Middle school only introduces iron, aluminum and concentrated sulfuric acid, concentrated nitric acid passivation, in fact, some other metals can also be
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The essence of metal passivation is that the metal is oxidized by concentrated sulfuric acid and concentrated nitric acid, and a dense oxide film is generated on the surface, which is insoluble in concentrated sulfuric acid and concentrated nitric acid, because the hydrogen ions ionized by concentrated sulfuric acid and concentrated nitric acid are relatively small. When diluted or heated, this oxide film is destroyed.
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reaction equation
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4Al 12HNO3(injection)=2Al2O3 12NO2 proposition 6H2O
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The surface of a metal darkens when passivated
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Chromium, aluminum, titanium and other metals are easy to be passivated by oxygen in the air and many kinds of oxygen-containing solutions, so they are called \"self-passivated metals\".
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Iron, nickel, chromium, molybdenum. Titanium and other metals can undergo electrochemical passivation due to anode polarization.