Corrosion Inhibition Mechanism of Sodium Tungstate
In order to protect the environment, human efforts to develop new, efficient, low toxicity, pollution-free corrosion inhibitors, sodium tungstate quickly favored by people.
Sodium tungstate was first used as a corrosion inhibitor for organic antifreeze, and subsequently developed in other functional packages. Tungstic acid can be used in different corrosive media, such as fresh water cooling water, seawater cooling water, oil recovery in the oil field, molten salt, water-cooled internal combustion engine antifreeze, adsorption type refrigerant circulating fluid and coal slurry. You can also add anti-rust paint and mold resin material from the role of corrosion inhibition.
Sodium tungstate alone has some inhibition, but the corrosion rate is not high, and the amount is large, the cost is difficult to control, therefore, sodium tungstate is mixed with other organic compounds in general industry, which can significantly improve the corrosion inhibition performance and reduce the cost of sodium tungstate.
Sodium tungstate can not only inhibit the uniform corrosion of metals, but also inhibit the pitting corrosion. Before the metal is immersed in the solution, the coverage of the surface metal oxide is quite high due to the action of oxygen in the air, and the oxidation rate is further increased after entering the solution, so that the anode area decreases and the anode current density increases. While WO42- can discharge rapidly at high current density, at this time, its oxidation ability is very strong, Fe2+ can be oxidized to Fe3+, which promotes the formation of iron oxide film, therefore, tungstate does not play a major role in the formation of metal passive film. It only acts as the maintenance and repair function of the film.
In addition to the oxidizing sodium tungstate inhibitor has in common, its specificity can not be ignored, such as: the oxidation of tungstate is relatively low, and the atomic weight of tungsten is larger; Tungstate can form a very small salt with many metal ions. Therefore, whether the passivation film theory or the characteristic adsorption theory, we only need to know that sodium tungstate has good metal corrosion inhibition, and it is the ideal material to inhibit metal corrosion, so that is enough.
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