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How hard the atoms hold on

Why Do You Need a Furnace to Melt Iron?

Melting means shaking atoms hard enough to break their grip, and iron atoms hold on far harder than ice does.

Mercurymelts at -39°C —liquid in your handLead327°C — a campingstove could do itIron1,538°C — needsa furnaceTungsten3,414°C — the highestof any metal
Same idea, wildly different numbers.

  1. Step 1 of 5

    Solid means the atoms are stuck in place.

    Solid Atoms jiggle but stayputLiquid Atoms slide past eachother

    In a solid metal the atoms sit in a fixed grid. They jiggle, but each stays in its own spot, and that is what makes the lump keep its shape.

  2. Step 2 of 5

    Heating makes the jiggling wilder.

    1 Cold — a gentlejiggle2 Hotter —shaking harder3 Hot enough —the grid givesway

    Temperature is really just how hard the atoms are shaking. Add heat and they shake harder, until the shaking beats the grip holding them in place.

  3. Step 3 of 5

    The melting point is where shaking wins.

    An iron bar at 1,538°CHeat shaking the atoms apartThe atoms' grip on each other

    Every metal has its own tipping point, and it is sharp. One degree below it the lump is solid; one degree above and it flows.

  4. Step 4 of 5

    Stronger grip means a higher furnace temperature.

    A bulb filamentglowing white-hot Tungsten — grips harderthan any other metal

    Tungsten atoms hold each other so tightly that nothing else metal comes close. That is exactly why old light bulbs used a tungsten wire.

  5. Step 5 of 5

    Melting is why metal can be shaped at all.

    Solid metal Melted in afurnace Poured into a mould Cooled into anew shapeRecast

    Melt it, pour it into a mould, let it cool and the grid rebuilds in the new shape. Nothing was used up, so the same metal can be recast forever.

    Iron melts at 1,538°C, but a blacksmith works it around 1,100°C — hot enough for the atoms to slide past each other under a hammer without the bar ever turning liquid.

The short version

Melting is heat shaking atoms until they break their grip on each other, and metals differ enormously in how hard that grip is.

Try it yourself

Hold a chocolate button in one hand and an ice cube in the other. Both melt from the same body heat — their atoms just grip very weakly.

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