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Question

Answer the following
A. What is done to prevent corrosion of metals?
B. What are the metals that make the alloys brass and bronze ?
C. What are the adverse effects of corrosion ?
D. What are use of Noble metals. ?

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Solution

a.We can prevent corrosion by selecting the following things:

  1. metal type
  2. protective coating
  3. environmental measures
  4. sacrificial coatings
  5. design modification

Metal Type :
One simple way to prevent corrosion is to use a corrosion resistant metal such as aluminium or stainless steel. Depending on the application, these metals can be used to reduce the need for additional corrosion protection.

Protective Coatings :
The application of a paint coating is a cost-effective way of preventing corrosion. Paint coatings act as a barrier between metal and atmospheric moisture to avoid its contact. For example : black paint.
Another possibility is applying a powder coating. In this process, a dry powder is applied to the clean metal surface to avoid its contact with surrounding oxygen. For example : acrylic, polyester, epoxy, nylon and urethane.

Environmental Measures :
Corrosion is caused by a chemical reaction between the metal and gases in the surrounding environment. By taking measures to control the environment, these unwanted reactions can be minimized. For example : this would be decrease by treating the water in water boilers with softeners to adjust hardness, alkalinity or oxygen content.

Sacrificial Coatings :
Sacrificial coating involves coating the metal with an additional metal type that is more likely to oxidize.
There are two main techniques for sacrificial coating:
Cathodic Protection : The most common example of cathodic protection is the coating of iron alloy steel with zinc, this process is known as galvanizing. Zinc is a more active metal than steel and when it starts to corrode it oxides which inhibits the corrosion of the steel. This method is known as cathodic protection
Anodic Protection : Anodic protection involves coating the iron alloy steel with a less active metal, such as tin. Tin will not corrode, so the steel will be protected as long as the tin coating is in place. This method is known as anodic protection

Design Modification :
Design modifications can help reduce corrosion and improve the durability of any existing protective anti-corrosive coatings. Ideally, designs should avoid trapping dust and water, encourage movement of air, and avoid open crevices. Ensuring the metal is accessible for regular maintenance will also increase longevity.

b.Brass: It is an alloy, that contains copper and zinc as major constituents.
Bronze: It is an alloy, that contains copper and tin as major constituents.


c.The adverse effects of corrosion are as follows:
  • Damage to commercial airplanes that could result in possible in-flight problems
  • Damage to oil pipelines that could cause a costly and dangerous rupture that creates significant environmental damage.
  • Damage to bridge supports that could cause a bridge failure
  • Release of harmful pollutants from iron corrosion that contaminates the air
  • Costs of repairing or replacing household equipment that fails
  • Lose of efficiency
  • Contamination of product
  • Damage of metallic equipments
  • Inability to use metallic materials
  • Lose of valuable materials such as blockage of pipes, mechanical damage of underground water pipes
  • Accidents due to mechanical lose of metallic cars, aircrafts etc.
  • Causes pollution due to escaping products from corrosion
  • Depletion of natural resource
d.Uses of Noble metals are:

Uses of Silver : It is a shiny, heavy metal, and the best conductor of electricity.

  • It is used for making silver ornaments and expensive utensils such as glasses, mugs, etc.
  • It is used for making coins.
  • Salts of silver like silver chloride are used for making photographic films.
  • Silver foils are used for decorating sweets.
  • Silver is also used for making mirrors using a process called sputtering.

Uses of gold : Gold is bright yellow and a highly malleable and ductile metal.

  • Gold is used as the index of wealth. The countries which have more gold reserve are considered to be wealthy.
  • It is used for making ornaments.
  • It is used for making high-value coins and medals.
  • It is used for covering the mainframe of artificial satellites.

Uses of platinum : Platinum is silvery white, a highly malleable and ductile metal.

  • It is used for making ornaments and watches.
  • It is used as a catalyst in the manufacture of sulphuric acid and nitric acid.
  • It is used in platinum catalytic converters.
  • It is also used in chemical laboratories.

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