Diamonds are known for their exceptional hardness and brilliance. While many substances transition from solid to liquid and then to gas upon heating, diamonds exhibit a more complex thermal response, particularly regarding their melting point.
How Diamond Behaves Under Extreme Heat
Under typical atmospheric pressure, diamonds do not melt into a liquid state. Instead, when subjected to extreme heat in an inert environment, they undergo sublimation, transforming directly from solid to gas.
This occurs because diamond is a covalent network solid, meaning each carbon atom is strongly bonded to four other carbon atoms in a rigid, three-dimensional tetrahedral structure. These robust covalent bonds require a substantial amount of energy to break, making it difficult for the atoms to rearrange into a less ordered liquid state.
The estimated temperature for diamond sublimation at normal atmospheric pressure in an inert atmosphere typically falls in the range of 6,332°F to 7,232°F (around 3,500°C to 4,000°C). If, however, a diamond is heated in the presence of oxygen, it will combust or burn at much lower temperatures, typically between 1,292°F and 1,652°F (700°C and 900°C), forming carbon dioxide.
Achieving Diamond’s True Liquid State
For diamond to genuinely melt into a liquid, it requires not only extremely high temperatures but also immense pressure. Research indicates that under pressures exceeding 10 gigapascals (equivalent to over 100,000 atmospheres), carbon in its diamond phase can indeed transition into a liquid.
Under these specific high-pressure conditions, the estimated melting point for diamond ranges from approximately 7,232°F to over 8,000°F (4,000°C to 4,430°C). Some studies suggest an ultimate melting point around 7,280°F (4,027°C) under high pressure. This liquid carbon phase is distinct from the gaseous phase formed during sublimation and can be observed within complex phase diagrams that map carbon’s behavior across vast pressure and temperature ranges.
Why Diamond’s Thermal Properties Matter
The unique thermal properties of diamonds, particularly their extreme stability at high temperatures and exceptional thermal conductivity, make them invaluable in various scientific and industrial applications. Diamond possesses the highest thermal conductivity of any known material, with values ranging from 1,500 to 2,200 W/mK. This property allows diamonds to efficiently transfer heat away from sensitive components.
Diamond is widely used as a heat sink in high-performance electronics, including computer CPUs and GPUs, LEDs, and laser diodes, preventing overheating and extending device lifespan. Its ability to dissipate heat quickly, combined with its electrical insulating properties, makes it a preferred material over traditional alternatives like copper and aluminum in demanding applications. Beyond electronics, diamonds are also utilized in industrial cutting tools, where the intense friction generates high temperatures, and in high-pressure research, such as diamond anvil cells, which replicate extreme geological conditions for material study.