Corrosion of Metals and Their Maintenance
Corrosion refers to the deterioration of any metal due to the chemical reactions between it and the surroundings. The rate and form of deterioration are determined by both the environmental conditions and the kind of metal. The environment that these metals react with mainly includes the gases that are in contact with them.
We use metals in our lives in various things like cans, utensils, vehicles, etc. When these corrode, they may become useless. Therefore, it is essential to prevent the corrosion of metals.
Which Metals Corrode?
All metals have the ability to corrode. While some metals like iron corrode quickly, others like stainless steel, that combines iron and other alloys, corrode very slowly. Therefore, the metals that corrode slowly are used more often in order to increase their durability.
Types of Corrosion
Corrosion can take place due to various reasons. The 4 types in which it can be categorised into are as follows:
- Environmental Cracking: Some metals may start becoming brittle, weakened, or cracked when the environmental conditions become stressful.
- Galvanic Corrosion: When two metals are situated together in any liquid electrolyte like salt water, this kind of corrosion can take place. The molecules of one metal are drawn toward the other one, resulting in the corrosion of one of the two metals.
- Localised Corrosion: This kind of corrosion attacks the parts of a metal structure only. The following are its types:
- Filiform Corrosion: This takes place when water goes under any coating like paint.
- Crevice Corrosion: This takes place at stagnant places like the ones found under gaskets.
- Pitting: This refers to the creation of very small holes on the surface of any metal.
- General Attack Corrosion: Caused by electrochemical or chemical reactions, the most common form of corrosion, the general attack corrosion, hits the whole surface of the metal structure. Since it is likely to cause the metal to fail, it is a predictable and known issue. Therefore, the prevention of this kind of corrosion can be planned and managed.
Rusting of Iron
Rusting is a kind of corrosion that takes place in iron and its alloys. In a humid environment, iron objects react with the oxygen present in the air and get rusted.
The rusting of iron makes the surface of the metal flaky and coarse. Moreover, it also makes the object fragile. Since the speed of rusting is the highest in humid environments, the pipes and water tanks are most likely to get rusted. Hence, many different methods are used to prevent metals from getting rusted:
- Controlling Humidity: By controlling the humidity of the environment, we reduce the chances of iron getting rusted.
- Painting and Coating: By coating a metal’s surface with a layer of either varnish or paint, we can break the contact between the atmospheric oxygen and the surface of the metal, making it eventually immune to corrosion.
- Galvanising: Galvanisation refers to the coating of a metal’s surface with a layer of metallic zinc. This inexpensive procedure provides the metal with protection against rusting.
- Alloying: Alloying refers to the combination of combining metal with various other substances in order to get a new metal with the best properties. Alloying iron with other alloys or stable metals can decrease the speed of rusting since the process happens because iron is attaining a more stable chemical state.
Corrosion of Steel
The process of corrosion taking place on uncoated steel is extremely complex. Factors such as exposure to the non-uniform environment, uneven internal stress, presence of impurities because of a higher instance of recycled steel, and variations in the structure or composition of the steel, all can affect the process of corrosion.
Prevention of Rusting of Steel
Whether you have a shed made of steel, parts of a car, or tools of steel, they are all likely to get rusted if their maintenance is not done properly. Mentioned below are a few ways to prevent rust formation on items that are made of steel:
- Protective Coating: Majorly depending on the kind of surface you want to protect, you may apply a coating to protect the metal from rusting. The addition of a layer of oil-based paint or acrylic latex paint helps in keeping the metal objects away from rusting.
- Keep the Metal Clean: Accumulated debris and dirt can hold moisture, allowing corrosion to take place even on a dry day. Therefore, using a pressure washer or a hose from time to time to clean up dirty areas near the metallic surfaces can aid in avoiding rusting for a long period.
- Keep the Metal Dry: Whether you forgot the tools out in the rain or have washed them, it is best to keep items made from steel dry. One must dry the tools posterior use and keep them in an enclosed place that has low humidity levels.
Other than being used to form useful alloys, manufacture stainless steel, and harden steel, chromium is also utilised for the prevention of corrosion. The metal helps in the prevention of corrosion since it possesses similar properties to that of stainless steel – it is highly resistant to corrosion.
Corrosion of Stainless Steel
Stainless steel is well-known for its resistance to corrosion in various environments in which low alloy steel tools and carbon would corrode.
The resistance is because of a thin oxide layer on the surface of the steel that is also known as the passive layer.
Stainless steel is made from iron and its alloys like carbon and chromium. Its property of high resistance to corrosion comes from chromium.
Although stainless steel is resistant to corrosion, in some situations, it can corrode. It would not corrode in usual water-based environments but may corrode in more aggressive circumstances.
The Bottom Line
Although all metals are corrosive, their rates differ according to their types. While metals like iron are highly corrosive, stainless steel and chromium take long periods to corrode. One can prevent their corrosion by keeping the metals dry, cleaning them, turning to non-corrosive metals, and by coating them. The maintenance of metals is extremely important since they are used in our daily lives.