When graphite is exposed to high temperatures, it undergoes several significant changes. These changes affect its properties in various ways, making it either more useful or more vulnerable depending on the conditions.
What happens to graphite at high temperatures? 5 key changes explained
1. Oxidation at Elevated Temperatures
Graphite is sensitive to oxygen. When exposed to air at temperatures around 500°C (932°F), it begins to oxidize. This process can be quite rapid, leading to a loss of mass by up to 1% per day under certain conditions. Prolonged exposure to these conditions results in the thinning of the graphite, eventually leading to structural failure.
2. Mechanical Strength and Structural Changes
Interestingly, graphite becomes stronger as it is heated from room temperature to 2,000 °C. This is due to the reduction of internal stresses that occur at lower temperatures, which increases the mechanical strength of the material. This enhanced robustness allows for smaller designs and fewer support systems, which can lead to larger batch sizes in industrial applications.
3. Thermal and Electrical Conductivity
Heating graphite rods exhibit very high thermal and electrical conductivity. The thermal conductivity of graphite is greater than that of common metals like iron, lead, and steel, and it increases with temperature until a certain point, after which it decreases. Electrical conductivity in graphite rods is also notably high, being four times that of stainless steel and twice that of carbon steel.
4. Graphitization Process
The process of graphitization involves the structural transformation of carbon from a disordered state to a highly ordered crystalline form of graphite. This transformation is initiated by heat treatment in an inert atmosphere up to 3000 °C. Initially, the carbon material contains small domains of graphene molecules. As the temperature rises, these domains grow and align, leading to the formation of large, straight layers of graphite. The early stages of graphitization occur between 1900 °C and 2000 °C, resulting in reduced interlayer distances, indicating a more ordered structure.
5. Summary of High-Temperature Effects on Graphite
In summary, high temperatures affect graphite by inducing oxidation, enhancing mechanical strength, improving thermal and electrical conductivity, and promoting the graphitization process, which transforms the material into a more ordered and structurally perfect state.
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