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In physics,
thermal expansion is the tendency of matter to change in volume in response to a change in temperature. When a substance is heated, its constituent particles move around more vigorously and by doing so generally maintain a greater average separation. Materials that contract with an increase in temperature are very uncommon; this effect is limited in size, and only occurs within limited temperature ranges. The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature.
Common engineering solids usually have thermal expansion coefficients that do not vary significantly over the range of temperatures where they are designed to be used, so where extremely high accuracy is not required, calculations can be based on a constant, average, value of the coefficient of expansion.
Materials with
anisotropic structures, such as crystals and composites, will generally have different expansion coefficients in different orientations.
To more accurately calculate thermal expansion of a substance a more advanced Equation of state must be used, which will then predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions.
For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the \frac{}{}\epsilon_{thermal} ratio of Strain (materials science):
\epsilon_{thermal} = \frac{(L_{final} - L_{initial})} {L_{initial-->
\frac{}{}L_{initial} is the initial length before the change of temperature and \frac{}{}L_{final} the final length recorded after the change of temperature.
For most solids, thermal expansion relates directly with temperature:
\epsilon_{thermal} \propto {\Delta T }
Thus, the change in either the strain or temperature can be estimated by:
\frac{}{} \epsilon_{thermal} = \alpha \Delta T
where
\frac{}{}\Delta T = (T_{final} - T_{initial})
and
\frac{}{}\alpha is the coefficient of thermal expansion in
inverse kelvins.
\frac{}{}\Delta T is the difference of the temperature between the two recorded strains, measured in
celsius or
kelvin.
A number of materials contract on heating within certain temperature ranges; we usually speak of negative thermal expansion, rather than thermal contraction, in such cases. For example, the coefficient of thermal expansion of water drops to zero as it is cooled to roughly 4 °C and then becomes negative below this temperature, this means that water has a maximum density at this temperature, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of sub-zero weather.
Common
Polymers expand roughly 4 times more than metals, which expand more than
ceramics. Thermal expansion generally decreases with increasing bond energy, which also has an effect on the
hardness of solids, so, harder materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids.
In many common materials, changes in size can also be due to water (or other solvents) being absorbed/desorbed, and many organic materials change size much more due to this effect than they do to thermal expansion. Common plastics exposed to water can, in the long term, expand many percent.
Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:
- Metal framed windows need rubber spacers
- Metal hot water heating pipes should not be used in long straight lengths
- Large structures such as railways and bridges need expansion joints in the structures
- One of the reasons for the poor performance of cold car engines is that parts have inefficiently large spacings until the normal operating temperature is achieved.
- a Gridiron pendulum uses an arrangement of different metals to maintain a more temperature stable pendulum length.
This phenomenon can also be put to good use, for example in the process of thermal shrink-fitting (also called "sweating"), parts are assembled with each at a different temperature, and sized such that when they reach the same temperature, the thermal expansion of the parts forces them together to form a stable joint.
Thermometers are another example of an application of thermal expansion – they contain a liquid which is constrained to flow in only one direction (along the tube) due to changes in volume brought about by changes in temperature.
External links
- Glass Thermal Expansion Thermal expansion measurement, definitions, thermal expansion calculation from the glass composition
In physics,
thermal expansion is the tendency of matter to change in
volume in response to a change in temperature. When a substance is heated, its constituent particles move around more vigorously and by doing so generally maintain a greater average separation. Materials that contract with an increase in temperature are very uncommon; this effect is limited in size, and only occurs within limited temperature ranges. The degree of expansion divided by the change in temperature is called the material's
coefficient of thermal expansion and generally varies with temperature.
Common engineering solids usually have thermal expansion coefficients that do not vary significantly over the range of temperatures where they are designed to be used, so where extremely high accuracy is not required, calculations can be based on a constant, average, value of the coefficient of expansion.
Materials with
anisotropic structures, such as
crystals and composites, will generally have different expansion coefficients in different orientations.
To more accurately calculate thermal expansion of a substance a more advanced
Equation of state must be used, which will then predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions.
For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the \frac{}{}\epsilon_{thermal} ratio of Strain (materials science):
\epsilon_{thermal} = \frac{(L_{final} - L_{initial})} {L_{initial-->
\frac{}{}L_{initial} is the initial length before the change of temperature and \frac{}{}L_{final} the final length recorded after the change of temperature.
For most solids, thermal expansion relates directly with temperature:
\epsilon_{thermal} \propto {\Delta T }
Thus, the change in either the
strain or temperature can be estimated by:
\frac{}{} \epsilon_{thermal} = \alpha \Delta T
where
\frac{}{}\Delta T = (T_{final} - T_{initial})
and
\frac{}{}\alpha is the coefficient of thermal expansion in
inverse kelvins.
\frac{}{}\Delta T is the difference of the temperature between the two recorded strains, measured in celsius or kelvin.
A number of materials contract on heating within certain temperature ranges; we usually speak of negative thermal expansion, rather than thermal contraction, in such cases. For example, the coefficient of thermal expansion of water drops to zero as it is cooled to roughly 4 °C and then becomes negative below this temperature, this means that water has a maximum density at this temperature, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of sub-zero weather.
Common Polymers expand roughly 4 times more than metals, which expand more than ceramics. Thermal expansion generally decreases with increasing bond energy, which also has an effect on the hardness of solids, so, harder materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids.
In many common materials, changes in size can also be due to water (or other solvents) being absorbed/desorbed, and many organic materials change size much more due to this effect than they do to thermal expansion. Common plastics exposed to water can, in the long term, expand many percent.
Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:
- Metal framed windows need rubber spacers
- Metal hot water heating pipes should not be used in long straight lengths
- Large structures such as railways and bridges need expansion joints in the structures
- One of the reasons for the poor performance of cold car engines is that parts have inefficiently large spacings until the normal operating temperature is achieved.
- a Gridiron pendulum uses an arrangement of different metals to maintain a more temperature stable pendulum length.
This phenomenon can also be put to good use, for example in the process of thermal shrink-fitting (also called "sweating"), parts are assembled with each at a different temperature, and sized such that when they reach the same temperature, the thermal expansion of the parts forces them together to form a stable joint.
Thermometers are another example of an application of thermal expansion – they contain a liquid which is constrained to flow in only one direction (along the tube) due to changes in volume brought about by changes in temperature.
External links
- Glass Thermal Expansion Thermal expansion measurement, definitions, thermal expansion calculation from the glass composition
Thermal expansion - Wikipedia, the free encyclopedia
Thermal Expansion is the tendency of matter to change in volume in response to a change in temperature. When a substance is heated, its constituent particles move around more ...
Coefficient of thermal expansion - Wikipedia, the free encyclopedia
When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of ...
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Thermal Expansion Over small temperature ranges, the linear nature of thermal expansion leads to expansion relationships for length, area, and volume in terms of the linear ...
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This is a page in The Physics Hypertextbook™. It is a work in progress. ... Liquids. Δ V = V 0 β Δ T. Liquids have higher expansivities than solids. β ≈ 10 −3 /K, 3α ...
Martin Dove: Negative thermal expansion in ZrW2O8
Studies of the negative thermal expansion in ZrW2O8 and ZrP2O7 ceramics . ZrW2O8 is a ceramic with negative thermal expansion over a wide temperature range, 0-1050 K.
Thermal Expansion Measurements : Thermal Performance : Material ...
Thermal expansion measurements can be made within the temperature range –140 °C to 1400 °C. ... The thermal expansion characteristics of a brittle material are perhaps much ...
DoITPoMS TLP - Thermal expansion and the bi-material strip
page of the Thermal expansion and the bi-material strip DoITPoMS TLP based at the Department of Materials Science and Metallurgy in the University of Cambridge
DoITPoMS TLP - Thermal expansion and the bi-material strip ...
Experiment 1 page of the Thermal expansion and the bi-material strip DoITPoMS TLP based at the Department of Materials Science and Metallurgy in the University of Cambridge
Negative thermal expansion (NTE) Materials
Research Overview. Recent Highlights. NTE Materials. Topas Academic. New Materials. Vacancies. Diffraction Facilities
