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2. Hot metal

Hot to cold
A hot object will always transfer energy to a cooler object by heating it. If they are in contact with each other, then the energy is transferred by conduction. In conduction, the moving particles pass energy between each other. Let’s see how this happens.
Animated diagram of air particles speeding up on collision with hot surface.
Picture 4. Conduction from a hot surface to cooler surroundings.

Conducting particles
Picture 4 shows the surface of an Electric Arc Furnace. The metal surface of the furnace is extremely hot (~200 ºC). The air around the furnace is not so hot.

We can zoom in on the surface to see the particles. The metal particles are vibrating fast because they are so hot. On the other hand, the air particles are not moving so fast. So, if an air particle bumps into a metal particle, it will rebound at a higher speed. Energy has been transferred by conduction to the surrounding air.

You can find out more about the electric arc furnace in the Chemistry of steelmaking e-source, which is aimed at 14 - 16 year olds.
Refractory materials in a blast furnace
Picture 5. Refractories in a blast furnace.
What are refractories?
The inside of a blast furnace is extremely hot (up to 1500 ºC in places). The inside surfaces have to withstand these extremely high temperatures without cracking. The inside is lined with firebricks made from special refractory materials. These can withstand extremely high temperatures without cracking or taking part in any chemical reaction.
You can find out more about the electric arc furnace in the Chemistry of steelmaking e-source, which is aimed at 14 - 16 year olds.
It takes a lot of energy to heat up the metal inside a furnace. It is important that as little of this as possible is wasted. Therefore the furnaces are well insulated. The refactory bricks that line the furnace are designed to be poor conductors of heat.
the scale of the nucleus
Picture 6. A cool lattice. If we heat the left hand end, then the energy will be carried along by conduction.
Conducting across a solid
The particles in the brick are bound together. Energy is transferred across the brick by the vibrations of the particles. The particles on the inside surface are vibrating fast because this surface is so hot. They make their neighbours vibrate and, eventually, the particles on the outside of the brick will be vibrating fast as well.
Metals and conduction
Metals are good conductors and so is carbon. Carbon, being a refractory, can be used at the extremely high temperatures in furnaces. Good conductors are useful in situations where we need to keep something cool by conducting the heat away. For example:
  • to stop the hearth of a blast furnace overheating
  • cooling the steel in the mould and rollers of a continuous casting mill

Question 2-2.

Fill in the gaps in the paragraph below. Choose the best answer in the first two and fill in the three blanks (make sure you spell the words correctly).

A is a material that is good at transferring energy from a hot place to a cooler place. Examples include all and . On the other hand, are poor at transferring energy.

A material is good at withstanding high temperatures.

Summary                   Close
  • Conduction transfers energy from hot bodies to cold ones
  • and from the hot to cold parts of a material
  • In conduction, energy is transferred by vibrating particles
  • Refractory materials can withstand extremely high temperatures
  • Carbon and metals are good thermal conductors