Influencing factors

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Influencing factors - thermal expansion
 
- the thermal expansion of a material is dependent on the actual material concerned. Pure metals, alloys, ceramics, organic substances, liquids and gases show completely different expansion behaviours; see the table for examples
- expansion depends on the physical state (solid, liquid, gas) of a given material
- for solids, the crystal structure (e.g cubic or hexagonal) as well the microcrystalline structure (single crystal or polycrystalline) strongly influence expansion behaviour
- the expansion of metals and alloys generally increases with temperature
Linear expansion coefficient of some common materials
Material α/ 10-6 K-1
Glass ~ 0.90
Concrete ~ 3.20
Steel ~ 12.0
Copper ~ 12.4
Aluminium ~ 23.4
Lead ~ 29.0
- negative expansion coefficients can be found in various anisotropic crystals, some rare metals (e.g. plutonium) and water (in the temperature range from freezing point to 4C)
- some alloys have been designed specially to have little or almost no thermal expansion with rise in temperature, e.g. Inconel, a nickel alloy

 

Influencing factors - density
 
- density depends on the physical state (solid, liquid, gas) of a given material
- the density of solids depends strongly on defects such as pores, cracks, lattice displacements, etc
- for all physical states, temperature is one of the main influences on density
- the density of liquids and gases is very dependent on the pressure of the surrounding atmosphere. For solids only very high ambient pressures will have a significant influence on the material density



Density is influenced by temperature.
Normally, a material when solid (= colder) is
more dense than when liquid (= warmer). A
solid metal usually sinks when immersed in
its liquid, whereas ice is less dense than its liquid (one of water's many anomalies) and
therefore floats on water, just as an iceberg
does on the ocean.


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