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Structure of Metals and Alloys

Metals and alloys are composed of atoms held together by metallic bonds, which involve a lattice of positively charged ions surrounded by a “sea” of delocalized electrons. Understanding their structure explains many of their characteristic properties, such as conductivity, malleability, and strength.

Metallic Structure

  • Metallic Bonding: Positively charged metal ions are embedded in a sea of delocalized electrons. This allows electrons to move freely, giving metals their conductivity.
  • Crystal Lattice: Metals arrange themselves in regular lattice structures to maximize stability and packing efficiency.

Common Metallic Lattices

  • Face-Centered Cubic (FCC): High packing efficiency, common in metals like copper, aluminum, and gold.
  • Body-Centered Cubic (BCC): Moderate packing efficiency, found in metals like iron and chromium.
  • Hexagonal Close-Packed (HCP): Found in metals like magnesium and zinc, offering dense packing.

Alloys

  • Definition: Mixtures of metals or metals with nonmetals designed to improve properties.
  • Types of Alloys:
    • Substitutional Alloy: Some metal atoms are replaced by other atoms of similar size (e.g., brass: Cu + Zn).
    • Interstitial Alloy: Smaller atoms fit into the spaces (interstices) between metal atoms (e.g., steel: Fe + C).

Properties of Metals and Alloys

  • Electrical and Thermal Conductivity: Delocalized electrons carry charge and heat efficiently.
  • Malleability and Ductility: Layers of ions can slide past each other without breaking metallic bonds.
  • Strength and Hardness: Alloying can increase strength, hardness, and resistance to corrosion.

Importance

Understanding the structure of metals and alloys is essential for:

  • Designing materials with specific mechanical properties
  • Explaining conductivity and thermal behavior
  • Engineering applications in construction, electronics, and manufacturing

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