【Daily Question】Principles of Chemical Engineering: Electrochemical Corrosion (July 1)

When an impure metal comes into contact with an electrolyte solution, a galvanic cell reaction occurs; the more reactive metal loses electrons and gets oxidized. This type of corrosion is known as electrochemical corrosion. The corrosion of steel in humid air is the most prominent example of electrochemical corrosion.

When impure metals come into contact with an electrolyte solution, a galvanic cell reaction occurs; the more reactive metal loses electrons and is oxidized. This type of corrosion is known as electrochemical corrosion.

When an impure metal comes into contact with an electrolyte solution, a galvanic cell reaction occurs, and the more reactive metal loses electrons and gets oxidized

When impure metals come into contact with an electrolyte solution, a galvanic cell reaction occurs; the more reactive metal loses electrons and gets oxidized. This type of corrosion is known as electrochemical corrosion. The corrosion that occurs in steel in humid air is a prominent example of electrochemical corrosion. In humid air, a thin layer of water forms on the surface of steel; this layer contains a small amount of hydrogen ions and hydroxide ions, as well as gases such as oxygen. As a result, an electrolyte solution is formed on the steel surface, which together with the iron and a small amount of carbon present in the steel creates countless tiny galvanic cells. In these cells, iron acts as the negative electrode while carbon acts as the positive electrode. Iron loses electrons and gets oxidized. Electrochemical corrosion is the main cause of steel corrosion. It occurs when metal materials come into contact with an electrolyte solution, through electrode reactions. Electrochemical corrosion reactions are types of redox reactions; in these reactions, metal loses electrons and gets oxidized, a process known as the anodic reaction. The products of these reactions are metal ions that enter the medium, or metal oxides (or insoluble metal salts) that cover the metal surface； The substances in the medium gain electrons from the metal surface and are reduced; this reaction process is known as the cathodic reaction process. In this process, the substances that gain electrons and are reduced are commonly referred to as depolarizers. During uniform corrosion, there is no significant difference in the probability of anodic and cathodic reactions occurring at various points on the metal surface, and the locations where these two types of reactions take place keep changing randomly. If certain areas on the metal surface primarily undergo anodic reactions, while other areas primarily undergo cathodic reactions, then the former are called anodic zones and the latter cathodic zones; together, these zones form a corrosion cell. It is the anodic reactions that directly cause damage to metal materials. Therefore, an external power source is often used, or wires are employed to connect the metal to be protected with another metal having a lower electrode potential, so that corrosion occurs on the metal with the lower potential.

When impure metals come into contact with an electrolyte solution, a galvanic cell reaction occurs: the more reactive metal loses electrons and gets oxidized. This type of corrosion is known as electrochemical corrosion. The corrosion that occurs in steel when it is exposed to humid air is a prominent example of electrochemical corrosion. As we know, steel does not corrode easily in dry air, but it corrodes rapidly in humid air. In humid air, a thin layer of water forms on the surface of steel; this layer contains a small amount of hydrogen ions and hydroxide ions, as well as gases such as oxygen. As a result, an electrolyte solution is formed on the surface of the steel, and this solution, together with the iron and a small amount of carbon present in the steel, creates countless tiny galvanic cells. In these cells, iron acts as the negative electrode while carbon acts as the positive electrode. Iron loses electrons and gets oxidized. Electrochemical corrosion is the main cause of steel corrosion. It occurs when metal materials come into contact with an electrolyte solution, through electrode reactions. Electrochemical corrosion reactions are types of redox reactions. In such reactions, metal loses electrons and gets oxidized; this process is called the anodic reaction. The products of these reactions are metal ions that enter the surrounding medium, or metal oxides (or insoluble metal salts) that form on the surface of the metal； The substances in the medium gain electrons from the metal surface and are reduced; this reaction process is known as the cathodic reaction process. In this process, the substances that gain electrons and are reduced are commonly referred to as depolarizers. During uniform corrosion, there is no significant difference in the probability of anodic and cathodic reactions occurring at various points on the metal surface, and the locations where these two types of reactions take place keep changing randomly. If certain areas on the metal surface primarily undergo anodic reactions, while other areas primarily undergo cathodic reactions, then the former are called anodic zones and the latter cathodic zones; together, these zones form a corrosion cell. It is the anodic reactions that directly cause damage to metal materials. Therefore, an external power source is often used, or wires are employed to connect the metal to be protected with another metal having a lower electrode potential, so that corrosion occurs on the metal with the lower potential.

When an impure metal comes into contact with an electrolyte solution, a galvanic cell reaction occurs; the more reactive metal loses electrons and gets oxidized. This type of corrosion is known as electrochemical corrosion. The corrosion of steel in humid air is the most prominent example of electrochemical corrosion.

When an impure metal comes into contact with an electrolyte solution, a galvanic cell reaction occurs; the more reactive metal loses electrons and gets oxidized. This type of corrosion is known as electrochemical corrosion. The corrosion of steel in humid air is the most prominent example of electrochemical corrosion. We know that steel does not corrode easily in dry air over a long period of time, but it corrodes rapidly in humid air. It turns out that in humid air, a thin layer of water forms on the surface of steel. This layer of water contains a small amount of hydrogen ions and hydroxide ions, as well as gases such as oxygen; as a result, an electrolyte solution is formed on the steel surface. This electrolyte solution, together with the iron and a small amount of carbon present in the steel, creates countless tiny galvanic cells. In these galvanic cells, iron is the negative electrode and carbon is the positive electrode. Iron loses electrons and is oxidized. Electrochemical corrosion is the main cause of steel corrosion. Corrosion that occurs when a metal material comes into contact with an electrolyte solution, as a result of electrode reactions. The electrochemical corrosion reaction is a redox reaction. In the reaction, the metal loses electrons and is oxidized; this reaction process is known as the anodic reaction. The products of this reaction are metal ions that enter the medium, or metal oxides (or insoluble metal salts) that cover the surface of the metal ； The substances in the medium gain electrons from the metal surface and are reduced; this reaction process is known as the cathodic reaction process. In the cathodic reaction process, the substances that gain electrons and are reduced are commonly referred to as depolarizers. During uniform corrosion, there is no significant difference in the probability of anodic and cathodic reactions occurring at various locations on the metal surface; the surface areas where these two types of reactions take place keep changing randomly. If certain areas on the metal surface are primarily involved in anodic reactions, while the remaining areas are primarily involved in cathodic reactions, then the former are called anodic regions and the latter cathodic regions; the anodic and cathodic regions together form a corrosion cell. It is the anodic reaction that directly causes damage to metal materials; therefore, an external power source is often used, or wires are employed to connect the metal to be protected with another metal having a lower electrode potential, so that corrosion occurs on the metal with the lower potential.

1. There are two regions: the cathode region and the anode region, where cathodic and anodic reactions occur respectively. 2. There is a current flow. These are the two most important differences; in chemical corrosion, electrons are exchanged directly, whereas in electrochemical corrosion, such direct exchange does not occur.