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Converters & Calculators
Coefficient Of Thermal Expansion
Coefficient of Thermal Expansion
The thermal expansion coefficient quantifies the extent to which a material’s dimensions change as the temperature varies. It is generally expressed in units per degree Celsius (°C⁻¹) or per Kelvin (K⁻¹). Although its precise description involves mathematical formulas, the principle refers to the linear, areal or volumetric changes that a material undergoes when its temperature fluctuates.
Factors Influencing Thermal Expansion
Several factors affect a material’s thermal expansion coefficient:
Material Composition
Different materials demonstrate distinct thermal expansion coefficients due to variations in their atomic and molecular structures. Metals, ceramics, polymers and composites respond based on their inherent structural properties.
Temperature Range
The coefficient can vary with the temperature. Some materials exhibit linear expansion within a certain temperature range, whereas others display non-linear behaviour at higher or lower temperatures.
Structural Anisotropy
Materials with anisotropic properties may expand differently along various axes. This aspect is particularly important for substances such as wood or specific crystals.
External Stresses
Existing stresses within a material can affect its expansion or contraction when the temperature changes. Stresses induced during manufacturing processes may alter the effective coefficient.
Environmental Effects
Exposure to factors such as moisture or chemicals can influence a material’s expansion properties over time.
Thermal Expansion of Common Materials
The following table lists examples of various materials and their corresponding thermal expansion coefficients:
|
Material |
Thermal Expansion Coefficient (°C⁻¹) |
|
23 ×10⁻⁶ |
|
|
Steel |
12 ×10⁻⁶ |
|
Glass |
9 ×10⁻⁶ |
|
Concrete |
10 ×10⁻⁶ |
|
Copper |
16.5 ×10⁻⁶ |
|
Brass |
19 ×10⁻⁶ |
|
8.6 ×10⁻⁶ |
|
|
Polyethylene |
100 ×10⁻⁶ |
|
Carbon Fibre |
0.5 ×10⁻⁶ |
|
Invar (Alloy) |
1.2 ×10⁻⁶ |
Thermal Expansion of Common Metals
|
Metal |
TAC (10⁻⁶/°C) |
|
Aluminium |
23.1 |
|
Brass |
19–21 |
|
Phosphor Bronze |
17.6 |
|
Copper |
16.5 |
|
Gold |
14.2 |
|
Iron |
11.8 |
|
Lead |
28.9 |
|
Magnesium |
25.2 |
|
Nickel |
13.3 |
|
8.8 |
|
|
Silver |
19.5 |
|
Stainless Steel (304) |
16.0 |
|
Stainless Steel (316) |
15.9 |
|
Carbon Steel |
11.7–13.0 |
|
Tin |
22.0 |
|
Titanium |
8.6–9.4 |
|
4.5 |
|
|
Zinc |
30.2 |
|
Zirconium |
5.7 |
Frequently Asked Questions
What is the significance of the thermal expansion coefficient in engineering?
The thermal expansion coefficient is essential for designing structures and components that can accommodate temperature variations without experiencing excessive stress or deformation. It contributes to maintaining dimensional stability and ensuring the longevity of materials in practical applications.
How does the thermal expansion coefficient affect everyday objects?
Everyday objects such as bridges, railways and buildings expand and contract as the temperature changes. Understanding the thermal expansion coefficient enables engineers to design expansion joints and similar features to accommodate these dimensional variations, thereby preventing structural damage.
Can the thermal expansion coefficient be negative?
Yes, certain materials exhibit negative thermal expansion and contract when heated. These materials are uncommon and are utilised in specialised applications where controlled contraction is required.
How is the thermal expansion coefficient measured?
The coefficient is generally measured using techniques such as dilatometry. In these tests, the change in length or volume of a material is monitored while it is heated or cooled under controlled conditions.
Does the thermal expansion coefficient depend on material purity?
Impurities and alloying elements can significantly affect a material’s thermal expansion coefficient. Pure materials may exhibit expansion characteristics that differ from those of their alloyed counterparts.
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