Extraction and Uses of Metals

What an alloy is

• An alloy is a mixture of a metal with one or more other elements, usually another metal or a non-metal such as carbon
• Examples already encountered:
  • Steel: iron + carbon (see section 3)
  • Brass: about 70% copper + 30% zinc — used for fittings, decorative work and musical instruments
  • Bronze: copper + tin — used for statues, bells and bearings

Why alloys are harder than the pure metal

• Pure metals deform easily because layers of identical-size atoms slide cleanly over one another (this was the malleability argument in topic 08)
• In an alloy, the added element has atoms of a different size, which disrupts the regular layered packing
• The disrupted layers can no longer slide smoothly, so the alloy is harder and more rigid
• Many alloys are also chosen because they resist corrosion (stainless steel, bronze) or tolerate higher temperatures (nichrome heating elements)
• The detailed structural picture sits in topic 08 Metallic Bonding, section 3