Graphite undergoes significant changes when exposed to high temperatures, particularly in terms of oxidation, mechanical strength, and structural transformation.
Oxidation at Elevated Temperatures: Graphite is sensitive to oxygen and begins to oxidize when exposed to air at temperatures around 500°C (932°F). This oxidation process can be quite rapid, leading to a loss of mass by up to 1% per day under certain conditions. Prolonged exposure to such conditions results in the thinning of the graphite, eventually leading to structural failure.
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.
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.
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.
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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