Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Aluminum () is widely used in aircraft manufacture because of its low density and its strength when alloyed. It is also used in food containers because of its resistance to corrosion caused by a protective layer of aluminum oxide, .
Copper () is utilized for electrical wiring due to its high electrical conductivity and ductility. It is also used in cooking utensils because it is an excellent thermal conductor and is relatively unreactive.
Iron () is extracted and primarily used to create steel alloys. Pure iron is relatively soft and easily corroded, so it is rarely used alone for structural purposes.
Mild Steel (containing approximately carbon) is used for car bodies and machinery because it is strong, tough, and malleable.
High-carbon Steel (containing approximately to carbon) is harder and more brittle, making it ideal for cutting tools and masonry nails.
Stainless Steel is an alloy of iron containing Chromium () and Nickel (). It is used for cutlery and surgical instruments because the forms a protective oxide layer that prevents rusting.
Zinc () is used for galvanizing (coating iron or steel) to prevent rusting through sacrificial protection, and in the production of the alloy brass ( and ).
📐Formulae
💡Examples
Problem 1:
Explain why Aluminum () is preferred over Copper () for overhead power cables, even though Copper is a better electrical conductor.
Solution:
Aluminum has a much lower density than Copper ( vs ).
Explanation:
Because overhead cables must span long distances, using reduces the weight load on the supporting pylons. Additionally, is cheaper than and develops a protective layer that prevents atmospheric corrosion.
Problem 2:
A manufacturer wants to create a bridge that resists rusting in a coastal environment. Which alloy of Iron () should be used, and why?
Solution:
Stainless Steel (alloyed with and ).
Explanation:
Standard mild steel reacts with oxygen and water to form rust (). In stainless steel, the Chromium () reacts with oxygen to form a thin, invisible, and stable layer of Chromium Oxide () on the surface, which blocks further oxygen from reaching the Iron.
Problem 3:
How does Zinc () protect an Iron () pipe through 'galvanization'?
Solution:
Zinc acts as a sacrificial anode because it is more reactive than Iron.
Explanation:
In the presence of oxygen and water, the Zinc will oxidize preferentially according to the half-equation . Even if the coating is scratched, the continues to protect the by providing electrons that prevent the from forming ions.