Tungsten Contacts Corrosion

The main factors affecting the corrosion rate of tungsten contacts corrosion are: impurities of air, humidity and metal surfaces state. If the humidity in the air is greater, the condensation of the water film on the metal surface will be thicker, so the resistance of the water film will be smaller, the corrosion will faster.

The chemical reaction formula of tungsten contacts corrosion process is as follows
W + O₂ = W - 4e + O₂ = WO₂
2WO₂ + H₂O – e = W₂O₅ + 2H
W₂O₅ + H₂O - e = 2WO₃ + 2H
WO₃ + H₂O = H₂WO₄（black gum）
H₂WO₄ – H₂O = WO₃（dehydration → tan dura）
As can be seen from the above formula, the nature of the electrochemical corrosion, which is the process of the metal atom loses electrons and be oxidized.
Electrochemical corrosion referring to the process that metal and the electrolyte have an electrochemical reaction so that the metal is destroyed.

Metal electrochemical corrosion conditions:
1. There is potential difference between metals
2. Reaction takes place in the electrolytic liquid, etc.
Tungsten contacts will corrode in humid (usually, it occurs when air humidity is greater than 60%), and is called atmospheric corrosion, which is a kind of electrochemical corrosion. Atmospheric corrosion occurs on the electrolytic film layer of the metal (dissolved a variety of salts and corrosive gas impurities), the formation of the film is due to water vapor in the atmosphere condensed or adsorbed on the metal surface.



 

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