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Electrochemical corrosion is the most common and important type of metal corrosion. The corrosion of steel in humid air is the most prominent example of electrochemical corrosion. In humid air, a thin layer of water film adheres to the surface of steel. If this water film is highly acidic, H+ ions gain electrons and hydrogen gas is released; this type of electrochemical corrosion is known as hydrogen evolution corrosion ； When this water film is weakly acidic or neutral, it can dissolve more oxygen; in such cases, O2 gains electrons and OH— is released. This type of electrochemical corrosion is known as oxygen absorption corrosion, and it is the main cause of steel corrosion. Hydrogen evolution corrosion, oxygen absorption corrosion – Conditions for occurrence: Acidic water film; Slightly acidic or neutral water film. Cathode reactions: 2H++2e—=H2↑; O2+4e—+2H2O=4OH—. Anode reactions: Fe—2e—=Fe2+; 2Fe—4e—=2Fe2+. The electrode at which the solution’s pH increases is the cathode. Other reactions: Fe2+ +OH—=Fe(OH)2↓; 4Fe(OH)2 +O2+2H2O= 4Fe(OH)3

　　 1. 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 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. 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 acquire 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. 　　2. There are various principles of metal corrosion, among which electrochemical corrosion is the most common. When metal is placed in an aqueous solution or in a humid atmosphere, a microcell forms on the metal surface, also known as a corrosion cell (its electrodes are commonly referred to as the cathode and anode, rather than positive and negative electrodes). An oxidation reaction occurs at the anode, causing it to dissolve, while a reduction reaction takes place at the cathode, which generally serves only to transfer electrons. The formation of corrosion cells is mainly due to the adsorption of moisture from the air on the metal surface, resulting in the creation of a water film. This allows substances such as CO2, SO2, and NO2 in the air to dissolve in this water film, forming an electrolyte solution. The metal submerged in this solution is usually impure; for example, industrial steel is actually an alloy that contains, in addition to iron, graphite, cementite (Fe3C), as well as other metals and impurities. Most of these substances are not as reactive as iron. In a corrosion cell formed in this way, iron serves as the anode while impurities act as the cathode; and because iron is in close contact with these impurities, the corrosion process continues unabated. 　　(1) Hydrogen evolution corrosion (when the water film adsorbed on the steel surface is highly acidic) Anode (Fe): Fe = Fe2+ + 2e- Fe2+ + 2H2O = Fe(OH)2 + 2H+ Cathode (impurities): 2H+ + 2e- = H2 Cell reaction: Fe + 2H2O = Fe(OH)2 + H2↑ This phenomenon is called hydrogen evolution corrosion due to the release of hydrogen gas. 　　(2) Oxygen absorption corrosion (when the acidic strength of the water film adsorbed on the steel surface is low) Anode (Fe): Fe = Fe2+ + 2e- Cathode: O2 + 2H2O + 4e- = 4OH- Overall reaction: 2Fe + O2 + 2H2O = 2Fe(OH)2 It is also called oxygen absorption corrosion due to the absorption of oxygen. 　　The Fe(OH)2 formed by hydrogen evolution corrosion and oxygen absorption corrosion is oxidized by oxygen to form Fe(OH)3, which then dehydrates to produce Fe2O3, namely rust. 　　4Fe(OH)2 + O2 + 2H2O = 4Fe(OH)3 The corrosion of steel products in the atmosphere is mainly oxygen absorption corrosion. 　　Fe + 2H2O = Fe(OH)2 + H2↑ O2 + 2H2O + 4e- → 4OH-  2Fe + O2 + 2H2O = 2Fe(OH)2  2H+ + 2e- → H2 Hydrogen evolution corrosion occurs mainly in strongly acidic environments, while oxygen absorption corrosion takes place in weakly acidic or neutral environments. 1# JFTANG726

Electrochemical corrosion: Corrosion that occurs when a metal comes into contact with an electrolyte solution in its surrounding medium, as a result of the formation of a corrosion cell. Corrosion cell: An oxidation reaction takes place at the anode (the metal loses electrons and is corroded) ； A reduction reaction occurs at the cathode. Hydrogen evolution corrosion occurs in acidic media, while oxygen absorption corrosion takes place in neutral and alkaline media. For example, electrochemical corrosion occurs on steel materials: 1. Hydrogen evolution corrosion: Anodic reaction Fe-2e=Fe2++ ； Cathodic reaction: 2H++2e=H2. 2. Oxygen absorption corrosion: Anodic reaction: Fe-2e=Fe2++ ； Cathodic reaction: O2 + 2H2O + 4e = 4OHˉ. 3. Oxygen absorption corrosion is the most common form of corrosion and also the most severe type of corrosion that affects metals. The rust resulting from this corrosion is a complex mixture, primarily composed of the products of the following reaction: 2Fe(OH)3 = Fe2O3 + 3H2O. 4. Differential aeration corrosion: In oxygen absorption corrosion, corrosion that occurs due to uneven distribution of O2 in the water film is known as differential aeration corrosion. Electrode reaction: O2 + 2H2O + 4e = 4OHˉ. According to the Nernst equation, assuming C(OHˉ) remains constant, areas with higher O2 concentrations (pO2) have higher φ values and are thus more likely to act as the cathode of a corrosion cell, while areas with lower O2 concentrations (pO2) have lower φ values and are more likely to act as the anode of such a cell; the metal in these areas is therefore more susceptible to corrosion. 5. Seawater corrosion: Seawater contains ions such as Na+, Mg2+, and Clˉ, which form corrosion cells that destroy the passivation layer on the metal surface. 6. Soil corrosion: Minerals in soil dissolve in water to form electrolyte solutions, which can also create corrosion cells. Differences in air permeability lead to variations in oxygen concentration, resulting in differential aeration corrosion. Factors that affect the rate of metal corrosion include the properties and state of the metal, as well as environmental factors such as humidity, temperature, and pH level.

Electrochemical corrosion refers to the process in which, when a metal comes into contact with an electrolyte solution, galvanic cells are formed due to the differences in the structure and composition of the metal material. The redox reactions that occur between the anode and cathode cause certain structures or components of the metal material to dissolve, ultimately leading to the failure of the material. The main factors affecting the rate of corrosion on metal surfaces (i.e., the corrosion current j) are: ① The electromotive force of the corrosion cell – the greater the difference in equilibrium electrode potentials between the two electrodes, the higher the maximum corrosion current. ②The polarization behavior of metals – under identical other conditions, the greater the degree of polarization (i.e., the slope of the polarization curve), the smaller the corrosion current. ③Hydrogen overpotential – During hydrogen-induced corrosion, the greater the overpotential for hydrogen to deposit on the metal surface, the steeper the slope of the polarization curve, and as a result, the corrosion current decreases.

The main factors affecting the rate of corrosion on metal surfaces (i.e., the corrosion current j): ① The electromotive force of the corrosion cell – the greater the difference in equilibrium electrode potentials between the two electrodes, the greater the maximum corrosion current. ②The polarization behavior of metals -- under other constant conditions, the greater the degree of polarization (i.e., the slope of the polarization curve), the smaller the corrosion current. 　　③Hydrogen overpotential – During hydrogen-induced corrosion, the greater the overpotential for hydrogen to deposit on the metal surface, the steeper the slope of the polarization curve, and as a result, the corrosion current decreases.

2# phifon Answer: The main factors affecting electrochemical corrosion are as follows: 1. Electrode reactions must occur on the surface of the electrode; therefore, the contact area between the metal and the corrosive environment influences the corrosion rate. 2. The reactivity of the metal itself. 3. The impact of impurities in metals.

①The chemical composition and structure of the metal material itself； ②Metal surface finish (oxygen concentration difference cell corrosion) ； ③Components of the solution in contact with the metal surface and pH value ； ④Ambient temperature and humidity ； ⑤Various environmental media in contact with the metal surface.

Based on the definition of electrochemical corrosion, the factors that affect the electrochemical corrosion of metals include at least: 1. The concentration of the electrolyte solution； 2. Potential difference between the two electrodes where corrosion occurs ； 3. Oxygen content, etc. Please point out any shortcomings; I am eager to learn from you!

1. Electrochemical corrosion refers to the corrosion that occurs when impure metals or alloys come into contact with an electrolyte solution, resulting in a galvanic cell reaction. In this process, the more reactive metal loses electrons and gets oxidized. For electrochemical corrosion to occur, there must be impure metals or alloys, as well as an electrolyte solution. 2. There are two types of electrochemical corrosion in metals: (1) Hydrogen evolution corrosion: In humid air, a thin layer of water forms on the metal surface; this water layer contains acidic gases such as CO2 and SO2, thereby creating an acidic environment on the surface of steel. This allows iron to form a galvanic cell with the carbon present in the steel. In this cell, iron acts as the negative electrode while carbon acts as the positive electrode. The electrode reactions are as follows: Negative electrode: Fe – 2e– = Fe2+； The cathode reaction is: 2H＋＋2e－=H2 ； The overall reaction for corrosion is: Fe + 2H+ = Fe2+ + H2 ； The main component of rust is Fe2O3·xH2O. (2) Under normal conditions, the water film on the surface of steel is weakly acidic or neutral, but it contains a certain amount of oxygen. In this case, the metal undergoes oxygen absorption corrosion: Anode: Fe – 2e– = Fe2+ ； The cathode reaction is: 2H2O + O2 + 4e- → 4OH-, and the overall reaction is: 2Fe + 2H2O + O2 → 2Fe(OH)2. Fe(OH)2 is unstable, and further oxidation leads to the formation of rust.

Chemical corrosion is actually the result of microcells forming on the metal surface. The crystal lattice of a metal is composed of many neatly arranged metal cations and free electrons between them. When metal comes into contact with an aqueous solution, it tends to dissolve in the water in the form of ions (Fe2+), while an equal amount of electrons remains on the metal surface, causing the metal surface to become negatively charged. Metallic iron enters water as hydrated ions, that is: Fe → Fe2+ + 2e. The excess electrons on the metal surface are attracted to the metal ions in the water, and this process reaches an equilibrium, preventing further dissolution of the metal (this phenomenon is known as polarization). Clearly, polarization reduces corrosion and ultimately stops it. When water contains oxygen, carbon dioxide gas, as well as cations of acids, bases, salts, etc., the electrons on the metal surface (K) combine with the cations in the solution. For example, in the case of H+ ions in water: 2e+2H+→2H→H2↑. As a result, the metal surface becomes positively charged, forming a cathode K. The excess electrons from anode A reach cathode K through the metal, forming a current. In the presence of a depolarizer, the electrochemical corrosion process continues, with the metal continuing to dissolve and thus suffering from corrosion. This is the process of electrochemical corrosion. From the perspective of electrochemical corrosion, there are three factors that contribute to its continuation: the presence of two metal electrode segments with different electrochemical properties, which result from uneven metal composition, different mechanical deformations, and varying surface conditions (scale, oxide films) ； electrolyte solution ； Depolarizers.