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The principle of passivation of stainless steel

Passivation is the transformation of the metal surface to not easily oxidized state, slow down the corrosion rate of metal.In addition, a kind of active metal or alloy, including chemical activity is reduced greatly, and become a phenomenon in the state of the precious metal, also called passivation.


Phenomenon: metal corrosion products generated as a result of the action of medium if has compact structure, forming a layer of thin film (often invisible), tightly covered on the surface of metal, is to change the surface state of metal, the metal electrode potential jump towards is greatly, and become a corrosion resistant passivity.Such as Fe - Fe++ standard potential is 0.44 V, after passivation jump to + 0.5 ~ 1 V, which shows the corrosion resistance performance of precious metals, this layer is called passivation film.


Metal passivation may also be a spontaneous process (such as on the surface of metal generates a layer of dissolved compounds, namely the oxide film).In industry is to use passivator (mainly oxidant) passivation of the metal, forming a layer of protective film.A common example: cold - H2SO4 and iron passivation will happen.


The principle of passivation
Available film theory to explain the mechanism of the passivation, that passivation is due to the nature of the oxidation of metal and, work on the metal surface to generate a very thin, dense, covering performance good, firmly adsorbed on the metal surface passivation membrane.The membrane into separate phase present, usually of metal oxide compound.It plays the metal with the corrosive medium completely separated, prevent metal contact with the corrosive medium, so that the basic stop dissolved metal forming passivity, reach the role of anti-corrosion.


Passivation and rust-proof oil distinction
Passivation and rust-proof oil generation is the main difference between products is not the same;Anti-rust oil is the use of the oil film closed stomata to isolation and oxygen on the surface of the metal contact and effectively prevent rust role, is a real physical reaction.Oil film more easily cleared, with production of the failure of destruction;And passivation is to use the passivation liquid oxidizing substances in REDOX reaction with the metal, prompted to generate a layer of metal on metal surface oxide compounds, achieve the goal of effective protection of metal.A process which belongs to the chemical reaction.The passivation membrane density, complete destruction.


The advantages of choosing passivation
(1) compared with the traditional physical method, after passivation has the characteristics of not increase the thickness of the workpiece and change color, improves the precision and value-added products, make the operation more convenient.(2) because of the passivation process belongs to the reaction condition, passivation agent can be used repeatedly, so the cost of living longer, more economical.(3) passivation prompted oxygen molecules structure of metal surface passivation membrane, membrane layer of dense, stable performance, and in the air at the same time have repair effect, so compared with the traditional method of tu rust-proof oil, passivation formation of the passivation film is more stable, more corrosion resistance.


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