Why does Carbon Have a High Melting Point?

In the field of chemistry and materials science, carbon has attracted much attention because of its unique properties and widespread presence. Its extremely high melting point gives it stability in extreme environments. And it plays a key role in pyrometallurgy, refractory and superhard material manufacturing.

Structural of carbon

Carbon has a variety of allotrope in nature, such as diamond, 흑연 and fullerene. Due to the different arrangement of atoms, physical and chemical properties vary greatly.

Diamond is an atomic crystal, carbon atoms to covalent bonds to build a three-dimensional network structure. Each carbon atom and the surrounding four carbon atoms connected to form a regular tetrahedron, the overall structure is stable.

The graphite is layered, the carbon atoms in the layer form a hexagonal network with covalent bonds, and the covalent bonds are strong. The layer is acted on by a weak van der Waals force. This makes the graphite have good conductivity and lubricity in the parallel direction of the layer, and has a certain stability.

Represented by C60, fullerene was football shaped and composed of 60 carbon atoms in a ball form. Each carbon atom was connected to three neighboring carbon atoms through covalent bonding. Based on covalent bonding, fullerene had certain stability.

Reasons for high melting point of carbon

Covalent bonding

The high melting point of carbon is mainly due to its powerful covalent bond between atoms. In diamond, each carbon atom forms a strong covalent bond with the surrounding four carbon atoms. Covalent bonds are the bonds formed by sharing electrons between atoms, which are essentially the strong attraction of the nucleus to the pair of Shared electrons. In the structure of diamond, this covalent bond can be very high. And to break these covalent bonds and separate carbon atoms, it requires a lot of energy.

Take diamond as an example, its C-C bond has a bond of about 347 kj/mol. When heated, the energy provided by the outside world must be enough to overcome the binding of these covalent bonds. To change the relative position of the carbon atom and thus transform from solid to liquid. By contrast, some molecules of matter, such as ice, interact with the van der Waals force through weaker hydrogen bonds and a melting point of 0. When the ice melts, it only needs to destroy these weak forces between molecules. Without destroying the covalent bonds inside the water molecules, so it requires less energy.

In graphite, although there is a weak van der Waals force between the layers. The carbon atoms in each layer form a stable plane network through covalent bonds. The covalent bond in this layer also has high bond energy. So that when graphite is heated, the structure of the layer can be maintained relatively stable. And require higher temperature to make the whole structure change significantly.

The carbon atoms are tightly packed

In addition to the action of covalent bonds, the tight accumulation of atoms in the crystal structure of carbon also plays an important role in its high melting point. In the three-dimensional mesh of diamond, carbon atoms are arranged in a highly orderly and compact manner. This tight accumulation makes the distance between atoms very small, and the interaction between atoms increases further.

According to the crystal structure theory, the dense accumulation of atoms can improve the density and stability of crystals. In diamonds, the lattice energy is larger because of the compact accumulation of atoms. Lattice energy refers to the energy absorbed by the ionic crystal into gaseous positive ions and gaseous negative ions under standard conditions. For atomic crystals, you can compare it to the energy required to break the crystal structure. The larger the lattice energy, the more stable the crystal, the higher the melting point.

Although there is a certain gap between the layers of graphite, the carbon atoms in each layer are also tightly arranged. This tight accumulation in the layer also helps improve the stability and melting point of graphite. In each layer of graphite, the hexagonal mesh structure formed by carbon atoms makes the interaction between atoms reach a equilibrium state. This requires high energy to break this balance.

Comparison melting point of carbon with other elements

Compared with other elements, the melting point of carbon has significant advantages over common elements.

Taking iron as an example, its melting point is about 1538 °C, it is a metal crystal, bound by metal bonds. And the interaction between metal cations and free electrons is overcome when it melts.

And sulfur often exist in S8 molecules, molecular crystals. It is by weak van der Waals force between molecules, melting point is only 115.21°C.

Carbon, whether diamond, graphite equivalent allotrope, because of the interatomic covalent bond and close packing structure, the melting point is far more than many common elements. The melting point of carbon is about 3550 °C (3824K)，it is extremely stable at high temperatures, become a key material in special applications.

Practical application of high melting point of carbon

Refractory materials:

You can widely use carbon in the manufacture of 내화 재료 because of its high melting point. In the metallurgical industry, the lining of high-temperature furnace needs to be resistant to high temperature and erosion. Graphite and carbon-containing composite materials can withstand harsh environment, protect the furnace body and extend the life of the furnace. For example, the graphite crucible can withstand high temperature molten steel melting in steelmaking.

Superhard materials:

Diamond, as an allotrope of carbon, has become the first choice for manufacturing superhard materials because of its high hardness and high melting point. You can use diamond tools in machinery, stone processing and other fields. When cutting at high speed, the high melting point makes it stable under high temperature and high pressure. Improving the processing accuracy and efficiency. You can also use synthetic diamonds to manufacture drilling tools for oil exploration and geological exploration.

Electronic devices:

In the field of electronic devices, the high melting point of carbon plays an important role. Semiconductor manufacturing requires high temperature environment for crystal growth, doping and other processes. Due to its high melting point, good electrical conductivity and chemical stability, you can use it to manufacture heating elements, crucible and other components. To ensure the precise control of semiconductor manufacturing process and high quality production.

결론

The high melting point of carbon is due to its unique structure, the covalent bonds between the atoms are strong and packed tightly, and the melting requires a lot of energy. Compared to other elements, this property makes it advantageous in many fields. And it will also help develop more high-performance carbon-based materials in the future.