Graphite can shrink under certain conditions, particularly when exposed to air at elevated temperatures, leading to oxidation and loss of thickness. However, under heat treatment in an inert atmosphere, graphite can become stronger and its mechanical strength increases.
Oxidation and Shrinkage: Graphite is sensitive to oxygen, and when exposed to air at elevated temperatures, it begins to oxidize around 500°C (932°F). This oxidation process can lead to a rapid loss of mass, up to 1% per day under specific conditions. Repeated exposure to such conditions results in the graphite losing thickness, which can eventually lead to structural failure. This shrinkage is a direct result of the material's interaction with oxygen, which breaks down the graphite structure.
Heat Treatment and Strengthening: Conversely, when graphite is heated in an inert atmosphere, it undergoes a process called graphitization, where the carbon atom structures transform from a disordered state to a perfect 3D crystal of pure graphite. This process involves heating the graphite up to 3000°C, which allows the small domains of graphene molecules to grow and align, leading to larger, straight layers. This alignment and growth enhance the mechanical strength of the graphite, making it stronger as the temperature increases. The internal stresses that occur at room temperature decrease with rising process temperatures, further contributing to increased mechanical strength.
Impact on Design and Functionality: The ability of graphite to strengthen when heated in an inert atmosphere allows for smaller designs and fewer fixture support systems, which can lead to larger batch sizes in industrial applications. However, when graphite is used in environments where it is exposed to air at high temperatures, the formation of a protective silicon oxide film on the surface can help prolong its life. If this protective film cracks due to temperature fluctuations, the antioxidant protection weakens, leading to an increase in the resistance value of the graphite rod.
In summary, graphite can indeed shrink due to oxidation when exposed to air at high temperatures, but it can also become stronger through controlled heat treatment in an inert atmosphere. The properties of graphite, including its tendency to shrink or strengthen, are highly dependent on the conditions it is subjected to, making it a versatile material in various high-tech applications.
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