Thermal Expansion of Graphite
Graphite is an allotrope of carbon, often referred to as a “miracle material” due to its unique and varied properties. Graphite has been used in the production of lubricants, graphite-epoxy composites, electrodes, refractory materials, and other industrial consumer products. It is also important to many scientific research applications such as nuclear reactors and space and fighter aircraft propulsion. Unfortunately, with its impressive list of properties, graphite has a few drawbacks as well. One of the more prominent issues is its relatively high thermal expansion coefficient.
Thermal expansion, or what is often referred to as thermal contraction or temperature dependency, is the ability of a material to expand or contract when exposed to varying temperatures. Thermal expansion is an important factor to consider in the design of parts and assemblies that must maintain secure and reliable connections during extreme temperatures. The coefficient of thermal expansion (CTE) defines how the material will behave at different temperatures when exposed to heat. The CTE is expressed in ppm/°C and typically ranges from 35-45 ppm/°C for graphite.
The CTE of graphite can be both a benefit and a limitation. When it comes to extreme temperature applications, the CTE may prevent secure connections from forming or maintain parts from being properly sealed. On the other hand, the CTE can be advantageous when creating parts that require a certain type of flexibility. For example, the CTE can be used to create connections that are less susceptible to thermal shock.
The CTE can also vary significantly depending on the type of graphite being used in the application. For example, carbon-graphite, anisotropic graphite, and pyrolytic graphite all have different CTE values, ranging from 3.2 ppm/°C to 16.9 ppm/°C. Understanding the type of graphite being used and expected CTE values are essential to creating secure and reliable connections.
Graphite is widely used in many industrial and scientific applications because of its impressive list of properties, but it should be noted that its thermal expansion coefficient can present challenges. Understanding and properly accounting for the thermal expansion of a particular graphite material is essential for ensuring secure and reliable connections at various temperatures.
