Alloys and their properties
Introduced| English | Meaning |
|---|---|
| alloy/ˈælɔɪ/ | A mixture of a metal with one or more other elements. |
| steel/stiːl/ | steel |
| brass/bræs/ | A mixture of copper and zinc. |
| bronze/brɒnz/ | bronze |
| stainless steel/ˈsteɪnləs stiːl/ | stainless steel |
Mixing metals for strength
- Pure metals are often too soft or weak for the job.
- Mixing them makes alloys 合金 — usually stronger and more useful than the pure metal.
Alloy property lab
See why mixing atoms changes metal properties.
An alloy is:
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Alloys are mixtures based on a metal.
Steel is an alloy of iron and:
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Steel is iron + carbon.
Brass is an alloy of copper and ______.
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Brass = copper + zinc.
What an alloy is
- An alloy is a mixture of a metal with one or more other elements.
- Examples: steel 钢 (iron + carbon), brass 黄铜 (copper + zinc), bronze 青铜 (copper + tin).
Different-sized atoms in an alloy stop the layers sliding, so it is harder
Alloys are harder than pure metals because the different-sized atoms:
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Disrupted layers cannot slide, so the alloy is harder.
Why alloys are harder
- In a pure metal, layers of identical atoms slide easily, making it soft.
- Different-sized atoms in an alloy disrupt the layers, so they can't slide — making it harder.
Stainless steel contains carbon, which stops it from rusting.
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False. Chromium (and often nickel) gives stainless steel its resistance to corrosion. Carbon makes steel harder but does not stop rusting.
Tailoring properties
- Alloying lets us tune properties: strength, hardness, corrosion resistance.
- Stainless steel 不锈钢 (with chromium) resists rust; this is why it's used for cutlery.
Worked example. Pure iron is soft and bends easily. Adding a little carbon to make steel disrupts the atom layers, making it much harder and stronger — ideal for construction.
You've got it
- an alloy is a metal mixed with other elements (steel, brass, bronze)
- different-sized atoms disrupt the layers, so alloys are harder than pure metals
- alloying tailors strength, hardness and corrosion resistance
Write from layers that cannot slide easily
- Brass is a mixture of copper and zinc.
- The zinc atoms are a different size from the copper atoms.
Why is brass harder than pure copper?
Odd-sized atoms stop the metal layers from sliding.
Why is brass harder than pure copper?
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A disrupted lattice is harder to deform.