• Alloys are mixtures of metals that have properties different from their constituent elements.
• NaK is a sodium-potassium alloy that's a liquid at room temperature and is used as a nuclear reactor coolant.
• Memory metals return to their original shape upon heating and are used for objects that get deformed through use (e.g., spectacle frames).
• Steel is an alloy of iron and carbon, harder and stronger than pure iron, ideal for construction and tools. Varieties depend on the carbon and other elements content.
• Bronze is an alloy of copper and tin, harder than copper, and resistant to corrosion. Used in shipbuilding, tools, and artifacts.
• Brass is an alloy of copper and zinc, highly malleable, used in musical instruments and door handles due to its acoustic and antimicrobial properties.

• Pure iron can be easily deformed, but when alloyed with carbon, it becomes steel, which is much harder and stronger.
• Steel is used for various applications, from construction to tools.
• The carbon content affects steel's hardness: the more carbon, the harder the steel.
  • Steels with 0.3% to 0.6% carbon by mass are known as medium steels.
  • The hardness of medium steels is measured using the Vickers hardness test, where higher values mean greater hardness.

💡 Real-World Example: A high-carbon steel knife blade is very sharp and can keep its edge for a long time but can be brittle and prone to chipping. In contrast, a low-carbon steel blade is softer and less likely to chip but doesn't retain a sharp edge as long.

• Rust is a problem because it turns iron into hydrated iron(III) oxide, which lacks metal's valuable properties.
• Rust also flakes off, reducing the metal volume and exposing more iron to corrosion.
• This has economic implications as large steel-containing structures (ships, bridges) need rust protection.
• Rust protection methods include barrier methods (painting, oiling) and sacrificial methods (galvanizing).

💡 Real-World Example: The Eiffel Tower in Paris is repainted every seven years with approximately 60 tons of paint to protect it from rust.