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Thermal Conductivity In Aerospace Materials

Jan 12

Aerospace Materials

Thermal Conductivity in Aerospace Insulation
The ability of a material to transfer heat is often dependent upon its thermal conductivity. Understanding Thermal Conductivity Materials is one of the three methods of heat transfer, the others being convection and radiation. It can be measured by a physical property known as the thermal conductance, and is defined as the amount of heat that passes per unit time through a plate of a given area and thickness where the opposite faces differ in temperature by one kelvin. A material’s thermal conductivity can be affected by several factors, including its phase, the temperature gradient, and the properties of the material itself.

Some examples of materials with high thermal conductivity include copper, aluminum, and nickel. These metals are highly conductive because they have strong electron bonds within their crystal structures, making it easier for free electrons to move across the lattice and disperse their thermal energy. This effect can be diminished if the crystal structure is not pure, with impurities causing local anomalies that can slow or divert the movement of these electrons, thus lowering the thermal conductivity.

Another factor that can affect a material’s thermal conductivity is its porosity. This can be a natural occurrence, or it can be deliberately added to the structure for purposes such as providing insulation or improving strength. A material with high porosity can exhibit low thermal conductivity because of the space that is filled with gas pockets, which reduces the flow of free electrons and lowers the overall conductivity.

The type of lattice structure can also influence a material’s thermal conductivity, with FCC (face-centered cubic) structures generally having higher thermal conductivity than BCC (body-centered cubic) ones such as those found in iron. This is because the larger lattices have fewer grains that can act as obstacles to the flow of free electrons. Finally, the chemical composition of a material can also impact its thermal conductivity, with ions that have a negative effect on the electrical potential creating distortions in the electronic potential and slowing or blocking the flow of free electrons, thereby reducing the thermal conductivity.

Like many other physical properties, a material’s thermal conductivity can be anisotropic. For example, carbon in the form of graphite has a high thermal conductivity when viewed along its basal planes but is much less conductive perpendicular to those planes. This characteristic can be beneficial for specific applications such as preventing thermal runaway in lithium-ion battery cells.

There are a variety of techniques for measuring the thermal conductivity of a material, some of which can be classified as steady-state or transient. Steady-state techniques measure the thermal conductivity of a material once it has reached its steady state, whereas transient methods are used to measure the instantaneous temperature profile as the system approaches that state.

Custom Materials, Inc offers a prefabricated layup for thermal conductivity measurements that includes multiple layers of ultrathin polyimide film separated by lightweight, low-conducting Dacron netting. This design can be customized to meet the exact needs of your application.