Almost none of the ancient ironware displayed in the museum rusted; If you don't use a kitchen knife for a few months, you will be covered with rust. As the saying goes, "A sharp knife needs no yellow rust." Iron rusts easily. Every year, tens of millions of tons of steel rust in the world.
Iron rusts easily, not only because of its active chemical properties, but also because of external conditions.
Moisture is one of the conditions for iron to rust easily. Chemists have proved that iron will not rust for several years in absolutely anhydrous air.
However, water alone will not rust iron. People have tried to put a piece of iron in a boiling, closed distilled water bottle, and the iron will not rust.
Have you noticed those water pipes by the river? They usually rust at the top and bottom, but only near the water surface. It turns out that iron will rust only if oxygen in the air is dissolved in water. In the section near the water surface, which is closest to the air, the oxygen dissolved in the water is also the most, so it is easy to rust. Carbon dioxide in the air can also rust iron. The composition of rust is very complex, mainly iron oxide, iron hydroxide and iron oxide.
It's too rusty. It is loose and soft, like a sponge. When a piece of iron is completely rusted, its volume can expand by 8 times. This spongy rust absorbs water very easily. Naturally, iron will rot faster. There are many factors that make iron easy to rust, such as salt in water, unclean and rough surface of iron products, and other metals in iron ... "
People must not sit idly by and watch the steam, oxygen and carbon dioxide in the air so rampant that they "steal" so much steel from people. People have come up with various ways to protect steel.
The most common way to prevent rust is to trim iron-paint the surface of iron or plate it with other metals that are not easy to rust. For example, a car is covered with shiny spray paint; The heating tube is coated with aluminum paint; Tinplate for canning is coated with tin; The iron sheet on the roof is covered with zinc; Plug in your fountain pen and plate it with chromium or nickel. A more thorough method is to inject iron with a "cardiotonic needle"-adding other metals to make a stainless alloy. The famous stainless steel is an alloy made by adding a small amount of nickel and aluminum to steel.
2。 From/lunwen/liveche/200611/517.html.
Proper measures should be taken against the causes of metal corrosion for rust prevention. Commonly used methods are:
[Changing the internal structure of metal] For example, making various corrosion-resistant alloys, such as adding chromium and nickel to ordinary steel to make stainless steel.
[Protective layer method] Cover the metal surface with a protective layer to isolate the metal products from the surrounding corrosive media, thus preventing corrosion. Such as: 1. Apply engine oil, vaseline, paint, enamel, plastic and other corrosion-resistant nonmetallic materials to the steel surface. 2. Using electroplating, hot plating, spraying and other methods, the steel surface is plated with a layer of metals that are not easy to be corroded, such as zinc, tin, chromium, nickel, etc. These metals usually form a dense oxide film due to oxidation, thus preventing the corrosion of steel by water and air. 3. A fine and stable oxide film is formed on the surface of steel by chemical method. For example, a fine black ferroferric oxide film is formed on the surface of steel parts such as machine parts and guns.
[Electrochemical Protection Law] The metal is protected by the principle of galvanic cell, and the galvanic cell reaction causing electrochemical corrosion is eliminated as far as possible. Electrochemical protection methods can be divided into anode protection and cathode protection. Cathodic protection method is widely used.
[Treatment of corrosive medium] Eliminate corrosive medium, such as cleaning metal equipment frequently, placing desiccant in precision instruments, and adding a small amount of corrosion inhibitor to the corrosive medium to slow down the corrosion rate.
[Electrochemical protection] The protected metal is used as the cathode of the corrosion battery to prevent it from being corroded, so it is also called cathodic protection. This method mainly has the following two kinds:
[Sacrificial anode protection method] This method is to connect an active metal (such as zinc or zinc alloy) to the protected metal, and when electrochemical corrosion occurs, this active metal acts as the negative electrode of the oxidation reaction, thus reducing or preventing the corrosion of the protected metal. This method is often used to protect steel piles and ship hulls in water, such as protecting steel gates in water. Usually, several zinc blocks are welded on the rudder below the waterline of the hull or near the propeller to prevent the hull from corrosion.
[External current protection method] Connect the protected metal to the negative pole of the power supply, and select another conductive inert material to connect to the positive pole of the power supply.
After electrifying, negative charges (electrons) accumulate on the metal surface, thus inhibiting the metal from losing electrons and achieving the purpose of protection. This method is mainly used to prevent the corrosion of metal equipment in soil, seawater and river water.
Another method of electrochemical protection is called anode protection, that is, the anode is passivated within a certain potential range by applying voltage. It can effectively prevent or prevent the corrosion of metal equipment in acid, alkali and salt.