Aluminum is a material that people often use in industry and for their own needs. Such a metal is flexible and also resistant to external influences. It is non-toxic and safe for human health. Silver color allows the use of metal for various purposes. This is industry and the domestic sphere.
When working in industry, people often wonder if aluminum rusts. Everyone knows that if damage appears on the sheet, corrosion can develop. You should find out why aluminum rusts differently than other alloys. It is necessary to find out the reasons why it undergoes corrosion. About all this and more - read in our article today.
The properties
Let's study the characteristics of aluminum. The described metal melts at a temperature of 659 degrees Celsius. The density of the substance is 2.69 * 103 kg / cm 3 . Aluminum belongs to the group of active metals. Resistance to corrosion processes depends on a number of factors:
- The purity of the alloy. For the production of various equipment they take metal that is distinguished by its purity. It should not have various impurities. Aluminum AI1 and AB2 are widespread.
- The environment in which aluminum is located.
- What is the concentration of impurities in the environment of aluminum.
- Temperature.
- The pH of the medium has a great influence. You need to know that aluminum oxide can form when the pH is between 3 and 9. In the environment where an oxide film immediately appears on the surface of the aluminum sheet, corrosion processes will not develop.
How is aluminum protected against corrosion?
Alloys of other metals are susceptible to rust. It manifests itself quickly enough. If you create certain conditions for aluminum, then it will not collapse for many years. To protect aluminum from corrosion, a special film is formed on it. It lies with a thin layer, which is from 5 to 10 millimeters. This coating consists of aluminum oxide.
The film is durable and gives the metal additional protection against external negative influences. Thanks to this layer, air and moisture do not enter the structure of the material. If the integrity of the oxide coating is violated, then the process of corrosion of aluminum begins. Metal loses its properties.
Causes of corrosion
When the question arises of whether aluminum rusts, it is necessary to think about the causes that lead to corrosion. Various external factors can accelerate this process. The causes of rust on aluminum can be as follows:
- Interaction with any acid or alkali.
- Mechanical pressure. For example, friction or a strong blow, after which a scratch appears on the upper layer of metal.
- There are industrial areas. In them, the decay products of the fuel affect the oxide film and destroy it. The metal begins to deteriorate. A similar situation occurs in megacities, where the decay products of the fuel will interact with sulfur, as well as with carbon oxides. A similar process destroys the film on aluminum. After this kind of external impact, aluminum corrodes.
- It should be remembered that chlorine, fluorine, as well as bromine and sodium can dissolve the protective layer of the metal.
- If building mixtures get on the metal, then it begins to deteriorate quickly. In this case, cement adversely affects aluminum.
- Does aluminum rust from water? If it hits the sheet, then the metal may be susceptible to corrosion processes. It is important to clarify which fluid has an effect. Many use a special alloy that is not susceptible to corrosion from water. It is called duralumin. A unique alloy is used together with copper, as well as with manganese.
What is electrochemical corrosion and can it be on an aluminum sheet?
Most often, the appearance of electrochemical corrosion provokes galvanic vapors. Damage appears at the junction of two different alloys. In this case, the rust will clearly catch your eye. The important point is that only one metal deteriorates, and the second is a source of triggering the corrosion process. In order not to be afraid of electrochemical corrosion, you need to use a magnesium alloy. Due to electrochemical rust, experts do not recommend using ordinary iron in contact with an aluminum body.
What factors can slow down the process?
There are a number of factors that slow down the corrosion of aluminum, and some of them stop this phenomenon. The following are distinguished:
- In order to maintain the properties of aluminum that prevent corrosion, it is necessary to maintain an acid-base balance. The range should be between six and eight units.
- It is believed that pure metal, without impurities, better resists aggressive environments. Scientists conducted experiments. According to the results, it can be said that pure aluminum alloys (90%) are more susceptible to corrosion than an alloy containing 99% of this substance. In the first embodiment, corrosion occurs 80 times faster than in the second alloy.
- So that in an aggressive environment the metal does not lose its properties longer, it is treated with a special paint. You can use a polymer composition. After processing, an additional protective layer appears.
- If 3% manganese is added to the alloy during production, it will be possible to avoid aluminum corrosion.
Under what conditions does the destruction of aluminum in air begin
Some people wonder if aluminum rusts in the air. If the oxide film on the upper metal layer is destroyed, the corrosion process can begin. As a result, rust may appear. Film growth usually slows down in the fresh air. It should be remembered that aluminum oxide has a good adhesion to the surface of the metal.
If the sheet is stored in a warehouse, then the film will be from 0.01 to 0.02 microns. If the metal is in contact with dry oxygen, then the thickness of the oxide film on the surface will be from 0.02 to 0.04 microns. If aluminum is subjected to heat treatment, the film thickness changes. It will be equal to 0.1 microns.
It is believed that aluminum has sufficient resistance to use it in the fresh air. For example, it is used in rural areas, as well as in remote industrial areas.
How does water affect the described metal?
Corrosion of aluminum in water can occur from damage to the top layer and protective film. The high temperature of the liquid contributes to the speedy destruction of the metal. If aluminum is placed in fresh water, then corrosion processes will practically not be observed. If you increase the temperature of the water, then you can not notice the changes. When the liquid is heated to a temperature of 80 degrees and above, the metal begins to deteriorate.
The corrosion rate of aluminum increases if alkali enters the water. The described metal has an increased sensitivity to salt. That is why sea water is fatal to him. To use this metal in sea water, it is necessary to add magnesium or silicon to the liquid. If you use a sheet of aluminum, which contains copper, then the corrosion of the alloy will proceed much faster than with a pure substance.
Is sulfuric acid dangerous for aluminum?
People are wondering if aluminum rusts in sulfuric acid. Such an acid is potentially hazardous to alloys. It has pronounced oxidizing properties. They destroy the oxide film and accelerate metal corrosion.
An interesting point is that concentrated cold sulfur does not affect aluminum. If aluminum is heated, then metal corrosion processes may begin. In this case, salt appears, it is called aluminum sulfate. It is soluble in water.
Durability of aluminum in nitric acid
The described metal is highly resistant to nitric acid in the solution. It is often synthesized in order to obtain concentrated nitric acid.
What substances do not affect aluminum?
Do not be afraid of corrosion processes if aluminum comes into contact with citric acid. Malic acid and fruit juice will not change the properties of its alloy. Oily has little effect on alloys, which include aluminum.
Will metal corrosion occur upon contact with alkali?
Do not allow contact of aluminum with various alkalis. They easily destroy the protective film on the top layer. The metal reacts with water, after which hydrogen begins to be released. The corrosion process occurs in this case quickly. Mercury and copper also adversely affect the protective layer of aluminum.
So, we found out if aluminum rusts. As you can see, it does not always have good corrosion protection.