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Corrosion is a gradual degradation of metal when it comes in contact with surroundings like moisture and air, thus forming the oxides of the metal on its surface. This phenomenon is called corrosion, and the metal on which the phenomenon occurs is known as corroded metal.
Metals undergo corrosion easily, and due to this, their strength is also affected.
Rusting is the process by which the corrosion of iron takes place. It can be prevented by certain methods, including applying oil on the metal surface. The corrosion of metals can occur any time it comes in contact with their surroundings, leading to deterioration.
Do all metals corrode?
Corrosion can occur in any metal. Corrosive metals, such as pure iron, corrode quickly. Stainless steel, on the other hand, which corrodes slowly when combined with iron and other alloys, is used more commonly. Noble metals are a type of metal with a lower reactivity than other metals. As a result, They don’t corrode very often. They are the only metals present in nature in their purest form. They include palladium, silver, platinum, and gold.
The metals that don’t corrode simply are Au and Pt. Since they’re unaffected by Oxygen and different acids, they don’t corrode visibly and are more stable than several of their compounds, like oxides and sulphides.
They are called “noble metals” due to “missing chemical reactivity”.
Gold is the least reactive of all metals, making it suitable for usage in both natural and man-made environments. Since gold does not react with oxygen it never tarnishes. Corrosion affects the surface of the metallic object with oxides. These oxides are present in the water or moisture.
For example:
- Tarnishing of silver
- Rusting of iron etc.
.
Gold and Platinum are used to make Jewellery.
Jewellery is created from Gold and Platinum
Since the metals utilised in jewellery are typically chosen on the premise of their reactivity, noble metal and gold are used to make jewellery. They are exceptionally lustrous metals and are corrosion resistant. They can be moulded into any form or pattern due to their extraordinary property of malleability and ductility. Hence, they are expensive compared to different metals.
The cause behind Corrosion of metals.
Apart from gold, noble metals such as platinum and a variety of other metals do not exist in their pure form in nature. They are usually bound to different substances in ores, like sulphides, oxides, etc.
To acquire pure metals, energy must be expended to separate metals from sulphides, oxides, and other compounds.
Pure metals have a greater energy state than sulphides or oxides seen in nature, indicating that they have more bound energy.
All matter in the cosmos aspires to return to its lowest energy state, and pure metals aspire to return to their lowest energy state as sulphides or oxides. Corrosion is one of the ways that metals might revert to an occasional energy state. Sulphides or oxides are the most common byproducts of metal corrosion.
Corrosion rate-affecting variables:
The following are the factors that influence metal corrosion rates:
1.Oxidizing agents: The corrosion process is dependent on the existence of both “anodic” and “cathodic” reactions at the same time. Because the anodal reaction causes the metal to dissolve and the cathodic reaction requires an oxidant, the most common dissolved agents are oxygen or hydrogen ions. When the supply of oxidising substances is reduced, corrosion processes are stifled or even halted.
2.The electrolyte’s electrical conductivity:
Chemical reactions are involved in corrosion, therefore an increase in the electrical conductivity of the solution can speed up the process.
3.Temperature:
A rise in temperature will usually increase the rate of corrosion.
4.Concentration:
When the concentration rises, the corrosion rate rises with it until it reaches a maximum. Higher concentrations than this will not result in a faster rate of corrosion.
Example-A chloride concentration of more than 1500 ppm, for example, will not accelerate corrosion.
Methods of Prevention from Corrosion:
- Protection by cathodic action:
It’s a method of preventing metal oxidation by employing a sacrificial anode and effectively transforming the metal to be protected into the cathode.
- Galvanised iron:
It is the method of protecting iron by covering it with zinc.
- Sacrificial anode:
In cathodic protection, a more active, less expensive metal is utilised as the anode; magnesium or zinc are usually used.
Conclusion
Corrosion as we understood is the degradation of metal due to exposure to atmospheric air and moisture. It can occur on any metal,depending on the purity of the metal. Highly reactive metals get easily corroded, whereas less reactive metals are hard to corrode.Inert elements like gold and platinum are used to make jewellery since they do undergo corrosion easily. Rate of corrosion gets affected by four principle factors. Preventive measures taken up to avoid corrosion include galvanising,sacrificial anode, and tin plating.
