**11. Inhibitors**

An inhibitor is a chemical substance or combination of substances which when added in very low concentrations in a corrosive environment effectively prevents or

**13**

*Corrosion Inhibitors*

**11.1 Definition of inhibitor**

**Figure 12**.

corrosion [11].

*DOI: http://dx.doi.org/10.5772/intechopen.80542*

are usually dissolved in aqueous environments [28].

• Identification of the corrosion problems.

corrosion. The inhibitor may cause:

• Cost of the inhibitor.

species.

reduces corrosion without significant reaction with the components of the environment. Concentrations of corrosion inhibitors can vary from 1 to 15,000 ppm (0.0001 to 1.5 wt %). Inhibitors play a vital role in closed environmental systems that have good circulation so that an adequate and controlled concentration of inhibitor is ensured [27]. Such conditions can be met, for instance in cooling water recirculation systems, oil production, oil refining, and acid pickling of steel components. One of the more recognizable applications for inhibitors is in antifreeze for automobile radiators. Inhibitors may be organic or inorganic compounds and they

An inhibitor is a substance which when added to an environment in small concentration minimizes the loss of metal, reduces the extent of hydrogen embrittlement, protects the metal against pitting, reduces over pickling and acid fumes resulting from excessive reaction between the acid and basic metals and reduces acid consumption. They reduce corrosion by either acting as a barrier by forming an adsorbed layer or retarding the cathodic, the anodic or both processes [10]. A schematic representation of inhibitor process is shown in

Any corrosion retardation process or the reduction in the oxidation rate of the metal by addition of a chemical compound to the system is caused by corrosion inhibitors. Inhibitors are often easy to apply and offer the advantage of in-situ application without causing any significant disruption to the process.

In order that they can be used effectively, three factors must be considered, namely:

Generally, the components of a corrosion cell (anode, cathode, electrolyte and electronic conductor) may be affected by corrosion inhibitors in order to reduce

• Resistance inhibition (increasing the electrical resistance of the circuit while

• Diffusion restriction (restricting the diffusion of depolarizers, e.g., DO).

However there are several factors to be considered when choosing an inhibitor.

• Toxicity of the inhibitor can cause ill effects on human beings and other living

The use of corrosion inhibitors is one of the best methods of combating

• Anodic inhibition (increasing the polarization of the anode)

forming a thin or thick deposit on the surface of the metal)

• Availability of the inhibitor determines the selection of it.

• Inhibitor should be environment friendly.

• Cathodic inhibition (increasing the polarization of the cathode)

### *Corrosion Inhibitors DOI: http://dx.doi.org/10.5772/intechopen.80542*

*Corrosion Inhibitors*

**9.1 Corrosion rate**

of the two ways:

decimeter per day).

**10. Corrosion control methods**

diverse. They may be broadly based on,

• Modification of corrosive environment

• Modification of metal environment potential

• Modification of metal

• Modification of design

• Use of inhibitors

method [25, 26].

**11. Inhibitors**

• Modification of surface

and cathodic reactions. Metals having a more positive (noble) potential in the galvanic series will tend to extract electrons from a metal which is in a more negative (base) position in the series and hence accelerate its corrosion when in contact with it [23]. Aggressive ions such as chloride tend to prevent the formation of protective oxide films on the metal surface and thus increase corrosion.

The rate of corrosion is expressed based on the loss per unit time. The rate at which the attack takes place is of prime importance and is usually expressed in one

• Weight loss per unit area per unit time, usually mdd (milligrams per square

• Decrease in thickness per unit time, that is, rate of penetration or the thickness of metal lost. This may be expressed in American units, mpy (mils per year) or

Corrosion is destructive and silent operating processes. It poses problems to big as well as small industries. Since corrosion is inevitable to eliminate but can be minimized by adopting certain anticorrosion method rather than preventing it [24]. The practical methods available for the protection of metal against corrosion are

These methods can be used individually or in combination.. One of the best known methods of corrosion protection is using corrosion inhibitors instead of using the various methods to avoid or prevent destruction or degradation of metal surface. Because using inhibitors is following stand up due to low cost and practice

An inhibitor is a chemical substance or combination of substances which when added in very low concentrations in a corrosive environment effectively prevents or

in metric units or mmpy (millimeters per year).

**12**

reduces corrosion without significant reaction with the components of the environment. Concentrations of corrosion inhibitors can vary from 1 to 15,000 ppm (0.0001 to 1.5 wt %). Inhibitors play a vital role in closed environmental systems that have good circulation so that an adequate and controlled concentration of inhibitor is ensured [27]. Such conditions can be met, for instance in cooling water recirculation systems, oil production, oil refining, and acid pickling of steel components. One of the more recognizable applications for inhibitors is in antifreeze for automobile radiators. Inhibitors may be organic or inorganic compounds and they are usually dissolved in aqueous environments [28].
