【Corrosion Technology Edition】Daily Question 20170712: What factors affect metal corrosion?
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To boost the popularity of the Corrosion Technology section, enhance communication among users, and facilitate mutual progress and improvement, the [One Question per Day] activity has been launched. Reward rules: 3 wealth points for replying, 10 wealth points for correct answers. This topic is valid for two days; no scoring or rewards will be given after that. Short answer question: What factors affect metal corrosion? 1. Material factors – including material composition, microstructure, heat treatment condition, surface treatment condition, workpiece structure, properties, etc ； 2. Medium factors — including medium composition, pH value, medium state, etc ； 3. Operating factors — temperature, pressure, flow rate. ================================ Event Promotion: Petrochemical Zone – “Creative Ideas for Energy Saving”: The Second Session of This Event is in Full Swing http://bbs.hcbbs.com/thread-1666758-1-1.html (Source: Haichuan Chemical Industry Forum) 2017: “My Technical Upgrades” in the Coal Chemical Industry http://bbs.hcbbs.com/thread-1786290-1-1.html (Source: Haichuan Chemical Industry Forum)
The essence of metal corrosion is the process in which metal atoms lose electrons and get oxidized. Metal corrosion can generally be divided into chemical corrosion and electrochemical corrosion. 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. If the water film is weakly acidic or neutral, more oxygen can dissolve in it, and at this point O2 ions gain electrons and OH- ions are released; this type of electrochemical corrosion is called 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. Cathodic reactions: 2H++2e-=H2↑; O2+4e-+2H2O=4OH-. Anodic reactions: Fe-2e-=Fe2+; 2Fe-4e-=2Fe2+. The electrode at which the pH of the solution increases is the cathode. Other reactions: Fe2+ +OH-=Fe(OH)2↓; 4Fe(OH)2 +O2+2H2O= 4Fe(OH)3. 2. Several important methods for metal protection: ① Altering the internal structure of the metal by creating alloys. ②Cover the metal surface with a protective layer. ③Electrochemical protection method, which involves protecting a metal by using it as the anode in a galvanic cell or the cathode in an electrolytic cell. 3. Methods for determining the rate of metal corrosion: ① In the same electrolyte solution: corrosion caused by the electrolysis principle > corrosion caused by the galvanic cell principle > chemical corrosion > corrosion under anti-corrosion measures. ②For the same metal, strong electrolytes > weak electrolytes > non-electrolytes. ③The greater the difference in reactivity among metals, the faster they corrode. ④For the same electrolyte, the higher the concentration of the electrolyte solution, the faster the corrosion occurs.
Metal corrosion is caused by various internal and external factors, which can be summarized as follows: ① The 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 ； ④Environmental temperature and humidity ； ⑤Various environmental media in contact with the metal surface.
Relative humidity, temperature, oxygen, etc
The factors affecting the corrosion rate of metals can be categorized into three aspects: 1. Material factors—including material composition, microstructure, heat treatment condition, surface treatment condition, workpiece structure, and properties, etc； 2. Medium factors—include medium composition, pH value, medium state, etc ； 3. Operating factors—temperature, pressure, flow rate.
External factors such as temperature, humidity, and acidity or alkalinity of the environment can affect the properties of metal materials. The interior mainly consists of factors such as the microstructural structure of metallic materials, grain size, and distribution.
External factors such as temperature, humidity, and acidity or alkalinity of the environment can affect the properties of metal materials. The interior mainly consists of factors such as the microstructural structure of metallic materials, grain size, and distribution.
Temperature, moisture, ion content; for buried pipelines, current is also a factor, as well as the contact between different metals. It seems there are quite a few factors.
Temperature, pressure, chemical corrosion
External factors such as temperature, humidity, and acidity or alkalinity of the environment can affect the properties of metal materials. The interior mainly consists of factors such as the microstructural structure of metallic materials, grain size, and distribution.