The melting point of diamond is 3550 ° C, and the melting point of Graphite Electrode is 3652 ° C ~ 3697 ° C (sublimation). The melting point of graphite is higher than that of diamond. From the inside of the sheet, graphite is an atomic crystal; from the perspective of the sheet, graphite is a molecular crystal (in general, Good Oxidation Resistance Graphite Electrode should be a mixed crystal); and diamond is an atomic crystal. The melting point of the graphite crystal is higher than that of the diamond, which seems unbelievable, but the bond length of the covalent bond in the graphite crystal layer is 1.42×10-10 m, and the bond length of the covalent bond in the diamond crystal is 1.55×10-10 m. The same as the covalent bond, the smaller the bond length, the stronger the bond, the more difficult it is to destroy it, and the more energy it needs to be, so the melting point should be higher. (mainly the molecular crystal properties of graphite lead to its high melting point) Graphite, which is a layered structure, C atom sp2 hybrid, forms a sigma bond with three C atoms, and a non-hybrid one p orbit forms a large bond. Diamond is a spatial network structure in which C atoms are sp3 hybridized and bonded to four C atoms. In sp2 hybridization, the composition of s orbital is more hybrid than sp3, so the covalent bond formed is shorter and stronger, that is, the covalent bond length of the layer of graphite is shorter than that of diamond, and the force is greater. Destruction of chemical bonds requires more energy. Therefore, the melting point of graphite is higher than that of diamond. Graphite is a thermodynamically stable structure, while diamond is thermodynamically unstable. Diamond is an atomic crystal and a spatial network.
Each layer of the graphite part is a mesh, and the layer is an intermolecular force between the layers, which is a crystal structure between the molecular crystal and the atomic crystal. However, due to the bond length, the covalent bond length of the graphite layer is shorter than the bond length of the diamond, and the interaction between the molecules is greater, and the destruction of the chemical bond requires more energy. It is common knowledge that an object consisting mainly of the same kind of element has a melting point higher than the melting point of the pure substance. Both graphite and diamond are composed of C mainly, but graphite is a mixture with impurities, diamond is pure, and impurities are negligible.
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