The 7 Main Heat Conductors

The Heat conductors Principal metals and diamonds, metal matrix compounds, carbon matrix compounds, carbon, graphite and ceramic matrix compounds.

Thermal conductivity is a material property that describes the ability to conduct heat and can be defined as: "The amount of heat transmitted through a unitary thickness of a material - in a direction normal to a unit area surface - due to a unit temperature gradient under steady-state conditions"(The Engineering ToolBox, S.F.).

The 7 Main Heat Conductors

In other words, thermal conduction is the transfer of thermal energy between particles of matter being touched. Thermal conduction occurs when particles of warmer matter collide with particles of colder matter and transfer some of their thermal energy to the colder particles.

Driving is usually faster in certain solids and liquids than in gases. Materials that are good conductors of thermal energy are called thermal conductors.

Metals are especially good thermal conductors because they have freely moving electrons and they can transfer heat energy quickly and easily (CK-12 Foundation, S.F.).

In general, good conductors of electricity (metals such as copper, aluminum, gold and silver) are also good heat conductors, while electrical insulators (wood, plastic and rubber) are poor heat conductors.

The kinetic energy (average) of a molecule in the warm body is higher than in the colder body. If two molecules collide, there is a transfer of energy from the hot molecule to the cold one.

The cumulative effect of all collisions results in a net flow of heat from the warm body to the colder body (SantoPietro, S.F.).

Materials of high thermal conductivity

Materials of high thermal conductivity are required for the conduction of heat in order to heat or cool. One of the most critical needs is the electronics industry.

Due to the miniaturization and increased power of microelectronics, heat dissipation is key to the reliability, performance and miniaturization of microelectronics.

The thermal conductivity depends on many properties of a material, especially its structure and temperature.

The coefficient of thermal expansion is especially important since it indicates the ability of a material to expand with heat.

Metals and diamonds

Copper is the most commonly used metal when high thermal conductivity materials are required.

However, copper assumes a high value of coefficient of thermal expansion (CET). The Invar alloy (64% Fe ± 36% Ni) is exceptionally low in CET between metals, but is very poor in thermal conductivity.

Diamond is more attractive because it has a very high thermal conductivity and a low CET, but it is expensive (Thermal Conductivity, S.F.).

Aluminum is not as conductive as copper but has a low density, which is attractive to aircraft electronics and applications (eg laptops) that require a low weight.

Metals are thermal and electrical conductors. For applications that require thermal conductivity and electrical insulation, diamonds and appropriate ceramic materials may be used, but not metals.

Metal matrix compounds

One way to reduce the CTE of a metal is to form a metal matrix compound using a low CTE filler.

For this purpose ceramic particles such as AlN and silicon carbide (SiC) are used, due to their combination of high thermal conductivity and low CTE.

Since the filler usually has a lower CTE and a lower thermal conductivity than the metal matrix, the higher the fraction of the charge volume in the compound, the lower the CTE and the lower the thermal conductivity.

Carbon matrix compounds

Carbon is an attractive matrix for compounds for thermal conduction due to its thermal conductivity (although not as high as those of metals) and low CTE (lower than metals).

In addition, carbon is resistant to corrosion (more resistant to corrosion than metals) and its low weight.

Another advantage of the carbon matrix is ​​its compatibility with carbon fibers, in contrast to the common reactivity between a metal matrix and its charges.

Therefore, carbon fibers are the dominant filler for carbon matrix composites.

Carbon and Graphite

A fully carbon material made by consolidating oriented carbon precursor carbons without a binder and subsequent carbonization and optional graphitization exhibits a thermal conductivity ranging from 390 to 750 W / mK in the material Fiber.

Another material is pyrolytic graphite (called TPG) enclosed in a structural shell. Graphite (highly textured with the axes c of the grains preferably perpendicular to the graphite plane), has a thermal conductivity in the plane of 1700 W / m K (four times that of copper), but is mechanically weak due to the tendency to Cut in the graphite plane.

Ceramic matrix compounds

The borosilicate glass matrix is ​​attractive due to its low dielectric constant (4.1) compared to that of AlN (8.9), alumina (9.4), SiC (42), BeO (6.8), cubic boron nitride (7.1), diamond (5.6) and glass ± ceramics (5.0).

A low dielectric constant value is desirable for electronic packaging applications. On the other hand, the glass has a low thermal conductivity.

The SiC matrix is ​​attractive because of its high CTE compared to the carbon matrix, although it is not as thermally conductive as carbon.

The CTE of carbon ± carbon compounds is too low, resulting in reduced fatigue life in chip-on-board (COB) applications with silica chips.

The SiC matrix carbon composite is composed of a carbon-carbon compound converting the carbon matrix to SiC (Chung, 2001).

References

  1. Chung, D. (2001). Materials for thermal conduction. Applied Thermal Engineering 21 , 1593 ± 1605.
  2. CK-12 Foundation. (S.F.). Thermal Conductors and Insulators . Retrieved from ck12.org: ck12.org.
  3. SantoPietro, D. (S.F.). What is thermal conductivity? Retrieved from khanacademy: khanacademy.org.
  4. The Engineering ToolBox. (S.F.). Thermal Conductivity of common Materials and Gases . Retrieved from engineeringtoolbox: engineeringtoolbox.com.


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