As a material scientist with a focus on carbon allotropes, I'm often asked about the properties of graphite, a form of carbon that is widely used in various applications due to its unique characteristics. Graphite is an allotrope of carbon where the atoms are arranged in layers of hexagonal lattices. These layers are held together by weak van der Waals forces, which allow them to slide over each other easily, making graphite a good lubricant and the "lead" in pencils.

The concept of a melting point for graphite is a bit nuanced. Unlike most substances, graphite does not have a well-defined melting point under standard atmospheric pressure. This is because graphite sublimates, meaning it transitions directly from a solid to a gas without passing through a liquid phase. This process is similar to what happens with carbon dioxide, where it transitions from a solid (dry ice) directly to a gas at atmospheric pressure.

However, under increased pressure, the behavior of graphite changes. At pressures of about 100 atmospheres, graphite begins to melt. The melting point under these conditions is estimated to be around 4300 Kelvin, though this is subject to some variation. It's important to note that these high pressures are not typical of everyday conditions and are usually only encountered in specialized industrial processes or scientific experiments.

The stability of different carbon allotropes, such as diamond and graphite, is also pressure-dependent. Diamond, another form of carbon, is not stable at atmospheric pressure and requires extremely high pressures, on the order of 100,000 atmospheres, to form and remain stable.

In summary, while graphite does not have a conventional melting point at standard atmospheric pressure, it can melt at elevated pressures, with an estimated melting point of around 4300 K. The behavior of graphite, like other carbon allotropes, is influenced by the environmental conditions, particularly pressure.

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Like carbon dioxide it goes directly from the solid state to the gaseous. So graphite has no melting point until you get up to about 100 atmospheres. At that point the melting point is about 4300 K (give or take). Diamond is not stable until about 100,000 atmospheres.read more >>