Cathodic protection - Cathodic protection

Japanese: カソード防食 - カソードボウショク

Also known as cathodic protection, this is a method of preventing corrosion by polarizing metal materials to a lower potential than their natural potential. Anodic dissolution reaction in which metal (M) becomes metal ions (M ^{n +} ).

M → ^Mn ^＋＋ ne－

The rate of corrosion, or the rate of corrosion, decreases as the potential decreases. There are two methods for polarizing to a low potential: the external power source method and the sacrificial anode method. The former is a method in which the object to be protected is used as the cathode and an insoluble electrode such as a carbon rod as the anode, and the potential of the object to be protected is polarized to the low potential side using an external power source. On the other hand, the latter is a method in which a metal with a higher ionization tendency than the object to be protected is electrically connected to the object to be protected as a sacrificial anode, thereby polarizing the object to the low potential side. It is empirically said that the optimal potential for cathodic protection is, for example, -0.3 V from the natural potential in a neutral solution. If the potential is polarized to a lower potential than this, the metal will not corrode, but hydrogen will be generated by the electrolysis of water, which can penetrate into the metal and cause hydrogen embrittlement. This state is called over-protection. [See other terms] Anodic protection

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Japanese:

陰極防食ともいい，金属材料を自然電位より低電位側に分極することにより防食する方法．金属(M)が金属イオン(M^n＋)になるアノード溶解反応

M → M^n＋＋ ne^－

の速度，すなわち腐食速度は電位が低くなるほど小さくなる．低電位に分極する方法としては，外部電源法と犠牲陽極法とがある．前者は，被防食体を陰極，炭素棒のような不溶性の電極を陽極として，外部電源を使って被防食体の電位を低電位側に分極する方法である．一方，後者は，被防食体よりイオン化傾向の大きい金属を犠牲陽極として被防食体に電気的に接続することにより低電位側に分極する方法である．カソード防食の最適電位は，たとえば中性溶液中では自然電位から－0.3 V であると経験的にいわれている．これより低電位側に分極されると，金属の腐食は進行しないが，水の電気分解により水素が発生し，それが金属中に侵入し，水素脆化を引き起こすことがある．このような状態を過防食とよんでいる．[別用語参照]アノード防食

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