Why doesn't aluminum rust?

Many people think that aluminum does not rust easily. In fact, aluminum rusts more easily than iron! But aluminum is rusty, unlike iron, which is full of scars, it is still beautiful.

In fact, rust is mainly a metal oxidized by oxygen in humid air. Oxygen is the biggest headache for iron. After iron rusts, oxygen can corrode under the condition of loose rust. Aluminum is easy to react with oxygen to synthesize aluminum rust-alumina, or alumina for short. This layer of alumina adheres closely to the surface of aluminum, which can prevent the aluminum inside from combining with oxygen.

But this kind of oxide film is afraid of both acid and alkali, so aluminum pot should only cook it. People often think that aluminum pot is not bright, and they always wipe it with plant ash or sand. In fact, this is a very unscientific practice. Plant ash can get rid of this "coat" of aluminum pot very well: First, it can scratch the oxide film when rubbing; Second, plant ash contains potassium carbonate, which is an alkaline substance and can dissolve oxide film through chemical action. However, when you just wipe off an oxide film, aluminum pot is a little brighter. Before long, aluminum continued to oxidize because it was not protected by an oxide film, and it was covered with an oxide film. aluminum pot was still gray. Although you pick up plant ash every day, aluminum pot still regenerates the oxide film every day. In this "seesaw battle", aluminum pot is getting thinner and thinner. Finally, aluminum pot opened the skylight-it was leaking. It took a lot of effort to break the pot.

Usually the oxide film in aluminum pot is very thin, only 0.0000 1 mm thick. In industry, in order to make aluminum products more durable, the finished aluminum products are often soaked in a solution containing 20% sodium sulfate and 10% nitric acid to make this oxide film thicker. The surface of those new aluminum pot aluminum pot in the shop is grayish white or yellowish, because it is thickened.