Causes of electrochemical corrosion and methods of metal protection

Metals are frequently impacted by electrochemical corrosion, which deteriorates them over time. When metal interacts with its surroundings, particularly when it is exposed to moisture and oxygen, this process takes place. Preventing damage and prolonging the life of metal components and structures requires an understanding of the causes of electrochemical corrosion.

Fundamentally, a chemical reaction between the metal and its environment causes electrochemical corrosion. Iron oxide, sometimes known as rust, is created when a metal, such as iron, comes into contact with oxygen and water. The flow of electrons in this reaction generates an electric current that quickens the corrosion process. Certain conditions are more caustic than others due to the exacerbation of this reaction caused by variables such as temperature, humidity, and the presence of salts or other chemicals.

Metals must be protected from electrochemical corrosion using a variety of techniques. Coating the metal with paint or another protective layer is one typical technique. By acting as barriers, these coatings keep oxygen and water from penetrating the metal surface. Additional methods include cathodic protection, the use of corrosion-resistant alloys, and routine maintenance to get rid of any early rust indicators.

The type of metal, the surrounding circumstances, and the intended use of the metal structure all play a role in selecting the best protection strategy. We are able to greatly lessen the effects of electrochemical corrosion and improve the robustness and longevity of metal materials by comprehending the underlying causes and putting efficient preventative measures in place.

The corrosive process known as electrochemical corrosion occurs when metals break down as a result of chemical reactions with their surroundings, which are frequently sped up by the presence of salt and water. This kind of corrosion, which results in rust and structural weakening, is caused by the movement of electrical currents between various regions on the metal surface. There are a number of ways to shield metals from this damage, including painting them, covering them with films, applying corrosion inhibitors, and using cathodic protection. These techniques aid in extending the life and integrity of metal surfaces by forming a barrier against corrosive substances.

What is corrosion

In a broad sense, corrosion is the process by which the outermost layer of metal material is destroyed due to external influences.

In this context, corrosion simply refers to the feature where the metal surface undergoes a chemical reaction and loses some of its original characteristics as a result.

There are four primary indicators that this process is present:

• a process that develops on the surface and over time penetrates inside a metal product;
• The reaction arises spontaneously from the fact that the stability of the thermodynamic balance between the environment and the system of atoms in an alloy or monolith is disturbed;
• Chemistry perceives this process not just as a reaction of destruction, but as a reaction of recovery and oxidation: when entering the reaction, some atoms replace others;
• The properties and features of the metal with such a reaction undergo significant changes, or are lost where it occurs.

Types of corrosion

Corrosion can take several forms, depending on the kind of metal and the redox reaction that is taking place.

• uniform or uneven;
• local and point (individual sites for some reason reacted, while others did not);
• ulcerative, also known as pitting;
• subsimanding;
• cracked;
• intercrystalline, which occurs along the boundaries of the metal crystal.

Additionally, corrosion is both chemical and electrochemical, depending on the external factors affecting the surface. Without the involvement of an electric current, chemical corrosion can result from certain reactions influenced by chemical interactions; it can even be intrinsic to oil and gas. Compared to chemical processes, electrochemical processes are more intricate.

In the video: corrosion of metals.

Causes and signs of electrochemical corrosion

In contrast to chemical corrosion, electrochemical corrosion occurs within the electrolyte system, which is why an electric current flows through it. The anode and cathode, two conjugated processes, remove unstable atoms from the crystal lattice. The anode-containing ions enter the solution, and the depolarizer binds the electrons that fall into the substance-oxidizer’strap.

Depolarization, then, is the discharge of free electrons from the cathode sections, and the substance that causes this process is called the depolarizer. The primary reactions involve the involvement of hydrogen and oxygen, which act as depolarizers.

Numerous instances exist of diverse forms of electrochemical corrosion that impact metal surfaces in the natural world and occur under a range of circumstances. In addition, oxygen functions in a neutral medium while hydrogen operates in an acidic one.

Since almost all metals are susceptible to electrochemical corrosion, they can be classified into 4 groups based on how much their electrode potential is:

• active corrosion even in the environment where there are no oxidizing agents;
• Medium -active reaction of oxidation in an acidic environment;
• Inactive do not react in the absence of oxidizing agents in neutral and sour media;
• They do not react – high stability (noble metals, palladium, gold, platinum, iridium).

Atmospheric electrochemical corrosion is the most prevalent kind.

However, the same reaction can happen in base, acid, and base solutions as well as in water. Marine and biological (flowing under the influence of bacteria) are distinguished in the highly specialized differences in soil, aeration, and atmospheric corrosion.

Electrical corrosion is a phenomenon that arises when someone uses electric current for a particular purpose. It is caused by wandering currents that work their way through an electrical system.

The environment’s thermodynamic instability destroys the uniform metal surface. Furthermore, heterogeneous—a result of the crystal lattice’s composition, which keeps one metal’s atoms denser than the foreign metals they are strewn with. The rate at which ions ionize and the environment’s oxidative components are restored vary amongst these reactions.

When two processes—the anode and the cathode—flow simultaneously, the anodes, which are closed to the environment and have many microelectrodes on their surface, dissolve the metal surfaces during electrochemical corrosion. These processes are distinguished by the fact that the anodes dissolve first.

Examples of typical electrochemical corrosion processes include those that occur on the seabeds of ships or on metal structures exposed to the atmosphere.

The need for anti -corrosion protection

One of the primary responsibilities of individuals who work with mechanisms, units, and machines, sea vessels, and construction processes, is protecting metal from substances that could destructively act on its surface.

All metals, with the exception of noble ones, are subject to damaging processes to varying degrees.

The more frequently a device or part is used, the greater the likelihood that it will be subjected to adverse atmospheric conditions, fluids that must be dealt with during the operation, and destructive effects. The protection of metal from corrosion is the subject of numerous scientific and industrial production fields, but the primary strategies remain the same and involve the development of protective coatings:

• metal;
• non -metallic;
• chemical.

Unlike other forms of protection, the principle of action of non-metallic coatings is quite effective and is derived from both organic and inorganic compounds. Paints, concrete, bitumen, and high molecular weight compounds are used to create non-metallic protection in industrial and construction production. These materials have been actively adopted in recent years as the chemistry of polymers has reached unprecedented heights.

The following are some ways that chemistry helped to create protective coatings:

• oxidation (creating a protective film on metal using oxide films);
• phosphate (phosphate films);
• nitrogen (saturation of the surface of steel nitrogen);
• cementation (compounds with carbon);
• enveloping (compounds with organic substances);
• changes in the composition of the metal by introducing anti -corrosion additives into it);
• modifications of the environment by the introduction of inhibitors affecting it.

One method of preventing corrosion through electrochemical means is reverse electrochemical corrosion. Anode and cathode protection are provided based on the displacement of the metal potential in the positive or negative sides. A cathode polarization is produced by connecting a tread to a metal product or a residue source on a metal surface. This stops the metal from being destroyed by the anode.

There are two varieties of electrochemical protection techniques:

• The metal coating is protected by other metal, which has a more negative potential (that is, the metal protecting the metal is less stable than the protected), and this is called anode coating;
• The coating is made of less active metal, and then it is called cathode.

Galvanized iron, for instance, provides anode protection against corrosion. Iron will be relatively safe until all of the zinc in the protective layer has been used.

Applying copper or nickeling provides cathodic protection. In this instance, the layer that the protective layer shields is destroyed along with it. The response in other situations is the same for the tread connection intended to safeguard the metal product. By creating the conditions that keep what is under its protectorate safe, the tread serves as an anode.

One of the main problems with metal components and structures is electrochemical corrosion. This kind of corrosion develops gradually as a result of reactions between metals and their surroundings. The main factors that cause it to happen are the presence of water, oxygen, and electrolytes, which make it easier for ions and electrons to transfer and corrode metal. Examples of common occurrences are the tarnishing of copper and the rusting of iron, which weaken the metal and alter its appearance and functionality.

For metal products to remain long-lasting and safe, electrochemical corrosion must be prevented. There are several techniques used to keep metals from corroding. Coatings and paints, which serve as a barrier between the metal and corrosive substances, are among the most efficient methods. By keeping oxygen and moisture from penetrating the metal surface, these protective layers dramatically lower the chance of corrosion.

Cathodic protection is another widely used technique, which entails using the metal as a cathode in an electrochemical cell. Sacrificial anodes composed of a more reactive metal or impressed current systems, which supply a constant flow of electrons to offset the corrosive process, can be used to accomplish this. These methods are widely applied in sectors like pipelines and marine vessels where metal structures are subjected to hostile environments on a regular basis.

Preventing electrochemical corrosion also requires routine upkeep and observation. Inspections at regular intervals can assist in identifying early indicators of corrosion, enabling prompt repairs and reapplication of protective coatings. The lifespan of metal structures can be greatly increased and maintenance costs can be decreased by comprehending the causes and putting in place the proper protective measures.

Video on the topic

Electrochemical corrosion of metals and protection methods

Grade 9 § 20 "Corrosion of metals and methods of protection against it".

The educational film "Corrosion of metals, methods of protection against it"