with a concentration of 250 ppm. The SEM confirmed crack-free surface for prepared substrates with different pretreatments. Inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles reported by Tavandashti et al. [87]. Organosiloxane sol was prepared by mixing GPTMS, TEOS and isopropanol to obtain a sol with 75 mol.% organic content. The high corrosion-resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites. Asadi et al. investigated the cloisite concentration effect on the protective performance of sol-gel coating, prepared from GPTMS, TEOS and methyltriethoxysilane on mild steel substrate [88]. The optimum concentration of nanoparticles was determined. The data indicated superiority of the hybrid film embedded with 1000 ppm of cloisite nanoparticles. Confirming the electrochemical data, FTIR spectra and water contact angles showed that the nanoparticles well dispersed in the silane film might improve barrier properties moreover, a good trend correlation was observed between the noise resistance and low-frequency *IZI* data. Naderi et al. studied the synergistic effect of incorporation of nanoclay along with cerium nitrate as a corrosion inhibitor into an eco-friendly silane layer consisting of GPTMS, TEOS and methyltriethoxysilane applied on pure Al [89]. EIS and polarization results showed that the high protective nature of film containing cerium is due to film deposition on cathodic regions, thus preventing entrance of aggressive species to the surface. FTIR spectra proved the presence of the inhibitor in the film structure. N-nanoparticles silane coating in the presence of cerium salt provided higher corrosion protection compared to the film with only incorporated nanoclay.

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73

Green Methods for Corrosion Control http://dx.doi.org/10.5772/intechopen.72762

## **Author details**

Khadija M. Emran1 \*, Shimaa M. Ali1,2 and Hamedh A. Al Lehaibi1

\*Address all correspondence to<EMAIL_ADDRESS>
1 Department of Chemistry, Collage of Science, Taibah University, Madinah, Kingdom of Saudi Arabia

2 Department of Chemistry, Collage of Science, Cairo University, Giza, Egypt

## **References**

[6] Belarbi Z, Farelas F, Singer M, Nešić S. Role of amines in the mitigation of CO2 top of the line corrosion. Corrosion. 2016;**72**(10):1300-1310

the defects within the coating, hindering the corrosion reactions at defective sites. Asadi et al. investigated the cloisite concentration effect on the protective performance of sol-gel coating, prepared from GPTMS, TEOS and methyltriethoxysilane on mild steel substrate [88]. The optimum concentration of nanoparticles was determined. The data indicated superiority of the hybrid film embedded with 1000 ppm of cloisite nanoparticles. Confirming the electrochemical data, FTIR spectra and water contact angles showed that the nanoparticles well dispersed in the silane film might improve barrier properties moreover, a good trend correlation was observed between the noise resistance and low-frequency *IZI* data. Naderi et al. studied the synergistic effect of incorporation of nanoclay along with cerium nitrate as a corrosion inhibitor into an eco-friendly silane layer consisting of GPTMS, TEOS and methyltriethoxysilane applied on pure Al [89]. EIS and polarization results showed that the high protective nature of film containing cerium is due to film deposition on cathodic regions, thus preventing entrance of aggressive species to the surface. FTIR spectra proved the presence of the inhibitor in the film structure. N-nanoparticles silane coating in the presence of cerium salt provided higher

corrosion protection compared to the film with only incorporated nanoclay.

\*Address all correspondence to<EMAIL_ADDRESS>
\*, Shimaa M. Ali1,2 and Hamedh A. Al Lehaibi1

2 Department of Chemistry, Collage of Science, Cairo University, Giza, Egypt

1 Department of Chemistry, Collage of Science, Taibah University, Madinah, Kingdom of

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72 Corrosion Inhibitors, Principles and Recent Applications

Khadija M. Emran1

Saudi Arabia

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**Chapter 4**

Provisional chapter

**The Impact of Drugs as Corrosion Inhibitors on**

on Aluminum Alloy in Coastal-Acidified Medium

DOI: 10.5772/intechopen.72942

The use of corrosion inhibitors has proven to be one of the effective methods of corrosion protection of metals and alloys. Aluminum alloys are good candidate materials for structural components in major industrial application owing to their excellent corrosion resistance. However in high intensity coastal and acidified medium the challenge of micro porosity and hydrogen embrittlement distributed along the interface cannot be neglected as suitable corrosion inhibitive compounds is needful without significantly reacts with the environmental components. The challenges of most effective organic and inorganic Inhibitors when dissolved in aqueous environments are increasingly due to their toxicity. Drug as inhibitive compound have been seen as suitable replacement for this high toxic organic inhibitors since both react by adsorption on a metallic surface. They are usually compounds that form film and cause the formation of precipitates on the metal surface, thereby blocking both cathodic and anodic and sites. Therefore, this study covers the general overview of impact of some drugs as corrosion inhibitive compound on aluminum for industrial applications and their environmental impact.

Keywords: corrosion inhibitors, protection, coastal, acidified, drug and impact

Aluminum is a silvery white material and a member of boron group. It is one of the most abundant metal in the Earth's crust, and the third most abundant element within, after oxygen and silicon. It is yielding, long-lasting, lightweight, malleable metal with physical appearance varying from silvery coloration to approximate gray, which depend on the roughness of the surface. Aluminum is not a Ferro-magnetic material. It is also not soluble in alkanols, despite the fact that, in certain form, it can be water-soluble. It has an appreciable yield strength of

> © The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Aluminum Alloy in Coastal-Acidified Medium**

The Impact of Drugs as Corrosion Inhibitors

Paul Apeye Lucky Anawe and Ayodele Daniyan

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72942

Ojo Sunday Isaac Fayomi,

Paul Apeye Lucky Anawe and

Ojo Sunday Isaac Fayomi,

Ayodele Daniyan

Abstract

1. Introduction

#### **The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium** The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium

DOI: 10.5772/intechopen.72942

Ojo Sunday Isaac Fayomi, Paul Apeye Lucky Anawe and Ayodele Daniyan Ojo Sunday Isaac Fayomi, Paul Apeye Lucky Anawe and

Additional information is available at the end of the chapter Ayodele Daniyan

http://dx.doi.org/10.5772/intechopen.72942 Additional information is available at the end of the chapter

#### Abstract

[78] Poznyak SK, Zheludkevich ML, Raps D, Gammel F, Yasakau KA, Ferreira MGS. Preparation and corrosion protective properties of nanostructured titania-containing hybrid sol-gel coatings on AA2024. Progress in Organic Coatings. 2008;**62**(2):226-235.

[79] Ali SM, Allehaibi H. Protective sol-gel coatings for zinc corrosion: Precursor type effect. Surface and Coatings Technology. 2017;**311**:172-181. DOI: 10.1016/j.surfcoat.2017.01.010

[80] Li YS, Tran T, Xu Y, Vecchio NE. Spectroscopic studies of trimetoxypropylsilane and bis(trimethoxysilyl)ethane sol-gel coatings on aluminum and copper. Spectrochimica Acta: Part A Molecular and Biomolecular Spectroscopy. 2006;**65**(3-4):779-786. DOI:

[81] Nemeth S, Liu YC. Mechanical properties of hybrid sol-gel derived films as a function of composition and thermal treatment. Thin Solid Films. 2009;**517**(17):4888-4891. DOI:

[82] Li Y, Lu W, Wang Y, Tran T. Studies of (3-mercaptopropyl)trimethoxylsilane and bis(trimethoxysilyl)ethane sol-gel coating on copper and aluminum. Spectrochimica

[83] Shi H, Liu F, Han E. Corrosion protection of AZ91D magnesium alloy with sol-gel coating containing 2-methyl piperidine. Progress in Organic Coatings. 2009;**66**(3):183-191. DOI:

[84] Shi H, Liu F, Han E. Corrosion behaviour of sol–gel coatings doped with cerium salts on 2024-T3 aluminum alloy. Materials Chemistry and Physics. 2010;**124**(1):291-297. DOI:

[85] Ali SM, Allehaibi H. Nano-structured sol–gel coatings as protective films against zinc corrosion in 0.5 M HCl solution. Journal of Saudi Chemical Society. 2017;**21**(4):473-480.

[86] Balan P, Shelton MJ, Ching DOL, Han GC, Pal niandy LK. Modified silane films for corrosion protection of mild steel. Procedia Materials Science. 2014;**6**:244-248. DOI:

[87] Tavandashti NP, Sanjabi S. Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor. Progress in Organic

[88] Asadi N, Naderi R, Saremi M. Determination of optimum concentration of cloisite in an eco-friendly silane sol-gel film to improve corrosion resistance of mild steel. Applied

[89] Naderi R, Fedel M, Deflorian F, Poelman M, Olivier M. Synergistic effect of clay nanoparticles and cerium component on the corrosion behavior of eco-friendly silane sol-gel layer applied on pure aluminum. Surface and Coatings Technology. 2013;**224**:93-100.

Coatings. 2010;**69**(4):384-391. DOI: 10.1016/j.porgcoat.2010.07.012

Clay Science. 2014;**95**:243-251. DOI: 10.1016/j.clay.2014.04.018

Acta Part A. 2009;**73**(5):922-928. DOI: 10.1016/j.saa.2009.04.016

DOI: 10.1016/j.porgcoat.2007.12.004

78 Corrosion Inhibitors, Principles and Recent Applications

10.1016/j.saa.2005.12.040

10.1016/j.tsf.2009.03.099

10.1016/j.porgcoat.2009.07.004

DOI: 10.1016/j.jscs.2016.12.001

10.1016/j.mspro.2014.07.030

DOI: 10.1016/j.surfcoat.2013.03.005

10.1016/j.matchemphys.2010.06.035

The use of corrosion inhibitors has proven to be one of the effective methods of corrosion protection of metals and alloys. Aluminum alloys are good candidate materials for structural components in major industrial application owing to their excellent corrosion resistance. However in high intensity coastal and acidified medium the challenge of micro porosity and hydrogen embrittlement distributed along the interface cannot be neglected as suitable corrosion inhibitive compounds is needful without significantly reacts with the environmental components. The challenges of most effective organic and inorganic Inhibitors when dissolved in aqueous environments are increasingly due to their toxicity. Drug as inhibitive compound have been seen as suitable replacement for this high toxic organic inhibitors since both react by adsorption on a metallic surface. They are usually compounds that form film and cause the formation of precipitates on the metal surface, thereby blocking both cathodic and anodic and sites. Therefore, this study covers the general overview of impact of some drugs as corrosion inhibitive compound on aluminum for industrial applications and their environmental impact.

Keywords: corrosion inhibitors, protection, coastal, acidified, drug and impact

### 1. Introduction

Aluminum is a silvery white material and a member of boron group. It is one of the most abundant metal in the Earth's crust, and the third most abundant element within, after oxygen and silicon. It is yielding, long-lasting, lightweight, malleable metal with physical appearance varying from silvery coloration to approximate gray, which depend on the roughness of the surface. Aluminum is not a Ferro-magnetic material. It is also not soluble in alkanols, despite the fact that, in certain form, it can be water-soluble. It has an appreciable yield strength of

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

releasing excess aluminum into it [12]. Therefore, temperature does have an effect on the corrosion of aluminum. The aluminum subjected to the higher temperature does corrode because of the increase in particles' collision [13]. Corrosion of aluminum depends on environment, design, alloy and preventive measures put into considerations. A dirt-free aluminum surface is highly reactive and will spontaneously react with air or water to form aluminum oxide. This oxide is usually stable and possess excellent adhesion to the surface of metal therefore protects the material (aluminum) from further corrosion or oxidation. Thus aluminum has excellent corrosion resistance in stable oxide layer environments [14]. This oxide layer will be weaken in environments where there is low or high pH particularly, in the presence of aggressive ions. That is, at a pH below 4 and beyond a pH of about 8.5, there will generally be an increase in the aluminum corrosion rate, though this depend on the ions that are present in that particular environment. The oxide layer will be broken down by the aggressive ions locally and localized corrosion attacks start. Of all the ions that display high aggression, chloride ion (Cl) is of the most practical importance [15]. From thermodynamically point of consideration aluminum is a metal with high activity. Nevertheless, in aerated environment, the metal is rapidly covered with an intense oxide layer [16]. This oxide layer is basically inert, and prevents further oxidation. The thickness of this layer depends largely on the temperature, environment and alloy elements. The oxide films that are formed in air at ordinary room temperature are about 2.5 nm of thickness on pure aluminum. Heating to about 400C may results in films up to about 25 nm (this is about 10 times that at room temperature [17]. If the oxide film is destroyed, e.g. by a scratch, new oxide will spontaneously and immediately form on the uncovered metal [18]. Thus pure and even many of its alloys display excellent perfor-

The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium

http://dx.doi.org/10.5772/intechopen.72942

81

Major reason for alloying aluminum is to increase hardness, strength and resistance to fatigue, stress relaxation, wear or creep. The Effects of different alloying elements and combinations of them on these properties are specific and related to the phase diagrams of constituent alloy

Figure 1 shows the relationships between some of the more commonly used alloys in the 6xxx series. The elements that are most frequently used in commercial aluminum alloys to provide better strength especially, when related to strain hardening via cold working or heat treatment, or both are; zinc, copper, silicon, magnesium and manganese (Figure 2). All these elements have high solid solubility in aluminum, and usually, the solubility increases as temperature

Aluminum and its alloys possess significant industrial and economic value due to its light weight, good thermal and electrical conductivity as well as low cost [20]. The most important property of aluminum is its ability to effectively resist atmospheric and several aqueous solution because of the quick formation of protective oxide of thin film which adhere tenaciously to the surface, that serves as barrier between the corrosive environment and the metal.

mance in corrosion protection.

3. Aluminum alloy

elements.

increases.

Table 1. Analysis of inhibitive drugs and their performance.

about 10 MPa for the pure metal, while that of its alloys can range from about 150 to 650 MPa. Aluminum is about 33% dense and stiff in comparing to steel.

The machinability and formability of aluminum is excellent with outstanding corrosion resistance due to its ability to form an effective and tenacious thin surface layer of its oxide in atmosphere. It is also noteworthy that the strongest alloys aluminum are less corrosion resistant because of the possibility internal galvanic cell that may be developed in service [1]. This corrosion resistance is also often greatly reduced in the presence of various salts or dissimilar metals and often corrosion of aluminum can be mitigated using corrosion inhibitors, even the use of inhibitive drugs (Table 1).

## 2. Passivity of pure aluminum and its alloys

#### 2.1. Corrosion of aluminum

Al has a reactive metal, can react with acidic, basic or salty foods to release itself into the food product. Also, an aluminum container that is worn out or pitted may contaminate the food by releasing excess aluminum into it [12]. Therefore, temperature does have an effect on the corrosion of aluminum. The aluminum subjected to the higher temperature does corrode because of the increase in particles' collision [13]. Corrosion of aluminum depends on environment, design, alloy and preventive measures put into considerations. A dirt-free aluminum surface is highly reactive and will spontaneously react with air or water to form aluminum oxide. This oxide is usually stable and possess excellent adhesion to the surface of metal therefore protects the material (aluminum) from further corrosion or oxidation. Thus aluminum has excellent corrosion resistance in stable oxide layer environments [14]. This oxide layer will be weaken in environments where there is low or high pH particularly, in the presence of aggressive ions. That is, at a pH below 4 and beyond a pH of about 8.5, there will generally be an increase in the aluminum corrosion rate, though this depend on the ions that are present in that particular environment. The oxide layer will be broken down by the aggressive ions locally and localized corrosion attacks start. Of all the ions that display high aggression, chloride ion (Cl) is of the most practical importance [15]. From thermodynamically point of consideration aluminum is a metal with high activity. Nevertheless, in aerated environment, the metal is rapidly covered with an intense oxide layer [16]. This oxide layer is basically inert, and prevents further oxidation. The thickness of this layer depends largely on the temperature, environment and alloy elements. The oxide films that are formed in air at ordinary room temperature are about 2.5 nm of thickness on pure aluminum. Heating to about 400C may results in films up to about 25 nm (this is about 10 times that at room temperature [17]. If the oxide film is destroyed, e.g. by a scratch, new oxide will spontaneously and immediately form on the uncovered metal [18]. Thus pure and even many of its alloys display excellent performance in corrosion protection.

## 3. Aluminum alloy

about 10 MPa for the pure metal, while that of its alloys can range from about 150 to 650 MPa.

S/N Research work Result Reference

concentration

molecules

temperature

The result showed that the drug excellently inhibited the aluminum in the acid medium at 303 K

The result indicated 92% inhibitive efficiency at 30C

The results pointed out that both drug server as

excellent inhibitors in the Medium

and 83% at 60C using 100 ppm inhibitor

Corrosion potential (Ecorr) was shifted to the direction that is more noble by the Inhibitor

It was deduced that chloroquine excellently inhibited the aluminum in the acidic environment and the efficiency of the inhibitor increased with concentration of inhibitor but not favored by

From the result, the inhibition efficiency displayed direct variation with inhibitor's concentration but demonstrated inverse relation with temperature

The result showed that Aloe Vera is potential green corrosion inhibitor in saline environment

The result showed the potential of the Omeprazole drug in inhibiting corrosion in the basic environment

The result displayed the antifungal drug as potential inhibitor of aluminum in the acidic environment

The result showed the extract as eco-friendly inhibitor in the acidic environment

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

The machinability and formability of aluminum is excellent with outstanding corrosion resistance due to its ability to form an effective and tenacious thin surface layer of its oxide in atmosphere. It is also noteworthy that the strongest alloys aluminum are less corrosion resistant because of the possibility internal galvanic cell that may be developed in service [1]. This corrosion resistance is also often greatly reduced in the presence of various salts or dissimilar metals and often corrosion of aluminum can be mitigated using corrosion inhibitors, even the

Al has a reactive metal, can react with acidic, basic or salty foods to release itself into the food product. Also, an aluminum container that is worn out or pitted may contaminate the food by

Aluminum is about 33% dense and stiff in comparing to steel.

2. Passivity of pure aluminum and its alloys

use of inhibitive drugs (Table 1).

1 Meclizine (Antihistaminic Drug) as Corrosion Inhibitors of Aluminum in HCl Environment

80 Corrosion Inhibitors, Principles and Recent Applications

2 Clotrimazole and Fluconazole (Antifungal drugs) as Corrosion Inhibitors of Aluminum in

3 Amine Compound as Corrosion Inhibitors of Aluminum in HCl Environment

4 Voltaren (expired) Drug to inhibit Aluminum in

5 Domiana Extract as inhibitor of Aluminum in

6 Corrosion Inhibitor of Aluminum using Chloroquine in HCl Environment Media

7 Corrosion Inhibitor of Aluminum using Aloe

8 Corrosion inhibition of Aluminum Alloy in NaOH Medium using Anti-inflammatory drug

9 Corrosion inhibition of Aluminum using Fluconazole & Clotrimazole in HCl Medium

10 Corrosion inhibition of Aluminum using green corrosion inhibitor in acidic medium

Table 1. Analysis of inhibitive drugs and their performance.

HCl Environment

HCl Environment

Acidic medium

Vera in NaCl medium

2.1. Corrosion of aluminum

Major reason for alloying aluminum is to increase hardness, strength and resistance to fatigue, stress relaxation, wear or creep. The Effects of different alloying elements and combinations of them on these properties are specific and related to the phase diagrams of constituent alloy elements.

Figure 1 shows the relationships between some of the more commonly used alloys in the 6xxx series. The elements that are most frequently used in commercial aluminum alloys to provide better strength especially, when related to strain hardening via cold working or heat treatment, or both are; zinc, copper, silicon, magnesium and manganese (Figure 2). All these elements have high solid solubility in aluminum, and usually, the solubility increases as temperature increases.

Aluminum and its alloys possess significant industrial and economic value due to its light weight, good thermal and electrical conductivity as well as low cost [20]. The most important property of aluminum is its ability to effectively resist atmospheric and several aqueous solution because of the quick formation of protective oxide of thin film which adhere tenaciously to the surface, that serves as barrier between the corrosive environment and the metal.

Figure 1. Relationships that exist among commonly used alloys in the 6xxx series (Al-Si-Mg). Their yield strength (YS) and tensile strength (TS) in ksi units [19].

The reaction is in line with the position of aluminum in the redox strength of metals (Figure 3). It has been observed that this film (oxide) is stable at a range of about 5–9 range of pH [21].

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83

Aluminum usually suffers pitting corrosion in the presence of chloride ions. Pitting corrosion is a dangerous form of localized corrosion that selectively attacks areas of a metal surface where there is; (i) a surface scratch or a mechanically induced break in an otherwise protective film, (ii) an emerging dislocation or slip step caused by applied or residual stresses and (iii) a compositional heterogeneity such as an inclusion, segregate or precipitate [22]. Pitting is one of the most insidious forms of corrosion. It is very destructive to many engineering materials since it causes perforation of the metal. As a result of its localized nature, it often causes sudden unexpected failures. Pitting is often difficult to detect because corrosion products may cover small pits.

General illustration of pitting corrosion on aluminum alloys is shown in Figure 4.

4. Pitting corrosion of aluminum

Figure 3. Aluminum in the redox strength of metals.

Figure 2. The principal aluminum alloys [19].

The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium http://dx.doi.org/10.5772/intechopen.72942 83

Figure 3. Aluminum in the redox strength of metals.

The reaction is in line with the position of aluminum in the redox strength of metals (Figure 3). It has been observed that this film (oxide) is stable at a range of about 5–9 range of pH [21].

## 4. Pitting corrosion of aluminum

Figure 2. The principal aluminum alloys [19].

and tensile strength (TS) in ksi units [19].

82 Corrosion Inhibitors, Principles and Recent Applications

Figure 1. Relationships that exist among commonly used alloys in the 6xxx series (Al-Si-Mg). Their yield strength (YS)

Aluminum usually suffers pitting corrosion in the presence of chloride ions. Pitting corrosion is a dangerous form of localized corrosion that selectively attacks areas of a metal surface where there is; (i) a surface scratch or a mechanically induced break in an otherwise protective film, (ii) an emerging dislocation or slip step caused by applied or residual stresses and (iii) a compositional heterogeneity such as an inclusion, segregate or precipitate [22]. Pitting is one of the most insidious forms of corrosion. It is very destructive to many engineering materials since it causes perforation of the metal. As a result of its localized nature, it often causes sudden unexpected failures. Pitting is often difficult to detect because corrosion products may cover small pits. General illustration of pitting corrosion on aluminum alloys is shown in Figure 4.

Figure 4. General illustration of pitting corrosion on aluminum alloys [18].

## 5. Corrosion inhibitors

Corrosion inhibitors have been established to be effective and easier means of corrosion control. Using chemical inhibitors to reduce the rate of corrosion processes is somewhat amenable. Corrosion inhibitors found applications in various industries, examples are; oil and gas, chemical industries, production, refineries, heavy manufacturing, water treatment and etc. [23]. In extraction the oil, chemical and processing industries, the use of corrosion inhibitors are usually considered to be the primary line of protection. Therefore, a large numbers of scientific research have been concentrated to the issue of corrosion inhibitors [24–29]. Table 1 shows application of corrosion inhibitors in some specific system environment. An inhibitor is a chemical substance or mixture of substances which when added in very little concentrations to a corrosive environment, it effectively retards or prevents corrosion without significantly reacts with the environmental components.

Inhibitors can be classified as either organic or inorganic compounds and they are usually dissolved in aqueous environments. Some of the most effective inorganic inhibitors are carbonates, chromates, nitrites, silicates and phosphates. The organic inhibitors comprise amines, nitrogen compounds, sulfur compounds such as thioethers, thioalcohols, thioamides, thiourea and hydrazine. Chromates and zinc salts are used increasingly less due to their toxicity and are currently largely replaced by organic inhibitors.

are being used as inhibitor in concrete reinforcement. While the organic inhibitors react by

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Figure 6. Adsorption mechanism of an organic inhibitor on an aluminum surface in an aqueous environment.

Anodic inhibitors generally act by forming a protective oxide film on the surface of the metal to be protected resulting in a large anodic shift of the Ecorr (corrosion potential). This shift usually forces the surface of metal into the region of passivation. That is, they slow down the anodic dissolution reaction rate of and produce products of reaction which form a thin film over

Cathodic inhibitors usually work by either slowing down the cathodic reaction or precipitating (selectively) on cathodic regions to inhibit the diffusion of reducing parts to the surface. That is, they interrupt the flow of electrons from the anode to the cathode and produce products of reaction which precipitate selectively at cathodic sites. Examples are zinc sulfate, nickel sulfate,

anode. Examples are; Chromates, nitrates, tungstate and molybdates.

adsorption on a metallic surface.

Figure 5. Classification of corrosion inhibition.

aminoethylene and polyphosphate.

Also, with reference to their influence on the electrochemical reaction relating to metal, and their environment corrosion inhibitors (the inorganic inhibitors) can also be classified as anodic, cathodic or mixed corrosion inhibitors (Figure 5). Figure 6 displays the adsorption mechanism of an organic inhibitors on aluminum. These have been in application for quite some years and the most common examples of their uses are in films and coatings on metals where chromate, nitrate, borates, phosphate, benzoates, and oxides are incorporated, Nitrites The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium http://dx.doi.org/10.5772/intechopen.72942 85

Figure 5. Classification of corrosion inhibition.

5. Corrosion inhibitors

84 Corrosion Inhibitors, Principles and Recent Applications

Figure 4. General illustration of pitting corrosion on aluminum alloys [18].

reacts with the environmental components.

currently largely replaced by organic inhibitors.

Corrosion inhibitors have been established to be effective and easier means of corrosion control. Using chemical inhibitors to reduce the rate of corrosion processes is somewhat amenable. Corrosion inhibitors found applications in various industries, examples are; oil and gas, chemical industries, production, refineries, heavy manufacturing, water treatment and etc. [23]. In extraction the oil, chemical and processing industries, the use of corrosion inhibitors are usually considered to be the primary line of protection. Therefore, a large numbers of scientific research have been concentrated to the issue of corrosion inhibitors [24–29]. Table 1 shows application of corrosion inhibitors in some specific system environment. An inhibitor is a chemical substance or mixture of substances which when added in very little concentrations to a corrosive environment, it effectively retards or prevents corrosion without significantly

Inhibitors can be classified as either organic or inorganic compounds and they are usually dissolved in aqueous environments. Some of the most effective inorganic inhibitors are carbonates, chromates, nitrites, silicates and phosphates. The organic inhibitors comprise amines, nitrogen compounds, sulfur compounds such as thioethers, thioalcohols, thioamides, thiourea and hydrazine. Chromates and zinc salts are used increasingly less due to their toxicity and are

Also, with reference to their influence on the electrochemical reaction relating to metal, and their environment corrosion inhibitors (the inorganic inhibitors) can also be classified as anodic, cathodic or mixed corrosion inhibitors (Figure 5). Figure 6 displays the adsorption mechanism of an organic inhibitors on aluminum. These have been in application for quite some years and the most common examples of their uses are in films and coatings on metals where chromate, nitrate, borates, phosphate, benzoates, and oxides are incorporated, Nitrites

Figure 6. Adsorption mechanism of an organic inhibitor on an aluminum surface in an aqueous environment.

are being used as inhibitor in concrete reinforcement. While the organic inhibitors react by adsorption on a metallic surface.

Anodic inhibitors generally act by forming a protective oxide film on the surface of the metal to be protected resulting in a large anodic shift of the Ecorr (corrosion potential). This shift usually forces the surface of metal into the region of passivation. That is, they slow down the anodic dissolution reaction rate of and produce products of reaction which form a thin film over anode. Examples are; Chromates, nitrates, tungstate and molybdates.

Cathodic inhibitors usually work by either slowing down the cathodic reaction or precipitating (selectively) on cathodic regions to inhibit the diffusion of reducing parts to the surface. That is, they interrupt the flow of electrons from the anode to the cathode and produce products of reaction which precipitate selectively at cathodic sites. Examples are zinc sulfate, nickel sulfate, aminoethylene and polyphosphate.

Mixed inhibitors act by reducing both the anodic and cathodic reactions. They are usually compounds that form film and cause the formation of precipitates on the metal surface, thereby blocking both cathodic and anodic and sites. Common examples are the phosphates and silicates.

Therefore, this study deals with general overview of aluminum, corrosion inhibitors, their classifications, Inhibitive drugs, considerations in employing them, their efficiency industrial applications and their environmental impact.

## 6. Properties of a good inhibitor

In order to prevent or mitigate the corrosion of materials (metallic), inhibitors in question must be able to satisfy these following measures [26]:

## 7. Drug inhibitors

Typical examples of organic eco-friendly inhibitors are fast green and carmine. The molecules of fast green have aromatic ring with electroactive nitrogen and oxygen atoms while molecules of carmine have aromatic rings (electron rich) with electroactive oxygen atoms. These molecular structures are shown in Figure 7. These compounds are adsorbed at the metal surface and they block the active site and consequently, decreasing the corrosion rate and consequently increase the inhibition efficiency [30]. Nevertheless, Most of organic inhibitors are poisonous and harmful to the environment. The increasing health and ecological awareness have drawn the attentions toward research and development of very effective and efficient eco-friendly inhibitors.

Therefore it is vital and essential to develop cheap and environmentally secure corrosion inhibitors [32, 33]. Recently drugs have now been used as corrosion inhibitors. According to Gece [34], the use of drugs as corrosion inhibitors of metals corrosion possesses some merits over using some inorganic/organic inhibitors because of their little or insignificant impact on the environment. Drugs are nontoxic, cheap, negligible negative effects on environment, so it

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Figure 7. Structure of (a) carmine and (b) fast green [31].

The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium http://dx.doi.org/10.5772/intechopen.72942 87

Mixed inhibitors act by reducing both the anodic and cathodic reactions. They are usually compounds that form film and cause the formation of precipitates on the metal surface, thereby blocking both cathodic and anodic and sites. Common examples are the phosphates

Therefore, this study deals with general overview of aluminum, corrosion inhibitors, their classifications, Inhibitive drugs, considerations in employing them, their efficiency industrial

In order to prevent or mitigate the corrosion of materials (metallic), inhibitors in question must

i. It must be effective in corrosion protection at a very little concentration of the inhibitor. ii. It must offer protection to all the part of the component that are exposed from the

iii. It must maintain its effectiveness at extreme operating conditions (high velocity and

iv. During application, over or under dosage of inhibitor, the rate of corrosion must not

v. The inhibitor or inhibitor's products must not form any deposit on the surface metal

Typical examples of organic eco-friendly inhibitors are fast green and carmine. The molecules of fast green have aromatic ring with electroactive nitrogen and oxygen atoms while molecules of carmine have aromatic rings (electron rich) with electroactive oxygen atoms. These molecular structures are shown in Figure 7. These compounds are adsorbed at the metal surface and they block the active site and consequently, decreasing the corrosion rate and consequently increase the inhibition efficiency [30]. Nevertheless, Most of organic inhibitors are poisonous and harmful to the environment. The increasing health and ecological awareness have drawn the attentions toward research and development of very effective and efficient eco-friendly

and silicates.

applications and their environmental impact.

be able to satisfy these following measures [26]:

especially at regions of heat transfer.

vii. The range of effectiveness should be long.

vi. It must mitigate both localized and uniform corrosion.

viii. It must not pose health hazard or pollution potential.

6. Properties of a good inhibitor

86 Corrosion Inhibitors, Principles and Recent Applications

corrosion attack of corrosion.

temperature).

7. Drug inhibitors

inhibitors.

drastically increased.

Therefore it is vital and essential to develop cheap and environmentally secure corrosion inhibitors [32, 33]. Recently drugs have now been used as corrosion inhibitors. According to Gece [34], the use of drugs as corrosion inhibitors of metals corrosion possesses some merits over using some inorganic/organic inhibitors because of their little or insignificant impact on the environment. Drugs are nontoxic, cheap, negligible negative effects on environment, so it

suggested replacing the traditional toxic corrosion inhibitors [35]. Many Researchers in this field generally agree that drugs are corrosion inhibitors that can compete favorably with discovered green corrosion inhibitors and that most of these drugs can be synthesized from natural products. The choice of some drugs used as corrosion inhibitors is based on the following: (a) drug molecules contain oxygen, nitrogen and sulfur as the main active centers, (b) drugs are reported to be environmental friendly and important in biological reactions and (c) some drugs are easy to produced. Therefore, it has been established from research findings that, since majority of these drugs are natural product or plants extracts have been discovered to accomplish the aim of employing a cheap, environmentally suitable, abundantly available and effective high inhibition efficiency and little or insignificant environmental impact. Tables 2 and 3 reveal application of corrosion in specific system environment and examples of drugs (quinolones) commonly used as corrosion inhibitors in our common environment respectively [34]. Nowadays, studies are now focusing on using pharmaceutical drugs nontoxic corrosion inhibitors to slow down the corrosion of metals and their alloys. For instance, Abdallah [36] used rhodanine azosulpha drugs to inhibit the corrosion of 304 stainless steel in HCl solution, [37] also anti-bacterial drug to control the deterioration of aluminum in HCl solution. Similarly, Obot and Obi–Egbedi [38] used antihypertensive drugs to slow down the corrosion of aluminum and aluminum alloys in aqueous solutions.

[10, 11]. The criteria used in selection of these drugs as corrosion inhibitors depend on the following (i) whether the molecules contain sulfur, oxygen and nitrogen as active centers, (ii)

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the ease of production as well as purification. (iii) They are eco-friendly.

Table 2. Application of corrosion inhibitors in specific system environment [24].

The presence of benzene ring in the molecules and heterocycles like pyridine, thiophenes, isoxazoles, others that present in drugs has sensitized researchers all over the world to intensifying their investigation of drug compounds as green corrosion inhibitors as save alternative to the conventional toxic corrosion inhibitors [39].

A number of studies have reported the use of drugs particularly antibacterial as corrosion inhibitors [40]. For instance, Eddy and Ebenso [40] investigated on Corrosion Inhibition and Adsorption Characteristics of Tarivid on Mild Steel in H2SO4 using thermometric and gasometric methods. Their finding showed that tarivid drug inhibits the deterioration of mild steel in the acid environment (H2SO4). The inhibition efficiency of tarivid was established to increase in values as its concentration increased however; it decreased as the temperature increases. The mechanism of physical adsorption was proposed from the acquired kinetic and thermodynamic factors. Also, Langmuir isotherm adsorption model was followed. Abdallah [36] studied the effect of Rhodanine azosulpha drugs as corrosion inhibitors on the corrosion of 304 stainless steel in HCl environment using gravimetry and potentiodynamic methods. Parallel adsorption technique was used for the inhibition process on the steel surface because of the presence of multiactive center within the molecules of the inhibitor.

Solmaz et al. [41] have shown that Rhodanine is a good corrosion inhibitor for low carbon steel in hydrochloric acid. They used electrochemical techniques for the corrosion findings.

The effect of a number of antibiotic drugs, like; spectinomycin, paromomycin and streptomycin on the corrosion performance of zinc metal in hydrochloric acid environment was studied by [42], using some electrochemical and gravimetric techniques. The percentage of inhibition efficiency was discovered to be increasing as the concentration of drug increases but decreases with temperature. It has been discovered that majority of the drugs used display vital roles in biological reactions due to their antibacterial, anticonvulsant, antidiabetic, and other properties [10, 11]. The criteria used in selection of these drugs as corrosion inhibitors depend on the following (i) whether the molecules contain sulfur, oxygen and nitrogen as active centers, (ii) the ease of production as well as purification. (iii) They are eco-friendly.

suggested replacing the traditional toxic corrosion inhibitors [35]. Many Researchers in this field generally agree that drugs are corrosion inhibitors that can compete favorably with discovered green corrosion inhibitors and that most of these drugs can be synthesized from natural products. The choice of some drugs used as corrosion inhibitors is based on the following: (a) drug molecules contain oxygen, nitrogen and sulfur as the main active centers, (b) drugs are reported to be environmental friendly and important in biological reactions and (c) some drugs are easy to produced. Therefore, it has been established from research findings that, since majority of these drugs are natural product or plants extracts have been discovered to accomplish the aim of employing a cheap, environmentally suitable, abundantly available and effective high inhibition efficiency and little or insignificant environmental impact. Tables 2 and 3 reveal application of corrosion in specific system environment and examples of drugs (quinolones) commonly used as corrosion inhibitors in our common environment respectively [34]. Nowadays, studies are now focusing on using pharmaceutical drugs nontoxic corrosion inhibitors to slow down the corrosion of metals and their alloys. For instance, Abdallah [36] used rhodanine azosulpha drugs to inhibit the corrosion of 304 stainless steel in HCl solution, [37] also anti-bacterial drug to control the deterioration of aluminum in HCl solution. Similarly, Obot and Obi–Egbedi [38] used antihypertensive drugs to slow

down the corrosion of aluminum and aluminum alloys in aqueous solutions.

of the presence of multiactive center within the molecules of the inhibitor.

to the conventional toxic corrosion inhibitors [39].

88 Corrosion Inhibitors, Principles and Recent Applications

The presence of benzene ring in the molecules and heterocycles like pyridine, thiophenes, isoxazoles, others that present in drugs has sensitized researchers all over the world to intensifying their investigation of drug compounds as green corrosion inhibitors as save alternative

A number of studies have reported the use of drugs particularly antibacterial as corrosion inhibitors [40]. For instance, Eddy and Ebenso [40] investigated on Corrosion Inhibition and Adsorption Characteristics of Tarivid on Mild Steel in H2SO4 using thermometric and gasometric methods. Their finding showed that tarivid drug inhibits the deterioration of mild steel in the acid environment (H2SO4). The inhibition efficiency of tarivid was established to increase in values as its concentration increased however; it decreased as the temperature increases. The mechanism of physical adsorption was proposed from the acquired kinetic and thermodynamic factors. Also, Langmuir isotherm adsorption model was followed. Abdallah [36] studied the effect of Rhodanine azosulpha drugs as corrosion inhibitors on the corrosion of 304 stainless steel in HCl environment using gravimetry and potentiodynamic methods. Parallel adsorption technique was used for the inhibition process on the steel surface because

Solmaz et al. [41] have shown that Rhodanine is a good corrosion inhibitor for low carbon steel

The effect of a number of antibiotic drugs, like; spectinomycin, paromomycin and streptomycin on the corrosion performance of zinc metal in hydrochloric acid environment was studied by [42], using some electrochemical and gravimetric techniques. The percentage of inhibition efficiency was discovered to be increasing as the concentration of drug increases but decreases with temperature. It has been discovered that majority of the drugs used display vital roles in biological reactions due to their antibacterial, anticonvulsant, antidiabetic, and other properties

in hydrochloric acid. They used electrochemical techniques for the corrosion findings.

Table 2. Application of corrosion inhibitors in specific system environment [24].

S/N Drug (used as corrosion

The molecular structure

The clinical usage

Antimalarial

 pneumonia

 Mixed

 Acidic (HCl)

 Class of

Type of

environment

inhibitor

(corrosive medium)

inhibitor)

6 7. 8. 9. Table 3.

Examples of drugs

(quinolones)

 commonly

 used as corrosion inhibitors [35].

Enrofloxacin

Infections in urinary

Mixed

 Saline (NaCl)

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tracts

Sparfloxacin

Urinary tracts, Typhoid

Adsorption

 Acidic (HCl and H2SO4)

The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium

Fever, Bones

Amifloxacin

Typhoid fever, Diarrhea

Mixed

 Saline (NaCl)

(infectious)

S/N Drug (used as corrosion

The molecular structure

The clinical usage Typhoid fever, Prostatitis,

Diarrhea

 Class of

Type of

environment

inhibitor

Mixed

 Saline (NaCl)

(corrosive medium)

inhibitor)

1. 2. Ofloxacin 3. Quinoline 4. Quinaldic acid

5. Quinaldine

Antimalarial

Mixed

 Acidic (HCl)

Antimalarial Antimalarial

Mixed

 Acidic (HCl)

Mixed

 Acidic (HCl)

Urethritis, Gonorrhea,

Mixed

 Acidic (HCl)

90 Corrosion Inhibitors, Principles and Recent Applications

Cervicitis

Ciprofloxacin

The Impact of Drugs as Corrosion Inhibitors on Aluminum Alloy in Coastal-Acidified Medium http://dx.doi.org/10.5772/intechopen.72942 91

## Author details

Ojo Sunday Isaac Fayomi1,2\*, Paul Apeye Lucky Anawe3 and Ayodele Daniyan4

\*Address all correspondence to<EMAIL_ADDRESS>
1 Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa

[10] Abood HA. The study of the inhibitory properties of Omeprazole on the corrosion of

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[11] Uma K, Rekha S. Investigation and inhibition of aluminium corrosion in methane sulphonic acid solution by organic compound. Journal of Chemical and Pharmaceutical

[12] Hackerman N, Hurd RM. Corrosion Inhibition and Molecular Structure, First International Congress on Metallic Corrosion. London: Butterworth; 1962. pp. 166-172

[13] Norayan R. An Introduction to Metallic Corrosion and Its Prevention. New Delhi: Oxford

[15] Jones DA. Principles and Prevention of Corrosion. 2nd ed. New Jersey, United States:

[16] Pourbaix M. Atlas of Electrochemical Equilibria in Aqueous Solutions. Huston: NACE

[17] Shimizu K, Furneaux RC, Thompson GE, Wood GC, Gotoh A, Kobayashi K. On the nature of "easy paths" for the diffusion of oxygen in thermal oxide films on aluminium.

[18] Davis JR et al., editor. Metals Handbook. Vol. 13. 9th ed. Ohio: ASM International; 1987.

[19] Davis JR. Alloying: Understanding the Basics. Ohio, USA: ASM International; 2001. pp.

[20] Fouda AS, Abdallah M, Eissa M. Corrosion inhibition of Aluminum in 1 M phosphoric acid solutions using some Chalcones derivatives and synergistic action with halide ions. African Journal of Pure and Applied Chemistry. 2013;7(12):394-404. DOI: 10.5897/

[21] Mazhar AA, Badaway WA, Abou-Romia MM. Impedance studies of corrosion resistance of aluminium in chloride media. Surface and Coatings Technology. 1986;29:335-345 [22] Baker MA, Castle JE. The initiation of pitting corrosion at MnS inclusion. Corrosion

[23] Van Delinder LS. Corrosion Inhibitors Basics: An Introduction. Houston, Texas, USA:

[24] Corrosion inhibitors www.chemia.odlew.agh.edu.pl/dydaktyka/Dokumenty/Corrosion/

[26] Yurt A, Balaban A, Kandemir SU, Bereket G, Erk B. Investigation on some Schiff bases as HCl corrosion inhibitors for carbon steel. Materials Chemistry and Physics. 2004;85:

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4 Department of Materials Science and Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria

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92 Corrosion Inhibitors, Principles and Recent Applications

Ojo Sunday Isaac Fayomi1,2\*, Paul Apeye Lucky Anawe3 and Ayodele Daniyan4

1 Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of

2 Department of Mechanical Engineering, Covenant University, Ota, Ogun State, Nigeria 3 Department of Petroleum Engineering, Covenant University, Ota, Ogun State, Nigeria

4 Department of Materials Science and Engineering, Obafemi Awolowo University, Ile-Ife,

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[3] Obot IB, Obi-Egbedi NO, Umoren SA. Antifungal drugs as corrosion inhibitors for

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**Chapter 5**

**Provisional chapter**

**Corrosion Inhibitors for Reinforced Concrete: A Review**

The objective of the topic is to review the recent trends in corrosion inhibitors for reinforced concrete and their application in the laboratory and field conditions. Inhibitors are chemical substances which when added to the concrete in small concentrations will inhibit or prolong the time to initiation of corrosion in concrete structures. This chapter focuses on the type of inhibitors used in concrete based upon their mode of action and the way of application. The section deals with anodic, cathodic, mixed inhibitors; performance of admixed inhibitor vs. migrating/surface applied inhibitor and their evaluation studies; and electrochemical injection of corrosion inhibitor (EICI) in concrete and elec-

**Keywords:** anodic inhibitors, cathodic inhibitors, mixed inhibitors, organic inhibitors,

Corrosion of steel in concrete structures plays a significant role in affecting the service life of the concrete structures. Various methods have been developed with the intent of preventing the corrosion and to enhance the service life. The methods include the coating to the concrete surface, the coating to the reinforcement, cathodic protection, electrochemical methods, alternative reinforcement, and corrosion inhibitors. Among all the available techniques, the use of corrosion inhibitors is one of the most appropriate and efficient methods for corrosion protection of reinforced concrete structures due to the easy operation, low cost, and excellent corrosion resistance effect [1–8]. Inhibitors which are added to the concrete in small concentrations are intended to delay and slow the onset of corrosion in reinforced concrete. Most of the inhibitors act by stabilizing the steel surface by forming the protective film, and some

**Corrosion Inhibitors for Reinforced Concrete: A Review**

DOI: 10.5772/intechopen.72572

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Han-Seung Lee, Velu Saraswathy,

Subbiah Karthick

**Abstract**

**1. Introduction**

http://dx.doi.org/10.5772/intechopen.72572

Seung-Jun Kwon and Subbiah Karthick

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Han-Seung Lee, Velu Saraswathy, Seung-Jun Kwon and

trochemical chloride extraction techniques has been reviewed.

migrating inhibitors, electrochemical injection, reinforced concrete

**Provisional chapter**

## **Corrosion Inhibitors for Reinforced Concrete: A Review**

**Corrosion Inhibitors for Reinforced Concrete: A Review**

DOI: 10.5772/intechopen.72572

#### Han-Seung Lee, Velu Saraswathy, Seung-Jun Kwon and Subbiah Karthick Subbiah Karthick Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Han-Seung Lee, Velu Saraswathy, Seung-Jun Kwon and

http://dx.doi.org/10.5772/intechopen.72572

#### **Abstract**

[27] Musa AY, Jalgham RTT, Mohamad AB. Molecular dynamic and quantum chemical calculations for phthalazine derivatives as corrosion inhibitors of mild steel in 1M HCl.

[29] Thomas JGN. The Mechanism of Corrosion. Oxford, UK: Butterworths Heinemann; 1994 [30] Hegazy MA, Abdallah M, Awad MK, Rezk M. Part I: Experimental results. Corrosion

[31] Prabhu RA, Shanbhag AV, Venkatesha TV. Influence of tramadol [2-[(dimethylamino) methyl]-1-(3-methoxyphenyl) cyclohexanol hydrate] on corrosion inhibition of mild steel

[32] Loto RT, Loto CA, Popoola API. Corrosion inhibition of thiourea and thiadiazole derivatives: A review. Journal of Materials and Environmental Science. 2012;3:885-894

[33] Ladha DG, Naik UJ, Shah NK. Investigation of cumin (Cuminum cyminum) extract as an eco-friendly green corrosion inhibitor for pure Aluminium in acid medium. Journal of

[34] Gece G. Drugs: A review of promising novel corrosion inhibitors. Corrosion Science.

[35] Mahdi AS. Amoxicillin as green corrosion inhibitor for concrete reinforced steel in simulated concrete pore solution containing chloride. International Journal of Advanced

[36] Abdallah M. Rhodanine azosulpha drugs as corrosion inhibitors for corrosion of 304 stainless steel in hydrochloric acid solution. Corrosion Science. 2002;44(4):717-728 [37] Abdallah M. Antibacterial drugs as corrosion inhibitors for corrosion of aluminium in

[38] Obot IB, Obi-Egbedi NO. Fluconazole as an inhibitor for aluminium corrosion in 0.1 M HCl. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2008;330:

[39] Khan G, Newaz KS, Basirun WJ, Ali HB, Faraj FL, Khan GM. Application of natural product extracts as green corrosion inhibitors for metals and alloys in acid pickling processes - A review. International Journal of Electrochemical Science. 2015;10:6120-6134

[40] Eddy NO, Ebenso EE. Corrosion inhibition and adsorption characteristics of tarivid on

[41] Solmaz R, Kardas G, Yazici B, Erbil M. Inhibition effect of rhodanine for corrosion of mild

[42] Abdallah M, Zaafarany BA, Jahdaly AL. Corrosion inhibition of zinc in hydrochloric acid using some antibiotic drugs. Journal of Materials and Environmental Science. 2016;7(4):

steel in hydrochloric acid solution. Protection of Metals. 2005;41(6):581-585

in acidic media. Journal of Applied Electrochemistry. 2007;37:491-497

Materials and Environmental Science. 2013;4:701-708

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hydrochloric solution. Corrosion Science. 2004;46(8):1981-1996

mild steel in H2SO4. E-Journal of Chemistry. 2010;7(1):442-448

[28] Rosenfeld IL. Corrosion Inhibitors. New York: McGraw-Hill; 1977

Corrosion Science. 2012;56:176-183

94 Corrosion Inhibitors, Principles and Recent Applications

Science. 2014;81:54-64

2011;53(12):3873-3898

207-212

1107-1118

The objective of the topic is to review the recent trends in corrosion inhibitors for reinforced concrete and their application in the laboratory and field conditions. Inhibitors are chemical substances which when added to the concrete in small concentrations will inhibit or prolong the time to initiation of corrosion in concrete structures. This chapter focuses on the type of inhibitors used in concrete based upon their mode of action and the way of application. The section deals with anodic, cathodic, mixed inhibitors; performance of admixed inhibitor vs. migrating/surface applied inhibitor and their evaluation studies; and electrochemical injection of corrosion inhibitor (EICI) in concrete and electrochemical chloride extraction techniques has been reviewed.

**Keywords:** anodic inhibitors, cathodic inhibitors, mixed inhibitors, organic inhibitors, migrating inhibitors, electrochemical injection, reinforced concrete

#### **1. Introduction**

Corrosion of steel in concrete structures plays a significant role in affecting the service life of the concrete structures. Various methods have been developed with the intent of preventing the corrosion and to enhance the service life. The methods include the coating to the concrete surface, the coating to the reinforcement, cathodic protection, electrochemical methods, alternative reinforcement, and corrosion inhibitors. Among all the available techniques, the use of corrosion inhibitors is one of the most appropriate and efficient methods for corrosion protection of reinforced concrete structures due to the easy operation, low cost, and excellent corrosion resistance effect [1–8]. Inhibitors which are added to the concrete in small concentrations are intended to delay and slow the onset of corrosion in reinforced concrete. Most of the inhibitors act by stabilizing the steel surface by forming the protective film, and some

inhibitors react with concrete forming the complex thus reducing the permeability of the concrete. Corrosion inhibitors are generally used as admixtures in concrete for new construction, but they can also be utilized for repairs by admixed with concrete for patches, sprayed onto the surface of the concrete or applied by saturation treatment [9–13].

As per NACE international, "a corrosion inhibitor is a substance when added to an environment, either continuously or intermittently to prevent corrosion by forming a passive film on the metal." In other processing industries, inhibitors are the first line of defense against corrosion [14].

Inhibitors slow down the corrosion process by:

#### **1.1. Classification of corrosion inhibitors**

Corrosion inhibitors for concrete are classified based on [15–18] (**Figure 1**):

### **1.2. Anodic (passivating) inhibitors**

This type of inhibitors forms an insoluble protective film on anodic surfaces to passivate the steel. An anodic inhibitor shifts the potential to the passivation zone causing the formation of a thin passive film on the anodic sites, which increases the potential of the anode and decrease the corrosion in rate. There are two types of passivating inhibitors.

• Oxidizing anions, such as chromates, nitrates, and nitrites, passivate the steel in the absence of oxygen.

concentration drops below the threshold/critical level [19]. Nitrates, benzoates, chromates,

Corrosion Inhibitors for Reinforced Concrete: A Review http://dx.doi.org/10.5772/intechopen.72572 97

Cathodic inhibitors slow down corrosion by reducing the rate of cathodic reactions in the corrosion environment. A cathodic inhibitor causes the formation of insoluble compounds precipitating on the cathodic sites in the form of a barrier film. These inhibitors are called precipitation inhibitors [20]. Zinc and magnesium salts are cathodic inhibitors that form precipitates of zinc hydroxide and magnesium hydroxide at the cathode [21, 22]. Phosphates precipitate as ferrous and ferric phosphates on the steel substrate [23]. Cathodic inhibitors are

not as effective as anodic inhibitors, but they are not likely to cause pitting [24].

molybdates, and orthophosphates are used as anodic inhibitors.

**1.3. Cathodic inhibitors**

**Figure 1.** Classification of corrosion inhibitors.

• Nonoxidizing ions, such as phosphate, tungstate, and molybdates, require the presence of oxygen to passivate the steel.

Anodic inhibitors are effective only when present in sufficiently high concentrations [15]. Typically, the concentration required is determined by the level of chloride present in the environment in which the steel is exposed. The most commonly used anodic inhibitor for concrete is calcium nitrite [18]. Calcium nitrates show similar inhibiting properties in concrete. Some anodic inhibitors, such as nitrites, cause accelerated corrosion and pitting if the

**Figure 1.** Classification of corrosion inhibitors.

concentration drops below the threshold/critical level [19]. Nitrates, benzoates, chromates, molybdates, and orthophosphates are used as anodic inhibitors.

#### **1.3. Cathodic inhibitors**

inhibitors react with concrete forming the complex thus reducing the permeability of the concrete. Corrosion inhibitors are generally used as admixtures in concrete for new construction, but they can also be utilized for repairs by admixed with concrete for patches, sprayed onto

As per NACE international, "a corrosion inhibitor is a substance when added to an environment, either continuously or intermittently to prevent corrosion by forming a passive film on the metal." In other processing industries, inhibitors are the first line of defense against

• The way of application; either mixed with concrete or applied on hardened concrete

This type of inhibitors forms an insoluble protective film on anodic surfaces to passivate the steel. An anodic inhibitor shifts the potential to the passivation zone causing the formation of a thin passive film on the anodic sites, which increases the potential of the anode and decrease

• Oxidizing anions, such as chromates, nitrates, and nitrites, passivate the steel in the ab-

• Nonoxidizing ions, such as phosphate, tungstate, and molybdates, require the presence of

Anodic inhibitors are effective only when present in sufficiently high concentrations [15]. Typically, the concentration required is determined by the level of chloride present in the environment in which the steel is exposed. The most commonly used anodic inhibitor for concrete is calcium nitrite [18]. Calcium nitrates show similar inhibiting properties in concrete. Some anodic inhibitors, such as nitrites, cause accelerated corrosion and pitting if the

the surface of the concrete or applied by saturation treatment [9–13].

Inhibitors slow down the corrosion process by:

96 Corrosion Inhibitors, Principles and Recent Applications

**1.1. Classification of corrosion inhibitors**

(migrating inhibitors).

sence of oxygen.

**1.2. Anodic (passivating) inhibitors**

oxygen to passivate the steel.

• Type of chemicals used (organic and inorganic).

• increasing the anodic or cathodic polarization behavior; • reducing the movement of ions of the metallic surface;

• increasing the electrical resistance of the metallic surface.

Corrosion inhibitors for concrete are classified based on [15–18] (**Figure 1**):

• Electrochemical mechanism of action (anodic or cathodic, or both).

the corrosion in rate. There are two types of passivating inhibitors.

corrosion [14].

Cathodic inhibitors slow down corrosion by reducing the rate of cathodic reactions in the corrosion environment. A cathodic inhibitor causes the formation of insoluble compounds precipitating on the cathodic sites in the form of a barrier film. These inhibitors are called precipitation inhibitors [20]. Zinc and magnesium salts are cathodic inhibitors that form precipitates of zinc hydroxide and magnesium hydroxide at the cathode [21, 22]. Phosphates precipitate as ferrous and ferric phosphates on the steel substrate [23]. Cathodic inhibitors are not as effective as anodic inhibitors, but they are not likely to cause pitting [24].

#### **1.4. Mixed inhibitors**

Mixed inhibitors quash both the anodic and cathodic reactions, and they reduce the corrosion rate by forming a thin protective hydrophobic film on entire surface of the metal through adsorption mechanism [25]. The material with the hydrophobic group that has polar groups, such as N, S, and OH, is effective. These inhibitors are called adsorption or film-forming inhibitors [26–28]. The effectiveness of the film depends on the chemical composition, molecular structure, and their affinities for the metal surface. Cationic inhibitors, such as amines, and anionic inhibitors, such as sulfonates, get adsorbed on the metal surface, whether it is charged positively or negatively. The strength of the bond is the dominant factor for organic inhibitors. Organic inhibitors can also act as pore blockers, reducing the permeability of the concrete. Amines and amino alcohols are the commonly used mixed inhibitors, which displace the chloride ion and form a durable passivating film [29].

Organic inhibitors are further classified into two categories, based upon their application: inhibitor admixed concrete and migrating corrosion inhibitors that are applied on the hardened surface of the concrete [10, 19]. Corrosion inhibitors may be a good alternative for repair concrete due to their lower cost and ease of application. The main application methods for corrosion inhibitors are: added to fresh concrete as an admixture, applied on the hardened concrete and damaged structures migrating corrosion inhibitors (MCI), added to repair mortars, used as a surface treatment to rebars before concreting [10].

#### **1.5. Effect of anodic, cathodic, and mixed inhibitors in concrete**

Corrosion of steel in concrete structures is the primary concern when the structures are exposed to the coastal marine environment. The use of corrosion inhibitors can delay the onset of chloride-induced corrosion, prolong the time to initiation of corrosion, and thereby reduce the corrosion rate [30, 31]. Calcium nitrite is the most commonly used anodic corrosion inhibitor for reinforced concrete. This inhibitor is a passivating inhibitor, which forms a passive film on the surface of steel and significantly reduces the corrosion rate of steel in chloride-contaminated concrete [1, 32]. The inhibitive action of steel with calcium nitrite is as follows [1, 10]:

$$2Fe^{2+} + 2OH^- + 2NO\_2^- \rightarrow 2NO \uparrow + Fe\_2O\_3 + H\_2O \tag{1}$$

$$Fe^{2+} + OH^- + NO\_2^- \rightarrow NO \uparrow + \gamma FeOOH \tag{2}$$

performance of calcium nitrite as an efficient corrosion inhibitor [1, 10, 15, 27, 33]. But, at the same time, possible increase of corrosion rate in case of low dosage or the presence of cracks [16]. Also, increase in dosage resulted in a decrease of the setting time and lowers the compressive strength of concrete and corrosion process may get accelerated [10, 32]. However, their application in corrosion protection is limited due to its toxicity and carcinogenicity [6, 34]. Chromates are carcinogenic, and hence its use is also prohibited [35, 36]. Haleem et al. [37] investigated the pitting corrosion behavior of phosphates, tungstate, and molybdates in

+ 2% Cl− −556 51 85 0.0007 89

+ 3% Cl− −566 51 81 0.0017 81

**Tafel slopes (mV dec−1)**

**ba bc**

**Corrosion rate (mmpy)**

Corrosion Inhibitors for Reinforced Concrete: A Review http://dx.doi.org/10.5772/intechopen.72572

**Efficiency (%)**

99

steady state values, which depend on the way of introducing the inhibiting anions in the solution. Studies revealed that sodium phosphate forms a protective layer on the surface of the steel in chloride-contaminated synthetic concrete pore solution. Besides pretreatment of

solution and found that pitting corrosion current reaches

chloride-contaminated Ca(OH)2

**Figure 2.** Impressed voltage test [1].

**System Ecorr**

Plain +0.5% NO2

Plain +0.5% NO2

**(mV vs. SCE)**

**Table 1.** Potentiodynamic polarization parameters for steel in ternary cement extract [45].

Plain −544 53 84 0.0010 — Plain +1% Cl− −566 58 88 0.0042 — Plain +2% Cl− −576 50 87 0.0062 — Plain +3% Cl− −580 58 85 0.0091 — Plain +0.5% NO2 −538 50 87 0.0001 92 Plain +0.5% NO2 + 1% Cl− −547 53 87 0.0004 91

Different authors have reported different threshold value threshold [Cl− ]/[NO2 − ] ratio depends on the environment. It was reported that the re-passivation of the corroded steel was observed at the [Cl− ]/[NO2 − ] ratio from 0.5 to 1 [32]. For chloride-contaminated concrete or mortar, the [Cl− ]/[NO2 − ] ratio ranges from 1 to 3, and for simulated alkaline solutions and chloride-contaminated concrete, the [Cl− ]/[NO2 − ] ratio ranges from 1 to 4 [3, 31]. Several laboratory studies have established the

**Table 1.** Potentiodynamic polarization parameters for steel in ternary cement extract [45].

performance of calcium nitrite as an efficient corrosion inhibitor [1, 10, 15, 27, 33]. But, at the same time, possible increase of corrosion rate in case of low dosage or the presence of cracks [16]. Also, increase in dosage resulted in a decrease of the setting time and lowers the compressive strength of concrete and corrosion process may get accelerated [10, 32]. However, their application in corrosion protection is limited due to its toxicity and carcinogenicity [6, 34]. Chromates are carcinogenic, and hence its use is also prohibited [35, 36]. Haleem et al. [37] investigated the pitting corrosion behavior of phosphates, tungstate, and molybdates in chloride-contaminated Ca(OH)2 solution and found that pitting corrosion current reaches steady state values, which depend on the way of introducing the inhibiting anions in the solution. Studies revealed that sodium phosphate forms a protective layer on the surface of the steel in chloride-contaminated synthetic concrete pore solution. Besides pretreatment of

**Figure 2.** Impressed voltage test [1].

**1.4. Mixed inhibitors**

98 Corrosion Inhibitors, Principles and Recent Applications

film [29].

follows [1, 10]:

[Cl−

the [Cl−

]/[NO2 −

> ]/[NO2 −

2*Fe* 2+ + 2*OH −* + 2*NO*2

*Fe* 2+ + *OH*− + *NO*2

Mixed inhibitors quash both the anodic and cathodic reactions, and they reduce the corrosion rate by forming a thin protective hydrophobic film on entire surface of the metal through adsorption mechanism [25]. The material with the hydrophobic group that has polar groups, such as N, S, and OH, is effective. These inhibitors are called adsorption or film-forming inhibitors [26–28]. The effectiveness of the film depends on the chemical composition, molecular structure, and their affinities for the metal surface. Cationic inhibitors, such as amines, and anionic inhibitors, such as sulfonates, get adsorbed on the metal surface, whether it is charged positively or negatively. The strength of the bond is the dominant factor for organic inhibitors. Organic inhibitors can also act as pore blockers, reducing the permeability of the concrete. Amines and amino alcohols are the commonly used mixed inhibitors, which displace the chloride ion and form a durable passivating

Organic inhibitors are further classified into two categories, based upon their application: inhibitor admixed concrete and migrating corrosion inhibitors that are applied on the hardened surface of the concrete [10, 19]. Corrosion inhibitors may be a good alternative for repair concrete due to their lower cost and ease of application. The main application methods for corrosion inhibitors are: added to fresh concrete as an admixture, applied on the hardened concrete and damaged structures migrating corrosion inhibitors (MCI), added to repair mor-

Corrosion of steel in concrete structures is the primary concern when the structures are exposed to the coastal marine environment. The use of corrosion inhibitors can delay the onset of chloride-induced corrosion, prolong the time to initiation of corrosion, and thereby reduce the corrosion rate [30, 31]. Calcium nitrite is the most commonly used anodic corrosion inhibitor for reinforced concrete. This inhibitor is a passivating inhibitor, which forms a passive film on the surface of steel and significantly reduces the corrosion rate of steel in chloride-contaminated concrete [1, 32]. The inhibitive action of steel with calcium nitrite is as

− → 2*NO* ↑ + *Fe*2

the environment. It was reported that the re-passivation of the corroded steel was observed at the

ratio ranges from 1 to 3, and for simulated alkaline solutions and chloride-contaminated concrete,

] ratio from 0.5 to 1 [32]. For chloride-contaminated concrete or mortar, the [Cl−

] ratio ranges from 1 to 4 [3, 31]. Several laboratory studies have established the

*O*3 + *H*2

− → *NO* ↑ + *γFeOOH* (2)

]/[NO2 −

*O* (1)

] ratio depends on

]/[NO2 − ]

tars, used as a surface treatment to rebars before concreting [10].

**1.5. Effect of anodic, cathodic, and mixed inhibitors in concrete**

Different authors have reported different threshold value threshold [Cl−

**Figure 3.** Rapid chloride penetration test [1].

**Figure 4.** Compressive strength vs. percentage of inhibitors.

steel with 0.5 M inhibitor solution for 72 h forms a protective layer which further enhanced

**Table 3.** Potentiodynamic polarization parameters for mild steel in concrete containing different inhibitors [15].

chloride-contaminated mortar and concluded that the addition of phosphate inhibitor in con-

Yohai et al. [43, 44] reported that the phosphate ions behaved as a mixed type inhibitor. Soluble phosphate compounds, such as disodium phosphate or mono fluoro phosphate, can be mixed with mortar or applied on concrete [42] by immersion or by surface application [45]. Song et al. [46] evaluated the role of alkaline nitrites on the inhibition of corrosion of steel in binary (OPC + PPC) and ternary cement (OPC + PPC + PSC) and reported that ternary system provides 81% protection efficiency (**Table 1**) for steel in concrete in the presence of 3% chloride concentration. Muralidharan et al. [47] evaluated the effect of various inhibitive ions (hydroxide, citrate, and stannate) in chloride-contaminated (OPC + FA) extract and mortar and found that the addition of inhibitive ions decreased the corrosion rate of the steel rebar in simulated concrete environments.

PO4

addition in

the protection efficiency [38–41]. Nahali et al. [42] studied the effect of Na3

crete decreases the chloride ions effect on localized corrosion.

**Systems Ecorr**

NaNO2

**(mV)**

OPC - Control −580 80 350 20.5 0.240

2% −450 120 230 2.72 0.031 3% −480 140 240 2.94 0.034 ZnO 1% −440 115 300 1.35 0.015 2% −490 140 280 1.29 0.014 3% −480 150 260 1.79 0.020 Mixed 1% −420 180 225 0.90 0.010 2% −485 120 200 1.20 0.013 3% −490 135 220 1.30 0.015 Triethanolamine 1% −470 110 292 4.52 0.052 2% −530 90 284 7.81 0.090 3% −545 75 248 9.73 0.112 Monoethanolamine 1% −510 83 306 10.5 0.121 2% −560 87 300 10.2 0.118 3% −550 82 301 12.7 0.147 Diethanolamine 1% −500 90 400 13.4 0.155 2% −570 85 356 14.8 0.172 3% −565 80 345 12.6 0.146

1% −440 110 260 2.51 0.029

**Tafel slopes (mV dec−1)**

**bc ba**

**Icorr (μAcm−2)** **Corrosion rate (mmpy)**

101

Corrosion Inhibitors for Reinforced Concrete: A Review http://dx.doi.org/10.5772/intechopen.72572

**Table 2.** Corrosion rate of rebar exposed to various types of inhibitors admixed with chloride [1].

**Figure 3.** Rapid chloride penetration test [1].

100 Corrosion Inhibitors, Principles and Recent Applications

**Systems Corrosion rate (mmpy)**

**Figure 4.** Compressive strength vs. percentage of inhibitors.

Control 0.0093 — — NaNO2 0.0023 0.0093 0.0250 ZnO 0.0022 0.0023 0.0024 Mixed 0.0009 0.0012 0.0037 Triethanolamine 0.0117 0.0038 0.0071 Monoethanolamine 0.0171 0.0042 0.0096 Diethanolamine 0.0203 0.0034 0.0083

**Table 2.** Corrosion rate of rebar exposed to various types of inhibitors admixed with chloride [1].

**1% 2% 3%**

**Table 3.** Potentiodynamic polarization parameters for mild steel in concrete containing different inhibitors [15].

steel with 0.5 M inhibitor solution for 72 h forms a protective layer which further enhanced the protection efficiency [38–41]. Nahali et al. [42] studied the effect of Na3 PO4 addition in chloride-contaminated mortar and concluded that the addition of phosphate inhibitor in concrete decreases the chloride ions effect on localized corrosion.

Yohai et al. [43, 44] reported that the phosphate ions behaved as a mixed type inhibitor. Soluble phosphate compounds, such as disodium phosphate or mono fluoro phosphate, can be mixed with mortar or applied on concrete [42] by immersion or by surface application [45]. Song et al. [46] evaluated the role of alkaline nitrites on the inhibition of corrosion of steel in binary (OPC + PPC) and ternary cement (OPC + PPC + PSC) and reported that ternary system provides 81% protection efficiency (**Table 1**) for steel in concrete in the presence of 3% chloride concentration. Muralidharan et al. [47] evaluated the effect of various inhibitive ions (hydroxide, citrate, and stannate) in chloride-contaminated (OPC + FA) extract and mortar and found that the addition of inhibitive ions decreased the corrosion rate of the steel rebar in simulated concrete environments.

Furthermore, the effectiveness of corrosion inhibitors was enhanced by using hybrid corrosion inhibitors; these inhibitors had good corrosion resistance and low toxicity, but the mechanism of protection is not clear [48]. The combined effect of pitting and uniform corrosion on the surface of the rebar was studied by using sodium molybdate (Na2 MoO4 ), cerium nitrate hexahydrate, 2,5 Dimercapto-1,3,4-thiadiazole (DT), 2-Mercaptobenzothiazole (MBT), and 1H-benzotriazole (BTA). All the inhibitors except DT and Na2 MoO4 are toxic. From the study, they concluded that Na2 MoO4 is the non-toxic inhibitor, which re-passivates the pits formed on the surface of the steel rebar by forming an insoluble FeMoO4 compound [36]. Saraswathy et al. [1] and Song et al. [15] studied the effect of anodic, cathodic, and mixed inhibitors in concrete by conducting various short- and long-term accelerated techniques. They concluded that the mixed inhibitor had shown higher time to cracking (**Figure 2**), lower coulomb values (**Figure 3**), higher compressive strength (**Figure 4**), and lesser corrosion rate (**Tables 2** and **3**).

## **2. Effect of organic inhibitors in concrete**

#### **2.1. Admixed vs. migrating corrosion inhibitors (MCI)**

Recently, organic inhibitors gained more attraction in the construction industry due to their promising application as admixtures in reinforced concrete with improved protection efficiency and low cost [49]. Organic inhibitors are used as an admixed corrosion inhibitor [13, 18] or migrating corrosion inhibitors (MCI) [18, 50–52]. Migrating inhibitors are also called as surface applied inhibitors. Both admixed and migrating corrosion inhibitors prevent steel corrosion by forming a thin layer of protective barrier film on the surface of the rebar through adsorption mechanism. Amines and alkanol amines [1, 52–54] and their salts are used as organic inhibitors in concrete. It has been reported that the alkanol amine-based inhibitors could be able to decrease the corrosion rate of the carbonation induced corrosion effect only for the chloride-induced corrosion of reinforcement [55]. Furthermore, the results indicated that penetrating corrosion inhibitors when applied to the surface of existing or new structures can able to reduce the corrosion rate below 0.1 μA/cm2 . Organic inhibitors can adsorb by chemisorption or physisorption. Chemisorption leads to the chemical reaction between active centers of corrosion onto metal and organic inhibitor, where charges from the polar group of inhibitor and charges from metal and metal oxides formed in concrete are shared. Then, organic inhibitor forms the thin coating film blocking the metal surface from the aggressive species by strong chemical bonds. Physisorption leads to the formation of a mechanical barrier, made by organic inhibitors [56]. This inhibitor can halt both the anodic and cathodic reactions, thus reducing the corrosion rate of the reinforcing steel [57]. It has been reported that carboxylate and amino alcohol-based corrosion inhibitors show dual actions in concrete as the amines and alkanol amines adsorb on the metal surface and form a protective film against chloride [58, 59], whereas the carboxylate ester compound reacts with calcium hydroxide, precipitates and blocks the pores of the concrete. This pore blocking property is said to be a secondary protection mechanism against reinforcement corrosion [16, 18, 44, 58]. Furthermore, another study reported that some organic inhibitors adsorb better on the iron surface in the active state than in the passive state [60]. Ormellese et al. [61] reported that amines and alkanol amines (**Table 4**) had poor corrosion inhibition effect on steel in chloride

containing alkaline solutions. They further observed that polycarboxylates are more efficient against pitting corrosion. Comparison of carboxylates with amines/alkanol amines and amino acids were investigated in the same study, and the results are summarized in Predeferri's diagram showing pitting potential vs. chloride concentration (**Figure 5**). From the figure, it is evident that amines/alkanol amines had only moderate effectiveness, while carboxylates showed the best behavior at low and medium chloride levels. It was reported that amines were reported to reduce the compressive strength of cement paste and the reducing effect increased with increasing dosage [62]. Heren et al. [63] showed that the decline in concrete

Surface-applied migrating corrosion inhibitors (MCI) are suitable for repairing the chloride-contaminated concrete. In concrete, chloride and inhibitor ions work on three mechanisms: natural

**Figure 5.** Pedeferri type diagram showing pitting potential vs. chloride ions and the range of corrosion organic inhibitors [61].

strength was enhanced by an increase in corrosion inhibitor concentration.

**Amines [61] Carboxylic acids [66]**

)2

CH2

CH2 CH2

–CH2 CH2