Chapter 1 Introduction

1.1 Research Background 1.1.1 Corrosion

Corrosion is defined as the natural process of transforming refined metals into more stable oxides. Most likely inevitable is the gradual destruction or degradation of materials (usually metals) due to chemical reactions with the environment. Corrosion is a natural and costly destructive process like earthquakes, tornadoes, floods and volcanic eruptions, but with one big difference. We can only be silent bystanders during the destruction process described above, but corrosion can be prevented, or at least controlled.

Although definitions vary, corrosion is essentially the result of the interaction of a material with its environment. Until the 1960s, the term corrosion was limited to metals and their alloys, not ceramics, polymers, composites, or semiconductors. The term corrosion now encompasses all types of natural and man-made materials, including biomaterials and nanomaterials, and is not limited to metals and alloys. The extent of corrosion is consistent with the revolutionary changes in materials development observed over the past few years.

Figure 1.1:
Corrosion attack on old ships Corrosion and its mechanism

Since metals are reactive, they do not exist in nature in the free state. Metals are generally in a high energy state as some energy is added from the ore during the manufacturing process. Ores in lower energy states are more stable than metals in higher energy states. As a result of this difficult thermodynamic struggle, metals have a powerful driving force that releases energy and returns to its original shape. Therefore, under a suitable corrosive environment, the metal reverts to its original state or ore. Electrochemical processes, which are intrinsically involved in corrosion, contrast with extractive metallurgy, which is involved in the production of metals. Corrosion is therefore sometimes considered a reverse process of extractive metallurgy, as shown below.

Figure 1..2:
Iron energy cycle showing energetic metallurgy


According to electrochemistry, the corrosion reaction he can be considered to proceed by two simultaneous reactions.

Oxidation of a metal at the anode (the corroded end that releases electrons) and reduction of the material at the cathode (the protected end that accepts electrons). For the reaction to occur, the following conditions must be met:

1. He of the structure must have different potentials in the two regions.

2. The areas designated as anode and cathode must be electrically connected to each other.

3. These areas should be exposed to a common electrolyte.

4. An electrical path must be available through or between metals to allow electron flow.

Under these conditions, a corrosion cell is created in which the cathode remains inactive while the anode is destroyed by corrosion. As a result of this process, a current flows through the junction between the cathode and anode. The cathodic area is protected from corrosion damage at the expense of metal consumed at the anode. The amount of metal loss is directly proportional to the DC flow. light Electrochemistry of corrosion

Corrosion is caused by an electrochemical process. This phenomenon is similar to what occurs when a ‘dry’ carbon-zinc cell produces a DC current. Basically, for corrosion to occur, you need an anode (negative electrode), a cathode (positive electrode), an electrolyte (ambient), and a circuit connecting the anode and cathode (see Figure 1.3).

Metal dissolution occurs at the anode, where the corrosion current enters the electrolyte and flows to the cathode. A common reaction that occurs at the anode (for alloys) is the dissolution of metals as ions.

M → Mn+ + en-

From where

M = metal involved n = valence of corrosive metal species e = electron

Figure 1.4:
Basic corrosion cell. A basic corrosion cell consists of an anode, a cathode, an electrolyte, and a metallic pathway for electron flow. Note that the corrosion current (z) enters the electrolyte at the anode and flows to the cathode.

Examination of this basic reaction shows that electron loss or oxidation occurs at the anode. Electrons lost at the anode flow through the metal circuit to the cathode where a cathodic reaction occurs. In alkaline and neutral aerated solutions, the dominant reaction is cathodic

O2 + 2H2O + 4e- → 4(OH) (1.1)

Cathodic reactions that normally occur in aerated acids are:

2H- + 2e- → H2 (1.2)

For air-entrained acids, the cathodic reaction is:

O2 + 4H- + 4e- → 2H2O (1,3)

All these reactions involve electron gain and reduction processes. The number of electrons lost at the anode must equal the number of electrons gained at the cathode. For example, when iron (Fe) is exposed to corrosive water, Corrosion protection

Some corrosion prevention methods include material selection, conditioning of the corrosive environment, electrochemical control, protective coatings, and the use of corrosion inhibitors. The most common and simplest way to prevent corrosion is to carefully select materials after characterizing the corrosive environment. Standard corrosion references are helpful in this regard. Cost can be a significant factor here, and it is not always economically feasible to use materials that offer optimum corrosion resistance. In some cases it may be necessary to use a different alloy or gauge.

Also, if possible, conditioning the corrosive environment can have a significant impact on corrosion. Reducing the temperature and/or velocity of the fluid will generally reduce the rate at which corrosion occurs. Increasing or decreasing the concentration of some species in solution often has a positive effect. For example, metal can be passivated.

Corrosion inhibitor:

Corrosion inhibitors are chemicals that react with metal surfaces or surrounding gases to cause corrosion and interfere with the chemical reactions that cause corrosion. Inhibitors work by adsorbing to the metal surface and forming a protective film. These chemicals can be applied as a solution or as a protective coating by dispersion techniques. The inhibitor process that retards corrosion depends on:

• Changes in anodic or cathodic polarization behavior

• Reduced ion diffusion to metal surfaces

• Increased electrical resistance of metal surfaces

Major end-use industries for corrosion inhibitors include petroleum refining, oil and gas exploration, chemical manufacturing, and water treatment plants.

The advantage of corrosion inhibitors is that they can be applied to metals in situ as a corrective action against unexpected corrosion.


1.1.2 Aluminum

Aluminum is regularly used in many ways, including consumer electronics, chemical reaction and storage bottles, vessels and containers, buildings, bridges, packaging films, automobiles, airplanes and ships. It is used in a wide variety of applications due to its light weight, extremely high strength, excellent thermal and electrical conductivity, excellent heat and light reflectivity, rust resistance, non-toxicity and attractive appearance. Due to the formation of a hard and tough oxide film on the surface, it is very positive and corrosion resistant. The surface film is amphoteric, so the metal readily dissolves in strongly acidic and strongly alkaline media. Despite these excellent properties of aluminum, it is not an ideal material for engineering applications in all environments as it is subject to corrosion due to chemical interactions with the environment (Khandelwal et al., 2010). Aluminum is used in industries such as shipping, offshore oil exploration, power and offshore industrial equipment (for cooling), firefighting, petroleum fuel injection, and desalination plants.

1.2 Problem definition

Failure of aluminum equipment and materials due to acid corrosion in industry has been widely reported (Abiola et al., 2012), so this general effect should be minimized. In virtually all situations, corrosion-induced aluminum failure can be managed, slowed, or even stopped using appropriate techniques.

The most common and easiest way to prevent corrosion is to carefully select materials after characterizing the corrosive environment. The use of chemical inhibitors is the most practical and inexpensive means of controlling corrosion of metals in acidic solutions. However, many aluminum acid corrosion inhibitors are toxic, non-biodegradable, and expensive. 1.3 Purpose

The purpose of this study is to investigate the inhibitory effect of alanine on corrosion of aluminum in 0.5 M HCl solution using a weight loss technique.

1.4 Scope of investigation

This research is limited to investigating the use of organic inhibitors to reduce damage to aluminum from acid corrosion. This is achieved by determining the inhibitory efficiency of alanine by testing various concentrations of alanine against aluminum in acidic solutions.

The problem of metal corrosion is a significant factor and it is estimated that about 5% of the income of industrialized countries is spent on corrosion prevention and maintenance or replacement of products lost or contaminated as a result of corrosion reactions. increase. The consequences of corrosion are many, and the impact on the safe, reliable and efficient operation of equipment and structures is often more severe than the simple loss of chunks of metal. Even a very small amount of destroyed metal can lead to the failure and need for expensive replacement of many types of equipment. Some of the major harmful effects of corrosion can be summarized as follows:

• Perforation of vessels and pipes allowing escape of their contents and possible harm to the surroundings. For example a leaky domestic radiator can cause expensive damage to carpets and decorations, while corrosive sea water may enter the boilers of a power station if the condenser tubes perforate.

• Loss of technically important surface properties of a metallic component. These could include frictional and bearing properties, ease of fluid flow over a pipe surface, electrical conductivity of contacts, surface reflectivity or heat transfer across a surface.

• Mechanical damage to valves, pumps, etc., or blockage of pipes by solid corrosion products. • Equipment that must be designed to withstand some degree of corrosion and to allow easy replacement of corroded components is complex and costly.

• Reduction in metal thickness leading to loss of mechanical strength and structural failure or collapse. A significant amount of metal loss can result in very severe degradation if the structure is cracked due to local loss of metal.

the anode


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