High Thermal Conductivity Insulators Can Improve The Insulating Properties
The Efficient Thermal Management in Electronics is important in many engineering fields, particularly power generation/delivery, energy storage, integrated circuits and aircrafts. Overheating in these areas reduces efficiency, reliability and life span, but is also a fire risk. Hence, the need for materials that provide good thermal conductivity and insulation properties.
One way to achieve this is through insulating composites, which combine a thermally conductive layer with a more traditional, insulating material. However, these are often limited in their temperature capabilities, so newer approaches are needed. The latest research from MIT is promising. The team has developed a high-performance electrically conductive material that can be used as an insulator.
The researchers have found that a nanostructured aluminum oxide/copper oxide matrix can improve the insulating properties of an existing insulator, such as glass, by increasing its electrical conductivity. The resulting composite is up to five times more conductive than the current state of the art, but it maintains its insulating properties at elevated temperatures. The composite is also highly flexible and can be easily formed into the required shape, so it is suitable for a wide range of applications.
To understand how this works, we need to look at the fundamentals of conductivity. The thermal conductivity of a material depends on its temperature: higher temperatures lead to lower conductivities, while lower temperatures mean higher conductivities. It is this variation in conductivity with temperature that causes a material to be a good or bad insulator.
For example, a solid metal such as copper has very high conductivity when it is cold. This is because the particles are very close together. However, if the metal is heated, the particles move further apart and the conductivity decreases. This is why you can touch a hot frying pan with its wooden handle, but get burned if you try to pick it up with a metal handle.
This property is generally described in terms of a material's thermal conductance (or thermal resistance): the ratio of its temperature gradient across the material to its linear dimension. It is defined as a scalar quantity, but can also be expressed as a second rank tensor if the material is anisotropic.
Most insulators, such as mineral wool and Styrofoam, work by trapping air in pockets or voids to obstruct the path of heat conduction. The same principle applies to biological insulators, such as fur and feathers. These insulators are also effective when they contain moisture, as the water vapour present in them increases their insulating properties.
Polyurethane foams are an excellent form of insulator, and are available in a variety of thicknesses. These can be made using non-chlorofluorocarbon blowing agents, which helps to limit damage to the ozone layer. They are also very light and offer a high R-value per inch of thickness. This makes them suitable for a number of applications where space is restricted or weight is important.