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Information about Thermal Expansion

Material Properties
Specific heat
Compressibility
Thermal expansion
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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 ratio of strain:


is the initial length before the change of temperature and the final length recorded after the change of temperature.

For most solids, thermal expansion relates directly with temperature:
Thus, the change in either the strain or temperature can be estimated by:
where
and
is the coefficient of thermal expansion in inverse kelvins.
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
compressibility is a measure of the relative volume change of a fluid or solid as a response to a pressure (or mean stress) change.



where V is volume and p is pressure.
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Physics is the science of matter[1] and its motion[2][3], as well as space and time[4][5] —the science that deals with concepts such as force, energy, mass, and charge.
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The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. One-dimensional figures (such as lines) and two-dimensional shapes (such as squares) are assigned zero volume in the three-dimensional space.
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coefficient of thermal expansion is used:
  • in linear thermal expansion
  • in area thermal expansion
  • in volumetric thermal expansion
These characteristics are closely related.
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Anisotropy (pronounced with stress on the third syllable, IPA: /ˌænaɪˈsɒtrəpi/) is the property of being directionally dependent, as opposed to isotropy, which means homogeneity in all directions.
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CRYSTAL is a quantum chemistry ab initio program, designed primarily for calculations on crystals (3 dimensions), slabs (2 dimensions) and polymers (1 dimension) using translational symmetry, but it can be used for single molecules.[1] It is written by V.R. Saunders, R.
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Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure.
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equation of state is a relation between state variables.<ref name="Perrot" >Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6.
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In thermodynamics, a state function, or state quantity, is a property of a system that depends only on the current state of the system, not on the way in which the system got to that state. A state function describes the equilibrium state of a system.
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strain is the geometrical expression of deformation caused by the action of stress on a physical body. Strain is calculated by first assuming a change between two body states: the beginning state and the final state.
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Strain can refer to:
  • Strain (materials science), the deformation of materials caused by stress
  • Strain (biology), a variant of a plant, virus or bacterium; or an inbred animal used for experimental purposes
  • Strain (injury), a muscle injury
  • Strain (music)

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Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). The degree Celsius (symbol: °C) can refer to a specific temperature on the Celsius scale
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The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero — the coldest possible temperature — is zero kelvins
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Negative Thermal Expansion (NTE) is a physicochemical process in which some materials contract upon heating rather than expanding as most materials do. Materials which undergo this unusual process have a range of potential engineering, photonic, electronic, and structural
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polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. The word is derived from the Greek, πολυ, polu, "many"; and μέρος, meros,
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The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
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ceramic is derived from the Greek word κεραμικός (keramikos). The term covers inorganic non-metallic materials which are formed by the action of heat.
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Hardness refers to various properties of matter in the solid phase that give it high resistance to various kinds of shape change when force is applied. Hard matter is contrasted with soft matter.
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An expansion joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials. They are commonly found between sections of sidewalks, bridges, railway tracks, piping systems, and other structures.
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The gridiron pendulum was an improvement of clock pendulums invented by John Harrison, consisting of alternating brass and iron rods assembled so that their different expansions (or contractions) cancel each other out.
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Shrink-fitting is a technique in which pieces of a structure are heated or cooled, employing the phenomenon of thermal expansion, to make a joint. For example, the thermal expansion of a piece of a metallic drainpipe allows a builder to fit the cooler piece to it.
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